DuMont Model RA-113 Television/Radio (1950)
This RA-113 is my second DuMont television. Made in 1950, it's
two years newer than my RA-103
and it shares many features with that fine set.
One difference you'll notice right away is the larger screen. The RA-113
has a 17-inch 17BP4 picture tube, while the RA-103 uses a 12-inch 12JP4.
The 17BP4 is also rectangular rather than round, so more of its face is viewable.
Meet the DuMont RA-113
DuMont used essentially the same chassis for two models: RA-112, with a
19-inch picture tube and RA-113, with a 17-inch screen. There were three
cabinet styles for each chassis. Mine is the Revere.
The cabinet is finished in dark mahogany and the doors are embellished
with gold pinstripes and brass corner stars. Here is the cabinet on the
day when I brought the TV home. The picture tube and other electronics had
been removed for transport.
My Revere cabinet is in great original condition. The burgundy grille cloth and gold
decals are flawless and the exterior has only a few scuffs and latex paint drips here and there.
It should look new after a little touching up.
Here is the TV in a couple of contemporary ads.
Herbert Rosengren designed the Revere and most of the other RA-113 cabinets.
The controls form a row next to the screen (this photo from
the Sams manual shows the Brookville cabinet).
All RA-112 and RA-113 TVs have a continuous tuner with integrated FM radio.
They also have a Phono jack for connecting an external phonograph.
The RA-113's one-piece chassis is mounted on the side of the cabinet.
RA-113 Owner Manual
Here is the DuMont RA-113 Owner Manual and warranty card. The manual contains useful
information such as the best procedure for tuning a station, as well as some
company history and a photo of founder Allen DuMont.
I have higher-resolution versions of these pages. If you would like these
to print the manual at full size, contact me via email.
RA-113 Electronic Design
You can download the complete Riders service manual and schematic
for this set at the Early Television Foundation
archive. I got a copy of the Sams Photofact manual from my local library.
You can also get it directly from Sams (folder
I recommend using both Riders and Sams. The Riders manual has extensive
descriptions of circuit operation, tuner stringing, and differences from
related DuMont chassis. The Sams manual has great component identification
photos and a resistance chart as well as voltage chart. The schematics are
also drawn somewhat differently, and occasionally you may find one style easier to
follow than the other. This article uses the Riders part numbers.
The Riders RA-113 manual makes many references to the RA-111A manual, so that
one is also worth getting if you want the full story.
The RA-113 uses 26 tubes:
||1st audio IF amplifier
||2nd audio IF amplifier
||Audio disc./1st audio amplifier
||2nd audio amplifier
||1st video IF amplifier
||2nd video IF amplifier
||3rd video IF amplifier
||4th video IF amplifier
||Video det./DC restorer
||Narrow band sync amplifier
||Horizontal AFC/saw generator
||Horizontal deflection amplifier
||Low voltage rectifier
||1st sync clipper
||2nd sync clipper/Vert. saw gen.
||Vertical deflection amplifier
||High voltage rectifier
||High voltage rectifier
The Riders manual does not list a tube V216 in its component list or schematic.
The RA-113 shares many features with the RA-103, including "split sound" audio,
a magic eye indicator, and continuous tuning with integrated FM radio. Since they are discussed in my
RA-103 article, I'll refer you there for more details.
One welcome addition is an AGC (automatic gain control) circuit. AGC automatically
adjusts between weak and strong stations, which means less fussing when you
change channels. The RA-113 does not have a time delay start-up circuit like the RA-103.
I suspect the delay's cost outweighed its benefits, since it was
not found in later DuMonts.
The 17-inch picture tube in my RA-113 needs higher voltage than the 10-incher in my RA-103.
The 17BP4 CRT is rated up to 16,000 volts, while the 10BP4 takes a maximum of 10,000 volts.
The RA-113 uses two 1X2 tubes in a doubler circuit to provide the higher voltage.
This diagram shows the circuit:
Here's a description of how the doubler works, adapted from one of my old
TV theory books.
At the appearance of an 8,000-volt positive spike at the plate of V401 the tube will conduct
and charge C403 to approximately the full value of this voltage. (Current flow is from
filament to plate. Positive spike is actually across plate and ground.) Between pulses
C403 will discharge through the resistor chain R402-R403-R404 and thus charge C402.
After several positive spikes have appeared both C403 and C402 will be charged to 8,000 volts.
During the arrival of the positive spikes at the top of the transformer primary, the 8,000
volts on C402 will add to the 8,000 volts of the incoming spike. Thus, when V402 conducts,
it has twice the spike voltage across it (16,000 volts). V402 will then conduct, and since
the current flow from ground to the cathode of V402 must be via C403 and C404 in series,
each of these capacitors will have an 8,000-volt charge across it. The sum of these two
charges, 16,000 volts, is applied to the second anode of the picture tube. Actually, a little
less than 16,000 volts will be available because of the rectification process.
A red caution tag on my chassis (below) says CAUTION 13,000 VOLTS. The voltage
delivered by this practical circuit is less than the maximum in the theoretical
discussion, and nicely within the CRT's design limits.
The three high-voltage capacitors mentioned above are all of the unreliable
paper type. I will replace them (along with other
paper and electrolytic caps) before applying power.
The complex low-voltage power supply delivers six different voltages: 305V,
200V, 135V, 75V, 35V, and -55V. The RA-113 also has two separate 6.3-volt filament
supplies. One of them (the "X" supply) handles the majority of the tubes
including the CRT. A separate filament transformer provides the "Z" supply
for the 6W4GT damper tube (V217). This transformer is insulated to 5,000 volts to
accommodate the high peak voltages in the damper circuit.
The DuMont Spiral Tuner
The RA-113's tuner is complex and intriguing, a successor to the
InducTuner in my RA-103.
Here's a description from one of my old TV books:
A new version of the Inductuner principle is the spiral type of tuner which takes its name
from the manner in which the coils are wound. These, because of their upright mounting as
shown in the photograph, make for a more
compact tuner despite the additional coil section as opposed to the older Inputuner. The four
coils comprise a tuned r-f input, a tuned r-f output, a tuned mixer input, and of course
a tuned oscillator.
Wiping contact points move over the coils as the shaft is rotated for station selection,
thus progressively shorting out sections of the coils and giving continuous tuning
from 54 megacycles to 216 megacycles. The schematic for the spiral tuner is shown in
Figure 62 and the heavily shaded triangles indicate coil assemblies which are tuned
by the wiping contacts, all of which are ganged together and rotated by the station
A 6J6 grounded-grid amplifier circuit is used for the r-f stage, with both halves of
the dual triode connected together. While the grids are at r-f ground because of C105 and
C106, the d-c potential is ungrounded and is applied by the a-g-c circuit of the
receiver proper. Because the grid is at r-f ground, the signal is applied to the
tube across a resonant circuit in the cathode.
