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Biasing
FWIW wary of Bruce's advice on the cathode bias level I went back and put a 330R cathode resistor in (measured 326R = 1R for the cathode resistor bias checking)
Here's what I got in Cathode Bias Mode:
Plate: 355-356
Screen: 357-358 (after 470R screen grid resistor)
Cathode: 24V /(327R) = .073
0.073/2 = .037 (0.036 measured over 1R)
(356-24) *0.036 = 12W
Sounds quieter than Fixed Bias, Trem doesn’t work nearly as well, but does give better note compression when plucked hard
Compared with the Fixed bias mode (which I changed to 28mA measured over the cathode resistor)
Plate: 367-368
Screen: 363-364 (after 470R screen grid resistor)
Cathode current 28mA
368*0.028 = 10.3W
Sounds good, Trem works well (very intense)
So overall verdict is I think I gt the best of both worlds - I love this amp
I will try a Jensen 12PQ later (got one on order)
A big THANK YOU to everyone here for the comments, feedback and advice. Can't wait till I beggar you all with my next build ;-)
FWIW wary of Bruce's advice on the cathode bias level I went back and put a 330R cathode resistor in (measured 326R = 1R for the cathode resistor bias checking)
Here's what I got in Cathode Bias Mode:
Plate: 355-356
Screen: 357-358 (after 470R screen grid resistor)
Cathode: 24V /(327R) = .073
0.073/2 = .037 (0.036 measured over 1R)
(356-24) *0.036 = 12W
Sounds quieter than Fixed Bias, Trem doesn’t work nearly as well, but does give better note compression when plucked hard
Compared with the Fixed bias mode (which I changed to 28mA measured over the cathode resistor)
Plate: 367-368
Screen: 363-364 (after 470R screen grid resistor)
Cathode current 28mA
368*0.028 = 10.3W
Sounds good, Trem works well (very intense)
So overall verdict is I think I gt the best of both worlds - I love this amp
I will try a Jensen 12PQ later (got one on order)
A big THANK YOU to everyone here for the comments, feedback and advice. Can't wait till I beggar you all with my next build ;-)
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