RCA 721TCS Console Television (1947)

              

              

This RCA 721TCS was among the earliest postwar TVs. After undergoing total restoration, this rarely-seen television reigns as one of my favorites.

Description

RCA introduced its model 721 in 1947, the second year of postwar TV production. This set derived closely from the famous model 621TS from 1946.

Here are four pages from RCA dealer brochures that describe the 721TS and 621TS in some detail (thanks to Jim Menning for providing these):

           

The 621 and 721 are electronically almost identical except for screen size. The 621's 7-inch screen was replaced by a larger 10-inch picture tube, making the 721 one of the "big screen" direct-view TVs of its day. (Projection TVs made a bigger image by projecting onto a screen, of course.)

RCA offered the 721 chassis (KCS 26-1) in two cabinets: the 721TCS console and the 721TS tabletop. Consoles like mine are much scarcer than the tabletops.

The two flavors of 721 have very few differences apart from cabinet size. My console has a pilot lamp in front, right below the grille. It also has a 12-inch cabinet-mounted speaker, whereas the tabletop has an oval 6 x 4-inch speaker mounted on the chassis. The generous speaker produces excellent audio, rivaling that of my DuMont RA-103.

Here is the 721 service manual from Rider's Television Volume One. To download it to your computer, right-click on the icon below and choose Save Target As...

The 721 has 21 tubes including the 10BP4 picture tube:

Tube Type Function
V1 6J6 RF amplifier
V2 6J6 RF oscillator
V3 6J6 Converter
V4 6BA6 1st sound IF amplifier
V5 6AU6 2nd sound IF amplifier
V6 6AL5 Sound discriminator
V7 6AT6 1st audio amp./bias clamp
V8 6K6GT Audio output
V9 6AG5 1st video IF amplifier
V10 6GA5 2nd video IF amplifier
V11 6AG5 3rd video IF amplifier
V12 6AL5 Video 2nd det./sync. limiter
V13 12AU7 1st & 2nd video amplifier
V14 6SN7GT Sync. amp./sync. separator
V15 6SN7GT Vert. osc./discharge/output
V16 6SN7GT Horiz. oscillator/horiz. control
V17 6BG6G Horizontal output
V18 5V4G Damper
V19 1B3GT High voltage rectifier
V20 5U4G Low voltage rectifier
V21 10BP4 Kinescope

If you're looking for 721 magazine ads, you can quit searching right now. In the immediate postwar years, RCA ran what I call technology ads, touting their picture tubes, TV cameras, and so on. When consumer sets appeared in these ads, it was only in a little corner inset, without any model number or pricing. For instance, this ad shows a model 630TS in an inset:

In case you're curious about RCA model numbers, in 1946-1947 the first digit indicated the year and the next two the number of tubes. TS meant television set and TCS meant television console set. Thus, model 621TS was a 21-tube tabletop made in 1946. 630TS was a 30-tube 1946 tabletop, and 721TCS was a 21-tube console from 1947. In later years, RCA introduced other model numbering schemes.

Finding the RCA 721TCS

I purchased this TV in August, 2011. My wife and I drove to pick it up in Forest Grove, Oregon, a 500-mile round trip. These photos show the set in our SUV after I removed the chassis and picture tube and stowed everything for the drive back to Washington.

  

As with other RCA TVs of this vintage, such as my 630TS, it's critically important to remove the picture tube for transport. The CRT's heavy front bell is supported only by small clips in the front of the cabinet, not by the chassis. (Before removing the chassis from behind, remove the front panel and pull the picture tube from the front.)

The next photo shows the cabinet after unloading at home:

I'd call this a Machine Age design, clean and stylishly understated. The cabinet has a walnut finish, with veneer on the top and sides. The removable front panel is built from several pieces of solid walnut, beautifully milled.

Here is the chassis as found. This TV was clean and obviously well cared for.

  

Seen from the rear, you can notice the family resemblance to my 630TS, with high-voltage cage at the right and a flat compartment for power resistors on the left.

The layout underneath is uncluttered. Recapping this television should be an easy task. In this view, the tuner is at upper left and the stout power transformer at upper right.

Electronic Restoration

After cleaning the chassis, I tested the tubes and cleaned all of their pins, as well as the tuner and all controls. The picture tube looked strong on my Sencore CR70 tester, a welcome sign.

Recapping did not produce any surprises. As often happens, the TV woke up in stages as I replaced more and more capacitors.

