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TR-3 Band Switch Wiring
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WARNING:? I am a hobbyist and I am learning vintage radios. I can usually find my way around schematics to some degree, but not well. I do better with service manuals and I've not found any for Drakes. I may also use wrong terminology for the parts I describe, so I have included photos. Please be patient with me and don't roll your eyes if my question is dumb.
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I'm refurbishing and recapping a TR-3. I have a mystery that I'm hoping the Drake brain trust can help me with...
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While cleaning up the very dirty band switch of this radio, I came across a white/brown wire that appears to go to nowhere.
I know I did not knock it off and without my flashlight, I would have never seen the unconnected end under the band switch. The wire begins on the top of the chassis on a lug attached to a little vertical circuit board adjacent to V11 I believe (see photo). This white/brown wire goes from this little board, through a rubber grommet, through a hole on the top end of a wafer board. Then it was bent downward next to the band switch wafer and not connected to anything.
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The other part of the mystery is oddly this end of the wire does not appear to have been ever connected. The strands of wire are far inside the insulation (see photo). There are no strands coming out of this wire, nor the bottom of the switch wafer.
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Many thanks. 73. Joe
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Joe - W7BWA
Custer, WA |
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It serves as the antenna for the calibrator signal. ?Not sure why Drake did it that way. It¡¯s confused many in the past including myself. Good luck with the TR-3. I have two of them. My favorite radio is my TR-3 with TR-4 sideband filters in it. ?You may find that audio is not ideal on one or both sidebands. The TR-3 filters are its greatest weakness. You can find more details here with some simple searches.
On Tuesday, April 1, 2025 at 10:39:51 PM CDT, Joe W7BWA via groups.io <w7bwa@...> wrote:
WARNING:? I am a hobbyist and I am learning vintage radios. I can usually find my way around schematics to some degree, but not well. I do better with service manuals and I've not found any for Drakes. I may also use wrong terminology for the parts I describe, so I have included photos. Please be patient with me and don't roll your eyes if my question is dumb.
?
I'm refurbishing and recapping a TR-3. I have a mystery that I'm hoping the Drake brain trust can help me with...
?
While cleaning up the very dirty band switch of this radio, I came across a white/brown wire that appears to go to nowhere.
I know I did not knock it off and without my flashlight, I would have never seen the unconnected end under the band switch. The wire begins on the top of the chassis on a lug attached to a little vertical circuit board adjacent to V11 I believe (see photo). This white/brown wire goes from this little board, through a rubber grommet, through a hole on the top end of a wafer board. Then it was bent downward next to the band switch wafer and not connected to anything.
?
The other part of the mystery is oddly this end of the wire does not appear to have been ever connected. The strands of wire are far inside the insulation (see photo). There are no strands coming out of this wire, nor the bottom of the switch wafer.
?
Many thanks. 73. Joe
?
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Joe - W7BWA
Custer, WA
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¿ªÔÆÌåÓýThat is what was known as a ¡°gimmick¡±. This was a way to tweak a circuit to work. Often they had two wires wrapped around each other, each end being tied to a circuit point. The calibration technician literally cut the length of this ¡°gimmick capacitor¡± to get the circuit to work.?This was a cheap, simple and crusty way to correct for uncontrollable variables in the radio assembly processes.? Your wire is likely meant as an adjustable stray inductance, whose value could be set with a wire nipper, once-and-for-all.? Don¡¯t remove it, put it back where it was and leave it alone. Gary W0DVN On Apr 1, 2025, at 10:05?PM, Barry KJ5GQM via groups.io <chasbg@...> wrote:
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¿ªÔÆÌåÓýOK, in this case, antenna for calibrator - but the gimmick story is still true.. A d using this as an antenna still counts as a ¡°gimmick¡± in my book. It takes the place of a capacitor that could have performed the same task.Gary W0DVN On Apr 1, 2025, at 10:13?PM, Gary Follett via groups.io <xntrick1948@...> wrote:
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Not dumb at all.? I did the same thing when I first dug into one of these Drake transceivers.? Your sideband filters may be OK.? These are very broad filters and thus sound great on the air if they are working, not so great for adjacent channel rejection.? If your audio is sounding very pinched or tinny you may have a problem.? The options to fix it are limited and can get expensive.? I was lucky to find a TR-4 parts radio to rob the filter from.? Even this is not easy.? The early TR-4 uses the same "soup can" filter as the TR-3 so you don't want that.? The later ones use the filter set that is used in the TR-4C radios.? These are great filters but they protrude through a cutout in the chassis floor.? A cutout that is not there in the TR-3.? Mid-generation TR-4s are the best donors since they used a filter that was better than the soup can but fit in the same space.?? If you have a spectrum analyzer you can wrap a probe wire around the 9MHz carrier oscillator tube and you will see the sideband passbands when you switch from one side to the other.? set you span to about 8KHz.? This is also a good way to center your carrier. Instead of a nice 2.4kHz passband I saw a spiky response with one filter even shifted.? If you don't have a spectrum analyzer your ear will still tell you what is going on.? Note that these filters are used in both directions so what you are hearing is what others are going to hear from you when you transmit.
On Tuesday, April 1, 2025 at 11:08:17 PM CDT, Joe W7BWA via groups.io <w7bwa@...> wrote:
Barry. You have saved my bacon and I am so grateful. I spent hours trying to track this down. Thanks so much! I¡¯m really not that dumb! Lol
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interesting on the filters. I will search it out and if I can get some, I¡¯d have a great tube radio.?
73 my friend.?
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Joe - W7BWA
Custer, WA
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Barry, this is awesome. Thanks so much!?
I have the equipment to do the sweep. I¡¯ll do as you suggested.? This TR-3 was not treated well. I¡¯ve cleaned it up and recapped it. I think I will sell it to someone that likes it as is - baked on old dust on the chassis. I¡¯ve cleaned it as much as possible without stripping the chassis.?
I think once sold, I¡¯ll look for a clean 3 and maybe invest in filters if I can hunt some down. Then I¡¯ll have one awesome TR-3!
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Many thanks again. 73.
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Joe - W7BWA
Custer, WA |
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