[amsat-bb] Solid State conversion (tube equivalents)?

Diane Bruce db at db.net
Sat Feb 25 21:35:58 UTC 2017

On Sat, Feb 25, 2017 at 04:07:53PM -0500, Robert Bruninga wrote:
> About 40 years ago, the topic of tube-to-FET conversions was popular for
> making 1-for-1 conversions of old tube stuff to solid state.
> Anyone feel good at doing this these days?  Or am I just wallowing in
> nostalgia...?
> Today at a small hamfest, (40 tables only) there were at least 4 of the old
> high quality FREQ meters (9" cube boxes) that could give frequency accuracy
> to 0.01% anywhere from 125 KHz to 20 MHz.
> https://www.pa3esy.nl/military/us/meet/LM20/pics/LM20-front.jpg

I've done it with a GDO and a signal generator. They have very
few parts compared to a full up transceiver/receiver/transmitter so
are relatively easy to do. Rip out the high voltage portion utilise
the filament for low voltage if possible and go from there.

> Going rate was about $10.  What an absolutely astonishing piece of 1930
> engineering when you open it up. , with 3 tubes. (6A7, 76 and a 77)

Very feasible, but with gear that old I'd not want to rip out the old
wiring etc. I'd look into a cosmetic plug in replacement. Then again,
they are only $10. ;)

Also, nowadays using a DDS as a signal generator is going to be 
more accurate, more stable. YMMWV

> I can do just about anything with bi-polar transistors... (my coming of
> age...) but I PRE-dated FET's which are good direct substitutes for tubes
> since they are both transconductance devices .
> There is an excellent 1969 QST article on doing tube conversions, but it
> assumes one already knows more about it than I do.  And one of the tubes is
> a penta-grid tube which does oscillator and mixer all in one...
> http://www.qsl.net/kh6grt/page4/tubesters/MOSFETs%20for%20Tubes.pdf

Easy enough with a dual gate MOSFET.

> I would have thought that a solid state conversion of this simple 3 tube
> but very useful device would be out there somewhere...  But haven't even
> found a schematic on line...

I don't know of any personally. If I had one, I'd have a crack at it!

> Thought I'd ask before all the old fuds are gone...
> Bob, Wb4APR

Diane, VA3DB
- db at FreeBSD.org db at db.net http://www.db.net/~db

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