Re: Valve frequency multipliers

legg <legg@nospam.magma.ca> wrote:

On Sat, 1 Feb 2025 10:50:22 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
 

john larkin <jl@glen--canyon.com> wrote:
>

On Fri, 31 Jan 2025 23:50:56 +0000, Cursitor Doom <cd@notformail.com>
wrote:

[...]
>

   Operating Point:
       Grid Voltage: Adjusting the grid voltage to operate closer to
cutoff can increase harmonic distortion since the tube's response
becomes more non-linear near cutoff.

 
Operate it deep in cutoff, off most of the time. A high amplitude
drive and grid-leak bias would be good.

>
That is exactly what I am doing and it doesn't appear to be working.
With 100v on the anode,  15 Mc/s at 25v pk/pk on the grid and a 22k grid
leak, the peak current for one triode of an ECC91 is around 20 - 30 mA
at the positive peak of the grid swing.  The average anode current is
around 2.5 mA, so the conduction period is about 10%.
>
A 75 Mc/s parallel-tuned circuit in the anode circuit is giving so
little drive to the following stage that I can't see any change in the
average grid voltage of that stage caused by the drive.

 
From old school notes, 5th harmonic peaks at 50degrees conduction,
3rd at 80degrees.

That's the sort of info I wanted.  I'll experiment with conduction
angles but my results are so far removed from what I need that I don't
think I shall get enough improvement that way..


--
~ Liz Tuddenham ~
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www.poppyrecords.co.uk