The grounded grid isolates the input and output circuits of the r-f tube and thus prevents
the stage from going into oscillation. With a conventional ungrounded grid circuit, some
form of neutralization would have to be employed to prevent oscillation. The grounded grid,
however, acts as a shield between input and output and facilitates the use of a triode
instead of a pentode amplifier. The triode, with fewer grid wires, suffers less from
thermal agitation effects and has a lower noise factor. Inasmuch as pentodes have to be
loaded down to a considerable extent for wide-band television usage, the plate impedance
drops to such a low value that the final gain is approximately equal to that of a triode.
Thus, the high-gain advantages of the pentode are not realized and the triode is preferred
by some manufacturers because of the reduced noise and less "snow" effect on
The tube capacity of the triode is large, however, and interfering signals find a relatively
easy path through it. Because of the tuned input, however, improved selectivity and higher
gain result in rejection of interference by television stations on adjacent channels as well
as interference caused by FM stations. The tuned circuit in the grid of the spiral tuner is
composed of the Inductuner L102A plus tube and circuit capacity. L103 is employed for tracking
at the high channels and is adjusted for greatest gain on channel 13. C100 tracks the low
channels and is set for best signal at channel 6.
A trap composed of L101 and C101 offers high impedance around the i-f range of frequencies
and helps to reject such interference signals which might enter and be accepted by the
wide-pass i-f amplifier stages.
Variable trimmer capacitors C110 and C112 track the r-f--mixer interstage circuits over
the lower television channels, while L108 and L113 are used for tracking purposes at the upper
television stations. Additional bandpass adjustments at channel 13 may be made with L107,
which consists of a small metal strip which is fastened to the chassis. Adjustment of the
position of this strip with respect to the chassis alters the bandpass.
A Colpitts-type oscillator is used in the spiral tuner, L109 shunting the spiral inductor so
that the oscillator frequency will always be higher than r-f and mixer frequencies to produce the proper sound
and video i-f outputs. The addition of L109 in shunt with L102D and L110 reduces total inductance
below what it would be without L109. reduction of inductance will tune the resonant circuit
of the oscillator to a higher frequency.
Capacitor C118 is used for tracking at the lower channels and L110 aids in tracking at the high
channels. C115 serves to couple the oscillator signal to the mixer grid into which is also
injected the incoming signal from the r-f amplifier. The i-f frequencies in the plate of the
mixer are applied to the primary of T202. Link-coupling is used to connect the tuner output
to the first video i-f amplifier grid electronically.
RA-113 Installation Manual
The installation manual for the RA-113 is written for the DuMont dealer, who
would install the yoke and make sure the set was operational. It
has detailed instructions for positioning the ion trap magnet.
Like some other DuMonts of the period, the RA-113 has a phono type
jack in the rear for a shielded coaxial antenna cable. If your input
is a coaxial cable from a DVD player or similar device, you can use
an inexpensive "F"-to-phono plug
My RA-113 came from Seattle. I got this television from the second owner, who watched it at a
neighbor's house as a girl and preserved it when the neighbor moved away. She remarked
that the neighbor "would only have the best." It was well cared
for during the last 60 years. When you open the doors, it looks like new except
for a very small wear mark behind the fine tuning knob.
Here's the chassis as found. It mounts vertically, bolted to
a sturdy plywood base that slides into brackets on the cabinet's right side.
Everything is there and it looks shipshape apart from the usual grime.
The base has a service cutout for access under the chassis. I'll
remove this to make sure I can reach everything during the obligatory
This photo shows the back, safety glass, CRT bezel, yoke,
yoke bracket, and a sack of knobs and small hardware.
The picture tube is a Sylvania replacement, type
In comparing notes with other collectors, it appears that DuMont used
a 17AP4 CRT for the earliest RA-113s but soon switched to the 17BP4,
an aluminized tube with superior brightness. My TV must have been made
soon after the switchover, as its label lists a 17AP4.
My back cover has a rather irregular circular cutout for the picture tube base,
which is needed because the 17BP4 is about 3/4 inch longer than a 17AP4.
Later RA-113s have a domed cap that covers this hole.
The photo shows the CRT bracket with mounting holes for
three stout bolts that come out the inside of the cabinet face. The yoke bracket
hangs from the cabinet ceiling. To remove the CRT, you first remove the
yoke from its bracket and then remove the bracket from the ceiling.
If you don't first remove the yoke, it's impossible to slide the assembly
back far enough to clear the CRT neck.
Removing the CRT is easier if you tilt the cabinet forward and rest it securely
against the workbench. It will be easier to get your hands under the heavy
bell and slip the CRT back and free of the mounting screws. Pad the workbench
to avoid scratching the cabinet, of course.
The only part not yet shown is the speaker, a 10-inch permanent magnet type.
I'll remove that and put it on the workbench when I'm ready to power
up the TV.
Cleaning and Testing
As in every project, I began by cleaning things up and testing the tubes.
The chassis was not particularly dirty. A chassis that hangs vertically will not
accumulate as much dust (and thus grime) as one that sits flat.
The high voltage cage looks ugly, but the discoloration seems to be corrosion on the
plating, the result of sitting unused for decades. Inside the HV cage, I found only
the usual light layer of dark soot, which will clean up easily with
isopropyl alcohol. Windex and paper towels will take care of the rest of
I tested the 25 small tubes and cleaned their pins. All of them tested
strong, except for one weakling which I replaced. All of these tubes except
one had non-DuMont labels, a sign that the TV was used and serviced
regularly over the years.
The initial check of my 17BP4B CRT gave mixed results. It showed
zero emission on my Sencore CR70 tester. However, the filament
was intact, measuring 1.5 ohms on my ohmmeter, and it glowed under normal
After a few minutes, the emission needle began to rise very slowly. I have seen other
long-unused CRTs wake up after a "slow cook" under normal or slightly
elevated filament voltage. I left it on the tester for a couple of days, and
the needle crept halfway up the scale, where it rested midway between the Bad
and Good zones.
