RE: Need help with diodes


Date: Sat Oct 01 1994 - 22:20:12 EDT

On 09-28-94 wrote to M405142%SLRC1.decnet@mdcg:

> I would very much like to find out ANY information on solid state tube
> replacements, commercial or homebrew.
> I my novice days, I transistorized an old Hammarlund Navy RBG (HQ-120)
> that worked fairly well. I took fet's (2n3819's) and made up octal
> socket plugs that replaced all the tubes. Then the thing ran on 24
> volts at about 50 ma or so. It worked fairly well, but I did not
> really know what I was doing back then..... (:+{{.....
> Anyone on the net have any further comments or ideas?
> Bob NA4G
Wasn't there once a line of FET plug-ins that would actually run on the old
high B+ voltages of the original tube rig? I think they're long gone.

You probably want to think more in terms of "transistorizing the circuit"
rather than finding "tube replacements", though. These days it is so easy to
make certain things work better without much additional effort.

You may most often want to preserve the RF tuned circuits, oscillators, etc. --
so FETs are the choice to offer the right hi-Z loads for these.

Using FETs for most RF tube circuits isn't too hard, as long as you reduce any
plate load/dropping resistors to a more appropriate value for the voltage used
(for most of us, 12V).

Mixers, you may want to just put diode ring mixers in, with the appropriate
circuitry before and after.

In the audio circuit, you might just start over and use a nice clean LM380
circuit, or a nice complementary-symmetry transistor output stage. Both
eliminate the transformers.

Is the thing still a boatanchor after such a change? You tell me! All I know
is that after doing this with the T-368 exciter, I have one hell of a nice
stable VFO.

: John Seboldt / I am Bach of Borg...
: Amateur radio K0JD... / your style will be
: Church of the Annunciation, / assimilated.
: Minneapolis /

 -> Alice4Mac 2.3 E QWK Eval:05Mar94

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