Any Heathkit-Thomas organ owners out there?

[PRL-89]

OK, I know this is a bit 'off topic' for this discussion group, but I'm hoping one of you Heathkit enthusiasts might be able to help me out.

Bear with me...

A few years ago, I drove down to CT (from NH) to rescue a Heathkit-Thomas organ that was about to be scrapped. The organ was one of the original Heathkit organ kits and although it didn't work (power light came on, but that's about it) it appeared to in good shape cosmetically and electronically.  Once I get the thing home as disassembled, I discovered a couple of cracked tubes (tubes!) which I promptly replaced.  No change.  I then started checking the various outputs from the power supply with my DMM and found them to be higher than expected .  So I solicited help from my friend whose hobby (among many) is church organs (!).  Rather than cart my organ up to him, I loaned him the assembly manual (with schematics) for him to look over, with the expectation that he'd look through it to get a general picture of the electronics and then come help me troubleshoot the thing.

Skip forward two years.  My same friend was diagnosed with advanced esophageal cancer, and died a few months later.  He was a hoarder extraordinaire with a basement literally filled to the ceiling with every possible piece of electronic 'junk', tools, old computers, etc.  His widow was kind enough to let me search through the basement, to see if I could find the assembly manual I loaned him, but the task proved impossible (it would have taken me months to go through everything), so I finally gave up.  Without the assembly manual or schematic I was pretty much at a dead end.  So I tucked the organ away in a corner of my basement, applied my usual I'll-figure-it-out-later strategy, and moved on.

Skip forward another year.

After a brief online search I concluded that my organ's model was GD-232 (there was no model number label or sticker of any kind on the organ itself).  I was able to find the assembly manual for the GD-232 organ on eBay and promptly bought it.  An initial scan of the manual left me hopeful - all the diagrams and photos in the manual seemed to match my organ exactly.  But to be more certain I started walking through the manual step by step, to confirm that the wiring and components matched those in my organ.  Everything lined up for the few few pages I checked, but then things went south.  I discovered that some of the wires attached to two of the tube sockets in the amplifier section were attached to different socket lugs in the manual than in my organ.  I then discovered why: the two tubes in the organ's amplifier section in the manual are different than the ones in my organ (6BQ5 tubes in the manual, 6GK6 tubes in my organ).  I stopped any further checking at that point, realizing that, even though the assembly manual's GD-232 organ appeared to be functionally identical to mine (same cabinet, same chassis, same circuit boards, same wiring harnesses, etc.) the two are different electronically.  I suspect if I keep comparing the manual's wiring steps to my organ, I'll find other differences too.

My conclusion is that either Heathkit sold two versions of the GD-232 organ over time (one replaced the other), or sold a different model (mine) that is 'close' but different electronically to the GD-232 they sold.  Not that it really matters. The fact is I can't use the assembly manual/schematic I bought to troubleshoot my organ, because the two are different electronically.

Are there any Heathkit-Thomas organ owners out there who might be able to shed some light on this?

To keep this discussion out of the 'mainstream' topics, feel free to contact me via email.

Thanks!

[G. Beat]

The 6GK8 is similar to the 6BQ5, BUT does have a different base pinout (differences in wiring),
the supressor grid (g3) is not connected internally to the cathode, can take a little more plate voltage (HV DC),
and price difference.

6BQ5 / EL34 Pentode Tube : $39.95 (NOS)
https://www.tubesandmore.com/products/6bq5el84-pentode-power

6GK6 Beam Power Tube : $9.95 (NOS)
https://www.tubesandmore.com/products/6gk6-beam-power-amplifier

These vacuum tubes are normally wires in a 18-watt Push-Pull configuration (Audio amplifier section),
found in numerous vacuum tube designs (guitar amps, old church PA amplifier systems, small home audio amplifiers).

The 6GK8 / EL509 is popular since it was used in Eastern European TVs (horizintal sweep tube),
production continued into the 21st century, and significantly cheaper.
https://frank.pocnet.net/sheets/084/6/6KG6.pdf

18-Watt forum (good place to start your education).
https://www.18watt.com/viewtopic.php?t=18672

Audio Karma — swapping from 6BQ5 to the 6GK8 beam power tube.
http://audiokarma.org/forums/index.php?threads/6bq5-to-6gk6-swap-question.287616/

Thomas Organs sold its kit version (popular) via Heathkit.
Fully assembled versions were sold under the Silvertone brand by Sears, Roebuck and Company.
The company closed in 1979 (bankruptcy), but the Thomas name did return in 1996, under German / Malaysian ownership.
http://www.thomas-orgeln.de/pages/english/organs.php

[dwight]

Heathkit was known to change parts when cost or availability became an issue.

I would think that the schematic is still close enough to use for debugging.

clearly, you should trace the G3 connection to see if it makes sense.

You should be able to quickly isolate the oscillators from the output amplifier.

Tube audio amplifiers are no real complicated.

Dwight

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Sent: Friday, October 6, 2017 1:10:11 PM
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Subject: [sebhc] Any Heathkit-Thomas organ owners out there?

 

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[Gary Kaufman]

Gregory -

Sounds like you're bouncing between 6GK6 and 6GK8 - very different
tubes.  Also the EL509 is a 6KG6, not a 6GK6.  Tube Dyslexia!

As you point out the 6GK6 is essentially a 6BQ5 with a scrambled pin
out.  Most 6GK6's I've seen will actually handle 7189 ratings easily.

I'm sure the 6BQ5 <--> 6GK6 swap was due to parts availability.

Paul - should you need 6GK6's I have literally hundreds, and I'm also in
NH.

Way more likely that any problems with the organ are due to electrolytic
caps (assuming it was constructed properly in the first place).

- Gary

[G. Beat]

Gary,
Yes, a few typos .... but these vacuum audio amp designs are well documented
and as I noted used in a variety of equipment from that era.

gb

[Gary Kaufman]

G -

Can't tell you how many times I've had tube dyslexia.  It wasn't helped by how many variants of essentially the same tube were made with small changes in pin out or basing..
The 6GK6 is actually a relatively unknown and underappreciated tube.  Shhhh...

- Gary