'goodtimes'
Member
Hello,
My St-70 has a left channel problem. The left channel is not as loud as the right and also is distorted. I have changed tubes (one at a time-rectifier, output, and driver) with no change whatsoever. I have tried known good used tubes and NOS NIB known good tubes with no change. I have checked resistors and caps and all seem to be in spec. Another odd thing is it will bias and hold the setting on both channels.
Upon checking voltages I get the following;
GZ34-
Pin 2 to ground - 454 VDC
Pin 8 to ground - 454 VDC
Pin 4 to ground - 374 VAC
Pin 6 to ground - 375 VAC
All EL 34's are the same give or take 1V
Pin 1 to ground - 1.5
Across pins 2 and 7 - 6.0 VAC
Pin 3 to ground - 437 VDC
Pin 4 to ground - 438 VDC
Pin 5 to ground - -24 VDC
Pin 6 to ground - -24 VDC
Pin 8 to ground - 1.5 VDC
Quad Cap
Section #1 - 454 VDC Half circle symbol back side of amp - one choke lead and wire to pin 8 of the rectifier tube
Section #2 - 442 VDC square symbol left side of amp - another choke lead and the two wires from the two output transformers
Section #3 - 373 VDC full circle symbol on right side of amp
Section #4 - 287 VDC triangle symbol toward front side of amp
I have installed the new "upgraded" quad cap where
half circle = 80uf
square = 40uf
triangle = 30uf
full circle = 20uf
Any help or suggestion would be greatly appreciated.
My St-70 has a left channel problem. The left channel is not as loud as the right and also is distorted. I have changed tubes (one at a time-rectifier, output, and driver) with no change whatsoever. I have tried known good used tubes and NOS NIB known good tubes with no change. I have checked resistors and caps and all seem to be in spec. Another odd thing is it will bias and hold the setting on both channels.
Upon checking voltages I get the following;
GZ34-
Pin 2 to ground - 454 VDC
Pin 8 to ground - 454 VDC
Pin 4 to ground - 374 VAC
Pin 6 to ground - 375 VAC
All EL 34's are the same give or take 1V
Pin 1 to ground - 1.5
Across pins 2 and 7 - 6.0 VAC
Pin 3 to ground - 437 VDC
Pin 4 to ground - 438 VDC
Pin 5 to ground - -24 VDC
Pin 6 to ground - -24 VDC
Pin 8 to ground - 1.5 VDC
Quad Cap
Section #1 - 454 VDC Half circle symbol back side of amp - one choke lead and wire to pin 8 of the rectifier tube
Section #2 - 442 VDC square symbol left side of amp - another choke lead and the two wires from the two output transformers
Section #3 - 373 VDC full circle symbol on right side of amp
Section #4 - 287 VDC triangle symbol toward front side of amp
I have installed the new "upgraded" quad cap where
half circle = 80uf
square = 40uf
triangle = 30uf
full circle = 20uf
Any help or suggestion would be greatly appreciated.