Tom Cathey wrote:
> I plan to use the 10 milliwatt output from my FT-1000D as a source. This is
> the low level stage just before it goes into the power amp board. I'm hoping
> this is class A stuff and a much cleaner starting point than its -32db IMD
> 200W solid state power amplifier board output. Any opinions on that?
> For this amplifier I am thinking of either a chain of grounded grid stages
> so that they have individual built in feedback and an additional loop of
> feedback around the whole chain.
> OR, use a tetrode final with regulated screen voltage with stages going back
> to amplify the 10MW level. Hopefully, use up to 15-20db of loop feedback
> assuming the gain is available.
> I would appreciate any pointers to URLs showing working schematics of the
> big commerical amps that Collins, Harris, etc use, and ideas you may have
> for a design.
Forexample the old Collins 204C-1 amplifier first has a 4CX250B in Class A
that drives a 4CX250B in clas AB1 that drives a 4CX5000 in AB1, I bet that
thing would show pritty good numbers if one stays inside AB1. This thing
needs 200 mW to drive it to full power which is an awful lot.
> For example... I don't know what good low level tubes to use, but lets just
> say it went something like, 6AU6, 12BY7, 6146, 811A, 3-500Z, GS-35B - all
> in grounded grid with an additional feedback loop.
> Or, for grid driven: The same low level stages, then 4CX-150, 4-1000A,
> 4CX-3000. Looking for conservative ratings at 1500W and high IMD figures.
> Another thing I wonder about is if a tube like the 6146 or 4-1000A which has
> modest IMD figures open looped, can successfully participate in a -45
> to -50db IMD chain when big feedback is used?
Collins uses 6CL6 and 6146A set up with negative feedback to get IMD
numbers around -55 dB I think it is. That might be a way to go and maybe
drive a 3CX3000 which has good IMD numbers.
> I will be building this amp over the next few months and will post the
> results once completed. Thanks in advance for any help!
> Tom, K1JJ
Only my 2 cents from the top of my head.
73 Jim SM2EKM
Amps mailing list