AO 28 fluctating distortion.

[uhoh7]

At first I thought my old Leslie had some kind of damage, but I've disconnected it at the speaker, and removed the cable. I have a trek II output and plugged it into my stereo, which never distorts playing music, even loud.

Exact same symptoms. You really hear it on the first two drawbars, but if I go low enough other bars will do it.

It will distort at low volumes, but more at high volume.

On the other hand, the same notes are clean with high drawbars.

With no notes depressed I can hear low flucuating static.

I've removed and reseated tubes on the A0 28.

Any advice apreciated.

Thanks

Edit: a bit of context: I've had the RT3 just a few days. It was in a garage/studio and seldom played in the past few years, but seemed fine. That climate was quite damp.

I've brought it to idaho, where it's in my living room. I noticed some eratic response to the swell pedal on early playing, which seemed to clear up well. These symptoms have just appeared, and might be related to the trim tower, or simply a short.

I have a Fluke 87v on the way, De Ox and a good soldering station. The organ has been oiled.

Thanks

[Sweet Pete]

Do you have a tube tester,or access to one? That's a great place to start. Don't have one? Get some spares.
Swap the 6AU6 tubes position.They are under covers beside each other.
Does the crackling occur no matter if vibrato is engaged or not?
Or does it occur on the vibrato or non vibrato tones? One 6AU6 is the normal channel; the other is vibrato.....

Sometimes there is dust and debris inside the expression control 'doghouse'
When the air cap vanes inside the cover get debris they short. Moving the pedal produces unmusical noises?
Careful with those little cover screws.A good blast of compressed air usually clears that issue up.
Have even encountered vanes that 'touch' which requires an allen wrench to reset the nut.They most certainly should NOT touch.
Can't remember the exact gap spec but eyeballing it centered as good as you can should be fine.A small amount of horizontal travel is normal.
While you have it open.....might as well set the trimmer to your liking.Mark/note the position before moving clockwise to it's end of travel counting the revs!
Back it off the same amount to 'reset' where it was,or play a while with different settings to see what you like.
The wider open you have it the less 'dynamic range' and expression travel.
Also note where the expression pedal fastener bakelite arm allen nut is before removing,wouldn't want to go beyond the set travel......
known to make bad noises when reset in the wrong place!

Could be a tube.Could be a resistor,a capacitor.....

All of this and more is covered in the service manual troubleshooting guides..Free downloads.Recommended.

[uhoh7]

Pete, you're a godsend. I will get cracking and report.

Since the doghouse has acted up from my first use, I'll try that first.

Vibrato does not seem to effect the static. I will double check and switch those two tubes.

I'd love to find a good tube tester, but I read it's not easy.

And I'll find the service manuals asap.

Fantastic outline of attack for newbie, I really apreciate it. I'll be set up to go after capacitors and resistors by next week, if it comes to that.

Charlie

[uhoh7]

OK, I've checked out and cleaned the doghouse. The dark green lead from pre-amp to trim and the coresponding line to air cap are sensitive and moving a hand near does increase static. I've moved them away from possible grounds. The air cap fins appear fine, no touching. I cleaned the Rheostat.

The 12BH7 did effect static on first touch, then settled down. I've ordered a new one.

Swaping vibrato tubes has no effect. Removing precussion tubes no effect. The 6x4 tube is bright red and hotest tube. But i get the idea my problem is unlikley to be related to this tube. Please correct me.

Ive ordered both Electrolytic Capacitor Kit and the AO-28 Refresh Kit from TWG.

Back to my piano for a bit, till the parts show up :)

Oh, one question: I have not remove the big Electrolytic Capacitors to clean. Is that a straight pull like the tubes, or is there a twist? They are well seated LOL

[Drawbar Dave]

The AO28 can caps have four tabs that go through four slots in the chassis mounting. They are twisted to hold it in place. You will see what I mean when you flip the amp over ;-)

On the tube Leslies the can plugs in to a socket so it’s easier to swap out.

[Sweet Pete]

Don't know your location,a tube tester like mine was a thrift store find for $50,and is certainly better than nothing,EICO 635,basic short and grid tests,not a full featured Simpson.
Good enough along with my ears,to find the weak ones and replace with better.A pencil eraser does a great job cleaning tube pins.Followed with an alcohol wipe.Good as new.

6X4 failure is bad news,rectifier tube should be 'known good',wouldn't want to let the smoke out of your transformers.
TWG has an AO28 fuse kit,pretty sure it's made by TrekII.A known good set of fresh tubes isn't really the answer.
I've still got the original 12BH7 in my '63,and the 6C4's too.They work great.Probably replaced the 6X4 twice in twenty three years.
12AX7,12AU7,6AU6 wear out faster.Nonetheless still last many hours/years of use.
I've had tubes that tested fine and sounded awful.My ears are the final test.

I have a Leslie147 that was recapped 'under the hood' with a 50/50 up top.A real botch 'get it done' type mod that worked for 15 years.
Located a Cinch Jones socket for the 4 section FP Mallory cans.
Will put things back to 'right' so the next custodian can replace it without re-engineering Don's great work!
Yeah,those cans are easy to replace.Don't forget to match up those symbols!

[uhoh7]

Thank You both again. I finally get the importance of the 6x4 LOL, ordered one.

Something else occcured to me as I slowly get up to speed here.


Leslie adapter by unoh7, What Leslie adapter is this?

My Brother (he's 78 and first played this blonde RT3 in 1960): "I had a guy come out and set the organ up to play any leslie, and multiple leslies. He died a few years back now." :( My brother sold all but a single leslie which he used connected to the trek II 1/4" output (825), but kept his cables and I got them. A number of 6-pin cables. I do know he had a 31H connected to the organ at one time. FYI I was the baby, now 61.

