• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

12B4 Updates

ray bronk

2005-08-22 7:10 am
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.

Francois G

Paid Member
2004-06-16 8:36 pm
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.