• 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.

El34 as triode

In my Hi-Fi tube amp, which I call the Music Box, I've got a push-pull output stage with a switch to select between triode mode and ultra-linear mode. The differences are subtle, and depend on several other variables (speakers and room acoustics), but it sounds real good to me. Triode mode gives me about half the wattage, but a lower output impedance driving the speakers, so it's probably a more accurate sound (speaker resonances (impedance variations) are better damped). Others tell me triode mode definitely sounds better in their system. My amp can be viewed at:
Bob's Website
I have a 2A3 S.E. amplifier, built by the same guy who proposed the other one. This guy is a mix between geniuos and foolish, but with amplification he is a whiz. So if his idea is to use EL34 as triode, I cannot immagine this could be a bad idea. To have less watt is not a problem, 3 W of 2A3 are really a lot with my drivers. The question is HOW this configuration sounds, but reading Bob's reply they seem not to be great problems. Any other idea is wellcome!


2008-12-18 2:29 am
If you can find the Yugoslavian EI EL34 (with tipped glass) that is the best sounding for me, especially in triode connection. In comparison to other EL34's I have also measured less distortion at low and medium levels in the same operative conditions. It appears to be more linear. The only problem with the EI is the plate dissipation. It can only dissipate 20-22 W max. However you can still get about 5 (very good) watts from a single ended amplifier and 10 W from a push pull in pure class A, in triode connection of course, limiting plate dissipation at 20W.