OT - Bizzare tube Hammond Keyboard

[Joe Hart]

I just picked up a 1950's Hammond Chord Organ (S6 model).  It doesn't work, but it has 30 tubes in it!!

Tubes: 12AU7 (18), 12AX7 (2), 12BH7 (3), 6BJ7 (1), 6C4 (1), 6BA6 (2), 6V6 (2, output amp), 5U4 (1, rectifier)

My question is... I'm afraid to play inside this thing (you know the dying by frying thing).  But I suspect that it's just a blown tube because the thing is in really nice condition.  If I just replaced all the tubes and sold the old ones (I would guess most of them still work), would it sound better or worse or different, and about how much would it cost (new prices minus selling the old ones).  I mean, would it be stupid to do when it may just be one bad tube?  And what type of place would be able to do this type of work (I'm in the southwest suburbs of Boston, MA, and things tend to be a little pricey around here -- especially repair services).

Let me know what you all think.  Thanks.
-Joe Hart

For those interested in more info (and it does sound very interesteing), here's a description (or search the web for pictures, too):

Description: The closest thing I have ever known to a tube synthesizer! It was originally designed for the nonmusical masses to learn how to play a musical instrument but features absolutely unique sounds and technology not common to Hammond. This does not sound like a Hammond at all, mostly due to the fact that the technology used that comes close to music synthesizer technology. To explain: If you look at a B3, or any tone wheel organ from a technological perspective these are built on the principle of additive synthesis; which means: harmonics are added by means of drawbars. The Tone generator was designed and developed by Mr. Hammond, who was a clock maker before he started his organ division. The results of a tone wheel organ are those: absolutely precise tone generation which is completely steady and pure. Any impurity has to be artificially introduced by means of for example a scanner vibrato. "What abut the Chord Organ?" You may ask. Well It's tones are generated by highly unstable tube oscillators, hence the completely different sound. If a chord is played the tone is extremely lush and warm as all oscillators are slightly off tuning. But now to the parts that make this instrument even more a synthesizer compared to an organ: First of all, technologically speaking this instrument implies subtractive synthesis. Besides that being the same technology implemented in analogue synthesizers, this means that harmonics are generated by the harmonically rich wave form of the oscillator and then passed through a filter that subtracts or removes harmonics from the original signal. Back to earth: the combination of tube oscillator and LC filter yields sounds that can't be produced with any other instrument - warm and lush. - Absolutely the preferred qualities of analogue sound generation. No analogue synth sounds like this. I know, too much tech-speak, but here what really brings this machine into the realms of synthesizers: It has a "percussion" function that implements an envelope generator featuring attack and decay (uncommon for Hammond - yet another difference - B3 percussion does not compare!) for the solo voice and sustain for the bass pedal. While in contrast to an analogue synth this unit does not sweep its filters a similar swept filter sound can be mimicked. This can be done by the fact that the envelope influences solo, but not the polyphonic generation. Playing both together means to change harmonic content over time similar to that of a filter sweep. The signal heard is generated by the mix of a constant signal and that of an "enveloped" signal.The result: a completely unique instrument with a variety of sounds; quite a unique voice for electronic music. The percussion (old term for EG) provides nice synth like attacks as well. Can you imagine replacing the switches with pots to have more control over the "envelope generator"; or more control over the filter qualities?
Overall Perspective: Hammond freaks - this instrument is not for you. It's a complete odd ball - Go for the L-100 above and to find the famous sound you were looking for! - But: Vintage analogue freaks: this is your dream ship to heaven!)



Features:

• SWITCHES (Registration - left to right):
Volume Soft; Sustain Cancel (Bass pedal); Chords Mute; Pedal Fast decay (!); Organ: Strings, Flute; Vibrato Cancel (! to make this sound even fatter: cancel one and not the other): Chords, Solo Wide, solo Small; "USE AT LEAST ONE OF THESE" (Filters!): Bass, Tenor, Soprano; Solo Wood Winds, Solo Fast attack (!) - "ALSO FAST DECAY WITH SOLO PERCUSSION"(!); Solo Percussion; "USE AT LEAST ONE OF THESE SOLO TIMBRES" (Filters): Deep Tone, Full Tone, First Voice, Second Voice, Brilliant.

• MIXING CONTROLS (round knobs , see top left picture):
Pedal, Organ, Solo

• KEYBOARD: 3 Octaves, 136 Chord buttons, that when pressed play the labeled chord, Chord "Accent" Bar, 2 Bass Pedals

• OTHER: Expression Volume Control - operated by right knee, 2 speakers

• ALL TUBE TECHNOLOGY:
Tubes: 12AU7 (18), 12AX7 (2), 12BH7 (3), 6BJ7 (1), 6C4 (1), 6BA6 (2), 6V6 (2, output amp), 5U4 (1, rectifier)

[Aharon]

Congrats!!!!!
First I would find what's wrong with it,if it's a tube change only that one,I doubt it very much that newer tubes would sound better.In the other hand you may have a small fortune in older tubes depending on the brand and it may help offset the cost of repair if you sell them.
Are the caps ok?
Good find !!!
Aharon

[RickL]

I've got one of these in working condition. It was given to me by a wonderful fellow who owns a high end home organ store. All I had to do was replace a frayed power cord.