The tube tested fine on the CR70's Cutoff test, indicating that it should have
good contrast if the emission is sufficient. The CR70 has several rejuvenate/restore
functions, which I had never tried before. This CRT seemed like a good candidate for
As suggested by the manual, I began with the Auto Restore function, gentlest among
the various options. This takes less than 30 seconds and I was delighted
to see immediate improvement. Now the emission tested well into Good zone.
The tube didn't fare so well on the Life test, so no doubt it's nearing the end
of its service life. Perhaps it's good enough to use during restoration, at least.
I'll set the tube aside until I finish recapping, a basic procedure you can
read about in our capacitor replacement article.
Replacing Electrolytic Capacitors
The RA-113 uses a lot of electrolytic capacitors—fifteen, to be exact—and
twelve of them are mounted in five cans above the chassis. Mounting all twelve
replacements under the chassis would make quite a tangle, so I'll restuff as
many of the cans as possible.
Let's start with a couple of easy ones. Capacitors C1 and C5 are contained in
two cardboard-insulated cans that protrude partly above the chassis.
After loosening the clamps above and unwiring the terminals below, the cans will easily
slide out. I labeled all of the wires before removing them.
Here are the C1 and C5 cans removed from the chassis.
I cut around the bottoms of the cans with a Dremel tool, warmed the
cans with a heat gun to soften the tarry adhesive, and then drew out the
innards with a screwed-in cup hook.
The black adhesive cleans up easily with paint thinner.
I ran the leads for new capacitor C5 through
holes in the old disk and soldered them to the original terminals. A
little hot glue secures the new cap. Then I'll glue this assembly back onto
the can with epoxy.
Rinse, repeat, and the job is quickly done. Here are the restuffed cans,
looking much as before, which is the whole idea.
The restuffed cans are back in place. I'll include notes
with the TV when I'm finished, so that a future owner won't
mistake these for originals and replace them all over again.
The remaining three cans won't be so easy. Here are C3, C4, and C6,
which hold a total of nine capacitors. The replacements are too large to
fit in the cans. I'll squeeze as many new caps into the cans as possible and mount the others
The C3 can contains four caps: one 30-mfd and three 10-mfd.
I was able to fit the three 10s in the can by mounting them sideways.
I'll wire the 30 separately under the chassis.
Before gluing the base to the can, I secured the caps to the base with
hot glue and wrapped them with electrical tape for added insulation.
Note the little blue stripes on the can's body and base. These allowed me to glue
the lid back in the original spot, ensuring a neat fit. The ink will wipe off
easily with isopropyl alcohol.
The C6 can contains two capacitors, 30 mfd and 25 mfd, which are used
in the vertical sweep section. Like C3, its
can tabs are used for negative connections, but the can is
insulated from the chassis by a diamond-shaped phenolic plate. In the
next photo, I have drilled out the rivets holding this little plate to the chassis
and slid it aside to reveal the mounting hole.
(The C3 can has already been reinstalled to its right.)
Remember when I mentioned that the RA-113 power supply provides six voltages?
The negative leads of the C6 capacitors connect to the -55V supply,
hence the need to isolate them from chassis ground.
Now I have unsoldered the can and turned it over. The can tabs are twisted
to fasten the can to the phenolic plate, but they don't touch the chassis.
Notice the two terminals on another phenolic plate farther inside the
can. These are the positive leads for the two capacitors and they
are marked with little square and triangle cutouts. The same
symbols are shown on the side of the can as well as the schematic.
The square indicates capacitor C6A and the triangle stands for C6B.
We'll need to reuse the plate. After cleaning solder from the tabs
and straightening them with a plier, I carefully pried the plate loose
from the can.
We'll also want the ring that forms the tabs. It's a separate piece, held in place
by the can's knurled-over edge. I sliced the edge with a Dremel tool and
then pried the ring loose with a thin screwdriver.
After warming the can with a heat gun, I removed the plate holding the terminals
and then inserted a heavy ring screw to pull out the innards. The photo shows the layers
that make up the capacitors: sheets of foil separated by paper impregnated with
The next photo shows the can, the ring, the little round inner plate, and the two terminals
that go through the plate. Only one of the new caps will fit in this can.
Its leads will slip neatly through the old holes in the plate, alongside the terminals.
I'll epoxy the terminals back onto the plate with JB Weld and use
them for that capacitor's positive and negative leads. When
I install the other cap under the chassis, it will share the same
Ba-da bing, ba-da boom. I have set the restuffed cap aside to let
the fresh epoxy cure under a lamp for a while.
I'll retwist the tabs to secure the can to
the diamond-shaped plate. When the restuffed cap is installed, it will look like new from above.
The C4 can holds three 10-mfd capacitors, but only one of the new caps fits inside.
Here's that can after restuffing.
All five cans (containing eight capacitors) are complete and back in place.
The four extra caps are
installed under the chassis, which would have been much more crowded
if I had wired all twelve electrolytics underneath. (The 10-mfd cap
at upper right replaced one that was originally located under the chassis).
In the previous photo, I have already replaced five of the smaller caps. There
a couple more electrolytics under the chassis, which I'll get to in the next
phase, along the remaining small fry.
Replacing Paper Capacitors
The next day, I replaced about 20 smaller caps and another under-chassis
electrolytic. All of this can be done with the chassis still mounted
on its wooden frame, although I'll need to remove it to reach a few
around the edge.
Two of the little guys, C98 and C99, are easier to reach if you loosen
the power-supply choke L1 and temporarily tape it out of the way.
Replacing Line Filter Capacitors
Speaking of molded papers, I found a pair of them on the AC power
line. These aren't shown in the Riders schematic but they are designated
C108 and C109 in Sams, with a note that they're found in RA-113s with
serial numbers above 1311795.
Each capacitor is connected from one leg of the power line to chassis ground.
Their purpose is to filter out radio-frequency interference, such as buzzing
from power tools. It's important to deal with these caps somehow, since a
leaky one can make the chassis "hot" with AC voltage. If an old
one burns up, it can also start a fire.
Some restorers simply take out line filter caps on the theory that RFI sources,
such as old-fashioned auto generators and diathermy equipment, are less
prevalent nowadays. I prefer to renew them, since there are plenty of
modern RFI sources, such as light dimmers.
The correct replacement is a "Y" type capacitor which will not
start on fire if it fails. This photo shows a new cap next to the old
The value specified here is .02 mfd, but the capacitance value is not very
important as long as the voltage rating is sufficient and the
cap's failure mode is correct.
You'll occasionally see a different sort of filter cap, wired
from one leg of the power line to the other. These should be replaced with an
"X" type capacitor.
