{"id":4801,"date":"2022-08-24T13:59:00","date_gmt":"2022-08-24T03:59:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2022\/08\/24\/solid-stating-an-ht-37-vfo-advice-needed\/"},"modified":"2025-07-22T18:02:56","modified_gmt":"2025-07-22T08:02:56","slug":"solid-stating-an-ht-37-vfo-advice-needed","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2022\/08\/24\/solid-stating-an-ht-37-vfo-advice-needed\/","title":{"rendered":"Solid-Stating an HT-37 VFO — Advice Needed"},"content":{"rendered":"<\/p>\n
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Original HT-37 VFO Circuit<\/span><\/div>\n
A couple of things before I start: <\/b><\/div>\n

<\/b><\/div>\n
First, this is not my fault. The Radio Gods are to blame. I innocently tried to by an HT-37 tuning capacitor on e-bay, but the seller sent me the entire VFO unit. The only thing missing was THE TUBE. Clearly, that was a sign, right? <\/b><\/div>\n<\/p>\n

Second, this is a work in progress. That is why my diagram (below) is a bit ugly. I am looking for your input and advice on how I might do this better. I will understand if religious principles prevent some of you from participating in this endeavor. <\/b><\/p>\n

I am trying to solid-state this device WITHOUT major surgery, and without adding any reactive components that would change the resonance or tuning range of the original. The original circuit tunes from 5 to 5.5 MHz and that is fine with me. <\/b><\/p>\n

I started out by just sticking a J-310 FET into pins 1, 2, and 5 of the tube socket. I put 12 V on the drain and the thing oscillated right where it is supposed to. That was a good sign. <\/b><\/div>\n

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Here is what I have done so far: <\/b><\/div>\n
<\/a><\/div>\n
Bill’s initial solid state conversion of HT-37 VFO<\/span><\/div>\n
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Mechanically, my effort has been very simple. At first I tried to fashion a more serious male socket for the FET using two broken 7 pin tubes. This didn’t work well. <\/b><\/div>\n

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So then I just ran three short wires up through the center hold of the tube socket to the connections for pins 1,2, and 5. I superglued the J-301 to the chassis and made some non-reactive connections: I put a 47 ohm resistor on the source, and a 220 ohm resistor on the drain. I grounded the drain for RF with a .01 uF cap to ground. I added a 100k resistor and a diode on the gate. Oh yea, I put a couple of ferrite bead on the FET gate lead. (See pictures below.)<\/b><\/div>\n

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\n
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Three lead up through the center hole<\/span><\/div>\n

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<\/a><\/div>\n
A rare look inside an HT-37 VFO<\/span><\/div>\n

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The original thermatron circuit has an output bandpass transformer, a 3900 ohm resistor and a coupling cap. I left them in the circuit, but they are not doing anything. <\/b><\/div>\n

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The output from the source of the FET looks pretty good. I can see some VHF on the trace, but I suspect this is from my FM broadcast nemesis at 100.3 FM (one mile away). On a receiver, I can hear some AF noise on the signal, but this may be the result of the RFI from THE BIG 100 — WASHINGTON’S CLASSIC ROCK. <\/b><\/div>\n

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So what do you folks think? What else could I do, or should I do? <\/b><\/div>\n","protected":false},"excerpt":{"rendered":"

Original HT-37 VFO Circuit A couple of things before I start: First, this is not my fault. The Radio Gods are to blame. I innocently tried to by an HT-37 tuning capacitor on e-bay, but the seller sent me the entire VFO unit. The only thing missing was THE TUBE. Clearly, that was a sign, … Continue reading “Solid-Stating an HT-37 VFO — Advice Needed”<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":4802,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[59,101,53],"tags":[],"class_list":["post-4801","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-hallicrafters","category-tubes","category-vfo"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4801","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/comments?post=4801"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4801\/revisions"}],"predecessor-version":[{"id":4807,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4801\/revisions\/4807"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media\/4802"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=4801"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=4801"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=4801"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}