Ampeg B22X with multiple problems

[Helmholtz]

[QUOTE=Randall;n911809
Another thing is as I have mentioned, using the line out jack as a temporary speaker jack wired to the yellow 8 ohm wire, This one is not isolated like the other one, it is getting it's ground thru the toothed washer. Would this be a problem?[/QUOTE]

Do you mean the ext. speaker jack?

[Helmholtz]

[QUOTE=Randall;n911901]I scoped the sections of the can cap as well as the two 30uF/600v, and while I see a little fluctuation when the machine gun happens, it isn't much, and I amd not letting it bang on my poor speaker long enough to get a real measurement.[QUOTE]

Your DMM may be too slow to show the supply pulsation. But a scope (DC coupled) should show it as a line moving up and down.

While I don't think motorboating could hurt your shop speaker (assuming it's sufficiently rated for the amp), a power attenuator would help.

You might try to swap OT primary leads.

Did you check schematic voltages?

[Randall]

The ext, speaker jack is the impedence switching jack. The normal speaker is fed by an LR jack wired to the ext. spaeker jack. I have temporarily repurposed the ext. amp jack (line out) and wired it to the 8 ohm OT wire. I have tried it grounded y chassis, and floating wired to cap can lug, like the ext. speaker jack is. No difference.

When I was looking for voltage fluctuations during the machine gun sound, I was using my scope, and I didn't see a lot of change, at least not what I might have expected.

While checking PS voltages I discovered some were very touchy when probed, and would send it into machine gun mode sometimes. I also noticed the 7199 PI tube was sensitive to movement and tapping. I found I could make it machine gun briefly by rapping on the board next to it, so I reflowed all the socket pins and neighboring pads. This made it even worse, it went into machine gun as soon as the tubes heated up. I removed plate capacitor C17 to have a look at it, it measured fine and wasn't leaking, so I put it back in. Now, no more machine gun, I don't know why, but I will take it.

So now both channels are passing signal, which is progress. I can turn Channel 2 all the way up and get a strong signal, as long as I dont turn the bass or treble up past half way. Then I get a lous audible bass or treble oscillation. Channel 1 sounds like a loud, angry charging elephant turned up past half way.

My voltages readings are:

A 468
B 467
C 458
D 448
E 394
Y 354 It's worth noting that on the other side of 47K R59 C voltage drops to 345v, and is extremely sensitive to being probed. I makes a anasty loud BRRRRRRRRR.

V8 voltages

1 - 278
2 - 64
3 - 73
6 - 344
7 - 2.5
8 - 6.7

These seem way off. I suspect something wrong with the tremolo circuit, maybe that black box module VMIA?

I tried reversing OT primary leads a second time after the machine gun stopped, with the same results, immediate loud noise similar to the machine gun noise.

[Helmholtz]

I'm tired, so just a few comments for now:

- An ext. speaker jack is no line-out (different signal levels). The ext. amp jack (J5) might be used as a line-out though.
- Did you clean and re-tighten the 7199 socket contacts? Did you try a different 7199?
- The voltage drop across R59 should be 150V acc. to schematic.
- Only one OT primary configuration can be stable (as reversing the wires turns NFB into positive feedback). It is the one with the lower gain.

What is an LR jack?

[Enzo]

ANy chance your new OT has its wires reversed?

[Helmholtz]

Y 354 It's worth noting that on the other side of 47K R59 C voltage drops to 345v, and is extremely sensitive to being probed. I makes a anasty loud BRRRRRRRRR.

R59 connects between 2 PS nodes/filter caps (points C and Y). If point Y is sensitive, something must be wrong with filter cap C 28 and/or R59.
You said you replaced all filter caps?

[Randall]

An LR jack is really a male XLR plug. Ampeg used them for speaker connections.

Enzo, as stated, I have tried reversing the OT leads twice now, amp certainly doesnt like it.

I have replaced all filter caps and a few other small electrolytics on the main board. It was the first thing I did. I pulled R59, it measures fine.

I have tried clipping a fresh cap across all filter caps with no positive results. To follow your point of C28 maybe being bad, I will substitute another cap in that position and report back.

[Helmholtz]

I have replaced all filter caps and a few other small electrolytics on the main board. It was the first thing I did.

So - as it's a filter cap - C28 is new and well grounded?

[Randall]

Yes C28 is new and well grounded, although as discussed it is an odd grounding scheme, as there is no apparent chassis ground other than the input jacks.

[Helmholtz]

Yes C28 is new and well grounded, although as discussed it is an odd grounding scheme, as there is no apparent chassis ground other than the input jacks.

Main thing is that its neg. terminal has very low resistance to other grounding points and chassis.

[Randall]

C28 was originally a separate cap mounted with a bracket along side the two 30uF/600v caps and grounded to the cap can ground lug. The two 30uF caps are still externally mounted caps, but the C28 is now one section of the new 40/40/20/20uF can cap. I don't see why this would cause a problem, but please correct me if it is. It does eliminate the question of its grounding with respect to the others. Should I try to run a can to chassis ground?

[Helmholtz]

C28 was originally a separate cap mounted with a bracket along side the two 30uF/600v caps and grounded to the cap can ground lug. The two 30uF caps are still externally mounted caps, but the C28 is now one section of the new 40/40/20/20uF can cap. I don't see why this would cause a problem, but please correct me if it is. It does eliminate the question of its grounding with respect to the others. Should I try to run a can to chassis ground?

Should I try to run a can to chassis ground?

Only if the resistance between cap and chassis is above 0.5R. Forget about the grounding scheme, it's much more important to have close to zero resistance between all grounding points. But the ESR of the filter caps adds to the ground resistance.

[Randall]

I an confirm that all grounds are reading 0.3 ohms to chassis and 0.02 ohms to each other. my meter reads 0.1 ohms with shorted leads. so, I'd say grounding may not be my problem unless maybe one is failing under load, and if so how do we know if clipping a fresh one to each cap made no difference?

[Helmholtz]

[QUOTE=Randall;n912338]I an confirm that all grounds are reading 0.3 ohms to chassis and 0.02 ohms to each other. QUOTE]

Does this include all circuit grounding points or only refers to filter grounds?

[Randall]

This refers to filter grounds, output tube cathodes, ground side of PT center tap standby switch, input jacks, speaker jack, and ground to main board.