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Old 19th September 2010, 05:13 PM   #1
bichela is offline bichela  United States
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Default home made tube amp with 12v b+ how to build one?

I saw on youtube a design for a AM radio reciever that uses a 12AU7 with a B+ of 12vdc. now can one build a small submini amp that uses sub-mini tubes with a b+ of 12vdc to drive a transisistor radio speaker? Any one got a schematic? I want to learn to build tube stuff in little easy steps.

such a teeny amp could be a conversation piece in its own right. also is a subminiture tube the same as a nuvastore tube? The ones I know of have long wire leads instead of pins on their base.

I do have a 12AX7 tube laying around. just got to get a socket for it. its minituare (obviously) but not a subminiture tube. Whats the subminiture version of this tube? I would love to combine this with that radio reciever I mentioned above. and make a nice little AM radio portable.
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Old 19th September 2010, 05:27 PM   #2
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See if you can find circuits for mobile aps from before sand days. Car radios all operated on 12V (actually, probably mostly 6V) and did pretty well. I would expect that they used some special hi-Z speakers, but maybe not.

Aloha,

Poinz
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Old 19th September 2010, 05:38 PM   #3
Arnulf is offline Arnulf  Europe
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Your "amplifier" is going to put out miniscule amount of power, far less than the input that is likely to be driving it (MP3 player or something like that).
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Old 19th September 2010, 06:02 PM   #4
kevinkr is offline kevinkr  United States
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Google tube AM car radio, there was a whole family of 12V space charge tubes for this application. Note that most of these radios will have a transformer driven, transformer coupled power transistor for the audio output stage. Will not find a tube capable of really doing this job at such a low voltage. (Before space charge tubes car radios had electro-mechanical vibrators and high voltage supplies using step up transformers, and used common tubes from the 6.3V or 12.6V filament families depending on the vehicle electrical system voltage.)

Note that most subminiature tubes were not designed for such low voltage operation although the 6088 and 6418 DHP and others start to work quite well at supply voltages well below 100V. (6GM7 as well, but getting rare and expensive as it's good for headphone amps at 24V..)
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Last edited by kevinkr; 19th September 2010 at 06:05 PM.
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Old 19th September 2010, 06:23 PM   #5
taj is offline taj
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Yeah, I seem to remember car radios just converted the battery DC to AC with a vibrator, then boosted it up to normal B+ values with a step-up transformer, and the rest was just normal (albeit tightly cramped).

..Todd
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Old 19th September 2010, 08:34 PM   #6
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Space Charge and Other Low-Voltage Tubes
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Old 20th September 2010, 03:13 AM   #7
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by mashaffer View Post
Thanks for posting, quite an interesting site, and the ones it links to, in particular the Lamphouse Hiker radios..
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Old 20th September 2010, 04:52 AM   #8
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A very serious military receiver Collins R392/URR used ordinary tubes (well, some of them were special versions of ordinaty tubes with 27V filament) powered by 27 Volt only. In audio output stage it used special double triode. But it was a receiver, not a hi-fi audio amplifier! Transistors on such voltages work much better and are much cleaner than tubes, even such good special tubes like 4P1L for example are.
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Old 20th September 2010, 05:54 AM   #9
soro is offline soro  Taiwan
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maybe you can try this one.
IT can ues 12AX7 or 12AU7 6DJ8 6922...
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Old 20th September 2010, 06:48 AM   #10
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I used to have a 32V B+ mantle radio, which used standard miniature valves, the high plate impedance of Valves does not lend itself to low voltage operation, car radios and military field radios used vibrator based power supplies with normal 250 or 300V B+ You probably could make a small mosfet based voltage multiplier to get 32 to 60V B+, don't much power output though.
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