DCPP - "Engineer's Amplifier" : Need a bit of help

[roline]

Any updates yet? Are you too busy listening to your favorite tunes to post?

 

[bdog]

Sorry for the delay but i was quite busy and didn't had time to work on it.

I started again this WE to check for issue.
A pot seemed to have the pad on PCB gone, i made a jump wire to ground to resolve the issue but i didn't changed anything.

Almost all voltage seems to be good.

With all pot at middle pos. and tube on i got 325V on one channel just before the output transformers but only 90V on the other. (i have to put the R22 pot all to the left to get aroutn 320V).

Still no sound on output. even with tubes on all mosfet seems cold ; even Q1 and Q2 which needs dissipator :-/
I'm going crazy

 

[bdog]

Is there anyone still reading this post?

Please

I found something, i accidently shorten gnd and the 6CB6 pin 7 in VT8) while resoldering (and forgotten to turn the amp off) and i got sound on right channel!

Still nothing on the left.

I remake major component groudn soldering on the right channel but nothing :-/

Any clue, my Stentaure LE just arrived and i'm dying to listen to some music

 

[chip647]

You may have blown the MOSFET on the left channel. A simple static shock can do that. If you have the right channel working, the left should be a snap to fix. Pop in a new MOSFET and measure voltages.

 

[bdog]

thr right is only working when i got the pin7 of the shorted to ground for the input stage; otherwise I still got nothing on the right.

Which mosfet? U1/U2 or Q1/Q2? Because now playing with potentiometer i got the 300+ V on the left plate/B+

 

[pmillett]

I found something, i accidently shorten gnd and the 6CB6 pin 7 in VT8) while resoldering (and forgotten to turn the amp off) and i got sound on right channel!

That means that either the driver balance pot or the CCS on the cathodes is not working. Most likely an open solder joint. Check R54, U2, R45, and R39. Hopefully you have verified that the C- voltage is there and about -60V?

Pete

 

[bdog]

First, thanks for support!

I got the -60V on C- (around -65)

I check soldering (and remade it) on r54, U2, R45 and R39 and got a low volume out on on the right.

I had -65 / -66V on pin 3 & 1 on U2, around 10V on pin 3 and aroudn same voltage on R54, VT8, VT7 pin 6 &7.

I manage to get between 25 and 30V on VT & R54 but after shutdown, it is back to 10V :-/

 

[pmillett]

Pin 6 of VT7 & 8 should be 150V, and pins 2 & 7 should be closer to ~2V.

Have you verified the 6CB6 tubes are OK? Swap between channels?

Trace the 150V signal back to R41, there should be 150V on both sides of it. If not either there is a short, or the screen regulator (Q1 and associated parts) has a problem.

Pete

 

[6L6]

If not either there is a short, or the screen regulator (Q1 and associated parts) has a problem.

I have been through both of the regulator Fets, (my fault, fried it with a probe) and if you fry the fet, the diode from Gate to Source will be dead as well.

If you replace Q1, then replace D6

If you replace Q2, replace D9

 

[bdog]

pmilette : sorry for the mistake, pin 6 is 150V ; the 2 & 7V are between 8 & 9V.

I think the IXCP10M45S are the issue; i didn't get them for mouser as they didn't delivered it to France but from another seller found online... maybe they were bad ones... i bought two new from an UK seller and will swap them ASAP.

 

[roline]

Any updates???

 

[bdog]

IXCP10M45S was replaced and i still got the same issue. I didn't had time with work to check more on it.

I'll take a picture from both sides of PCB and note down every voltage ASAP as i really don't know what else can be wrong