Recapping the High-Voltage Section
The high-voltage cage contains three critical capacitors, needed to
produce HV for the picture tube. The originals are rated at 470 pfd (.00047 mfd)
and 10 kilovolts. It's not easy to find tubular capacitors at that value.
The 470pfd/15KV caps from Justradios will
work fine. Avoid using ceramic disc capacitors, which can become
unstable under heat and high frequencies.
Removing the cover exposes the high-voltage components. This section is
roomy and easy to work on, with two phenolic platforms.
On the right platform you can see the two 1X2 rectifier tubes
used in the voltage doubler circuit mentioned earlier.
A small plate above the tubes holds one of the high-voltage capacitors (C402),
wired between the plate caps of the tubes.
Capacitor C404 is a "black beauty," nestled
at an angle between the tubes. The third one (C403) lurks beneath the platform:
All of these HV caps had been replaced at some time during the past, but this
type is so unreliable—and so vital to correct operation—that I don't
hesitate to replace them with fresh ones. While I was in the cage, I also
replaced a 68-ohm resistor and 1000-pf capacitor. Here is the HV section
after cleaning and initial rehab:
Mounted under the left platform is the TV's flyback transformer. The sooty grime seen
in the "before" photo of this section is easy to clean up with
isopropyl alcohol, paper towels, and Q-tips.
Notice the chubby doughnut-shaped solder terminals on these boards. It's
essential to make smooth solder joints everywhere inside a HV cage. Sharp
lead ends or spiky solder tails may induce corona and create
Under the 1X2 tube sockets you'll find their 2.2-ohm filament resistors. Their values tested
about 25% high, probably not enough to cause problems, but I replaced them
anyway, in the interest of being thorough. This is another area that you'll want
to clean carefully, whether or not you replace anything.
Those thick rings suspened below the sockets are called corona
rings. They prevent HV leakage or arcing in and around the rectifier sockets.
Reaching Those Last Few
We're nearly done recapping.
You'll need to remove the chassis from the wooden mounting board to
reach the capacitors in this corner:
These include the very last electrolytic (evidently a replacement)
plus five paper caps. One of the tiny paper guys is completely hidden
behind the others. To gain full access to this corner, I screwed two
heavy "L" braces to the chassis, letting me lean it securely
on its side.
When I took the previous photo, I thought that I was done, but I had overlooked
the small rectangular shield at the lower right. Hmm, I wonder what's in there?
The shield is held by eight screws from inside and outside the chassis.
Behind it are three more capacitors to replace: two papers and a bumblebee.
Done recapping at last, and not a moment too soon. At this stage in a TV
project, I'm ready to do something different!
Removing the Tuner
This DuMont's tuner is immovable, stuck fast with petrified lubricant. It needs
disassembly, careful cleaning, and relubrication.
Seen from underneath, the tuner looks like a rectangular box. Before
removing it, I'll need to disconnect three wires underneath, two
on top, and a shielded cable leading to the rear antenna jack.
The tuner and dial come out as one assembly. The black cable brings in the
signal from the antenna. The phono type plug is tack-soldered
on its jack; use a soldering gun to loosen its ground connector for removal.
This tuner is complex, with dual strings, five pulleys, four gears outside,
and more gizmos inside.
On the outer mechanism, old lubricant has dried very
hard and the pulleys and shafts are seized. The strings are
In the next photo, I have loosened the dial frame and removed the
tuner cover, exposing the four tuning spirals described in a
previous section. Despite the crusty outside, the interior is
still lubricated and not too dirty.
Lubricating the Tuner
I'll disassemble the tuner from the outside in, to get
at troublesome parts. The dial pointer simply pulls off. The dial
face lifts off after you straighten four twisted tabs at its corners.
Both pulleys on the dial frame are stuck. The little idler pulley
keeps the string aligned and the big pulley drives the pointer.
I freed the pulleys by applying penetrating oil to their shafts and letting
it soak in overnight.
The next assembly looked simple enough, but it spelled trouble. On this little
frame are three components: a swinging arm with a small idler pulley,
the main tuning knob shaft (with a big gear) and the fine tuning knob
shaft with a smaller gear. The assembly is sitting on the tuner's big front plate,
which, as I later learned, I need not have removed.
The two shafts are concentric—the fine tuning shaft moves inside the main tuning shaft—
and their gears mate with a pair of gears on the tuner body. Since the gear ratios are
different, the fine tuner moves more slowly than the main tuner, requiring more turns
to move the dial pointer a given distance.
One problem is apparent, although I didn't notice it when the previous
photo was taken. Not only has the small gear come loose from the black
shaft, but it has a crack, seen clearly in these closeups.
This gear is supposed to fit tightly on the shaft, secured by the grip of
splines on the shaft and matching grooves inside the gear. When it cracked,
the gear opened slightly and was able to slip, which eventually wore away
most of its inner grooves. I don't have the equipment to machine a new one, so I'll try to
refasten the gear to the shaft.
From a different angle, you can see the swing arm with a little brass
idler pulley on its end. This pulley was seized. After cleaning it up,
I soaked it overnight in penetrant and then gently tapped and wiggled it free and
The swing arm is also seized on the main tuning shaft. This is
more difficult to loosen, since you can't apply much force without damaging
the delicate gear. I began by heating it with a heat gun and then dipping
it in a bath of penetrating oil. The next day, it was still firmly seized.
I heated it again and squirted Liquid Wrench on the joints,
in hopes that some penetrant would be drawn inside as it cooled.
After a few of these heating and cooling cycles, I tried to free it by tapping the
shaft end on an anvil. Still no go. After one more heat-up, I left it
in a penetrant bath for a second night. The next day, I finally got it free by
heating the whole assembly and then cooling the shaft with ice. It shrank enough
to gradually come free with more tapping.
Repairing the broken gear was not as easy as I had hoped. The open crack had
widened the distance between those two gear teeth. It would need to be
clamped back in place, for those teeth to mate with the opposing gear.
I tried reattaching it with silver solder and a micro torch, but
it proved impractical to clamp the gear completely without obscuring it
for a decent soldering job. I cleaned off the solder and glued it with
JB Weld two-part epoxy, using a small hose-type clamp to force the
gear closed. Here are these pesky little parts, ready to lubricate
Notice the screws of different lengths in the previous photo. The frame
for these parts is secured by four screws. A small screw in the bottom
lets you position the shafts and idler arm on the main tuner frame.
The three longer screws go through the dial frame as well as this
small frame, securing the entire dial and drive mechanism to the tuner.
