A100 Distortion

[gtojimmy]

Hammond A102/Leslie 122A

It's like the movie "Ground Hog Day"! Every time I do something to this organ, something else pops up!

I now have a distortion in the bass, and if I select A# preset and set drawbars to 80000000, and then play a C chord, it sounds weak, and modulates like vibrato!
So far, I've recapped the AO28 along with changing some resistors, the AO39, cleaned drawbars with deoxit, did a buss bar cleaning a year or so ago.
Due to other issues that were popping up like a very pronounced hum, I pulled the preamp back out and went through my work. Although I didn't see anything, I rerouted a few wires, resoldered a few joints, and put it back in the organ. At that point, it sounded great, with really good strong bass response, nice crisp treble, everything worked great.

A few days pass, start it up, sounds like it's getting worse every time I start the organ. Weak distorted bass that makes the organ unplayable!
Pulled the preamp tubes, shot a little deoxit in the tube sockets, worked the tubes in a out a couple times, put that all back together...no difference.
The only thing I haven't done is replace the tubes in the preamp, and some are hammond, so they're 60yrs old. I've held off on changing the tubes, as several knowledgeable people say it's rarely tubes that cause problems like this, but I'm out of options. I just can't understand what would degrade so quickly from great to nasty other than tubes?

It sounds the same through the internal speakers, and through the leslie, so I'm assuming it's upstream of the power amp.

It's getting close to becoming firewood !
The sound in the video is coming through the organs internal speakers, leslie unplugged, vibrato off.

https://photos.app.goo.gl/RSjXHmnCt2qsQFPC8

[Goff]

How's the Leslie cable connectors? How is this connected organ to Leslie? Sometimes the Amphenol doesn't sit right in the socket and you get weird sounds and responses.

You didn't mention the power tubes in the Leslie. You have a spare set to swap out just to check?

Just a thought.

[gtojimmy]

How's the Leslie cable connectors? How is this connected organ to Leslie? Sometimes the Amphenol doesn't sit right in the socket and you get weird sounds and responses.

Just a thought.

Installed an 8101 kit to control the leslie, but I can unplug it from the organ and I get the same symptoms through the organs internal speakers.

[Goff]

Installed an 8101 kit to control the leslie, but I can unplug it from the organ and I get the same symptoms through the organs internal speakers.

Ok...can you clip a pair of headphones to the out on the AO-28 to see if the pre amp is distorting?

You should have at the ready a complete set of AO-28 preamp tubes as well as for the AO-39 power amp.

It's part of owning a console.

[gtojimmy]

You should have at the ready a complete set of AO-28 preamp tubes as well as for the AO-39 power amp.

It's part of owning a console.

I do for the AO39 but not the AO28...
I used to work on old TV's and had boxes of tubes everywhere. But that was back in the day when you could run over to the corner store and you'd find a tube tester, and a stock of tubes. TV's went solid state, and I had a "cleanout" one day, and I got rid of all of the stuff..tubes to signal generators, o-scope, the whole shebang!
I've owned a D, BV, B3, C3, A100, and now A102, and several leslies, all 122's and a 222. Never worried much about tubes because there was always a local source but no more.

[handyczech]

A fine source is Tonewheel General Hospital. Please do not dump the organ. An enthusiast would probably take it off your hands. Others here much smarter than me would tell you to start at the generator output and trace back to and from the preamp based on the service manual, which is an essential part of owning an older Hammond. The BV I bought was inop, I am mot an electrical expert, but I worked my way through replacing caps, tubes, cleaning, spraying and today, it works as new. Patience!

[Goff]

Never worried much about tubes because there was always a local source but no more.

That makes it even more critical to have a set of AO-28 tubes because those odd 6x4, 12BH7, 6AU6, 6C4 are not common anymore. When the people who sell these version tubes do what you did and get rid of it all or pass and leave the lot to someone else who hasn't a clue, there goes the hope to find them and in good running condition. And as these organs get passed to others, equipping them with spare tubes for these will help assure they won't end up modified or in the junk yard for a few more decades down the line.

Anyway if you had pre-amp tubes for the AO-28 you would have one way to check if it's the tubes or not.

I don't go along with the notion that it's rarely the tubes. 60 year old tubes are just old enough to be end of life tubes.

There are still vintage NOS made in USA tubes available for the AO-28. Get some while you can.:-B

[gtojimmy]

A fine source is Tonewheel General Hospital. Please do not dump the organ. An enthusiast would probably take it off your hands. Others here much smarter than me would tell you to start at the generator output and trace back to and from the preamp based on the service manual, which is an essential part of owning an older Hammond. The BV I bought was inop, I am mot an electrical expert, but I worked my way through replacing caps, tubes, cleaning, spraying and today, it works as new. Patience!

I was joking when I said I'd chop it up...just a little frustrated!
I've owned several tonewheel hammonds for the last 55yrs and will always have one. Just driving me nuts as to why it changes day to day ! I've done enough electrical and electronics work to have enough knowledge to know what not to grab or touch, and can read a schematic, so I'll just keep plodding along. I've made quite a few purchases from Tonewheel, and I'm going to order a set of preamp tubes and go from there.

Update: Just ordered a set of tubes for the preamp from Tonewheel...we'll see what happens. Maybe V3 and/or V4 are the offenders?

[Hamman]

I know you said you went through the preamp AO28, but I have, in the last 3 or 4 years have had Can Caps go bad within months of replacing them. Not all failed can caps produce a hum when failed......your symptoms are suspicious on my list for rechecking those can caps....just saying

[gtojimmy]

I know you said you went through the preamp AO28, but I have, in the last 3 or 4 years have had Can Caps go bad within months of replacing them. Not all failed can caps produce a hum when failed......your symptoms are suspicious on my list for rechecking those can caps....just saying

You think it would be a problem if I subbed them with axial electrolytics and left the cans for aesthetics?

[David Anderson]

Just a general thought: I find it more helpful to identify the problem first and then take steps to fix it rather than replacing parts based on guesswork and speculation.

[gtojimmy]

David, I agree with that,and would apply in any discipline, but it's like trying to hit a moving target...every time I go near this thing something's different!

I was a mech. tech in an industrial plant for 35 yrs and did not and would not start changing components to repair a hydraulic circuit, for instance. You followed a tried and true troubleshooting procedure by following a schematic and common sense to find the issue, and in this case, maybe I'm dealing with multiple issues, as it won't stay broke!

[KC9UDX]

You think it would be a problem if I subbed them with axial electrolytics and left the cans for aesthetics?

I do this all the time with radios. If I get ambitious, I even gut the can and install new capacitors inside. (If you do that make sure the can is vented or you're building an eventual pipe bomb).

[David Anderson]

These days, the most advanced technology is actually found in radial electrolytic capacitors. Axials are mostly legacy production, and within the last year, I had a Sprague Atom that was questionable out of the box.

[Drawbar Dave]

What would be your favoured brand of radial electrolytics now? When I use Farnell I tend to go for Panasonic if I can.

[David Anderson]

Panasonic, Nichicon, United Chemi-con. Never had a failure with any of those.

[KC9UDX]

I've been much chided for waiting until it's absolutely necessary to replace electrolytics for this reason. I've had just enough brand new capacitors go bad in a short time over the last twenty years to justify leaving a working eighty year old electrolytic in service almost every time.