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Old 13th May 2011, 01:38 PM   #1
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Default Red board add-on phono/RIAA pre-amp

Good morning everyone,
Can anyone offer some ideas for a "red board" add-on phono/RIAA pre-amp? Perhaps one that would have multiple inputs for perhaps tuner, phono, tape, cd, etc.... Any decent compactrons that might fit the bill???

Thanks,
Ray
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Old 13th May 2011, 11:54 PM   #2
tomchr is offline tomchr  United States
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Lemme see if I get the question right. You're looking for a RIAA preamp with a low-gain input for CD, tape, etc. that uses Compactrons?

I suggest looking at RIAA preamp designs that use tubes which are available as Compactrons. There's one here: My own RIAA tube preamp One could follow that up with a cathode follower rather than the source follower used. You could then switch the CD, etc. in at the input to the source follower. Not saying that's the best design, I'm just throwing ideas at you.

~Tom
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Old 14th May 2011, 12:23 AM   #3
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There is a compactron that is 3/2 of a 12AX7. I am 1200 miles away from my notes but it is a 6_10 (6C10 maybe) and it was used in Ampeg guitar amps among other things. I question this route since the compactron tubes are only available from one or two manufacturers, and 12AX7's are available everywhere in mulltiple flavors. A tube phono stage will usually need some tube selection for low hum, noise, and microphonics.

My current phono stage is made from sand (a single National Semi chip) and fits inside the turntable. The line stage it feeds uses a 12B4 feeding several mosfet followers. That gives me a few independent outputs for running several amps without cable swapping. The input switching is via tiny relays.
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Old 14th May 2011, 12:29 PM   #4
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Well here's what I came up with compactron wise:

6AY11 - Twin Diode - Twin High-Mu Triode - Close to the specs of the 12AX7
6C10 - Triple High-Mu Triode - Same specs as the 12AX7 - What can I use the addtional triode for?
6Q11, 6K11 - Twin High-Mu Triode - Medium-Mu Triode - Same specs as the 12AX7 - What can I use the addtional triode for?

The circuit I was looking at is the circuit from the RCA tube manual. (I attached a PDF)
If I did use one of those triple triodes, any thoughts what to do with the additional triode?

Thanks,
Ray
Attached Files
File Type: pdf RCA Pre-Amp.pdf (85.9 KB, 39 views)

Last edited by rsumperl; 14th May 2011 at 12:39 PM.
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Old 14th May 2011, 12:34 PM   #5
SY is offline SY  United States
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Quote:
Originally Posted by rsumperl View Post
6Q11, 6K11 - Twin High-Mu Triode - Medium-Mu Triode - Same specs as the 12AX7 - What can I use the addtional triode for?
Cathode follower output.

The RCA circuit is intended for mass market console stereos of the 50s and 60s, not for high quality audio.
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Old 14th May 2011, 04:40 PM   #6
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So what about using the two Hi-Mu Triodes as the "amplification" for the magnetic cartridge then feeding into the Med-Mu Triode as a cathode follower? Looking at the RCA circuit, what would you change to perhaps make it better?

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Ray
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