240V stereomour

[Paul Birkeland]

Can you triple check that you have a 12AT7 in the 9 pin socket?

It's also possible that you don't have a ground reference for the grids of the 12AT7.  Try soldering a jumper between 7 and 8, as well as 8 and 9, the see if that makes your OA/OB voltages fall into line.

-PB

 

[srhombeus]

Yes it's written U.S.A. 12at7 in the tube. You mean terminal 7-8-9 or pin 7-8-9 ?

 

[Paul Birkeland]

Terminals.

-PB

 

[srhombeus]

I've assemled these jumpers.Now terminal 2 is 206-207 but terminal 14 is 77-78.  I think this is the problem with this left channel.Where should I look?

Edit : Now there is only a little popps when turning on  the amp.But there is no sound on both channels..

 

[Paul Birkeland]

This suggests that there is an issue with the volume pot, either the pot itself or the way it is wired.

Are the Kreg voltages the same on both sides of the board?

 

[srhombeus]

I don't use potentiometer now,i am waiting for alps potentiometer to arrive.I just connected the left channel cables from the switch,red to 7 black to 8 and for the right channel's red to 9,black to 8.Ground cables are not connected to 8L.  Is there a mistake?

Kregs are same value..

 

[Paul Birkeland]

Yes, the 100K pot provides resistance to ground for the grids of the 12AT7.  Without that path to ground, the operating point of the 12AT7 will move around.

 

[srhombeus]

I have a cheap B100k potentiometer,i will try with it.Do i have to remove the jumper between 7-8 and 8-9 ?

 

[srhombeus]

I've connected the potentiometer.I've dettached the jumpers.Now I can hear the sound from right channel,there are no cracks pops but I can hear the sound from left channel when I turn on the volume pot at maximum.  I dont understand but the kreg at near power supply is 0,6 now. The terminal 14 , Ob and kreg at B side values are lower than needed range..

 

[Paul Birkeland]

I think the best course of action here is to take the amp all the way back to stock.

This means obtaining the stock volume pot, and potentially replacing the TL431 regulator that's giving you low voltage. 

-PB

 

[srhombeus]

Now I have connected alps potentiometer,changed the tl431,changed every part right side to left side.Now kreg is 2,5 finally at b side.But voltage at terminal 14 is low,around 80.  I can hear the left channel volume when i turn the potantiometer at maximum.Could the problem with the 12at7 tube ?

I've noticed that at maximum volume kreg is 2,5 at b side.And also terminal 9 value is not 0 , it's around 2-3.

 

[Paul Birkeland]

I've noticed that at maximum volume kreg is 2,5 at b side.And also terminal 9 value is not 0 , it's around 2-3.

This is either a problem with your volume pot, or you have the connections to pins 7 and 8 reversed at the socket. (220 Ohm resistor goes to pin 7, black wire to the PC board goes to pin 8)

If these pins are touching each other, this would also explain the symptoms. 

 

[srhombeus]

I've ordered gold lion 12at7 tube,I will try it tomorrow.My suspect is from the tube's left channel.Because,before when I first assemble the amp,I've burned the potentiometer,and Dac's left output.And I saw some flashing in the 12at7 tube.I think tube's left channel is also burned. Because I've changed every part except this tube. Is it possible?

 

[srhombeus]

Finally I have great news,I've tried the amp with the new 12at7 tube.This was the last part which is not replaced.It works perfectly.Real music,incredible details..

Thank you very much again Mr.Paul and Mrs. Eileen and all for your great support.