Cathode follower driver stage - Page 3

dhaen · 13th November 2002, 09:14 PM

Except that I found the 6550 and excellent cathode follower to drive SV573-3's into A2; got 25W easily.
Now find me a double triode that will swing 400v P-P @ 15mA as a cathode follower, and stay linear.

No, no, no, I ended up with a massive interstage transformer driving my 845 amp, but the bias supply to the secondary "cold end" still needs to be "stiff", otherwise it's the same problem when the output valve's G/K goes into "rectifier mode".
The poor lovelys now peak at +75v on the grids.
Even with tone, there is no grid deformation, and no characteristic change, short (or long term) as yet.
So I don't think music is a problem at all.
But a big good transformer is expensive, and Joel is on a budget.

Damn, that's my warranty gone; jac please close your eyes!

I don't think valve noise is a big issue with driver stages is it?

Here's to grid current.........

fdegrove · 13th November 2002, 09:45 PM

Hi,

Quote:

Now find me a double triode that will swing 400v P-P @ 15mA as a cathode follower, and stay linear.

I haven't looked into this really but I suppose the big triodes could swing it.(pun intended)

The thing is that it would be hard to justify their use there.

These beam tetrodes aren't that expensive and if they do the job,why not?

Quote:

but the bias supply to the secondary "cold end" still needs to be "stiff", otherwise it's the same problem when the output valve's G/K goes into "rectifier mode".

Agreed,regulate it or clamp it with a glow discharge tube.

Quote:

But a big good transformer is expensive, and Joel is on a budget.

He'll find a "used" one.

Quote:

I don't think valve noise is a big issue with driver stages is it?

No,if I can avoid it I will.
Remember those microdetails....

Quote:

Here's to grid current.........

The bottle is open.

Cheers,

Circlotron · 14th November 2002, 12:34 AM

I always thought it would be an interesting experiment to use a source follower when driving a stage that drew grid current on the peaks. The cct would be dead simple and plenty of HV fets available. The lower the capacitance the better. Should have a stiffer output than any reasonable size tube. That's if a fet suits you of course.

dhaen · 16th November 2002, 06:55 PM

Honestly, this isn't a cruisade but:

What would be the gate capacitance of a suitable device?

Cheers,

13th November 2002, 09:14 PM	#21
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	I admit nothing... Except that I found the 6550 and excellent cathode follower to drive SV573-3's into A2; got 25W easily. Now find me a double triode that will swing 400v P-P @ 15mA as a cathode follower, and stay linear. No, no, no, I ended up with a massive interstage transformer driving my 845 amp, but the bias supply to the secondary "cold end" still needs to be "stiff", otherwise it's the same problem when the output valve's G/K goes into "rectifier mode". The poor lovelys now peak at +75v on the grids. Even with tone, there is no grid deformation, and no characteristic change, short (or long term) as yet. So I don't think music is a problem at all. But a big good transformer is expensive, and Joel is on a budget. Damn, that's my warranty gone; jac please close your eyes! I don't think valve noise is a big issue with driver stages is it? Here's to grid current.........

14th November 2002, 12:34 AM	#23
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	Source follower instead I always thought it would be an interesting experiment to use a source follower when driving a stage that drew grid current on the peaks. The cct would be dead simple and plenty of HV fets available. The lower the capacitance the better. Should have a stiffer output than any reasonable size tube. That's if a fet suits you of course. __________________ Best-ever T/S parameter spreadsheet. http://www.diyaudio.com/forums/multi...tml#post353269

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16th November 2002, 06:55 PM	#24
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	Honestly, this isn't a cruisade but: What would be the gate capacitance of a suitable device? Cheers,