Peavey Valve King 100 head

[jondoe]

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

[glebert]

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.

[drewl]

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?

[glebert]

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.

[g1]

All schems and parts list in attached file are labelled 212/Head

[jondoe]

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.

[jondoe]

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

[Jazz P Bass]

Have you tried resoldering V2's socket?

[jondoe]

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!

[nickb]

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.

[jondoe]

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!

[nickb]

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.

[jondoe]

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

[nickb]

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?

[jondoe]

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?!