I have a large Allen organ that followed me home in the fall of 2009. It had one helluva hum in the audio output amplifier, so I recapped it, all except 2 bumblebee caps, and a tiny electrolytic between the first and second audio stage. It has performed well until now.

I've got some distortion that I *think* seem to be getting from the low tones off the tone generator. It's power supply is filled with electrolytics, but seems to work properly.

The audio comes from the generator, thru a tone control network of capacitors and resistors. All caps have been replaced here, and the resistors checked. Then, it goes to the amplifier.

Im looking at sine waves on my scope, and I can see definite distortion.

The Allen Organ Company kindly sent me a PDF of the organ systems, and voltages on B+ are about 35 volts low. It has a large selenium rectifier that supplies power to the relay networks, and it checks out OK.

I am concerned with the type 83 rectifier. I replaced the original, which would glow bright blue when a chord was played on the keyboard. The replacement, also marked as an 83, shows nothing when chords are played.
I know this rectifier has mercury vapor, and requires some warm-up time. The system has a 15 second time-delay on B+ to the tone generator.

The electrolytics on the power supply chassis are cool to the touch, and are not leaking. There is no hum anywhere.

Does anyone on this forum know how to troubleshoot this creature? Should I start replacing the electrolytics in the generator supply? Like I said, the B+ is constant throughout the generator, but a bit low. All tones are correct, except for a couple, and I am substituting capacitors to bring them back to life. When it arrived here, about half of the keys didnt sound correctly.

I am posting this here because there is no real place at Audiokarma for this.

Here's some images of what I'm dealing with here. Also, the rectifier on the main power supply in the pics is an 84. It's all I had at the time. The 83 is in there now. The tone is still distorted using the 84, also.

Thanks for looking!!

I've never worked with an 83 rectifier, but I understand that it's best to run them with just filament voltage for a minimum of 15 minutes before applying the HV if they've been shaken around by handling and installation.

We used to have a Thomas Organ. To generate the tones they used 12AU7 oscillators. One for every three keys. They assumed you wouldn't be likely to play notes adjacent to each other.

The initial power draw must have been enormous.

John

I sure hope to get some ideas here on this. This Allen is FULL of 6SN7's, all Sylvania branded. All check right at 100%.

I rebuilt the generator on a Baldwin about 20 years ago, but it was nothing like this Allen. Plus, it is still working today... It has about 60 12AU7's and around 15 12AX7's, along with several 6L6GA's. If it ever dies, I will have a load of valuable tubes!

Got email from Allen Organ Company this morning. The B+ should be higher than what I am getting. They suspect the 83 tube. It's only a year old, and was expensive!!
When I got it, I let it run without B+ for about 30 minutes... I pulled the time-delay relay per instructions. The organ is too big to move around. I have it sitting where I can get in the back with very little work.

When this organ is running right, it sounds great. This new problem happened all at once...

We're going to dig up the OEM 83 tube today and see what happens.

Bruce

Good luck with this project! It's good to hear of an organ being restored and fixed
rather than cannibalized for parts...

Thanks Electroking.

I couldn't let this organ get trashed. The cabinet is beautiful, and we have always wanted something like this to play with.

I was looking for a big Baldwin, since I have a pair of nice Baldwin tone cabinets, but this came along.

The Allen company told me this organ was built in April of 1955, and was sold to someone in Chicago. How it wound up in Asheville, NC, is the little mystery. The people that donated it to the thrift store told them that it worked. There's no way, as the 5U4G rectifier on the amplifier chassis was missing. I tested it for the thrift store, and after I told them it would only work with some work, they told me to haul it off, if I wanted it. So, here we are.

I'm going to sub some of the electrolytics on the big power supply chassis. An Allen tech sent me email to let him know what I find. How about that?!! A 55 year old organ, and they are willing to help me with it!

I forgot to mention, when I got it, the expression (volume) pedal was broken. It's pot metal. The Allen company GAVE me a new pot metal assembly that I simply had to transfer parts onto the new one from the old assembly. I tried to pay for it, but they told me they were just happy to see one of these old instruments being saved!

