Peavey 6505 Head problem

[Trollmakt]

Hello!

I have a problem with my preamptubes not heating up .

It is the V1 - V2 - V5 - V3 not heating up

V4 and all of the Main tubes heat up

Also checked all of the tubes in those slots in the V4 slot to see if they heat up, they do

All fuses external and internal has been taken out and checked with multimeter

I don`t know if this is relevant, but the C9 capacitor gets quite hot (check this link for schematics http://www.thetubestore.com/lib/thet...-Schematic.pdf - Page 1 placement C-8) none of the other capacitors on the board gets this hot

Does anyone have any clue what to do?
What should I check for?

[Enzo]

Well, replace C9 for sure.

Those four tubes are wired in series in 12v mode across +24 and -24 supplies. SO 48v of supply to feed 48v of tube heater.

Any element goes open and they all go dark.

Look at power supply page. FIL1 and FIL2 are the 6vAC for the power tubes and V4. And nearby are +/-24vDC.

Now upper right-ish see +24 and -24 passing over to the V4 area? -24 goes PAST V4 to V3a, and continues through the series heater string. +24 goes over to R47, R49 in parallel just above V4. They are then the source of FIL. And FIL is the other end of the heater string, look upper left page 1 at V1A. Also that is where C9 connects.

Wanna know what I think happened? Back to power supply page, note +24 also goes through R69 to elevate the 6vAC heaters to +24vDC as well. I suspect one of your power tubes failed and shorted B+ to the heater. That then went through R69 and frotzed your C9. It is also possible instead of a power tube itself, one of the sockets may have arced pin 2 to pin 3. Same difference.

[Trollmakt]

Well, replace C9 for sure.

Those four tubes are wired in series in 12v mode across +24 and -24 supplies. SO 48v of supply to feed 48v of tube heater.

Any element goes open and they all go dark.

Look at power supply page. FIL1 and FIL2 are the 6vAC for the power tubes and V4. And nearby are +/-24vDC.

Now upper right-ish see +24 and -24 passing over to the V4 area? -24 goes PAST V4 to V3a, and continues through the series heater string. +24 goes over to R47, R49 in parallel just above V4. They are then the source of FIL. And FIL is the other end of the heater string, look upper left page 1 at V1A. Also that is where C9 connects.

Wanna know what I think happened? Back to power supply page, note +24 also goes through R69 to elevate the 6vAC heaters to +24vDC as well. I suspect one of your power tubes failed and shorted B+ to the heater. That then went through R69 and frotzed your C9. It is also possible instead of a power tube itself, one of the sockets may have arced pin 2 to pin 3. Same difference.

Thanks for the fast reply!

I have measured the voltage between +24 at J56 and -24 at J67 .. I measure this to 55v . is this correct? Shouldn`t this be 24v? or does it get divided somehow?

The R69 you speak of . It says it goes to FIL1 that goes to V4 in the upper right . but only to V4 and the power tubes . This one still works
Do you mean that it went through R69 . then through 24+ all the way through Filaments and then to C9?

[Trollmakt]

What if I replace C9 capacitor

Won`t the problem that caused it to frotz still be there?

[Enzo]

I suspected a bad power tube, so if they are still there... C9 can be left out during tests if you like, but since it gets hot, we know it is bad.

I mentioned R69 only to point out I suspect it was the path FROM FIL1 TO the +24, the path of the fault from a possible bad power tube.

The difference between +24 and -24 is 48v, not 24. 55v is high, but then we have no heaters running to drag it down. First suspect would be the two resistors up top, R47, 49. Check for open there.

Also, 55? 48? this is just a guitar amp, not a lab machine at NASA Close enough.

Remember, all four of those tubes are in series, along with the two resistors, any point in that series goes open, and the tubes all four go dark.

[Trollmakt]

I suspected a bad power tube, so if they are still there... C9 can be left out during tests if you like, but since it gets hot, we know it is bad.

I mentioned R69 only to point out I suspect it was the path FROM FIL1 TO the +24, the path of the fault from a possible bad power tube.

The difference between +24 and -24 is 48v, not 24. 55v is high, but then we have no heaters running to drag it down. First suspect would be the two resistors up top, R47, 49. Check for open there.

Also, 55? 48? this is just a guitar amp, not a lab machine at NASA Close enough.

Remember, all four of those tubes are in series, along with the two resistors, any point in that series goes open, and the tubes all four go dark.

:UPDATE:
From another forum I got a tips to check the Diodes .

I measured all the 8 diodes .the 4 connected to the Power tubes and the 4 connected to the 24V that supplies the preamptubes.

- The 4 to the power tubes, that heats up. checks out . all of them have perfect reading

- The 4 to the preamptubes, all of them shows fault . I do not know if this is because it still is in circuit or if there still are any leftover charge somewhere. But they do not show any visual signs of being faulty.


edit: I also measured resistors R47 and R49 while they are in circuit.. and their measurement is supposed to be 22Ohms .. but I get unconsistent readings . got one of 300kohms and that doesnt make sense , and one reading 1,82Mohm. this happens on both resistors.. And an OM reading when I disconnect the cables from the power board to the preamp board

[Enzo]

Those resistors are open. Otherwise you would get your 22 or 11 ohms. (A pair of 22 in parallel makes 11)

[Trollmakt]

Those resistors are open. Otherwise you would get your 22 or 11 ohms. (A pair of 22 in parallel makes 11)

So these must be changed. But what about the diodes ? All 4 diodes in the 24v do not measure OM the one way and 0.500ish the other way.

Do these need to be changed too?

So the C9 , R47, R49 and the 4 diodes must be changed?

[Enzo]

I suspect the four rectifiers are really OK, but they are cheap, and if it gives you comfort, go ahead and change them too.

[Trollmakt]

I suspect the four rectifiers are really OK, but they are cheap, and if it gives you comfort, go ahead and change them too.

Thanks for all the help!

I changed C9 and the resistors R47 and R49 and it works perfectly now!

[Trollmakt]

Thanks for all the help!

I changed C9 and the resistors R47 and R49 and it works perfectly now!

eehmm .. Almost perfectly!

It seems like I forgot to connect one cable
When I connected it I get a crackling sound when I palm mute

without it connected it gives a sharper sound but no crackling sound . but with it I get a smoother sound but crackling when I hit the strings hard with palm mute with distortion
Even more crackling if I play mutes on clean sound

https://drive.google.com/open?id=1-C...QaSARHhBklmxL8

It is the white cable with the red connector
Connected from the preamp board to the power board, straight into speaker circuit

What could be the problem?

[Pedro Vecino]

That wire corresponds to the feedback line. I don't know if it could be related to the problem but:

- make sure that have a strong contact on both connectors.
- Pass the wire under the multiconnector (8) and separate from it as much as possible.

[Trollmakt]

That did not work . And the crackling is unbearable on higher volumes

Seems like it could be some broken tubes .
They make noise when I hit them

[Pedro Vecino]

You could try with just a pair of 6L6. You can remove 1 and 4 or 2 and 3 for this.

[Trollmakt]

Tried to change all tubes .

No change

Still the loud schreeching and crackling when the red connector (https://drive.google.com/file/d/1-CQ...HhBklmxL8/view) is connected.
I guess this is the feedback loop
When I use the clean channel it is worse. when I use overdrive I have to turn it up and the higher it gets, then the shcreeching gets louder

The sound is not crackling when it is disconnected, but the sound is unclear and really high pitched

Can mention that it is just as bad through the effects return

Any ideas?