• 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.

EL84 Triode PP Design

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An externally hosted image should be here but it was not working when we last tested it.

I have the EL84's, the OPT's, and the 6N23P's are on the way.

Power supply:
Hammond 273BX (350-0-350 175mA) rectified by two UF4007 per leg bypassed by .1uF 1KV, into 193M choke (10H 300mA 63 ohms) and 440uF 450V cap, bypassed with 1uF 630V, feeding B+. B++ taps off a 20H 20mA 1.67K and 100uF 400V bypassed with another 1uF 630V, for the two 6mA regulators at 275V. The C- supply is a voltage doubler running off the unused 5A tap.
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But how it works in Baby Huey? Is it partial?


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Is there any way to get 5mA+ through the 6DJ8s other than to use a negative voltage supply? I'm looking at doubling off a Hammond 166G80 (80V .5A) for a -210V supply, which, with a 21K 5W tail resistor, should spit out 10mA for the cathodes to share right? My plate resistors would be 24K 2W.

I assume that a LM334 won't like putting out 10mA very much...

About the bias adjustment setup: would a 10K pot and 5K resistors to ground work better?

Perhaps neither Stuart or I have explained completely (Stu, if I have you completely wrong, scold at will). The problem here is a regulator (voltage or current) that will reliably operate at a drop of 2v or less. Under conditions of dynamic cathode swing, maybe a lot less. What if your tail is going in and out of regulation with signal?

With the right CCS chip, maybe you could even take a bridge and supply off the heater winding (the heaters, with their several amps draw would probably never even notice), and get your chip over the problem; but the bias supply looks like the best bet to me, maybe because I'm planning to do the exact same thing.

To me, trying to regulate current over a volt or two drop looks pretty shaky.


All right. I've finalized design with a negative voltage supply feeding a simple tail resistor as in the Musical Machine. I'm open to experimentation once the amp is done, however, and a CCS might be worth it. If it's legit to tap off the heater voltage to feed a CCS, the 9V or so that would result seem ideal. Anybody got any chips/implementations that can do 10mA? Kind of a broad question, I know..

Also. this one is for Poindexter about his Musical Machine gain. What is the reason for the ~4-5% difference between the top and bottom plate resistors? I echo this setup in my latest iteration, 51K and 47K on the top, 2x51K on the bottom. I read somewhere that this corrects phase imbalance between the top and bottom triodes or something? I'm using snooty quality PRP 1-watters from PartsConnexion, for peace of mind :)
One reason to buy Morgan Jones "Valve AMplifiers" is the current sink designs he has there. They work very well - something like page 134 b) or c) - they also use a -15v supply.

I'm listening to exactly such an amp as I write. The front end in in this case is an ECC40 with one of the CCS above under it. Sounds very detailed. I have the EL84s in triode and no global feedback.

I prefer the ECC40 by some way - it has glorious treble - but it is a rimlock socket and so not eerybody's cup of tea. Socket and tube easily available in Europe and on ebay, though.
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