As per the last post I have changed the two plate resistors R10 & R11 to 56K @ 2 watt resistors, reinstalled the 12AT7 as the phase inverter in the Poseidon circuit, powered up the amps using a Variac and obtained the following results:
B+ 485 VDC, C+ 345 VDC, D+ 310 VDC
Current set resistor is 10 ohms resulting in a current of 3.5 MA per plate at 35* C.
12AT7 - Pin #1 = 245 VDC Pin #6 = 260 VDC Pin #3 & #8 = 3.9 VDC
Amps run stable up to maximum power.
Amps sound great - tight bass, well defined mids and highs.
I then changed the current set resistor to 15 ohms resulting in a current of 2.3 amps per plate at 35* C, slowly powered up the amps using a Variac and obtained the following results:
12AT7 - Pin #1 = 310 VDC Pin #6 = 340 VDC Pin #3 & #8 = 5.9 VDC
Shut down amps because the plate voltages were above the maximum specified for a 12AT7.
Shannon, why does the voltage at Pin #3 & #8 have to be 9 to 13 VDC?
At 3.9 VDC at Pin #3 & #8 the amps run stable to full power and sound very good.
Should I increase the plate resistors back up around 100K, use the 15 ohm cureent set resistor to set the current at 2.3 ohms per plate and try the test again?
Any other suggestions?
Regards
WLK