Peavey Valve King 100 head

[g1]

Do you think the tank is original? If not original you would want to make sure the tank code matches, as there are different grounding schemes on different tanks.

Don't think you ever answered this, please do so. Post any numbers found on the tank.
Also, when you had that short term where it seemed to be cured (by tube swap), did you check that the amp was otherwise passing signal and working, or was it just that the hum was gone?

[nickb]

It sounds to me that you are just hearing normal hum pickup off the power transformer. The only way to confirm is to use extension leads so you can move it away from all AC magnetic field sources. I had forgotten that this is the head you have there and not the combo. That it is going to make it worse for reverb hum.

C109 is a ceramic cap ( cost saving) and they do tend to be monophonic. I would not worry about it unless it's excessive. Same for the microphonic tube. Not a problem unless you can hear adverse effect when playing.

One little bugaboo here is the report that the hum went away temporarily. This one-off has not been repeated so could possibly be for other reasons and misinterpreted. Try your hardest to make it happen by chopsticking, pushing, pulling and so on. If it doesn't happen again I'd ignore it. If it's real it will surface again sooner or later for sure. If you can't make it happen there's really nothing you can do with any confidence.

[jondoe]

Sorry I missed the reverb tank details, it's a Ruby RRVS2EB2C1B, it looks like the original, or at very least it had acquired equal amounts of dust and grime as the rest of the head, it was passing signal and sounded fine.

I think the microphonic cap is a little excessive, it takes the very lightest stroke of the chopstick to sound like I'm hammering on it with a crow bar, I can imagine that causing problems. I've never encountered one like that in my short time tinkering with broken amps so this is a new experience for me. I'm going to pop out later and grab a new one, it can't hurt to swap it out. I've tried the head on a couple of different places in the house, just to see if it made a difference, but no dice on the humming.

The texture dial no longer causes oscillation in the low power mode, but does still the in high power mode, so I'll see if swapping out the cap makes any difference to that and the resonance squealing. I think this heads going to keep me busy, I have a Laney VC30 that is giving me the run around too, it's been one of those weeks

[nickb]

Just so happens I have a Valveking 2x12 combo on the bench today. The reverb is also rather hummy. With an instrument plugged in and it's volume turned down, I can turn every control to max and not have any instability even using the OD channel and with it's vol & gain boosts on. So, it looks like you may have a problem with instability but not with the reverb.

[jondoe]

Just so happens I have a Valveking 2x12 combo on the bench today. The reverb is also rather hummy. With an instrument plugged in and it's volume turned down, I can turn every control to max and not have any instability even using the OD channel and with it's vol & gain boosts on. So, it looks like you may have a problem with instability but not with the reverb.

I hope your ribbon cable doesn't fall apart like mine Nice to know that maybe the hummy nature of the reverb is a standard issue, I found it intrusive past 1/4 turn and gaining intrusiveness the more you cranked it. I've changed out C109, the microphonic nature of that cap is now drastically reduced to almost nothing, but in the process of taping and plugging/unplugging a signal from the high input I've noticed it can sometimes cause V1 to become microphonic, so I assume something's up with that jack

Further testing of the instability has shown that if I remove the Presence & Resonance section of the circuit (P400 connector) I can adjust the texture back and forth with no problems and the amp remains stable. If I reconnect it and play with the actual Presence & Resonance knobs I can make it unstable, or, setting them to a position that is stable, adjusting the texture will throw the amp out into crazy screeching again, so I assume this points to a problem with the Presence & Resonance section of the circuit.

[nickb]

I would interpret your results simply to mean that V1 is microphonic rather than that there is a problem with the jack. Try swapping them around to see if you can find a better one.

Instability can be quite tricky to fix. My gut tells me that there is nothing specifically wrong but rather just a combination tolerances of that are giving you higher than typical gain at that frequency. I don't agree that it points to a problem with the resonance/presence/texture controls as all these things affect the gain in one way or another. It's the total combined effect that matters.

Am I right is saying you need all of the controls cranked to get it to happen?
What is the frequency of the instability?
Do you have to have anything plugged in to make it happen? If so what is it's volume control set to and does it have any affect on the problem?

[jondoe]

I would interpret your results simply to mean that V1 is microphonic rather than that there is a problem with the jack. Try swapping them around to see if you can find a better one.

Instability can be quite tricky to fix. My gut tells me that there is nothing specifically wrong but rather just a combination tolerances of that are giving you higher than typical gain at that frequency. I don't agree that it points to a problem with the resonance/presence/texture controls as all these things affect the gain in one way or another. It's the total combined effect that matters.

Am I right is saying you need all of the controls cranked to get it to happen?
What is the frequency of the instability?
Do you have to have anything plugged in to make it happen? If so what is it's volume control set to and does it have any affect on the problem?

