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Thread: Peavey Valve King 100 head

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    Lightbulb Peavey Valve King 100 head

    Hi all,

    I picked up this poorly head recently and was told "all it needs are some power valves" - which of course hasn't turned out to be the case. Since opening it up I've found a couple of dry solder joints that were causing the head to go dead after a few bumps or pressure in the right places, but for the most part with new valves it's working, however, after buttoning it up and testing it on a speaker cab I found the reverb function has increasing hum as you turn the reverb up, turning it down again makes it go away entirely. I've had the reverb tank off, checked it inside, made sure the resistance on each spring is good, cleaned the RCA plugs, etc. I thought maybe the OPAMP IC for the reverb might be dying, so I removed the old one, popped in a socket and put in a similar 4560 while I wait for the exact one to arrive in the post, but this made no difference. I've double checked most of the capacitors in the region of the reverb circuit, they all seem good, I've been over the power section for it and I think it's ok, although the multiple grounds confused me a little. I've found a number of Valve King schematics, but not one specifically for the head, just the combos, does anyone here have the head version? Although they seem almost identical there are a few bits missing here and there.

    Any nudges in the right direction greatly appreciated.

    Thanks,

    J

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    Does the reverb function other than the hum? 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.

    I would suspect a bad ground on an RCA cable, but that is just a guess.

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    How bad is the hum?

    They do make a little noise. Try moving the tank around. Is it near any transformers? Anything else nearby that could cause the tank to hum?

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    Quote Originally Posted by drewl View Post
    How bad is the hum?

    They do make a little noise. Try moving the tank around. Is it near any transformers? Anything else nearby that could cause the tank to hum?
    Good suggestion, also try moving cables around.

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    Don't forget the joker g1's Avatar
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    All schems and parts list in attached file are labelled 212/Head
    Attached Files Attached Files

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    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

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    Thanks for the input everyone, I must hang my head in shame as although I was sure I'd swapped all the 12AX7's out for known good ones, I hadn't swapped out V2, taking it out and putting in a random spare made the increasing hum problem go away instantly, putting back the one that was there made it come back, so it's a bad tube.

    Three new tubes on order for good measure, then I'll know they are all good!


    Many thanks.

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    Damn it, now the problem has come back, after plugging it back it to test with some fresh valves, the hum has returned, with new and old valves

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    Have you tried resoldering V2's socket?

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    Quote Originally Posted by Jazz P Bass View Post
    Have you tried resoldering V2's socket?
    I've had both boards out this afternoon and had a good look around for dry joints, I re-flowed all the tube sockets for good measure even though they looked OK. No signs of leaky caps, burn resistors or anything untoward, I cleaned the pots while I was poking around.

    I needed to repair the flat cable between the boards as after moving them they weren't always making a good connect, causing HTR to not always make a good connection. In that process I discovered that pin 8 of the flat ribbon cable (SCREEN) doesn't actually connect to anything on either end, this board is different to the schematic in that way. There is an additional 3 pin lead connecting the two boards so perhaps that's the way it's routed?

    To add insult to injury the amp now squeals loudly with a very high pitched whine if the texture knob is anything other than at 12 o'clock, if you take it off in either direction i.e. higher or lower power.

    To answer reverb tank suggestions I've had it out, cleaned the sockets and jacks, tested the resistance of both springs and they look fine. The reverb is working when it's humming, it's just the hum completely over powers the reverb and the output. For a brief moment when it was working the reverb was loud and clear, before the above happened :/

    I suspect the +7v and +14 lines aren't right as I can't seem to get a good reading on them, 14+ is much higher (23v) from where i've taken readings, but I think I might be using the wrong ground point, as there are three GND0, AGND1, AGND2. I'm an amature so you'll have to excuse my ignorance!

    So far this simple re-tube hasn't got to plan at all!

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    When it hums, unplug the drive to the reverb i.e. the connector marked IN on the tank. Then at least you will know if the problem before or after the reverb and so it's suddenly half as big .

    If the hum after i.e it still hums, unplug the OUT from the tank, does the hum go away? If yes you've narrowed it to the tank connector or direct pick up into the coil.

    Give it a try and we can go from there.

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    Quote Originally Posted by nickb View Post
    When it hums, unplug the drive to the reverb i.e. the connector marked IN on the tank. Then at least you will know if the problem before or after the reverb and so it's suddenly half as big .

    If the hum after i.e it still hums, unplug the OUT from the tank, does the hum go away? If yes you've narrowed it to the tank connector or direct pick up into the coil.

    Give it a try and we can go from there.
    That's an excellent idea. The hum goes away when you remove the white RCA lead, which is P104 and P107, which based on the schematics is the return path unless I'm mistaken? I guess the easiest thing to do is check the 10 components on that half of the OP amp for starters.

    I've also discovered if I turn up the presence past 12 o'clock the amp sequels the house down, maybe related, maybe not, one thing at a time!

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    I asked you unplug just the drive i.e. the cable that goes to the IN of the tank and at the tank. Nothing else. Please try again.

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    Quote Originally Posted by nickb View Post
    I asked you unplug just the drive i.e. the cable that goes to the IN of the tank and at the tank. Nothing else. Please try again.
    Sorry I should have been more clear, the tank isn't marked in or out, but I think I have them the right way round, with just the IN (Red) removed the hum is sill there. With just the OUT (white) removed the hum is gone.

    Thanks

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    Thanks - that'a better!

    So it's either direct pickup from the power transformer or an issue with the connections. If think you already eliminated the connections - right? In that case unscrew the tank. Now with the cables plugged in you can move the tank around. How does that affect the hum? Same, less different?

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    With the tank unbolted from the chassis there are a few positions in space above it's normal position that seem a little less hummy, with it being much more hummy if it's near the power transformer. Unrelated to this I noticed when placing the cap back over V1 there is was some mechanical noise transmission through the speaker (tapping/scrapping noises as the cap is pushed on), after a great deal of chop stick poking I found C109 is in some way harmonic, the slightest touch of it and i can hear it, is that possible?!

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    Quote Originally Posted by glebert View Post
    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?

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    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

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    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.

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    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

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    Last edited by jondoe; 01-12-2019 at 01:49 PM.

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    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.

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    Last edited by nickb; 01-12-2019 at 03:01 PM.
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    Quote Originally Posted by nickb View Post
    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.

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    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?

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    Quote Originally Posted by nickb View Post
    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

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    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.

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    Quote Originally Posted by nickb View Post
    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.

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    Quote Originally Posted by nickb View Post
    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.

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    Quote Originally Posted by jondoe View Post
    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.

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    Quote Originally Posted by nickb View Post
    '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

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