Hammond Solovox Tone Cabinet (1948)



The Hammond Solovox is a pioneering electronic keyboard instrument, dating from the 1940s and manufactured by the Hammond Corporation, famous for their organs. It was created by Laurens Hammond, the company founder, and engineers John Hanert and George Stephens.

Much of the following article was written thirteen years before I acquired another, similar 1940s electronic instrument, a Gibson Clavioline. The following photos picture the two instruments separately, with the Solovox on the left:


My Clavioline is a recent (Fall, 2011) acquisition. When I get a little more time, I'll compare their performance and perhaps have more to add to both of their articles.

Finding a Solovox

When I spied a mysterious cabinet with a speaker at a thrift store, I was immediately intrigued. The brass plate on the back declared it to be a Hammond Tone Cabinet. Now, Hammond was a big manufacturer of tube-powered organs, but if this is a musical instrument of some kind, where's the keyboard?


If you have ever peeked inside a tube organ, you know that it will have many more tubes than the thirteen seen in the back of this device. With so few tubes, what kind of music could this critter make—if it generates music at all? Pondering for a moment, I decided that the tubes alone were worth more than the asking price, so, partly out of curiosity and partly to save it from a worse fate, I handed over the cash and hauled it home.

The mystery was quickly solved when I posted a query to the rec.audio.tubes newsgroup on USENET.

One of these followed me home, and now I'm curious.
This is a knee-high wooden cabinet, very shallow, with
13 tubes and a decent-sized speaker inside, and a big 
flat sixteen-pin connector on the end of a cloth-covered cable.
The cabinet has a flat back and rounded edges -- perhaps 
it was meant to stand against one end of an organ. A brass 
plate identifies it as a Model L tone cabinet, to be used with 
a Model A keyboard.

Anybody familiar with this mystery device?

This reply came from Thomas Lehman:

This is a Hammond Solovox cabinet. The part you are
missing is the little keyboard that attached to the front of
your regular piano keys. It allowed you to play single note
organ solos while you played the piano. The keyboard had
voice controls and a leg operated volume lever.

This patent drawing shows the Solovox keyboard, mounted on a piano:

All very interesting, but without a keyboard, the Solovox can't make any music! I owned the silent tone cabinet for about two years before I found a keyboard for sale. The seller owned a complete Solovox but he wanted to use his tone cabinet for another purpose. After we had made a deal for the keyboard alone, he abandoned that scheme and offered me the tone cabinet for an additional $15.

I didn't particularly want two cabinets, but I decided to buy his complete Solovox, including keyboard, and that's the one which I restored:

I later sold the first cabinet to another collector who had nothing but a keyboard.

The next photo shows my new keyboard, mounted to the workbench.

From left to right, the control buttons are labeled Bass, Tenor, Contralto, Soprano, Mute, Fast Attack, Vibrato, Deep Tone, Full Tone, First Voice, Second Voice, and Brilliant. You can learn more about these controls, and Solovox playing in general, from the Owner's Manual provided later in this article.

Restoring the Hammond Solovox

Restoring my Solovox was not difficult. Although its purpose is quite different, the Solovox's internals are not much different from what you'll find inside a typical tube radio: tubes, resistors, paper capacitors, and a few coils.

The keyboard, of course, has no counterpart in the radio world. It is complex, with delicate switch contacts and a number of coils and resistors inside. Unless a keyboard has been damaged, however, it should only require some cleaning.

My new tone cabinet worked, but its sound was rather weak and the vibrato didn't work at all.

My first step was to open the keyboard and clean the switch contacts with DeOxit. It's not necessary to completely disassemble the keyboard; as this diagram suggests, it's not a simple mechanism.

I also cleaned the volume control and four additional controls located under the keyboard. Those four controls are used to tune the keyboard to your piano and regulate the minimum and maximum volume.

Another important step for every old tube device is to remove every tube and clean its pins. If you do this one tube at a time, you won't accidentally switch two of them around. While each tube was out, I also checked it on my tube tester, to cull any weaklings (there weren't any).

