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Author Topic: Homebrew AM tube rx tx single control.  (Read 3357 times)
VE3LYX
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Posts: 160




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« on: September 26, 2011, 07:35:48 PM »

Since I got back at the hobby homebrewing with tubes I have had more fun than a barrel of monkeys. This week I am putting the finishing touches on my latest. It is a rx/tx. You could call it a transciever but it might be a stretch. It is tuned by a single dual gang 365 Pf variable cap stolen from a 1920s Grimes batteryless radio. It has four tubes. Two 12sl7 and two 50l6. You you guessed it! I forgot to use a transformer. Tubes filments are in series. (AC)
The rx is based on the Powerhouse receiver in Pop electronics (aug 1966) except I used these octal tubes. It has a hartley based design . It works well and drives a speaker easily. Yes it is a regen.
The Tx is my own although I stole some from R Weavers website. It uses 1/2 the 12sl7 for an osc. I built the same hartley circuit here as the rx has so it would tune the same. I am happy to say it does. The other half is a amp driven by a carbon mic/battery/ audio transformer circuit and it modulates the screen of the 50l6. The osc feeds the control grid of course. The balance between power and modulation is important and so it is a fairley low power deal but it does work and very well. I still have to finalize the output tank link but it has enuf power to use it as a driver or exciter for a PA of some sort. (Probably a 50C6 I will build) The tank of the output tunes on its own variable cap and coil but the osc tunes right with the rx  nicely. SInce it is experimental it isnt pretty anymore. Many things have been tried and changed to get this far but it works. It is running on 40 right beside me right now, in SWL mode. I bought an old 1920s radio cabinet and so built it in there. Al  wood chassis and panel. I am looking forward to getting on AM on 40 M. I ll need the PA to  do it I imagine if I expect t raise a reply but I have monitored it and it isnt bad for sound. Building this stuff is a blast. I even enjoy when it doesn't work the first time because I always learn a bunch. I would be intersted in hearing from any other AM ers and especially those playing with screen modulation.
Don VE3LYX
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KB4QAA
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Posts: 2488




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« Reply #1 on: September 27, 2011, 08:19:43 PM »

Paragraphs, and photos, please!  Smiley
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VE3LYX
Member

Posts: 160




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« Reply #2 on: September 28, 2011, 03:07:11 PM »

I dont know how to do the Picture thing here. I am working on a decent schematic though. I have lots of photos. I would send them to anyone who emails me direct.
I have a couple of small deals. I have some minor hum to deal with but much is because I run it AC DC . A transformer would help huge. Actually that is what is still to do. I can run it pure Dc as I have a full voltage battery supply but otherwise it is done and painted.
Don VE3LYX
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KG4NEL
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Posts: 443




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« Reply #3 on: September 28, 2011, 05:56:37 PM »

Go to Imageshack.us, and select the photos to upload...it'll give you a bunch of links that you just copy & paste into the body of the message here. Smiley

I love seeing homebrew tube stuff  Cool
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VE3LYX
Member

Posts: 160




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« Reply #4 on: September 28, 2011, 08:25:13 PM »

http://seniordragster.bravehost.com/mystreytx.html

At the bottom of this page on my website you will find a pic of the front panel. I will put more there later. it is running right now beside me as I type.
Don VE3LYX
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