5150 problem

[Enzo]

You have no bias at C41, then you won;t have bias anywhere else either. Is your meter set for DC volts?

Bias doesn;t care about standby, it is always there.

C43, C42 ought to have bias voltage on them, so do they? Is the bias fuse OK? You MUST remove it from its clip and check with a meter.

[Valvehead]

fuse is ok--just checked out of circuit.

So-- looking at the 3 caps (negative side)... from the fuse going onto the rest of the bias circuit in order .. i have -073mv / -066mv / -048 mv .

this is the 3 , 10uf caps

[Enzo]

Y'see? There is no voltage there. Is there AC to ground at the fuse? Both ends? Is there the same AC at the cathode end of the diode CR12?

[Valvehead]

Im sorry---i think my main meter is done for

56 acv at those points . i tried another meter...main one reads -056 , the other 56

the 2 wires coming out of the trans. show + 56vac

another thing- at the 2nd 220k just before the ribbon, i get -48v on one side and 0 on the other. I clipped the res out and tried a new one. same reading . bad trace or joint ? it all looks ok from the top

[g1]

You are measuring right on the actual resistor? If so, some point connected to the "0volt" side of the resistor is shorted to ground. Could be the grid resistor I mentioned earlier, or a solder bridge at the ribbon wire. Did you do any resoldering at the ribbon?

Also, if C201 or C202 at the power tube grids shorted, you would get the problem you have.

[Valvehead]

yes at the res. the end going to the ribbon which is a short trace, is 0v . no solder bridge under ribbon

[Valvehead]

if you look at the scem ,page 3, it shows J9 feeds r206 on the pwr tube pcb and J10 feeds r202

but on page 2 it says no connection at J9 ?

also--im getting 0 ohms when measuring 2 of the 2.2k's . im pulling the board and going over it again.

http://www.blueguitar.org/new/schem/peavey/5150evh.pdf

[g1]

but on page 2 it says no connection at J9 ?

I can't see a J9 on page 2 anywhere. J58 and J57 (from R55 & R54) on page 2 go to J9 & J10 on page 3 (R206 & R202).

The 0 ohms you measure at the 2K2's, is that measured to ground or from end to end of the resistors?

[Valvehead]

sorry--page 1

under v2b

[g1]

Ok, I see them. They are unrelated and connect to the points shown directly under them.
Look at the upper right area of page 2. The points I mentioned are labelled "to power amp board".

[Valvehead]

ill check c201/202 next

i pulled the board and i only found 1 problem (so far) . There are 2 , 100 ohm 1/4 w res on the pcb --but not on page 3 of the scems .

one of them was open , and one end of it connected to 2 of the 2.2k resisitors

[g1]

Back in post #9, you replaced two 100R that you said were 1/4W. Is the one that's open now one of those? Are they for the heater virtual ground, R200 and R201? Modern 1W resistors can be quite small, if it was R200 and R201 you should have installed 1 watts.
And not sure if you tried the same original power tubes after the original repair, they could have done more damage.

Edit: This is the head and not combo, correct? And have you received the layout from Peavey yet? If so, please post.

[Valvehead]

yes same one ....ok--ill have to get some 1w for the 100 ohms.

i forgot to get a layout. this is the head .

also--i cant find any 100p caps --c201/202 . none on the tube board...none anywhere !

[g1]

It's possible they are not used. Find out why you have that short or 0 ohms at the 2K2 resistors. If you locate the short, it doesn't matter about C201/202.
And neither of those 100R's should be connected to the 2K2's.

[Valvehead]

ok---sorry g-one. let me clarify .

ignore the 0 ohms thing--my mistake. all the 2.2k are ok

now--there ARE 2 big 1w 100 ohm resistors on the board that go to the heaters. those are fine .

there are also 2, 1/4w 100 ohm . one of those was open. Ill have to look again but i think they went to pin1 or 8 ?