Ok, so this will make you laugh or cry. As usual I took photos of the tear down as I went, rebuilding it exactly how I found it, I do this so I don't miss/forget something. This head had been apart before I picked it up as a scrapper, so that should have been a warning sign. As I was concentrating on the resonance/presence area (perhaps wrongly as you say) I tested every component and found them all to be fine, so started to make my way through the circuit back to the main board. This is when I realised that the 3 pin cable connecting the two boards was plugged in the wrong bloody way round, so the circuit was working in reverse of how it should have been! Swapping the plug around immediately solved the problem, I can play with the texture/resonance/presence as much as I like and no instability. Problem solved.

The only reason I think the jack is at fault is it only manifests on the high input and can be cured by simply unplugging and plugging in a lead a few times, but i will swap the tubes around just to be sure, it's quite intermittent.

I'm making progress

[nickb]

Finding the plug thing is quite a relief. Glad you found it before too many hours and tears were shed Instability can be quite a rabbit-hole.

Yes, the jack has a bad shorting contact by the sound of it, but I would never describe that a microphonic. You can try contact cleaner but usually best to replace.

[jondoe]

Finding the plug thing is quite a relief. Glad you found it before too many hours and tears were shed Instability can be quite a rabbit-hole.

Yes, the jack has a bad shorting contact by the sound of it, but I would never describe that a microphonic. You can try contact cleaner but usually best to replace.

I guess someone gave up chasing gremlins, or caused them by their own actions. I had to replace the valve grips as the nickel plating was flaking off all over the place, I was worried that might be causing a short somewhere, but I had spent an age brushing, vacuuming and cleaning every trace of it before even turning it on.

I've re-flowed both the jacks and a good spread of components near them, that has resolved the intermittent problem that the chop stick was displaying when giving the jacks a good prod. So all I have left now is the noisy hum, which by the sounds of things is an additional Peavey feature? I've seen quite a few videos with the same symptoms on YouTube, seems a common complaint.

[jondoe]

Just so happens I have a Valveking 2x12 combo on the bench today. The reverb is also rather hummy. With an instrument plugged in and it's volume turned down, I can turn every control to max and not have any instability even using the OD channel and with it's vol & gain boosts on. So, it looks like you may have a problem with instability but not with the reverb.

nickb, if in the unlikely even of you having the Peavey still on your bench, could you take a voltage reading on the +14V circuit please? I'm assuming R212 should have +14v on one side, but mine is considerably higher.

[nickb]

nickb, if in the unlikely even of you having the Peavey still on your bench, could you take a voltage reading on the +14V circuit please? I'm assuming R212 should have +14v on one side, but mine is considerably higher.

'tis gone now. The +14 is unregulated and will vary dependent on a number of things e.g. relay settings, line voltage, tube types etc. I think you could have quite a bit more or less on there and it would not matter much.

[jondoe]

'tis gone now. The +14 is unregulated and will vary dependent on a number of things e.g. relay settings, line voltage, tube types etc. I think you could have quite a bit more or less on there and it would not matter much.

Hmm OK, that's good to know, its 10 volts higher, which seemed a little too high, but I admit I don't have enough experience so I was guessing. I have a crappy pocket oscilloscope so I might try and see if i can see where that excessive humming reverb sound is coming from, if that's possible. Fixing the hum is the last thing on the list

[jondoe]

I haven't made much progress with this head, although the stability of the clean/lead sections is now rock solid, I think I've re-soldered half the board, no amount of flexing and poking makes it drop out. This does still leave me with a reverb problem.



On the reverb diagram in the schematic there are P105/P108 leaving the opamp and P104/P107 returning I've discovered I have +11 DC on the P105 and P108, no DC on P107/P104, what I don't know is if this is expected? The wiring for P108/P107 is black, I thought these would be GND so wasn't expecting +11V there

[52 Bill]

On the reverb diagram in the schematic there are P105/P108 leaving the opamp and P104/P107 returning I've discovered I have +11 DC on the P105 and P108, no DC on P107/P104, what I don't know is if this is expected? The wiring for P108/P107 is black, I thought these would be GND so wasn't expecting +11V there

If you look at the schematic, the reverb drive side of the circuit has the tank connected in the feedback loop of the op amp. So the input of the tank must be isolated. And yes, there could be a voltage on those connections.

[jondoe]

If you look at the schematic, the reverb drive side of the circuit has the tank connected in the feedback loop of the op amp. So the input of the tank must be isolated. And yes, there could be a voltage on those connections.

I does look like R129 ties pin 1 to pin 2 on the opamp, so that does make sense. I don't have much experience on these circuits so I'm struggling where to find the source of the humming :/ Do you have any suggestions on the best way to progress with this?