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Author Topic: need advice troubleshooting twinplex receiver  (Read 3202 times)
KG6ADQ
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Posts: 1




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« on: July 31, 2010, 08:01:38 PM »

Hi all,
I recently built the twinplex regen receiver from a reprint of "The Radio Handbook" of 1936 (reprinted by Lindsay Publications). The schematic is for "Simple Receiver With One Type 19 Tube). It is indeed a simple design. Despite the simplicity, I seem not to be able to get it to work properly. I followed the design very closely, and with an 80 meter coil in, I am able to hear KGO (which is a strong station in the bay area on 810). Moving the tuning around does nothing - the station even comes in when I have the 40M coil in.

I note it is very sensitive to hand capacitance. I used a plastic front panel but behind it is a copper plate, all rotors of variable caps are grounded to it. It has a reasonable amount of hum. I dont know how to get around that. When I put my MFJ antenna analyzer near it, I can find the signal on the 80M band and follow it around with the tuning. It appears to have a pretty wide bandwidth, from about 2.5 to 5 MHz. I did hear an SSB qso on 80M when I got my hand in just the right place, but that only happened once.

I tried pulling a wind off the tickler and one off the L1, adjusting the coupling capacitor, different antennas, etc. Nothing really seems to change the one-station KGO receiver. Anyhow, it is my first homebrew receiver, so I don't have a lot of experience troubleshooting even thought its a pretty simple design. Any ideas about how to get it operating?

Thanks much!
-karl
kg6adq
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AA4PB
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Posts: 13032




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« Reply #1 on: August 01, 2010, 09:36:33 AM »

No experience with that particular receiver but in general regenerative receivers were not very selective. If you have a very strong signal from a station nearby you are often stuck. You might try reducing the antenna length (i.e. pick up less of the strong signal) and playing with the regeneration control.
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N2EY
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« Reply #2 on: August 02, 2010, 03:18:58 AM »

I don't know how much hollow-state experience you have, so please bear with me if these things seem too basic.

Couple of things to check:

1) The Twinplex and similar receivers were intended for use with short single-wire antennas, not 50 ohm coax. The adjustable antenna coupling capacitor is usually very small - only a couple of uuF at most. Too tight coupling to the antenna will prevent the detector from oscillating.

2) The tickler coil and the tuning coil must be phased correctly or the detector won't regenerate. With the regeneration control turned up (lots of plate voltage), you should be able to hear the detector oscillating on another receiver when both are tuned to the same frequency. You may have to reverse the connections to the tickler coil socket to get it to work.

3) Check the tube pin connections. Remember that tube pins are counted clockwise looking at the bottom of the tube.

73 de Jim, N2EY
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N0WVA
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Posts: 16




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« Reply #3 on: August 03, 2010, 03:09:46 PM »

Hi Karl,
 In addition to checking the phasing of the tickler coil as mentioned above, you might also want to make sure you have enough tickler turns. I would also check your DC voltage to make sure its high enough. Is the choke value high enough? Touching your finger to the grid terminal should cause a loud buzz. Also, to make sure your not loading down the tank with the antenna, Id just use one turn link coupling. You probably have it coupled too tight if KGO is all over the dial. A regen only needs very light antenna coupling.

Doug
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KC9KEP
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« Reply #4 on: August 13, 2010, 08:27:48 AM »

Karl,

I think you've received some good suggestions.

I've built this radio myself 

http://www.bignick.net/Morgan_Radio/Radio_4.htm

If you need to compare notes, let me know.

--Tom Nickel  KC9KEP
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