I want to build an AM Tube Tuner - diyAudio
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Old 8th June 2006, 08:42 PM   #1
sbelyo is online now sbelyo  United States
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Default I want to build an AM Tube Tuner

I want to build an AM Tube Tuner. Can this be done today? I know I can just get some old tube tuner off ebay, but I like to make stuff rather than adapting something.

Are there any schematics or kits available that will work?
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Old 8th June 2006, 09:26 PM   #2
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I'm looking at RCA receiving tube manual RC-17. Page 277, circuit 17-8. 3 tube AM receiver. 5Y3 rectifier, 6BA6 RF amp, 12AU7 detector & audio amp. 10 Rs, 15 Cs, 1 RF xformer, 1 power xformer, 1 loop antenna.

Looks easy...

RCA RC-xx must be online somewhere. That's where I would start. Hard part will be finding the variable Cs, and would guess layout is everything.

I personally would start with an existing tuner. You can get it working, then gut it for your scratch build. Fer'git Fleabay, and get one from one of the antique radio sites for $30. Don't tell 'em you will gut it.

Bad news, is that when you are done, you will get AM broadcasts. 'round here, it is Rush Limbaugh and Mexican.
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Old 8th June 2006, 09:29 PM   #3
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AES has some simple kit stuff.

How complex do you want to get? A superhet circuit is not out of the question, but your test bench needs to be fairly sophisticated. OTOH, you could use the pentode section of a 7059 as a regenerative detector to feed the tube's triode section set up as a common cathode audio gain stage. While a regen circuit is not nearly as sensitive or selective as a superhet circuit, you don't have the alignment issue.

Dude, you're taking me back 50 years.
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Old 8th June 2006, 10:30 PM   #4
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Struth Eli, we must be similar in age (my fullest sympathy).

I have used a detector of a diode directly coupled to a cathode follower for superior linearity (dual triode used - circuit can be posted). But as Eli said you must first say where you want to go as in how complex.

A regenerative circuit is fun but very narrow-band. A tuned rf gives purer sound - if stations are so situated that poor selectivity is not a problem. Otherwise a superhet, for which you will need at least a decent rf signal generator, apart from multimeter etc. What are the frequencies in your region, medium wave, long wave - or were you thinking of a more complex all-wave job? For the latter, unless you have experience or are VERY adventurous, a kit might be less prone to drive you to suicide, if still available.

Ah, yesteryear... In South Africa in the 50s there was available those extremely good-looking multi-band Geloso kits from Italy.....

Regards.
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Old 8th June 2006, 10:59 PM   #5
sbelyo is online now sbelyo  United States
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Thanks guys....

I don't want to get too crazy because I don't have all the test equipment.

I just need 880 Mhz and 1050 Mhz.

I didn't realize that AES had those tube kits.... Are there any other
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Old 8th June 2006, 11:02 PM   #6
sbelyo is online now sbelyo  United States
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Quote:
Originally posted by ethermion
[B]RCA RC-xx must be online somewhere.
I think I have a copy on PDF I'll check
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Old 8th June 2006, 11:10 PM   #7
paulb is offline paulb  Canada
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Quote:
Originally posted by sbelyo
.

I just need 880 Mhz and 1050 Mhz.
That's kHz, right?
I built one in high school. Not too difficult. Need an RF signal generator to set it up.
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Old 8th June 2006, 11:14 PM   #8
sbelyo is online now sbelyo  United States
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Quote:
Originally posted by paulb

That's kHz, right?
I built one in high school. Not too difficult. Need an RF signal generator to set it up.
Yeah... That's right Khz The other bands are for listening in on phone conversations
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Old 8th June 2006, 11:31 PM   #9
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Quote:
I just need 880 Mhz and 1050 Mhz.
I think you mean 880 KHz. and 1050 KHz. Mmmm, 880 KHz. is WCBS in NYC.

Only 2 stations, you say. A superhet might be in the cards even with limited test equipment. You could try to source 455 KHz. crystal filters. That would eliminate aligning IF trafos. Ceramic filters are a possibility too, but voltage followers would be needed to protect them from the B+ rail. You would need 2 sets of coils for the front end. An antenna coil for the freq. of interest and a local oscillator coil tuned 455 Khz. higher than the freq. of interest. Relatively large inductances and a small capacitance are indicated for the antenna "tanks", while a relatively large capacitance and small inductances are indicated for the local oscillator "tanks".

The 7059 would make a fine 1st detector and local oscillator. The Hartley circuit will do nicely for the local oscillator. 2 or 3 12AU6s would take care of IF amplification needs.
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Old 9th June 2006, 01:25 AM   #10
lndm is offline lndm  Australia
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Quote:
Originally posted by sbelyo
I don't want to get too crazy because I don't have all the test equipment.
What about a crystal set, then amplify the output?

Disadvantages: needs a good signal

Advantages: Sounds good, no drift, no test equipment, simple.

A good antenna will be the key. For good sensitivity and selectivity you could try a passive tuned loop antenna like this for example http://www.mindspring.com/~loop_antenna/
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