After replacing the electrolytics, I got faint audio and a dim raster with severe sweep problems and little hint of the video signal. Click the following icon to view an animated .GIF picture that gives you an idea what I saw:

After further replacements, the audio was outstanding and the picture had greatly improved, with better brightness and contrast, although the vertical and horizontal sweep remained imperfect:

Here's a look at the chassis after most of the work was done. In front is a pile of capacitors and resistors replaced up to that stage.

Not shown in the discard pile are the old electrolytic capacitors. Rather than restuff the old cans, I installed new caps underneath and left the originals above the chassis for appearance. For more on the pros and cons of restuffing, with illustrated descriptions of various techniques, see my recapping article.

While I was engaged in recapping, a fellow 721TCS owner reported trouble with mica capacitors in the horizontal circuits (you can read the full discussion in the antiqueradios.com TV forum). I decided to replace all of those micas to head off trouble.

The next photos show a cluster of six mica caps on the horizontal drive, frequency, and locking adjusters, before and after replacement:

  

One of the caps in that group had a value not easily found: 5pf, rated for 1.5 kilovolts. You could make a substitute by connecting two 10pf/1KV caps in series, which doubles the voltage rating and halves the capacitance, but I had no such caps on hand.

The next photo shows the best that I could do using available parts. Inside the insulating sleeve are four 22pf caps, each rated for 500 volts. The result is one 5.5pf cap rated for 2KV.

This replacement looks a little kludgy, and you normally want to stay very close to the rated capacitance when changing caps in horizontal circuits. I hoped that this cap would work well enough to let me continue restoring the TV, anyhow, while searching for an exact replacement.

After finishing off those mica caps, I replaced some marginal resistors in the vertical circuits and tried the television again. The results did not disappoint:

Here is the restored chassis. I like the compact size of this set. It's considerably smaller than my 630TS, yet it performs very well.

Time for some final adjustments, including an alignment of the audio section. In this photo, I have begun setting up by temporarily installing my 5AXP4 picture tube in place of the unwieldy 10BP4.

The little substitute CRT is much easier to manage on the workbench. After the chassis is back in the cabinet, I'll make the final adjustments for width and height.

Following a few more tweaks, the 721TCS performed as well as any of my 1940s TVs, with an extraordinarily bright picture.

Cabinet Restoration and Final Assembly

When purchased, the cabinet was in average shape, with assorted nicks and scuffs, plus a few little veneer chips around the edges. The bezel around the front panel had other problems; the finish had been scraped off in a few spots and its whole surface had a network of "alligator" surface cracks.

Before sending it off for refinishing, I took the cabinet apart. You need to remove the front panel to do electronic restoration, anyway, since the picture tube is drawn out through the cabinet front, just as with my RCA 630TS and Philco 49-1240.

The entire cabinet front can be removed as one piece. Notice how the rear of the CRT mask is recessed to fit the bulbous face of the picture tube.

  

The safety glass is held between two pieces of wood: the gold painted mask and the finished walnut front bezel. In the next photo, the gold mask and glass are sitting on the ground.

The cabinet was restored by Michael Mueller, who also restored my RCA CT-100, DuMont RA-103, and RCA CTC-11 cabinets.

I brought the refinished cabinet home in pieces and temporarily reassembled it for a coming-home photo.

In the next shot, I have installed the chassis and brought in the CRT. It will slide in from the front, of course.

It's vital to adjust the CRT supports to hold the picture tube snugly in place. This photo illustrates the four supports:

Each support can be slid in or out by loosening its screw. To ensure that the tube neck is straight within the yoke, the edges of the CRT should be an equal distance from the cabinet opening on the sides, top and bottom. You also want the supports to exert a bit of pressure, to keep the tube from rattling or slipping if you move the television.

After sliding in the picture tube, press it back as far as possible, so that the rear of the bell rests against the front of the rubber yoke cushion. If your CRT supports are adjusted correctly, they'll hold the tube securely in place long enough for you to put on the front panel.

After I reinstalled the front, I made final adjustments for height, width, and centering, and declared the project done at last. Here's the finished set.

The picture is outstanding and the audio quality is all that I had hoped. With a very strong CRT, this is the brightest 10-inch television in the house.

Final Thoughts

The 721TCS is not particularly difficult to restore and it's an excellent performer. As I accumulate more TVs, I need to become much more selective, but this one is definitely a keeper. It's historically important as well as a pleasure to watch.

This RCA will make a nice companion to my Capehart-Farnsworth 661-P, another 10-inch TV-only console with a tall, narrow cabinet:

One of these days, I should take a photo of the two side by side.

©1995-2017 Philip I. Nelson, all rights reserved