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Old 17th September 2004, 07:04 PM   #1
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Default Tube mic preamp/mixer

This is a schematic of a circuit in RCA's "Receiving Tube Manuel" from 1959- "Low Distortion input amplifier stage"----
would it be suitable for a microphone preamp?

7199 characteristics

7199 (continued)
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Old 17th September 2004, 10:10 PM   #2
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You'll need more gain if you use a dynamic mike. Try a 470k resistor in the pentode plate and adjust the cathode resistor accordingly for bias.
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Old 17th September 2004, 11:22 PM   #3
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Unavailable and pretty noisy.
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Old 17th September 2004, 11:52 PM   #4
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She's not unobtanium

http://shop.store.yahoo.com/thetubes...ovtek7199.html
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Old 17th September 2004, 11:56 PM   #5
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But she's still a noisy (for this app) pentode.

Thanks for the correction- owners of stock ST70s will be delighted.
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Old 18th September 2004, 12:39 AM   #6
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Hi,


..........And why use a triode/penthode where a single LOW noise penthode would do nicely already?

Isn't there a circuit using the 5879 in one of the RCA Receiving Tube Manuals designed for micpreamp use.......?

Or an EF86/6267?
At least that one's still around in abundance and likely to stay with us for another twenty years.
Plenty of low level circuits available to pick from as well.

No idea about the US but in Europe at least there are still some absolutely amazing small signal penthodes around that are hardly used by anyone anymore.
Quite a few of those could be just the ticket you need.

Cheers,
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Old 18th September 2004, 07:33 AM   #7
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Default other circuits?

I can either try Geek's Idea(which I don't have a problem with), or go with fdegrove's idea, but there are no other circuits like this in my manuel.

Does anyone in this thread hav a schematic of a circuit that would work better? A single pentode?... What about phantom power?

Thanks
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Old 18th September 2004, 02:04 PM   #8
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There's a good mic preamp here: http://gyraf.dk/gy_pd/g9/g9pd.htm

But it's not exactly simple and cheap...

Best regards,

Mikkel C. Simonsen
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Old 19th September 2004, 01:17 AM   #9
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Phantom power injector

http://www.diyaudio.com/forums/attac...&postid=472164
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Old 19th September 2004, 06:45 PM   #10
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Default Thanks Geek!

Cool! Phantom power !

-Trevor

PS- I was thinking...could I replace the one 7199 tube in my circuit with 2 tubes (a triode and a pentode) that would provide similar gain characteristics? Before I even posted this thread I had heard unfavorable comments about the 7199...
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