Peavey Valveking troubles

[Valvehead]

I forgot---the fsw jack is grounded to the chassis--checks out ok.

i put in the new channel switch = nothing changed.

the boost switch is the same type--maybe i should swap that one out ?

[DrGonz78]

ok , diode mode on my meter i get -

D110 .4v / 1.3v

d115 .4v / 1.25v

To me .4v would appear fine on both diodes here, but 1.3v approx. on both make me think something else. I am not looking at a schematic here... Still I think I would pop up a leg on each of the diodes to get an accurate check. My guess is that something in circuit is confusing the diode test in this case. Also, 400mv seem a little bit low but is almost right. Better check the parts that are in the amp before adding anymore at this point.

[Enzo]

The switch itself might be OK, but the circuit it is in still has something wrong. So we still can take rtests on it as it sits.


I know it can be hard to explain something I could show you in 20 seconds if you were here when we are posting like this.

Look at your photo. The lower section is longer, sticks out the back past the upper section. Look on the right end of the lower. See the three solder lugs sticking up? There could have been some on the upper section but they have been nipped off.

Look at those three solder lugs all in a row. They are one of the groups of three I referred to. Specifically, if we were looking at the switch from the front, they would be on the right rear of the asembly. Still with me? The switch has in and out positions. And within that group of three, all that does is connect the center lug to either the right end one (in position) or to the left lug (out position). The switch selects the left or right end lug to connect to the center one. SO we want to check with a meter to see that the left two (center and left) are shorted together when the switch is out, and then the right two (center and right) are shorted together when switch is in. Nothing cosmic there.

Now on the far side of the switch where we cannot see well, there is another grop of three lugs that works the same. Now the upper section has no lugs, but it has the nubs where they used to be, and your meter can touch them. They work exactly the ssame.

If the switch you removed is OK, try the test on it, without a circuit around it, there is nothig to confuse things.

I also described the circuit board as having some of those groups of three that were not needed, so they wired the three together. I pointed it out so you would expect some of the groups to not measure right.

Something is leaving the switching circuit closed. WHy the other switch would have this effect is a mystery from here, so measuring the switch function with a meter is a way to explore why.

[bnwitt]

I don't want to muscle in on this thread but does anybody have any idea what would prevent the boost function from switching and blowing the footswitch LED?

[Enzo]

Might be better to just start a different thread for yours so we don;t get them confused.

But you did suggest a question:
I don't remember, and do not see scanning back, are we using a footswitch, or is that jack empty? I could see footswitch wiring involved or even the presence of LEDs in the pedal.

[Valvehead]

enzo-- the switch checks ok. also- i dont have a foot switch for the amp.

i clipped 3 diodes to check them out of circuit :

D110 1.3v / .4v
D115 1.3v / .4v

D104 .6v / open

Im confused here. Shouldnt these measure open 1 way and about .6v the other ?? they are 1N4148

[Enzo]

yes, that is exactly how they should measure, just like D104.

1N4148 costs about 2 or 3 cents each. Just replace all of them.

[Valvehead]

i will--- let me ask you this--- will a 1N4007 work in place of those ? Because i have a gaziliion of those sitting here, yet no 4148

[Enzo]

Oh probably, sure. But if you are going to work on amps, invest two bucks and get 100 of the things in your next parts order. Fender always specifies 1N4448 instead. very similar part, and if you happen to have some, they would work as well.

[Valvehead]

just replaed d110 / 115 . nothing changed...

[Enzo]

Well they needed changing even if they are not the bottom line issue.

And what of D116, D117? Let us not forget them.

[Valvehead]

IT IS DONE !!!!!!

it was either 116 or 117 -- not sure which - i threw them in a pile of diodes...

amp switches fine now !!

wow...that was a long one...... THANK YOU ENZO and anyone else that posted.

I should have pulled diodes and tested them all ---but , as you know, it can be a PITA if there is a bunch of them in the problem area

what a relief....

my offer for a steak dinner still stands Enzo

[Enzo]

Great!!

It takes so long inching along like this, but we have to be sure to communicate and all.

Much as I like beef, my response to a dinner is this: find someone local who really NEEDs some food, a single teenage mother, an old lady eating cat food, a homeless shelter. Give THEM some food.

[Valvehead]

will do my friend. thanks again

[Tony Ramone]

i know---he's the man !

so Enzo, can you tell me where i should have voltages to try and narrow this down ?

Sorry to chime in here, but I was just surfing through VK related threads and found yours.
I'm just wondering: did you buy this amp new or second-hand? A popular mod for the amp is to remove R171 so that the gain boost switch can be used as a "crunch" switch on the clean channel - basically, R171 is part of the circuit that stops the boost switch affecting the clean channel, so without it, you get the added gain from Q103 being switched.
EDIT: oops, for some reason only half the thread was showing up, so I didn't see all the replies...