Peavey 5150 combo pre lead low volume

[pontiacpete]

I grounded the sleeve of the footswitch jack and now R28 has no voltage on it.

How can the lead volume and lead post be by-passed and routed thru the clean vol pot and it's post? The relay must be working since it's sounding normal when switched.

[Enzo]

K1b puts one or the other post control in parallel with R28, so if they are dialed down to zero, R28 will measure zero. They are 1 meg pots, so if you max them, R28 should measure whatever 2.2M and 1M in parallel makes. I'm too lazy to calculate. 600k maybe? R28 is there to keep C29 charged.

K1 has two sections. One selects the post control, and the other selects the pre control. The coil of K1 is series with the coil of K2, so when one energizes, so does the other. K2 controls the amount of signal going to the grid of V2a, as well as adjusting the gain/response at the cathode of V2a.

SOunds to me like K1 is not switching, so the "wrong" set of volume controls remain selected. Since both coils are in series, if K2 toggles, then K1 must be getting the current. However, if you changed it out, the new relay may not have the same coil resistance, and so may not be sharing voltage well. The current through the pair may be enough to toggle K2, but not the new K1. Meanwhile K2 toggles, so the volume/gain goes up or down, but the controls do not transfer.

There are at least four grounds in this unit. Each with its symbol. Look by the input. The jack is grounded to what I call the rake and the triangle grounds. Just to the right is the end of the heater string, and that is the circled rake ground. Now look down to the footswitch jack. It is grounded to the rake and circled triangle grounds. Most of the preamp uses the triangle ground. The later half of the preamp ises teh circled triangle. The power amp uses the circled rake. The FX loop jakcs also join two grounds.

Especially if you have the boards out, you must be cautious to join all the grounds. Just above the power supply are the lonesome R118,119. 47 ohms each. They join three of the grounds. Usually if you measure across them, they measure zero, because those grounds are connected together by grounding at the jacks. Those resistors are just there to maintain a connection if the jacks get loose.

[pontiacpete]

I bought the relay from peavey, I seem to recall, but it is a 12v G5V-2, but what was in there was G6A-274P. hmmm

I happen to have another G6V and sure enough you are right. It works and switches change channels, and all controls are working.

Hooked up the reverb and that works too, yeh!
I'm hesitate to put Q1 and Q4 back in.. but I'll give it a go.

Thanks for explaining the ground, you must have heard me thinking about asking you that very question, about the circled triangle ground symbols and the rake and the uncircled triangle.

[pontiacpete]

great, I put it back the chassis and the clean ch isn't working, what PIA!

[pontiacpete]

As ridiculous as it may seem, I'm back to work on this amp and it is running fine. Both channels work.
Now there is one problem, the reverb is back to not working.
I should more accurately say that it is working but R56 and R65 start to smoke after running it for a brief time.
The problem is that there is a -5.8vdc on J8, no voltage on the rest of the pins.
I have repeatedly replace CR8 and CR11 and Q3,Q9,Q6 and Q10.
I replaced the 2 22uf caps and R56 and R65 and R58
The voltages look like this
Q10 E -5.8 vdc
B -5.6
C -23
Q3 E -5.8
B -5.6
C 22
Q9 E -.06
B -.6
C 12
Q6 E 14
B 13
C -4.5

The -5.8vdc is on either Q3 or Q10 or both.
I checked solder joints and continuity and number of times over.
I realize not many here are interested in this amp but I'm desperate for insight or suggestions.
thank you
and I hope all here have a safe and happy new year.
pete