When I tried reinstalling this assembly,
I initially thought something was wrong because the lower gears didn't mesh with
the upper ones. A fellow collector suggested that I look for a way to adjust them.
Sure enough, there is a way, as the next photo shows.
At bottom is the small frame. In addition to screws, it has two little
pegs to ensure that the knob shafts will be aligned. Notice the four
mounting screws on the front plate. Although it's not evident from looking,
their holes have enough elbow room to permit up-and-down adjustment. After
you attach the small frame to the front plate, you can move the whole business
up or down to make the gears mate properly and then tighten the plate.
Here is the tuner: cleaned, repaired, and relubricated. In this
photo, you can clearly see the four delicate wipers, which move
around their spiral coils as you operate the tuner.
When I tried out the mechanism, it worked exactly as designed! Click on the following
thumbnail to see a brief video of the tuner in action.
Installing the Tuner
At this stage, I couldn't wait to reinstall the tuner. Once this was done,
I could slide the chassis back in the cabinet, plug in the CRT, yoke, and
speaker, and power it up for the very first time!
The first step was to reattach the dial frame to the tuner and then restring it.
Restringing was no problem, given the detailed instructions in the Riders manual.
In so doing, however, I noticed that the shaft of the second idler pulley,
mounted on the dial frame, was slightly bent. No doubt this happened when
someone tried to force the tuner to move after the big dial pointer pulley had seized.
I thought I was being careful, but to my dismay the soft aluminum shaft immediately
popped out of the dial frame. Grrr! This shaft is held in its hole like a rivet.
Once it was out, I could see that the shaft wasn't bent. It had already
been pulled halfway out, leaving it attached at an angle. If I hadn't tried to
straighten it, the shaft probably would have fallen out before long, under
the tension of normal use.
JB Weld to the rescue! I glued the pulley shaft back into its hole—straight, this
time—leaving a dollop of epoxy around the base and on the other side of the frame
for reinforcement. A lick of tape holds it steady while the epoxy cures.
When it's ready, I'll lift the
string back over the pulley where it belongs. The swing arm is held
in tension with a spring and there is enough play in the mechanism to
do this without damage.
This little setback is irritating, but there are other things I can do
while the dabs of epoxy cure overnight, such as reinstalling the picture
tube and yoke in the chassis.
It's a new day and I can verify that the tuner works with the
strings in place. Click on this thumbnail to watch it in action.
The brass idler pulley is free to move sideways as the string winds
onto the spiral pulley.
The RA-113 dial is very stylish, gold on black. Like the continuous
tuner in my
RA-103, this one covers the FM radio
frequencies, which lie between TV channels 6 and 7.
At last we can see the reason for this fancy mechanism. Although there
are only 13 TV channels, the FM radio portion of the dial includes dozens
of stations. To aid in tuning, the dial pointer moves faster in the
radio portion than the TV portions, so that a fine adjustment of the knob
produces a greater response from the pointer.
Two short videos illustrate the difference. In the first one, three
half turns of the fine tuning knob move the pointer from channel 13 to 10,
a fairly short distance. In the second video, the same number of turns moves
the pointer farther, all the way from 108 to 96 in the FM band.
These continuous tuners were elegant and ingenious, but their complexity made
them expensive. They also, by their nature, could not tune in AM radio.
As DuMont and other manufacturers found, if you wanted to combine radio and TV, it was cheaper
to bolt an existing radio chassis into the same cabinet.
Now for an exciting moment in every TV restoration: the first power-up.
Here is the chassis in place, mounted sideways on the cabinet wall.
The picture tube hangs from the front wall and the yoke hangs from the
On top of the cabinet is a rabbit-ear antenna, allowing us to receive a broadcast
home TV transmitter. The gizmo in a clear Lucite
case with dials is my metered variac, which lets me increase the line voltage while
keeping an eye on how much current the TV draws.
When the power came up to normal, I was delighted to hear nice audio from
the speaker. The TV's front end and audio section are basically functional.
The power supply must also be working reasonably well.
The screen was completely dark at first, but that's not too surprising when you
haven't yet adjusted the ion trap magnet. When I did that, and turned up the
brightness control, a dim raster appeared. This is more good news, indicating
that the TV's yoke and precious flyback transformer are intact.
The television doesn't work perfectly, but it passed the initial smoke
test. Evidently, I didn't make any mistakes in replacing
all of those capacitors.
Adjusting the Ion Trap Magnet
Speaking of ion trap magnets, here's what this one looks like.
It's a flat metal bar with an adjustable collar to fit around
the neck of the picture tube.
There are various types of ion magnet, with one magnet or two, and some
use an electromagnet rather than a permanent magnet like this one. They
all serve the same purpose, which is to prevent "ion burn," a
darkening of the phosphor coating on the inside face of the picture tube.
The gun in the neck of a picture tube emits a mixed stream of electrons and ions.
To light up the screen, we want electrons to hit the phosphors in
the screen face, but we want to send the ions elsewhere.
The name ion trap is a bit of a misnomer, since the ions aren't really
trapped at all.
In picture tubes of this type, the electron gun is angled so that the
electron/ion stream initially points toward the side of the tube neck
rather than straight ahead. Electrons are
lighter than ions and they are easily diverted by a magnetic field.
The ion trap magnet bends the electron stream back into a
straight line with the picture tube face, while allowing the
heavier ions to shoot harmlessly out the neck at an angle. (For that
reason, a couple of manufacturers use the more descriptive term
"beam bender," rather than ion trap.)
An ion trap can be adjusted in two ways, by sliding it forward
or back on the tube neck or by rotating it around the neck. Like all
magnets, it also has polarity, so it makes a difference which side
faces forward. Some magnets have a little arrow to show
which side to point at the screen.
To adjust an ion trap magnet, simply move it around until you find the
"sweet spot" where it produces maximum brightness on the
picture tube. If it has no effect at all, try flipping it to face
the other side forward.
You can't hurt your TV by experimenting with an ion trap magnet
for a few minutes. Ion burn is a slow process and it takes many hours
to visibly damage a picture tube, causing a darker area in the center.
Service manuals are often silent on the subject of ion trap
adjustment, assuming that every technician already knows how to
do this. However, I found a helpful little note in the Sylvania
data sheet for my 17BP4 tube:
Direction of the field of the ion-trap magnet should be such that the
north pole is adjacent to vacant pin position number 8 and the
south pole to pin number 2.
Further information is found in the Installation Manual,
provided earlier in this article. If your RA-113 has a 17AP4
picture tube, the optimum ion trap placement may differ from
that for my 17BP4.