Bruce

With the help of the Allen company tech, I pulled the B+ supply line for each of the generator tone sections. B+ is staying constant at 370 volts. Should be 390 or so. So, I have eliminated the generators as being the problem, as the LV should have gone up to normal if there was a problem here.

I have replaced 7 of the 13 electrolytics in the power supply now. There are 4 large power resistors there, too, but they check within specs. No change, yet in the B+.

I'm still looking for the old 83 tube. I moved it when I moved my 23" Maggie B/W TV combo into the house. It's probably in the bottom of a box right now. It will turn up, but the problem is when?

Fascinating piece of equipment.

Are all those tubes 6SN7's? so many of these get trashed because there's $1000 worth of Audio tubes in them.

I don't know anything about fixing an Organ but I would guess they suffer the same problems as all gear that old, bad caps, drifted resistors and so on, recapping this looks like a year long project!

What does the big gray Selenium do?

The big selenium is the rectifier for the 48v supply for the relays. Allen told me that they rarely cause any problems being used this way. It is running perfectly at 47v. IF something happens to it, there is a 1 amp fuse on the power transformer on the chassis that WILL blow.

All of the tubes in the generator, other than the 83, and the tubes in the amplifer on the chassis to the bottom right, are 6SN7's, all Sylvania, and all original, and all good.

I have about 70 more 6SN7's that are Baldwin branded that were pulled from a water-soaked very damaged console that I ran across a few years ago. Someone else had snatched the speakers from it, but I did get 6 6L6GB's, and a 5R4GY.

The amplifier uses a 5U4G, 2-6L6GA's, 1-6SL7GT, and 1-6J5. It's driving a 12" woofer, and the pair that are belt driven, are 6" ones. They produce a bizarre vibrato effect when they are turned on.

I'll be glad when we get this fixed again. I want to do some more work on the bass pedal generator... the one with the white coils in the picture... beside the 83 power supply. Only one bass tone series sounds, and there are 4 that can be selected.

The good thing here is that all I have to do is ground individual wires on the keyboards to make the generator sound any given note. I'm learning as I go with this one.

Bruce

I've subbed and/or replaced all electrolytics on the power supply. Nothing has changed on the B+.

I've located a new 83 tube. I couldn't find the one that came with the organ.

Allen says that occasionally, the rectifier could arc and short the winding on the power transformer. Sure hope this is not the case.

I replaced the GE 83 tube with a NOS RCA 83. I'm getting the good blue glow around the plates now, like the original 83 did, when playing any note on the generator.

The B+ jumped 25 volts. Now, the generator sounds good again.

We moved on to another minor problem. Now, the expression pedal, which is tied to the first pre-amp stage of the amplifier, has little effect on the volume of the organ. The PDF that Allen sent me has a problem with this page. I can barely see it.

I have a feeling that the few remaining capacitors in the amplifier itself are failing. Unfortunately, I cant tell what they are by reading the cases. They've been cooking in this oven for 50 years!! Hopefully Allen has a clean copy they can spare.

Just wanted you to know that progress is happening here. I'll get back to the DuMont, and the Magnavox TV's very shortly.

All the best,
Bruce

Success!

Got a schematic from Allen this week. I discovered that I had the capacitors that are burned on hand, and replaced them. The amplifier is clean again.

Now, I can continue with the repairs on the generator. Nearly everything is working now on the main keyboards. The pedals are another story. Only one tone is working on the bass right now. Should be 6 of them.

I have never worked on an organ but I found a neat book about a month ago:

Title: Servicing Electronic Organs AKA Sams Org-1
Authors: Pittman and Oliver
Publisher: Howard W. Sams & Co.
First edition, 2'nd printing 1965

Covers the circuitry used by various manufacturers.
If anyone is interested, you might find one on EBay or Amazon.com

Thanks for this information.

I'm having good luck with substituting capacitors and getting the tones to respond again here. I have a friend that drops by every few days and he has 'perfect pitch' when it comes to music. I've got almost perfect pitch, and an A-440 tuning fork, and can hear irregularities in chords.

I now have 2 of the bass tones sounding.