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Old 19th February 2008, 07:06 PM   #1
diyAudio Member
Join Date: Aug 2005
Default 12B4 Updates

hi all,

Well I remember on one of the 12B4A threads reading about putting together one of those preamps using only 5 parts, including the power supply. Now, being blind, can't see the schems. So could someone at least verbally describe the circuit? I might have to perf board this project. I can solder. This is one Place where my old trusty Weller soldering gun will come in handy.
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Old 19th February 2008, 07:52 PM   #2
diyAudio Member
Join Date: Jun 2004
Location: Champaign, Illinois
The plate resistor is 12kohm, cathode is 500ohm and B+ of 260VDC. This gives a 15 ma plate current.

I built this circuit and just love the sound. I have been using it in my main system for 15 months and had no itch yet to replace it. Actually I planned to use a really good CCS as load, but tried the resistor first to get everything working. Well, I still have those CCs lying around - even with the lowly resistor it sounded that good that I did not want to bother with the CCS.

One caution -- depending on your needs you may find the gain low - I did not have any problem feeding my Eico HF87, which has high gain. I think the gain is around 3-4 times

And you will need a very quiet power supply.

I basically built the "Etude" described here http://www.diyparadise.com/etude.html

Good luck.

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