Frank, I read most of this thread and am in a discussion with someone else on the enhanced triode mode. His experiments hint that the distortion with screen drive is much higher than with 'normal' grid drive.
What is your experience?
Jan
What is your experience?
Jan
Please discribe what your (or his ) view of "enhanced mode" is.
I never use "enhanced mode" i use "triode" mode with G1 shorted to C. This is not Tim's version but David's version (please see patent).
I have build a couple of amps with great results (most of them beeing PP amps btw with 600V B+ or higher and DC feedback for high stability).
Then the next question: How is the grid driven? If the tube is not driven with a low impedant source it will add to the distortion (but i think you already know this).
Best wishes,
Frank
I never use "enhanced mode" i use "triode" mode with G1 shorted to C. This is not Tim's version but David's version (please see patent).
I have build a couple of amps with great results (most of them beeing PP amps btw with 600V B+ or higher and DC feedback for high stability).
Then the next question: How is the grid driven? If the tube is not driven with a low impedant source it will add to the distortion (but i think you already know this).
Best wishes,
Frank
I was looking at Bob Danielak's amp, screen driven output tube, with cathode bias and G1 to gnd.
He drives that screen directly from a cathode follower, no resistor involved. I have seen another example with several 100 ohms series R between cathode follower and screen, and complaints of high distortion.
BTW What is the sensitivity of screen drive, is it higher or lower than grid drive?
Jan
He drives that screen directly from a cathode follower, no resistor involved. I have seen another example with several 100 ohms series R between cathode follower and screen, and complaints of high distortion.
BTW What is the sensitivity of screen drive, is it higher or lower than grid drive?
Jan
Bob Danielak is actually using a standard grid modulator (as can be see in RF transmitters).
This will even need more current as G2 is on a higher voltage and therefore attracts electrons.
In triode or enhanced mode it also needs a higher voltage swing but is more linear as the voltage on G2 is much lower (near 0 V). Because of the higher voltage swing you will need a better buffer/driver...
No resitors on G2 as you like curent to flow if needed....
This will even need more current as G2 is on a higher voltage and therefore attracts electrons.
In triode or enhanced mode it also needs a higher voltage swing but is more linear as the voltage on G2 is much lower (near 0 V). Because of the higher voltage swing you will need a better buffer/driver...
No resitors on G2 as you like curent to flow if needed....
What is the purpose of the 50ohm pot? There is no mention of it by Bob. Probably to do with the dc coupling. But I don't see how 50ohm will make a difference.
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Hi Bas,
just to complement. changing the pot changes the current through the driver tube. This changes the voltage drop over the plate resistor and therefore at the drivers plate. This changes the voltage at the CF's grid, consequently at it's cathode, and so the voltage at the G2 of the output tube.
Good luck with the build!
erik
just to complement. changing the pot changes the current through the driver tube. This changes the voltage drop over the plate resistor and therefore at the drivers plate. This changes the voltage at the CF's grid, consequently at it's cathode, and so the voltage at the G2 of the output tube.
Good luck with the build!
erik
BUT: This potentiometer also impacts closed loop gain. I didn't want this, so I went another way in my build.
Best regards!
Best regards!
Hi Bas, how do you manage the lack of a potentiometer in your amps?
IIRC you posted other amps without it. What do you have upstream?
Thanks!
IIRC you posted other amps without it. What do you have upstream?
Thanks!
Thanks Francois!
Currently a lightspeed attenuator. But not optimal I guess because the DAC has highish output impedance I think. When and if don't have a preamp I usually just digital volume on my streamer.