• 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.

Recommendations for PP EL84 circuits

The Z565 overview on Triode Electronics site suggested "a healthy inductance over 1000."

That was a typo on the triodeel site, for sure. It's 100H (two zeroes, not three).

Still, that's an excellent OPT, if it's still available...

I have the transformers from an ST35 I bought in the late 1980s ($40 USD for that and a PAS2 preamp, together). The downside of the vintage iron is that it only has 8 ohm and 16 ohm secondary taps. I'd much prefer to have a 4 ohm tap. The new, repro one has 4 ohms and 8 ohms, much better with contemporary speakers.
 
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If the question was, "Which push-pull EL84 amp design should I build?" then I think it's all at least somewhat relevant. Right?


Agreed.
As was once thrown at me on this site: take note of the heading: Projects by Fanatics - For Fanatics".

Since many of the subjects tend to go on forever, and discussions/opinions are widely spread, I see no reason to contain things if they're part of the deal. 😉
 
This is a good one

I just finished this old RCA design. Exchanged the 12au7 at the front for the Russian 6n16b (cathode resistor 4K7). Used a mosfet regulator.
Sounds incredibly good with a 60 year old OPT..
I believe you can use the EL84 instead of the 6V6 if you want.
 

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I'm rebuilding a Leak Stereo 20 and wondering which circuit to choose. I'm most tempted by a concertina first stage like Tubelab and Bevois Valley. See post #20. I don't really want to add a negative voltage source for a LTP.

I'd prefer to use an ECC40 in the input stage and would adjust the operating point accordingly.
 
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Please keep us informed of your thinking and progress. Are you planning to use GNF? If so I wondered it the 25x gain of the ECC40 would be sufficient.

I also have an interest in trying an ECC40 in this manner to drive an EL84 output stage.
 
Please keep us informed of your thinking and progress. Are you planning to use GNF? If so I wondered it the 25x gain of the ECC40 would be sufficient.
I also have an interest in trying an ECC40 in this manner to drive an EL84 output stage.
Hello Francois. So you're another fan of the ECC40? Excellent.

My first thought was a triode amp with no GNF. So I was planning a type 37 front end and a mosfet splitter. That would still work and be better still with a 27 mesh plate, which would require an extra 2.5V transformer. An alternative would be a 6AH4 which I've used before and sounds good.

In answer to Merlin - I wanted something better than the Leak circuit. If I stayed with triode mode I could use e.g. a 6N30P in concertina though I'm not a big fan of that tube. Since I do like the ECC40 I'm thinking to use ultralinear with a bit of GNF to get more output.

Still up in the air about this build.
 
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I took this sort of thing on recently. Used for my build Sherwood S5000 OPT's. They have 28% U-L. I used 6P15P-EV finals. Power supply is a 300V plus heaters SMPS from Ali that I got for about $35 delivered. Schematic is below. Mostly complete... 🙂

Douglas
 

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I made this, it seems to be good



Walter
 
I have a question about the input valve for an EL84 PP amp in UL mode. I want to use a voltage stage coupled to a concertina, like the Bevois Valley or Tubelab circuits. The Bevois uses an E88CC, the Tubelab a 12AT7. Gains of 33 and 60 respectively. I've considered using a 6SN7 with gain of 20. A better valve in itself than the other two. But how would the GNF loop work with a valve of lesser gain?

What would be the pros and cons of using a 6SN7 in the first stage?

EL84 Bevois Valley.pngEL84 SimplePP correct.png