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In Reply to: RE: RH84 test amp: multiple problems found ... posted by Tre' on September 24, 2016 at 11:50:44
In the original rh circuit one could also use tubes of similar characteristics, like 5965, or 7062, and 12ay7, but microphonics is not a problem in this circuit. I have tried all those tube types and my current favorite driver tube is the 7062. I have not check the load lines of thee tubes so i am not sure how they stack up against the 12at7.
Follow Ups:
The 12ay7 is by far the most linear tube of the bunch.Pick a spot. The datasheet says 250vdc plate at 3ma. and -4vdc bias.
Load it high for a near horizontal load line. Nice even spacing between grid lines and the plate voltage moves very close to the same going to the left vs. going to the right.
With a horizontal load line I see (very close to) the plate voltage moving 87.5 volts from -4 to -2 volts grid and (very close to) the plate voltage moving 87.5 volts from -4 to -6 volts grid. If true in practice, that means that there is (very close to) no harmonic distortion.
The plate resistance is high but I don't think that would be a problem driving a pentode (pentodes don't have much Miller capacitance to worry about driving).
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/24/16
I am breaking in a RH 6l6 amp with Norelco outputs from Switzerland. They sound very nice with the 7062 and 6L6 metal tubes. very clean sound on my Altec. Although i think it is mostly the NOS 6L6 that i just started listening to today. I will plug in some 12ay7 and let you know how that fares. cheers.
I'm not sure you can just plug the 12ay7 in a circuit designed for a 7062.
But even if you could, to get the full benefit of the 12ay7 you would need to optimize the circuit for the 12ay7.
Plate voltage, plate load resistor, cathode bias resistor.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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