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Constant Current Sources in Tube Amps
Constant Current Sources in Tube Amps
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Old 16th October 2003, 04:40 PM   #41
Antonio Tucci is offline Antonio Tucci  Italy
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Thank you very much for your interest.

I believed that high inductance in the plate could perform as a current source... and that a diode in the cathode could improve the behaviour of the tube.
On the contrary, your preliminary results demonstrated that this is not the true. Moreover, they seems to be in contrast with Boyle's considerations.
Can you comment this discrepancies ?
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Old 16th October 2003, 10:17 PM   #42
PRR is offline PRR  United States
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> High impedance plate choke loading.

For a given supply voltage, a good choke will always beat a resistor load.

In commercial design, it is sometimes a better plan to use a higher supply voltage, a low-cost resistor instead of a high-cost choke, and put the money saved into something else: better output transformed, gold knobs, or the maker's profit.

> 1) Un-bypassed tube diode in the cathode circuit

I wanted to see Runeight's comment. I'm not sure I understand what it does. But my feeling is: it is a little better than fixed-bias or cathode bypass, but not as clean as an unbypassed cathode resistor. It adds a nonlinear resistance in series with the nonlinearity of the cathode, and does not even work in phase opposition which would tend to cancel distortion (see long tail differential pair, where one of the triode can be replaced with a diode and still cancel 2nd harmonic). It may be a good in-between technique for some situations. I sure do not see how it can be a "Miracle Cure For Distortion", despite Axiom's numbers.

It leads to an amazing number of hot bottles on the chassis. Maybe that is a Good Thing.
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