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FM transmitter with one 2C39A

AbaddonD

Member
2015-08-20 1:49 pm
Hello again!

This time, I wanna make a good use out of my 2C39A.

OK. I don't have that Eimac 2C39A anymore cause it broke when it rolled off my desk (I didn't throw it out, LOL). I got another one for
a cheaper price, a Siemens one which seems to have better construction and is quite heavier. Anyway...

I want to build a single tube (If possible) FM transmitter with that 2C39A. I have access to common parts and I have a power supply which can go up to around 500V. I don't think for moderate power we'd need anything more than 300V or so.
I also have a few different tubes like:
1x 6AQ5
2x PCL805
And a few which I can take out of my amp, but I'd rather not do that since I'm trying to repair it and then use the amp:
3x 12AX7
2x EL84

For all of you who are concerned about regulations, where I intend to use it, it doesn't really matter. I will not broadcast it on occupied FM channels. I want it to have a few watts of power, maybe like 10W?

I searched online and found a few schematics for a VT FM transmitter, but either they were a bit weird or they didn't work at all (The one with the 6C4).

Any help is appreciated
Thanks!
 
There are really two parts for what you want to do. First you must generate an FM signal then you can use your tube to amplify it.

Very easy to buy a small solid state transmitter and use it to drive your tube. Quite a bit harder to make a small tube version of what would be called an exciter.

Drifting around the internet are easily found circuits to use your tube as an amplifier. You might have to adjust the frequency tuning element values to get those circuits to work well in the Commercial FM bands.

I would start with an FM transmitter for a few dollars and then play with one of the amplifier circuits at low power.

So first I would try to get a low power FM transmitter working.

Second I would build an amplifier and optimize it.

Finally I would build a tube FM exciter or small 1 watt-ish transmitter to make better use of the amplifier.

However I suspect no matter where you are located there will be rules against using such a transmitter at any appreciable power level.
 
Last edited:

AbaddonD

Member
2015-08-20 1:49 pm
There are really two parts for what you want to do. First you must generate an FM signal then you can use your tube to amplify it.

Very easy to buy a small solid state transmitter and use it to drive your tube. Quite a bit harder to make a small tube version of what would be called an exciter.

Drifting around the internet are easily found circuits to use your tube as an amplifier. You might have to adjust the frequency tuning element values to get those circuits to work well in the Commercial FM bands.

I would start with an FM transmitter for a few dollars and then play with one of the amplifier circuits at low power.

So first I would try to get a low power FM transmitter working.

Second I would build an amplifier and optimize it.

Finally I would build a tube FM exciter or small 1 watt-ish transmitter to make better use of the amplifier.

However I suspect no matter where you are located there will be rules against using such a transmitter at any appreciable power level.
I actually made a single transistor one with a power consumption of 0.1W and it had a decent range and quality.

I can remake that.

Because I have never made a class C amplifier, I need some guidance.
And a question: in class C for the tuning capacitor, can I use these cheap and commnon variable capacitors found in FM recievers and stuff? Should I be worried about it heating up or something?