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Saturday, August 20, 2022

TRIGGER WARNING: Solid-Stating Old Tube (Thermatron) Gear (Including -- GASP -- R-390As)

Look at that.  Well, maybe some of you shouldn't. (I'm thinking of you Grayson.)  I found the Charles Smith YouTube channel while innocently looking for ideas on how to solid-state the HT-37 VFO assembly I recently bought on e-bay.  Charles Smith has some really great ideas in this area.  He solid-stated a Heath VF-1.  But he took it all to an extreme when he solid stated an R-390A.   Take a look at how he built the replacements for the thermatrons:  He used those plastic wall sockets that you screw into sheet-rock when you need to hang a picture.  This is real genius. He used the tube filament lines to carry DC to these new sockets. 

R390A Solid State Conversion Video #1:  https://www.youtube.com/watch?v=xhWzX874wYo

Charles Smith's YouTube Channel 

He has videos on the HQ-170 (DEAN:  Just say NO!) and the SP-600.  He also covers the HQ-110, which is uncomfortably close to my HQ-100.  

Who is Charles Smith?   What is his callsign?    Charles Smith is KV4JT.  Here is his QRZ page: 

He has some great humor and wisdom in his videos: Procedures that are difficult or more trouble than they are worth are called "bugger-bears."  He advises that if your IF cans are stuck, you should "find a way to unstick them!"  Indeed you should!  He builds a cool jig to hold the IF section of the R-390A while you are working on it.  He provides similar protection (with two long screws) to the VF-1.  

Even though some of you will have to go to therapy after seeing all this, I say THREE CHEERS FOR CHARLES SMITH! 


  1. The only think I can think of to say is WHY? Solid stating these radios will not improve anything and destroy any value of the receiver. At least if you're going to do it, please do it better than these videos. However, it is just a hobby and and Charles is very clever and each to their own as they say. But I totally don't get it.
    There were a series of "tubesters" manufactured for a short time back in the 70's I think, the electrical and mechanical engineering was fairly good for that time. But it became obvious soon enough that performance was much worse than the original thermatrons and they all but disappeared. I used to own a few but long gone at hamfests.

  2. Grayson: Charles answers the question on his QRZ.com page: https://www.qrz.com/db/KV4JT "There are many advantages to a converted radio: No high voltage to kill you, no heat, less drift, no tubes to replace, lighter, instant on, more reliable. The radio should last a lifetime without repairs. This is a good way to preserve many of the radios destined for the junk pile. The conversion costs about the same price as a set of tubes on E-BAY."
    I found his page when I was looking for a way to solid-state the VFO from an HT-37. I just didn't want to deal with the high voltage and the heat. 73 Bill

  3. Thermotrons....Ugh. Please let's not call them that, they don't like it! 🙂

  4. There's also the issue of Thermotron being a possible copy right infringement. They manufacture environmental chambers.

  5. You are misspelling it. They are thermatrons, not thermotrons. Our lawyers at Dewey, Cheatham and Howe are prepared to fight this all the way to the Supreme Court. And beyond! 73 Bill


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