JCM2000 DSL Silver Edition problems.

[gtrplayr1976]

It did.

[gtrplayr1976]

If C14 blew apart then it was the likely cause of the problem.

I finally got the parts I needed ,and installed ,but when I try to get it to full voltage the bias is too high. I replaced R77 to 15K as suggested, and I only have it to 110VAC with variac ,and the bias is over 100MV already with the bias pots all the way down. Should I increase R77 ,or try something different ?

[g1]

Pull the power tubes and measure the DC voltage at pin 5 of power tube sockets.

[gtrplayr1976]

Pull the power tubes and measure the DC voltage at pin 5 of power tube sockets.

I have the board out. I think the low bias resistor ?R68 is wrong according to the schematic. It shows a 33k ,and I think this has a 22k. I'll get it back in ,and check voltages.

[Enzo]

WHy not check voltages first, to make sure resistor changing is what we need?

[gtrplayr1976]

Pull the power tubes and measure the DC voltage at pin 5 of power tube sockets.

-46Vdc

[g1]

I replaced R77 to 15K as suggested

Keep us in the loop. Where was this suggested and for what reason?

[gtrplayr1976]

WHy not check voltages first, to make sure resistor changing is what we need?

Yes sir. I changed it back to original ,and checking again. This appears to be a newer issue that already had some changes made. I can only find a schematic up to issue 7. I believe this is 10.

[gtrplayr1976]

Keep us in the loop. Where was this suggested and for what reason?

I read it on some other places about bias issues with these. Of course I believe these were with the older boards. I changed it back to 10k.

[g1]

So how are you measuring the idle current of the tubes?
Did you have the pot set so there was the most negative voltage at pin 5 of power tubes?

[gtrplayr1976]

So how are you measuring the idle current of the tubes?
Did you have the pot set so there was the most negative voltage at pin 5 of power tubes?

I have a Weber bias probe connected to each set of tubes ,and a DMM connected to the pins on the back of the amp head. The pots are currently at zero position.

[g1]

The pins at the back of the head are each for a pair of tubes with the 100W head. So if it said 100mV, that would be 50mA per tube.
Was that as low as it could go?

[gtrplayr1976]

The pins at the back of the head are each for a pair of tubes with the 100W head. So if it said 100mV, that would be 50mA per tube.
Was that as low as it could go?

Yes it was ,but I changed the bias resistor back to 10K ,and both sides are at 81ma per side with pots still at zero. I think if I increase R68 to 33k I might get some adjustment room?

[g1]

Not sure what you mean by pots at 'zero', I assume that is wherever gives you lowest idle current?

[gtrplayr1976]

Not sure what you mean by pots at 'zero', I assume that is wherever gives you lowest idle current?

The bias adjustment pots are bottomed out. I can only go up in current. I noticed after leaving it on for a bit the bias crept up about 2-3 mA.