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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

3K or 5K OPT in EL35 SimpleSE?

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There are some trade-offs with choice of OPT. I plan on building the SimpleSE using EL34 running at approx 55mA on 450V B+. With a 3K OPT, I should get around 8W, with a 5K OPT, I get something more like 5W.

I appreciate that the 5K would have lower distortion, BUT to what extent am I really likely to notice it to be detrimental to the sound?? Maybe this is a goofy question as preferences will differ. I doubt that I'll play my SimpleSE at full volume (assuming that my speakers are sufficiently efficient). I suppose that I could buy the 3K Edcors, followed a little later by the 5K. I mean they're cheap. Once I have a preference, I could then fork out the dosh for some higher quality ones.

Any thoughts?


I am running the 5K version and have no problems with volume with my 91-92 dB speakers. If you wand a little more grunt, just put in a switch to select between triode mode and ultralinear, the Edcor transformers will allow that and the TubeLab site has a good diagram on how to wire it. I would suggest that you wire it for triode mode only to begin with, then when you have it working properly wire it switcheable for U/L if you wish.

As an aside, I plugged in a set of JJ KT88s last night to compare with the E34L, and noticed that the power transformer and chassis got MUCH hotter. Was not too worried about the transformer, but was concerned for the components within the chassis.

The JJ E34Ls seem to be good value. One of the winged C EL34s I have shows some red glow on the plate in my setup, but the JJs have shown no problems since building the amp about six months ago.

Hope you love this amp as much as I do!

I have both 3 and 5 K ohm transformers in several flavors that I have used in my SimpleSE's. I can not always hear the difference in volume between the the two impedance transformers, but I can always hear the difference in distortion. At high B+ voltages (over 400 volts) the peak currents become too high leading to audible distortion on signal peaks, especially bass. The 3K ohm transformers work best with B+ voltages in the 350 to 400 volt range, but 400 and higher volt amps sound best with 5K transformers. Tubecad simulations also show this relationship.

I am using a 6K ohm transformer in my Industrial Amp (actually a 3K transformer with the 8 ohm speakers on the 4 ohm tap). I usually listen to the amp in triode (with EL34's or KT88's), I get about 5 watts. When I need to get loud, I switch to UL with cathode feedback and plug in the KT88's, I get 13 watts. It is audibly louder with better bass.

If you are thinking about getting both 3K and 5K transformers, I would get the 5K version first.
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