11-29-2017, 03:36 PM
jjmt,
for each tube, following the process explained by Uncle Doug in his youtube video:
- (power off) measure the resistance between pin 8 of the 5Y3 and pin 3 of the 6V6. This is the impedance on half of the input side of the output transformer ®
- (power on) measure the voltage drop across that same region (V).
- calculate plate current as V/R (PC)
- measure plate voltage relative to ground (PV)
- calculate Power Dissipation (PD) PD = PC*PV = 10 watts
6V6 tube has a max rating of 12 watts. 10/12 = .83
I installed independent bias resistors (550ohms and 680 ohms) and capacitors for each 6V6 to make the outputs approximately equal at 10 Watts. The amp has plenty of volume, so you may be correct that I can reduce the output of the tubes further.
I did not chart the results after I replaced the cathode bias resistors and caps, I just assumed that the results would fall out of my plot at 10 watts per tube (red dots on plot I posted earlier). To get down to 70%, I would be at 8.4 watts. To do that I think I would need 680 and 1000 ohm bias resistors by interpolation for the outer tube and extrapolation for the inner tube.
I am happy to hear your thoughts. Am I on the right track in your mind?
Larry
for each tube, following the process explained by Uncle Doug in his youtube video:
- (power off) measure the resistance between pin 8 of the 5Y3 and pin 3 of the 6V6. This is the impedance on half of the input side of the output transformer ®
- (power on) measure the voltage drop across that same region (V).
- calculate plate current as V/R (PC)
- measure plate voltage relative to ground (PV)
- calculate Power Dissipation (PD) PD = PC*PV = 10 watts
6V6 tube has a max rating of 12 watts. 10/12 = .83
I installed independent bias resistors (550ohms and 680 ohms) and capacitors for each 6V6 to make the outputs approximately equal at 10 Watts. The amp has plenty of volume, so you may be correct that I can reduce the output of the tubes further.
I did not chart the results after I replaced the cathode bias resistors and caps, I just assumed that the results would fall out of my plot at 10 watts per tube (red dots on plot I posted earlier). To get down to 70%, I would be at 8.4 watts. To do that I think I would need 680 and 1000 ohm bias resistors by interpolation for the outer tube and extrapolation for the inner tube.
I am happy to hear your thoughts. Am I on the right track in your mind?
Larry