Next, I removed the chassis and speaker from the tone cabinet. Here is the chassis on my workbench, ready for restoration.

The tan tubular components are old wax paper capacitors. I replaced them all with modern ones. My capacitor replacement article explains that process for those who aren't familiar with recapping.

When I was done, the tone was much stronger, the various voices were distinguishable, and the vibrato worked again. The vibrato was harsh, however, creating almost an on/off effect rather than a soft variation of pitch. I remedied this by replacing a resistor connected to the vibrato oscillator tube. As with some old resistors, its value had "drifted" with age beyond normal tolerance.

After restoring the electronics, I restained the cabinet to blend away a few scratches. Then I reassembled everything and mounted the keyboard under my workbench:

As you can see, new "orange drop" capacitors have replaced the old paper caps on the chassis.

Here is a photo of my younger son, Peter, trying out our freshly restored Solovox in the late 1990s:

A single-voiced instrument can't play chords, of course, but the Solovox can create a surprising variety of sounds. And, as Peter told me, you can use techniques such as arpeggios for chord-like effects.

In 2011, while home on a break from music school in Boston, Peter obliged me by recording a brief audio sample on the Solovox. Click the musical icon to hear it:


Solovox Schematics and Manuals

When I bought my Solovox, the deal included the original owner's manual and technical manual, both dating from 1948. I also have run across a couple of magazine articles which include schematic diagrams and technical information about the various models of Solovox (J, K, and L). The total documentation amounts to about 50 pages.

You can download this documentation from the following links. These are rather large files—a few megabytes each—and they are in .PDF format. To save a file on your computer, right-click on the link and choose Save Target As.

The Solovox Owner's Manual tells you how to install and use the Solovox, including settings for register (voice), tone, vibrato, attack, and so on. There are charts showing 77 different settings for orchestral instruments, church organ, and other interesting combinations. It also includes some music written for the Solovox.
The Solovox Technical Manual explains theory of operation and includes a schematic diagram, parts layout diagrams, voltage charts, etc., for Model L.
The Solovox Magazine Articles are from Radio Craft, November, 1940, and Radio & Television News, December, 1948. Written for electronic dealers and technicians of the time, they provide additional technical details, including schematics for models J and K.

Note that different Solovox models are not interchangeable. If you have a keyboard from one model and a tone cabinet from another, they will not work together without extensive modification (which is well beyond my talents).

If you are not able to download the documentation, just send me an email with your mailing address. The charge for the Solovox documentation is US$5 to cover the cost of photocopying and postage.

Thanks to Nils Sundquist of Eskilstuna, Sweden, for creating these electronic files for me to share with other Solovox owners.

Solovox Repair Article

More than 10 years after writing this article, I ran across a 1949 issue of Radio Electronics magazine that features an article about repairing the Solovox. Click on the icon below to read that article.

Written when Solovoxes were still fairly new, the article deals with a range of problems that might be found in any Solovox. Nowadays, sixty-odd years later, every Solovox will have additional problems due to aging, primarily aged capacitors and dirty or oxidized switch contacts.

Solovox Design

In 2011, I got email from Wilfred Høsteland, a Hammond historian in Bergen, Norway. He advised me that the Solovox was designed by John M. Hanert and the tone cabinet was designed by Laurens Hammond himself.

Wilfred provided this additional information:

The Solovox was introduced in 1940 (model J) which had a 
mechanical vibrato device. Then the model K came (1946), and
finally model L (1948). The main differences were in the number
and types of vacuum-tubes in the tone cabinet. It was said
that the Solovox was taken out of production in 1950, but it 
was still advertised in the Hammond Times until October 1953.
(The two last versions had electronic vibrato.)

There was also a "military" version, self-contained with speaker
and keyboard in the same cabinet, for officer clubs, etc.

And, the Solovox was made in different colors: black, white
and mother-of-pearl. The last two versions were made mostly
on special order from famous organists, such as Milt Herth,
who wanted to use it with their Hammond organs. A number of
Hammond recording artists, such as Lenny Dee, also used the
Solovox as a special effect.