I grabbed the RT3 last week, and cables, then bought a converted 22H (and others), and brought everything home. Long story short, I plugged the 22H into the 6-pin and it seemed great. But now I understand the 22H likely has a hot B+ 200 vdc coming back into the RT3, which does not need it, and I'm starting to wonder if that could be the source of my problems.

At first I had no idea what the adapter above was. LOL. It's newer than the pre-amp, for sure. it's connected to three outlets below: 110AC, 5-pin, and 6 pin. My understanding is the B+ was needed with C2s etc and older as primary power source, and this arrived from the Leslie. But this changed with the B3, RT3 etc. These no longer needed B+. The 8000 kit handles that, I guess, but I have no idea what this kit is, and I fear it may not have been prepared for B+. I'm not positive the 22H is even sending it, as it has a 2-speed kit, and has been worked on, no switch tube.

I was in hog heavan blaring away with the half moon switching away, seemingly fine. But was I wrecking my AO 28, even possibly the transformer in the process?

OK, My fancy multi-meter is not here yet, but I have a couple basic ones. I want to be sure I don't fix the problem and then cause it again. ;)

1) 3 types of 6-pin cables no? Balanced, with pin 5 200vdc "B+", Unbalanced, Pin five is just part of switch circut, and the last is two channel I think. Is this a difference only at source and destination, or are the cables actually wired diferently, if so, how does a person check?

2) Leslie adapter aparently DIY by the now dead tech. Has a 60.00 price tag on the side. What should it do with that 200VDC coming from 21H? Could that be getting into the AO 28 and frying something? How can I determine the adapter's intent, and performance?

3) Inside the 22H, the B+ may be capped for all I know. Any easy way, short of pulling the amp, to find out...e.g with meter?

4) Fliping the A0 28 over to swap cans....am I removing the soldered leads to do that? Which is fine, but tips on removing the pre-amp for work apreciated. Good solder station in route also.

5) That warm red/orange 6x4 tube. I better order one? Or it being hot is normal?

6) Transformer: best way to test it?

I have the older Hammond manual now, but I don't see trouble shooting yet...Online there is another "B3/C3" service manual which seems maybe newer, but I have to join something to see it. Any links to what anybody thinks I should know/study right now apreciated.

Charlie

[uhoh7]

PLEASE IGNORE those questions, I've answered most myself. Just missed the edit post dealine, sorry. Really apreciate everyone's patience here. I hope to edit it shortly.

I should rename the whole thread: idiot's progress. ;)

I now understand the normal 8000 style adapter and pinouts and use of B+. My adapter is different as you see above. I'm not getting where the DC is coming from.....
Here are outputs to leslie:

Outputs by unoh7, "dot" at 9 o'clock,

pin 5 is untaken......so no B+ is taken for adapter here.

The tech who set this up, unfortuneatly no longer living, has split both Gs at the pre-amp, and sent a pair direct to the 5-pin and a pair to the mystery adapter, which adds the half-moon switch signal, I presume, and then two and only two modified Gs come out and we see them hooked to the G. AC as you see is bridged.

What I don't get at the moment: My converted 22H was switching with half moon. Doesn't that require DC current from either the B+ input (not used) or a socket which taps the 6x4? But it's also possible to tap it inside the preamp right?

Tracing wires I find the only hot input to the adapter is from the covered BN under the AO28 transformer.


Ben by unoh7, BN supplies mystery adapter, along with one ground.

This is a A0-28-1 with giant F

SO, isn't that BN normally a ground? I'm starting to wonder if the tech tapped B+ inside the preamp and routed it out there.


Adapter path by unoh7, on Flickr

Let's take a look. Note BN incoming upper center red. It joins the big Can, right next to where a line comes down from the 6x4. I'm gonna guess.....B+?

I think it may be time to learn to discharge capcitors.....

I have to say, this is getting fun, and I'm learning the basic electronics I should have studied years ago. I've put together literally 100 computers, and I swap drives and memory in an out of laptops all the time. I keep two specialized backcountry motorcyles going for a decade. It's about time I learn some basics.

Please, all input and abuse greatly apreciated. :)

PS Asuming this is 200 vdc on the BN, I could replace that by coming directly from pin 5 (untapped now) on the 6-pin amphenol receptcle. Would that be preferable?

While I'm down, maybe I should pull the amp on the 22H for inspection?

[uhoh7]

Hi everyone,

So, I'm slowing marching to Jerusalem on the A0-28, but now I have a queston.

I grabbed two kits from tonewheel general, which arrived:
https://ssl.tonewheelgeneral.com/bui...em_no=AO-28CAP

https://ssl.tonewheelgeneral.com/bui...o=AO-28REFRESH

I also have replacements for the left hand tubes, which I have not tried. My plan was to go after the electrolytic Cans, and use the refresh kit as well. I'm proceeding slowly though. I've got my new solder station and a Weller 260v as well. I'm getting some practice with them, and learning to read schematics. Also making up a capcitor discharge tool. I found a used fluke 87V.

But in reading today, I learn that recaping does not always improve the organ. Not just the TG caps. Also the amp caps?

Looking at the stuff I have from TonewheelGeneral, what do you think?

I think I will put those tubes in, and order the rest of my tubes maybe before I go after the cans. Just to see if my issue cleans up.

Input apreciated :)

[Jaim]

The recap argument is usually reserved for the TWG.
Recap the AO28 - should clean things up a bit. The resistors in the kit replace those prone to failure.

Jim

[uhoh7]

Thanks Jim.

I decided to replace tubes and check it out.

I had the doghouse cover off. I was getting some hum, which went away when I put the cover on. Percussion not working, it was before. So I don't think my issues have anything to do with caps at all, frankly. Just random crusty connections. :)

For now, I think I'll play it. :)