Peavey Valveking troubles

[Valvehead]

I searched on here and didnt see these issues.

I have the 212 model.

1st issue = the Resonance and Presence controls dont work --either channel. Ive tested everything in that circuit except c6--have to pull the pcb to test it . What else is there ??? d108/109 test ok in circuit . The cable tests good. Possible solder joint--again i havent pulled the pcb yet..


2nd issue =

with the Boost Gain switch (its on the dirty ch. ) IN , the amp wont go to the clean channel .

with it out , the amp switches channels fine .

I can hear the relay click--but no switching. It should switch from clean to dirty ?

[Enzo]

D108,109 won't have anything to do with it, they are flyback diodes protecting the transformer.

Those are power amp controls and so have the most effect when the amp is played loud. They control the negative feedback, so look at it as a circuit, not as a collection of parts. Look at the phase inverter tube V3, specifically R162 under the cathode. That 820 ohm resistor is where the NFB feeds back in. Ground your meter and measure for roughly 820 ohms to ground from the top of that resistor. Now go over to the output jack board, looks likie a red wire carries that NFB from P9, so still have the 820 ohms there? From P9, it goes through the small cable over to the controls via pin 3. It arrives there at R10, another 820 ohmer. Still have 820 to ground there? ACtually it ought to read lower than that due to the parallel action of VR12. Now to the other end of R10. Now you are reading resistance of VR12 with that pair of 820's in parallel. I'd guess about 1400 ohms, get anything close? What I am doing is checking resistances from the other end of the wiring. It isnlt enough that a resistor be whole, it also has to have its leads make connections with the rest of the circuit.

You could unplug the little three wire cable, and check for resistance through the circuit between pins 1 and 2, and between pins 2 and 3.


Not sure about your switching, are you using a footswitch?

[Valvehead]

ok, it might be r 162 .
measuring each end to gnd i get 1.2ohms / 0.2 ohms . across it i get 1.4 ohms . should be 820ohm , but , its still in circuit . I will have to remove the entire pcb to get to it

r160 to gnd = 1.4k / 1.0 ohm

r10 to gnd = 730ohm / 0.2 ohm


also--i dont have the fsw for this amp

EDIT--- i pulled r162 out of the circuit and , of course, it measures 820 ohm

[Enzo]

R162 is not going to get shorted internally, so I am not surprised it measuers OK out of circuit. But in circuit it should not have 1 ohm to ground from its top end. With it removed still, do you still get that reading? R10 ought not to have ground at the one end. Something is shorting that line to ground. You have the three wire little cable that connectws the two places, by disconnecting it, we can explore just where this grounding occurs, and once solved your controls ought to work.

[Valvehead]

ok, i unplugged 1 end of that cable , measured each end to ground =

r162 = 1.5 ohm / 1.0 ohm

r160 = 1.4k / 2 ohm

r10 both ends open

[Enzo]

OK, so even with the cable unplugged, R162 still has the top end grounded. Find out why. The "wire" from the top of R162 runs over to the right to P7, where it says a red wire connects to be connected at the other end to P9 on the output jack board. Unplug the red wire from P9, is R162 still shorted to ground? If so, then the pronlem is on the main board, but if not, then the problem is on the output board. For example is there a solder blob between pins 2 and 3 on the three pin connector on that output jack board?

[Valvehead]

ok---the wire from p9 is black. It goes from the output tube pcb to the output jack pcb. I tested r162 and r160 with that wire unplugged from the jack pcb and plugged back in. The readings are the same either way. All the joints on both pcb's look clean under my magnifier . No solder bridges or cracks

[Enzo]

Um... You have a black wire on P9? Schematic says red. Do you have a red wire on P8? (Schematic says black.)


ANy chance your red and black wires are reversed?

With the red and black wires off, verify if P8 is ground and P9 is not. There should be a red wire coming from the power tube board, right at the end of the board by the phase inverter tube. Is it? And a black wire comes from the other end of the board? The red wire (or whatever color is coming from by the phase inverter) is what connects to P9 on the output jack board.

[Valvehead]

I took some more measurements , one thing is BOTH wires are black--no red wire.

P8 is labeled Ground goes from power tube pcb to jack pcb

P9 is next to the pi tube -its labeled Feedback. it also goes to the jack pcb.

So with p8 + p9 un hooked i get =

r160 1.4k / 1 ohm
r162 800 ohm / 1ohm

plug p8 / p9 back in , i get the exact same readings .

At p8 (ground) , i get 44 ohms

at p9 (feedback) i get 800 ohms

no matter which wire is plugged in or not , and if the long 3 pin wire is in or out , i get the same readings at r160/r162 / p8/p9 -- they dont change

[Enzo]

r162 = 1.5 ohm / 1.0 ohm

r162 800 ohm / 1ohm

no matter which wire is plugged in or not , and if the long 3 pin wire is in or out , i get the same readings at r160/r162 / p8/p9 -- they dont change

See why I might be confused? ALl along I thought we had a situation where when it was all together we had about an ohm from the top of R162 to ground, more or less a short across it. Niow you seem to be getting 800 ohms across it. If you can get 800 ohms across R162 with everything connected up, then try the amp and see if those two controls are now working.

[Valvehead]

sorry about that--i did scrape between a few solder joints and ive been moving those boards all around during testing -- maybe something changed or moved ?

ok...i fired up the amp and the controils work now ---- thanks for your time enzo !!

the amp still has the channel switching problem , but now i feel bad and dont want to bother you with that one...

[Enzo]

I guess the lesson there is not to lose sight of the forest for the trees. We had to keep in mind the problem was that R162 was coming up shorted. (The net result of the top and bottom ends both being real close to ground). We got into chasing this or that wire around without keeping in mind the goal. I am glad it is now working. I will assume we had a small solder blob or other short between two points that shunted that resistor.


I genuinely do not mind helping, and I am patient. When we go through these things, there are a lot of other folks following along, and we want them to also learn something in the process about a systematic approach with the circuit in mind.

Explore the footswitch jack.

[Valvehead]

Ok, I will try to focus more


The fsw jack is on a mini pcb with 1 resistor--that all looks good.

I thought I would pull the main pcb to check for issues and sure enough there were at least 10 cracked joints. I re-flowed those and swapped out 3 transistors in that area of the circuit (because I had them) .
Those are
Q101 / Q103 / TR105

The amp still wont switch channels with the Boost switch engaged. Suggestions ?

[Enzo]

Hey, I was focusing on the same stuff, so the lesson is for me too.

The boost switch and switching relays involve diodes and the contacts in the footswitch jack. teally, I don;lt see this as much different from the last problem, I;d be looking for continuity where it belongs and hopefully where it does not belong there is none. Paths to ground through the jack contacts need to be complete.

And on the jack board, does that 10 ohm resistor really have about 10 ohms?
here is one to look at: From the switch, see teh string of diodes going up to Q103? What if Q103 is shorted? Then the diodes will complete a circuit to ground turning on the relays.

[Valvehead]

Alright my friend...I have more info for you...

r170 -- tests 10 ohm out of circuit

theres a 4 pin cable from jack to main pcb --

pin 4 shows 7.6v with boost sw out
5.8v boost in


on the 3 series diodes =

Power OFF

d110 to ground , 22k/35k

d115 6.7k / 22k

d117 6,7k / 0 ohm


Power ON

D117 to ground at the negative end 74ohms with boost on / boost off = open


am I wrong here--- D117 looks like its shorting to ground ??