The Solovox also was the basis for other Hammond products
like the Chord organ S-series from 1950, the Extravoice organ
(introduced in 1959), and the pedal-solo system in the RT and
D-100 concert organ series.

Wilfred's email inspired me to a little more research, which turned up three interesting Solovox patents.

Patent 2253782 covers the Solovox keyboard design and it was granted in 1941. It lists Laurens Hammond and George H. Stephens as the inventors.
Design Patent 124405 was issued to Laurens Hammond in 1940 for his design of the Solovox tone cabinet.
Patent 2233258 describes the electronics in the Solovox tone cabinet. Granted in 1941, it lists John M. Hanert and Laurens Hammond as the inventors.

Notes from Solovox Owners

Since originally posting this article over a decade ago, I have gotten hundreds of emails from Solovox owners, from as far away as Denmark and Japan. Some of these are pretty interesting. For example, did you know that there was a Solovox songbook? Here is a description:

Solovox Album, complied and arranged by John Finke, Jr. for
Theodore Presser Co. of Philadelphia. It has a copyright
date of 1941. It is subtitled: A Collection of Special 
Arrangements of the World's Best Loved Melodies for the 
Hammond Solovox. It contains 32 tunes, including Arkansas
Traveler, Oh! Susanna, Old Folks at Home, Turkey in the 
Straw, Home On the Range and Auld Lang Syne. 

I have never seen that book, but it sounds like a lot of fun.

The following note indicates that the Solovox is alive and well in polka circles:

I am a accordionist and have had a polka band for 22 years.
My first introduction to the Solovox came from America's 
Polka King and First Polka Grammy winner, Frank Yankovic. 
Frank had Solovoxes in his band in the late 1940s when they 
first came on the market and Frank had two of them in the 
band until the 1960s when he went to the Casio M-10 keyboard.
Many albums Frank recorded for Columbia records had the 
Solovoxes in use. Frank and his piano player in the band 
harmonized with two Solovoxes. Anyway, I have always wanted
one and yesterday I got one from a oldtimer here. He gave me
the Solovox that he bought in 1968 and used in his band.

In 2001, this email arrived from Hamburg, Germany:

Hello! This is Jurgen Lamke from Hamburg in Germany. I am a 
pianist and organist for North German Radio (NDR). In our 
broadcasting house we have a fine old "Welte-Funkorgel," a 
theatre pipe-organ. In the 1950s, the organist Gerhard Gregor 
installed a Hammond Solovox at this console. We still have 
this Solovox and I would like to repair it for further use. 
I am very interested in the documentation which you offer

In exchange for the documentation, Jurgen sent me two CDs featuring Gerhard Gregor playing the Welte-Funkorgel in the 1960s and 1970s.

This note arrived in 2003:

While helping clean out the basement of an old house, my 
son found a Hammond Solovox keyboard. He was told he could
keep it, as the house was to be sold and had to be emptied.
It looked pretty darn weird to us, never having seen or 
heard of one. The neat thing is that the vintage lettering
on front said "Pee Wee King!" He was in the Country Music 
Hall of Fame and co-wrote "Tennessee Waltz" and many 
other well known songs. 

Here's another trivia note about the use of a Solovox in recordings:

If you knew "Sugar Shack" and "Daisy Petal Pickin'" by Jimmy
Gilmer and the Fireballs, you may have noticed there was a 
Solovox in both of those songs. Norman Petty, who was also a
producer for Buddy Holly and the Crickets, did that part.

A Model K Solovox with Custom Cases

In 2014 I received an email from a fellow collector named Bruce, who purchased a beautiful Model K Solovox with custom-built carrying cases.


One of the cases holds the tone cabinet and the other holds the keyboard and a pair of telescoping support legs. Presumably, the legs and cases were fabricated for a Solovox player who traveled.

If you compare the rear photos side by side, you'll see that my Model L is constructed differently than Bruce's Model K, although they play essentially the same.


I have received many other emails from people who either owned a Solovox or had a family member who played one in a band. Keep those cards and letters comin', folks!

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