Moving the Chassis to the Workbench
Before powering down, I made some quick voltage checks to get some clue how
well the multiple power supplies were working. The lower-voltage supplies (filament,
B+, and so on) were reasonable. The high voltage for the CRT anode
was lacking, however, producing only 4KV, whereas this picture tube requires 12KV-13KV.
Small wonder the picture was dim, if the CRT was getting only one-third of the needed
voltage! It's pointless to mess with fine adjustments until I address this
fundamental issue. For that, the chassis will have to come back out, but I don't
need to remove everything. By scooting the cabinet up close,
I can leave the yoke and picture tube in place and plug them in while the
chassis is on the workbench.
The speaker is placed on the bench and plugged in. The CRT anode lead is left
disconnected. It's too short to reach the picture tube, and the tests I'll be
doing don't require looking at the screen, anyway. To keep the HV lead out of harm's way,
I taped it so that it hung inside a cardboard tube and then taped the tube
securely to the top of the chassis, with plenty of air space between the
connector and the nearest metal.
In the previous photo, I had just begun to poke around, using
my pattern generator for input and my oscilloscope to see what each stage
is doing with that test pattern. Here, the scope is connected to the video amplifier tube input.
The resulting pattern is ragged, but roughly what you'd want to see.
Not bad for a patient who just underwent many
transplants and who may still have undiagnosed ailments.
Replacing the Focus Potentiometer
In checking voltages, I soon discovered an obvious problem. This wirewound
focus potentiometer has three breaks in its windings. You can't simply solder
the resistive wire back together and the resistive element is cemented into a
trench in the heavy ceramic body. I'll need a replacement.
Rated for 1200 ohms and 25 watts, this is not an easy component to find.
The folks in the VideoKarma forum advised me that the focus pot is a notorious
weak spot in early DuMonts but you can get a 1000-ohm/25-watt rheostat from
Surplus Sales of Nebraska. The
replacement's shaft was longer than the original. I cut it down and
filed the end to fit the knob.
Troubleshooting Feeble High Voltage
With the new focus pot in place, I turned my attention to the high voltage
supply. In previous tests, the voltage doubler seemed to be doubling, but the
highest output was around 8KV, far short of the desired 12KV-13KV. Now
it measured under 4KV. With such insufficient HV, the raster was only visible in a
completely dark room.
A quick earlier check with my oscilloscope had shown a sawtooth waveform at the grid of the
horizontal output tube, so I initially focused on the circuits downstream of
that point: horizontal output, HV rectification, and the damper.
I made a lot of voltage and resistance measurements in those
circuits without finding a smoking gun. Calling on the folks in the Antique Radios
forum for ideas, I got lots of advice, and eventually
became convinced there was nothing seriously wrong in those circuits.
The only alternative was to look farther upstream, so I checked
waveforms around the horizontal oscillator tube,
comparing them to the models in the Rider schematic.
It didn't take long to find something peculiar. Here's the waveform
from terminal C of Z210, the horizontal oscillator transformer:
That's a nice sawtooth waveform, but it's a little too regular. This
portion of the schematic shows that we want a modified sawtooth, combined with
a sine wave to produce a shape with rounded "shoulders"
at the top, rather than sharp points.
An alert forum member from Italy remembered that he had had a TV with
exactly the same symptom (missing sine information at the oscillator, plus
deficient high voltage), which he cured by replacing the coupling capacitor
labeled C245 in this schematic. This photo shows the oscillator transformer
on which I have already installed the replacement. The little mica
culprit is in my hand.
The change was immediate. Here's the new waveform from the
same circuit location, now matching the model in the schematic:
I like easy fixes like that (thanks, Guilio!). The bad capacitor was the mica
type, which I usually consider quite reliable. Micas can fail, however, as
I found out when restoring my RCA 630TS and in a few other cases. Although
the other waveforms in this circuit looked decent, I replaced two other
micas in the oscillator circuit, while I was at it.
Earlier, I had replaced all five capacitors in the high-voltage doubler.
The last original parts in this circuit were three 470K resistors,
which form a chain between capacitors C402 and C403. Their values had
drifted somewhat upward, so I replaced them in the interest of
thoroughness. Again, the doughnut-shaped terminals are there to
impede corona formation.
These replacements significantly improved the high voltage output.
Troubleshooting With an Oscilloscope
I'm far from an expert in using an oscilloscope, but I try to learn a little
more in each TV restoration. In this case, the scope quickly revealed a
trouble source that I had missed.
I had previously checked both resistance and voltage values on the
tubes in the horizontal circuits, comparing them to the values given
in the Sams charts. Such tests can reveal certain defects, but not in
this case, where the voltage was correct but the shape of the
waveform was not.
Here's the oscilloscope set up to check the horizontal waveforms.
Everything is connected except the second CRT anode.
Watching the TV screen isn't important in these
tests. The useful information appears on the scope.
Most TV schematics include at least a few key waveforms and the test points
where they can be observed. I try not to get too slavish about these things,
but I've found it useful in recent projects to make a little library of
waveform photos, recording what I observed at certain points during
the restoration. These help me improve my scope skills and they may be
handy for reference if the TV develops a problem later on.
In hindsight, perhaps I should have been more systematic the first time I applied the
scope. I might have discovered cause of the HV problem earlier and avoided
testing circuits farther downstream, which turned out to be problem-free.
First Screen Images!
I had been working on this TV for a long time, never once having seen a
coherent image on the screen. A quick check showed around 10 kilovolts from
the high voltage supply, so I installed the chassis in the cabinet and
powered it up.
Wahoo! Test patterns aren't exciting to look at, but I was very gratified
to see this one. It confirms that the power supplies are working reasonably
well, the flyback transformer and rejuvenated picture tube are operational,
and so is everything else needed to produce a basic picture.
After more checking and adjustment, I tried showing a live picture,
using a rabbit ear antenna to receive a broadcast from my
in-home transmitter. That worked
well, so I switched to a DVD and got an even better image. Good morning,
This is a major project milestone, but my DuMont still hides a number
Curing the Horizontal Blip
Before long, another symptom appeared. At erratic
intervals, part of the picture would blip or twitch horizontally
for an instant, from left to right.
These blips almost never appeared when viewing a static test pattern but
they were frequent, although unpredictable, when viewing live content such
as a movie. Clearly, something was disturbing the horizontal synchronization.
When I reviewed the schematic, capacitor C264 seemed a likely culprit.
