Bias Resistor Increase = lower gain?
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Re: Bias Resistor Increase = lower gain?
Make yourself a dummy load with a large 100W wirewound resistor the same impedance as your speaker i.e.8ohm,16ohm.
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Re: Bias Resistor Increase = lower gain?
With line voltage at 117.5VAC I measure:geoff 1965 wrote: ↑Wed 12/01/21 7:25 pmif you don’t mind give us some reference voltages with the stock 91R bias resistor i.e. B+ at first capacitor,plate,screen & cathode voltage of the el 84’s.
* 329VDC @ CT
* 314VDC @ plates
* 302VDC @ pins 9
(Forgot to measure @ cathode)
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Re: Bias Resistor Increase = lower gain?
Colin’s 1966 amp in the downloads shows 325V at first cap so that is very close,thanks for posting those voltages.
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- colossal
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Re: Bias Resistor Increase = lower gain?
But we should also consider the Mains AC for the measurement, if trying to make some connection between historic reference amps and today's copies. Junior's mains is running a cool 117.5VAC. Most places in the U.S. run 122-125VAC and on a PT wound for 117 or 120VAC input, the secondary is going to run hot.geoff 1965 wrote: ↑Sat 12/04/21 10:14 amColin’s 1966 amp in the downloads shows 325V at first cap so that is very close,thanks for posting those voltages.
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Re: Bias Resistor Increase = lower gain?
That’s the reason I have 275-0-275 HT colossal,not to simulate colin’s amp or the 1974X but to get the sweet spot B+ with the higher wall voltage.
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Re: Bias Resistor Increase = lower gain?
I just mention that because the 1974X diverges from what we consider the 18W Lite foundation. I will be interested to see what Junior Marbles reports for his cathode voltage in his 1974X with the stated conditions.
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Re: Bias Resistor Increase = lower gain?
Just going back to the question in the thread title,No, since the power tube cathode resistor is bypassed with a cap, the resistor's value will have virtually no effect on gain.
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Nature abhors a clean tube amp