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Old 04-17-2012, 01:30 AM
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jbivy jbivy is offline
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6418 sub mini tube amplifier

So i recently picked one of these up online and couldnt think of what to do with it. Ive seen one tube radio designs for these and showed them to my uncle (hes been playing with tubes since the early 50s and was a tv repairman in the 60s and radar technician in the late 60s and 70s). He thought the radio designs were okay, but is trying to convince me to let him help me create a tiny amplifier with it. Since its only 18v on the play 1.5v for the filament, he says it would be perfect to power a headset for one of my crystal radios.

What are your opinions on this? Hes coming over this weekend and i want to be sure about what to do.
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Old 04-17-2012, 02:04 AM
bob91343 bob91343 is offline
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I am not familiar with that tube. If it has enough capability, it could very well serve as an amplifier. I suspect we are talking about milliwatts here, which of course is fine for headphones. I don't anticipate much gain, as the transconductance wouldn't be very high. Of course, if the signal from the crystal set is weak, this could help.

Actually, I sense that you are just anxious to play with this stuff, and of course that's just fine. Make sure you don't damage the tube with too much current.
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Old 04-17-2012, 02:16 AM
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Supposedly raytheon designed this pentode tube (though it was often used as a mere triode) in the late 50s for hybrid radios, transistors with sub mini tubes, to make a more powerfull "transistor" radio. Semi-rare even then.

Well.. yes, im just very anxious to play with this technology. Ive had two dates this year and not much of a social life. I just find it fun to try things that are out of my comfort zone. Well ill have my uncle to help me, he hasnt played much with tube technology in a while, but is excited to help me with it.

Ive found a few one tube radios people have built with these and even a headphone amp that uses two of these tubes. So i assume my uncle is correct in that this COULD be made into an amp that would give me some gain in my crystal set, maybe power a tiny speaker or standard headphones.

Here is dave schmarders design for a one tube regen.



and here the tube itself.



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and the link for the two tube headphone amp.

http://diyaudioprojects.com/Tubes/64...Headphone-Kit/
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Last edited by jbivy; 04-17-2012 at 03:01 AM.
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Old 04-17-2012, 10:13 AM
bob91343 bob91343 is offline
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Two things - there is no regeneration control, and that choke in the output seems like overkill.
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Old 04-17-2012, 11:03 AM
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Well what is your advice, considering ive two of these tubes (ive a spare in case i make a mistake). Do i try to build a mini amplifier or go for a simple regen radio or?

so to recap, ive no social life, way too much time on my hands, a little skill and knowledge and lots of ambition.
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Old 04-17-2012, 07:04 PM
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Quote:
Originally Posted by bob91343 View Post
Two things - there is no regeneration control, and that choke in the output seems like overkill.
Another circuit by the same author appears to have a proper "regen" control, but still the high value choke. Many of his circuits show the usual 2.5 mh choke.



Frankly, I think a 2 stage audio amp for your Xtal set would be cool, since you have 2 of the little tubes.

jr
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Old 04-17-2012, 07:20 PM
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Ironically a few months back I was trying to make a portable AM transmitter using that same tube. I had a trial and error circuit that actually sort of worked. At some point I'm going to use proper math and try to assemble a coil and tuning cap combo that can work across the the AM band.
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Old 04-17-2012, 07:44 PM
bob91343 bob91343 is offline
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There is no need for that choke. You can just connect across it.

In addition, you need the right polarity of regeneration. If it doesn't work, reverse connections to the tickler coil.
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