This 180-pf mica cap carries a signal from V220-A, the
second sync clipper tube, to V214, the horizontal oscillator, and to
V215, the horizontal output tube. If C264 is leaky, it might
pass a flaky signal and disrupt horizontal stability.
"Coupling caps" like this are found all over the television,
carrying signals from one stage to another. I had already replaced all
paper coupling caps as a matter of course, but this mica
had been left alone.
The first photo shows the old cap in place, a flat brown rectangle tucked
behind the adjustment pots on the rear panel. Not having a 180-pf cap on hand,
I decided to wire a 100-pf in parallel with a 82-pf cap, resulting in a
182-pf cap, which should be close enough. The second photo
shows the new cap in place.
Behind the new cap you'll see a new resistor. This is R288, the plate
resistor for the clipper. Since it shares a terminal with C264, I checked
its value and found it had drifted upward almost 20%. Better safe than sorry, so
out it went! Incidentally, this resistor's value is either 2700 or 3300
ohms, depending which RA-113 version you have.
Replacing that little cap cured the blips for good. It also convinced me
that the mica capacitors remaining in the TV deserve a close, hard look,
especially if they perform a coupling function.
Waking Up the Tuning Eye
Like my RA-103, this TV uses a 6AL7 "magic eye" tube as a tuning
indicator for both television and FM radio, and you can read more about the 6AL7
in my RA-103 article.
Every tuning eye that I've seen has a resistor hidden in its socket, and this one is no
exception. Replacing the resistor is often necessary, because when the resistor
drifts upward in value, it degrades the tuning eye's response.
Here's the old resistor tucked inside the 6AL7 socket. Its value had drifted to almost
double the original 3.3K.
Prying the tight-fitting metal cover from the socket took longer than replacing
the resistor. I had to fit a thin blade in the side slots and gently open them all
around, and then gradually lever off the cover.
With a fresh resistor inside, I saw a nice, responsive glow from the 6AL7 for
the first time. The magic eye is useful for tuning the TV as well as
the radio, giving a very precise indication when you have centered on the
target frequency. Tuning in this TV is different than on most sets, so refer
back to the owner's manual for the correct procedure.
My to-do list is shrinking!
Trying a Picture Tube Brightener
The high voltage remained stuck at a stable but deficient 10KV.
The picture was watchable in dim light, but if you turned up the brightness,
it would lose contrast and bloom (grow in size) slightly.
The faint slanted retrace lines are a signal that the brightness control has
been turned up beyond the optimum level. This is normal in a TV of this type.
What we want to do is improve the brightness so that you're not tempted
to crank that knob up too far.
While looking for solutions, I retested the CRT and discovered that it's
on its last legs. When I tried a second restoration with the Sencore CR70, it temporarily showed better emission but quickly reverted to its old weak state.
Further rejuvenation attempts probably won't do any good and they might kill the tube completely. Yes, the HV is low, but you can't expect much from a picture tube
whose emission tests far down into the Bad zone.
Someone in the VideoKarma forum asked whether I had tried using a CRT brightener,
which reminded me that I had a couple of old brighteners somewhere in the
workshop. I had gotten them in a box of assorted parts years ago, and
forgotten about them completely. Amazingly, one of them fit this tube.
The brightener definitely helped! After another round of testing and adjustment, the
TV looked good enough to watch and enjoy in a normally lit room. I'm almost ready
to take a break from electronics and think about touching up the cabinet.
A brightener is a small step-up transformer, usually in a round container, with
a picture tube base on one end and a socket on the other. When you connect it between the
TV and the picture tube, it slightly increases the CRT filament voltage,
producing higher emission and hence a brighter picture.
Most brighteners have short extension wires like the one shown above. This allows
them to be tucked into the available space near the CRT's backside. The following
photo shows another, smaller type of brightener. I found this on my
crusty old Admiral 24C15 TV, which is still waiting in the garage for attention.
No extension wires on this brightener. It simply piggybacks onto the
Picture tube brighteners were the cheapskate's friend in the old days.
When the serviceman informed you that your picture tube was almost worn out, he
could install a brightener to squeeze a few more months of life from it.
(If you're shopping for old TVs, always look for a brightener hanging
from the back of the picture tube. If one is present, it's a sign that the tube's days
Incidentally, I wouldn't put a brightener on a TV that doesn't really need it.
The elevated filament voltage might shorten the tube's life. I doubt that
my tube has much time left in any
case, so like the cheapskates of yesteryear, I'll leave in the brightener
and squeeze out a few more hours while I shop for a replacement
Adjusting the Screen Geometry
In the next session, I worked on screen geometry: vertical and horizontal
size, linearity, and so on. I also readjusted the yoke and ion trap
magnet. Here's the TV before I began, showing one of the test patterns
that I used.
The screen has plenty of brightness and you can also see the green
tuning indicator shining in the top of the dial. Geometry adjustments
don't make interesting reading, so I won't bore you with a bunch of
photos and descriptions like, "Note how I have adjusted the
vertical height and linearity so that the tiny white crosses at
center top and bottom now have equal size and just barely touch the
Another photo taken during the process. Sometimes, as here, it's useful
to temporarily reduce the height and width to fit more of the test
pattern on the screen. Otherwise, the rounded corners of the mask cut
off the pattern's corners.
Many later TVs have separate controls for vertical and horizontal
centering, but the DuMont does not. Instead, there are mechanical
adjusters in the back for canting the yoke up or down, and left or right,
relative to the screen face. These adjustments, together with
size and linearity, let you center the image with correct proportions
Geometry adjustments are interactive—for instance, increasing the
vertical linearity also increases the height—so it's normal
to go back and forth, tweaking one adjuster and then another, until
everything looks right.
Are We Done Yet?
Here's a brief video clip of the TV at this stage.
Click on the image of Scarlett to play the video.
The picture has really shaped up, but the audio volume is weak, much quieter
than my RA-103 tuned to the same station and using the same volume setting.
Increasing the Audio Volume
While checking the audio, I noticed that switching the function selector from
Television mode to FM radio mode dramatically increased the volume.
What's going on here? I first wondered whether this signaled
a problem in the AGC (automatic gain control) circuit, since the
function selector switch (S201) disconnects AGC for FM mode.
AGC, as you may know, equalizes signal strength between weak and strong
stations as you change channels. When you tune in a stronger station,
AGC reduces the gain of the IF (intermediate-frequency) amplifier tubes.
The purpose is to prevent overloading the video circuits and thus
distorting the picture. The audio signal is "picked off" the video signal following
the first video IF stage, so reducing the gain of that stage will
diminish both the video and audio signals.