You'll find when you get it working that the pedals give the root and fifth of whatever chord you happen to be playing at the time, a very cool, easy to use feature.

I would guess that if someone took the time to get good at playing it, it could sound very cool with an almost accordian vibe to it.

[Peter Snowberg]

Congratulations!

Few things make me wish I lived on the East coast..... this is one of them.

I'm somewhat of a Hammond slut (even though I can't play organ or piano at all), I just love the engineering and innovation.

Here's a picture for the rest of the viewing public: http://www.premierorgans.co.uk/hammonds6.htm

I would NOT sell the tubes!!!! There may be some serious gems there! Chances are that the tubes (or all but one or two) are probably fine. I would guess that the organ needs all the electrolytic caps changed (just an age related problem). A dead filter cap may have caused the destruction of a 5 cent resistor and that might be the bulk of the problems.

I would first look at the filaments to see if they all light, if they do, the next thing would be to find a tube tester and test them all however that step isn’t mandatory. Make note as to which tubes came from which location and don't mix 'em up even though they're the same types. A moving target can be harder to repair when you're just getting started with tubes.

Now is a great opportunity for you to get into tube amp service. I haven't been killed yet and I've taken some NASTY jolts. Just give the circuit 100% of your concentration, discharge supply caps before soldering anything, do all testing with one hand in your back pocket, and don't do any of it after a chonger. You'll be fine.

Also make sure your meter is rated to take 600V. Just about every meter is. I like using an alligator clip to attach the ground probe so that I'm only dealing with a single probe. I also put some heatshrink on the end of my probes as insulaion against shorting adjacent pins. I like to use two or three layers because the heat shrink is soft stuff. Just leave 1/16" of metal sticking out.

Download a copy of TDSL from http://www.duncanamps.com/tdslpe/ so that you have pin references for the tubes.

You should be able to remove all the tubes except for the 5U4 and find high voltage at (probably) every plate connection. Again... keep track of which tubes came from where. If you have the 6V6s installed then be SURE to have a speaker connected!

Follow the power supply and see where the power stops flowing.

With the 5U4 as the only tube in there, test for voltage at pin 3 of each 6V6 and if it's there, I would add the 6V6s and speakers. You can use a 600V .01uF cap with an insulated probe connected to one of those 6V6 grids as an audio probe. The better probe connection spot is at the phase inverter input which will be the tube right in front of the 6V6s.

Test for voltage at pin 1 and pin 6 of each of the 12A_7 series tubes and the 12BH7s. Chances are that you should get voltage at most or all of them. If you don't get voltage, look at the wiring and see if those pins head off through a resistor and to the power supply. If you see the resistor and don't get voltage on both sides, you may have found a problem. You should be able to follow most (at least 50%) of the plate connections (pins 1 and 6 on 12A_7 & 12BH7) to a power resistor chain that ends up at the 5U4. Somewhere along that string of resistors I'll bet you have a dead resistor or a cap that is shorted to ground unless it's something simple like a single dead tube.

For replacement tubes, I think 12A_7 tubes with big plate structures sound much better in guitar and hi-fi apps.

With such a cool piece of hardware, you might want to seriously consider buying the service manual and the owner's manual. This place http://www.mitatechs.com/organcom.html has them and even at the $65 it's going to cost for both, the service manual will worth it's weight in gold just getting the thing running and the set will increase the resale value if you ever offload it. (and please PM me if you ever do!)

With a schematic this unit should be easy to repair. What a cool synth!!!!  Add a heavy duty distortion pedal for some really fun tones!

take care,
-Peter

[Joe Hart]

Congratulations!

Few things make me wish I lived on the East coast..... this is one of them.

I don't mean to rub it in, but I bought it at a yard sale... for $10.00... and they delivered it 4 miles to my house and carried it into my studio!!  I was very excited when I saw it and almost died when he told me the price!!

Anyway, thanks for a TON of great info.  I'll start looking into it!
-Joe Hart

[Peter Snowberg]

$10...... :shock:  $10........   $10........   $10........ :cry:

To quote EL&P....

Ooooooooooh .... what a lucky man.... he was!

I would love to know how it goes! Keep us posted!

Take care,
-Peter

[Gus]

First simple check.  Does it smell like anything is burnt?  Do the fils glow?

I would guess it is monophonic keyboard. you have an amp section and tone generator(s) and what ever else. work on it in sections