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