A quick check of the AGC section showed nothing seriously amiss.
The VideoKarma folks confirmed that it's normal for this DuMont to
sound somewhat louder in FM mode and they suggested that I try aligning the
In a "split sound" TV, the audio section is essentially what
you'll find in an FM radio of the era except that it uses a different
IF frequency. The textbook alignment method uses a sweep generator and
oscilloscope, but I don't own a sweep generator. An alternative method
uses an ordinary RF generator and a voltmeter, and I have aligned a couple of
FM radios that way.
An even simpler method, if you're feeling brave, is to align it
"by ear," adjusting the audio IF transformer (Z202) and
discriminator (Z203) while listening to the TV.
I gave this method a try, first tuning the TV with a careful eye on
the 6AL7 indicator. The idea is to choose the spot that gives you
the best picture and then—without touching the tuner—peak the
volume so that you get the best audio at the same spot.
At the same time, I replaced a capacitor and two resistors at pin 1 of
the second IF tube, V202.
When recapping the TV, I had already replaced most of the capacitors
in this area: C281, C205, C206, and C207A. Now I tested
resistors R205 and R206 and found that both had drifted over 20% in value.
I had already found more than one questionable mica capacitor elsewhere,
so I decided to replace the coupling capacitor C204, too. Since they're
all wired to the same pin, it was simpler to replace all three than to
install two resistors and work around the old capacitor.
The result was a definite improvement in volume. It's plenty strong
in TV mode and will shake the rafters in FM mode if you turn the volume
up full. I'll repeat the process using a signal generator and voltmeter,
just to see how close I got with this simple method.
Substituting an 8XP4 Test Picture Tube
Ever since I got this TV, I had been seeking an 8XP4 test CRT. Designed
solely for TV service, the 8XP4 is much smaller in size and can substitute
for a number of tubes like the 17BP4.
Up to now, I've been able to power the TV on the workbench
by backing the cabinet close enough to connect the yoke and picture tube.
The CRT anode lead is too short to reach, however, so I've had to
leave it disconnected, which means no image on the screen. And with that
big cabinet in the way, it's hard to reach the chassis.
With the 8XP4, I can make tests and adjustments that require
watching the screen while accessing something under the chassis.
After patient searching, I finally got my hands on an 8XP4. Hooray!
This will allow a more practical bench setup.
Connecting the 8XP4 CRT
The first step in using the 8XP4 is to remove the yoke and focus coil from the cabinet.
They come off as a unit, shown here. The yoke with its copper coils
appears below and the focus coil is the larger doughnut shape above.
Because the 8XP4 is self focusing, leaving the focus coil in place would
result in a very blurry picture. I'll remove the focus coil's connecting
bolts and move it to the side, still connected by its part of the common
cable from the TV.
Here's my first view of the 8XP4 in action. The yoke is slid forward on
the CRT neck and I have plugged the CRT cable and yoke cable in as usual.
The sides of the image are circular, indicating that I haven't slid the
yoke forward far enough. The sides of the electron beam image are hitting
the sides of the CRT bell instead of its face. By pushing it all the way forward
and temporarily taping it in place, and then adjusting the height and width,
I was able to get almost all of the rectangular image on the screen.
I also built sturdy chassis supports by bolting heavy L
braces through existing holes in the plywood mounting board
and then screwing the brace bottoms into "foot" boards.
Now I can view the screen and reach every part of the chassis
without risk of tipping it over.
If you look closely at the screen shots, you'll notice a little
dark smudge at the very center. Because it uses no ion trap magnet, the
8XP4 unavoidably suffers ion burn over time. This is normal and it doesn't
detract from the 8XP4's usefulness as a temporary substitute.
These little sub CRTs are wonderful time savers. I also own
a 5-inch 5AXP4,
which substitutes for earlier round picture tubes.
With my test CRT and chassis supports, the final adjustments went quickly.
After one more pass at the screen geometry and audio, I put the TV back
Here is the restored television.
While the CRT wasn't the greatest bulb in the world, with a brightener it was
adequate for watching in a normally lit room. I used the TV in this
condition for more than a year, keeping my eyes open for a stronger
A New 17BP4 Picture Tube!
In late December, 2011, a stock of NOS (new old stock) picture tubes
became available and I purchased a fresh 17BP4, still in its original
box. The brand name was Silver Glo and I believe the company was in
the business of rebuilding picture tubes.
The CRT was shipped in its original sturdy carton. Here it is on
the day of receipt, ready to be installed in my RA-113.
My Sencore CR70 tester showed that the new tube has very strong
emission—just what I was hoping to see!
My tube's warranty card was date-stamped September 20, 1965. Although
46 years old, there's no reason why it shouldn't perform as well
as if manufactured yesterday.
The old CRT can be removed without disturbing the chassis. After you slide
off the ion trap magnet from the CRT neck, taking out three
small hex screws allows you to remove the yoke from the hanging frame. Then
you can unscrew four nuts from the cabinet's "ceiling" and carefully slide the hanger down, and then back from the CRT neck.
The picture tube is supported entirely by a clamp around its front. To simplify
removal, I tilted the cabinet and rested its front edge against the wall, padded
with a towel. Then I removed the mounting nuts from the cabinet
front and carefully lifted out the CRT.
Here are both tubes side by side. I can't wait to try out the new one!
Notice the brilliant shiny coating inside the new tube. No question, it's
aluminized, just as the box says. Perhaps the company name Silver Glo
means that they rebuilt only aluminized tubes. An aluminized picture
tube is brighter than its non-aluminized counterpart and it
doesn't require an ion trap magnet as my old one did.
The CRT clamp has three parts: the hanger that screws onto the cabinet
front, a thick rubber cushion, and a steel band that tightens around
the tube's perimeter to hold it safely in place. After cleaning, the clamp
ready to install on the new tube.
For the first trial, my pattern generator produces a crosshatch
image, allowing me to level the yoke. The new tube looks very bright—so strong
that I had to turn the brightness way down to avoid washing out the image
in a photo.
A few minutes later, I was trying it out with a movie DVD. Hello, Scarlett!
In my eagerness to play a movie, I hadn't noticed that the vertical centering
needed a little adjustment, to eliminate the black bar at the bottom of
the screen. No worries, within a couple of minutes that was fixed and
my RA-113 looked like a million bucks.
My picture tube cost a little over $100 including shipping, but I consider
it money well spent. Finding a NIB picture tube for a vintage
television is almost unheard of these days, and with a sassy new CRT, I should be
able to enjoy my DuMont for a long time to come.