• 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.

6V6GT in the SimpleSE

With all the SimpleSE chatter this week, I decided to convert mine back to 6V6GT. I ran it with 6V6 for a bit when I was testing it on my bench, but since have used beefier tubes.

I have my B+ set to 395 volts (ref. gnd), and this produces about 28.5 volts across the 820 ohm cathode resistor, or about 13 watts dissipation. The OPT's are the 5K:8 Transcendars, and the amp is wired as triode, no feedback.

The voltage and dissipation are a bit past the design max ratings, but the cathode current is well within limits and the tubes (generic Sylvania's from my junkbox) are stable and do not seem at all stressed.

This 6V6 configuration is easily the best my SimpleSE has ever sounded. It's like a completely different amp. As a bonus it produces almost no heat - it has been on 18 hours straight today, and I just measured my power transformer at 118 degrees F!

I also have a 6V6 SimpleSE. It uses an Allied 6K56VG power transformer (540VCT) and the B+ is about 320 volts. I agree that it sounds best in triode mode, without feedback, and I am using the Edcor 5K OPT's. It does sound very nice, but is not quite as good as my TubelabSE with 45's. To be fair that one uses Electra-Print OPT's.

If you have any 6K6's, try them. They give a slightly different sound, but I don't know if they would like your voltages though.
tubelab.com said:
If you have any 6K6's, try them. They give a slightly different sound, but I don't know if they would like your voltages though. [/B]

That's a great tip - I hadn't thought about the real pentodes. I don't recall having any 6K6 so I'll have to look for some this Summer. I have some 6G6, but that's probably a two or three watt tube and I would have to change the OPT's.

I looked at the sims for 6V6 on the Tubes and Transformers page of the SimpleSe manual and considered running mine at +325, but in the end I went for the +375 volt because I wanted that 3dB or so of extra headroom.

I have a lower voltage screen tap on my transformer, so I'll probably get around to trying the 6V6's at lower voltages sometime this Spring or Summer.

I have two SimpleSE's. One has an Allied 6K7VG power transformer and the B+ is 430 volts or higher. I haven't tried 6V6's in it yet, they might self destruct.

My second SimpleSE has an Allied 6K56VG power transformer. The B+ is 320 volts. 6V6's live here. I have a box full of 6G6G's, but haven't tried them yet. I found some 6Y6's and plugged in a pair without looking up the ratings first. One of them sparked out on power up, the other had glowing grid syndrome. I have tried 6550's in this amp, but I think they sound better in the other amp.
I found about a dozen more 6V6, and about a half dozen each of 6K6 and 6F6 in a big box of octal pulls.

It does look like it is a stretch to run 6K6 at my voltages, but 6F6 looked like it would be OK. I pulled the 5Y3 and put in a 5W4 to shed a few more volts, plugged in a set of 6F6, and they work fine and sound good.

That was a great tip to consider some of the small power pentodes. It looks like there is lot of opportunity and fun to be had tinkering around with the SimpleSE and these little tubes.

I now have the SimpleSE rigged so that I can toggle between the two B+ secondaries on my power transformer. This makes working with the little tubes a lot easier.

As suggested, 6K6 sounds very good in the SimpleSE. Just for fun, I also tried some NOS 6G6G and these sound very good as well. Within their power limitation. they may very well be the best sounding of the bunch, and the little coke bottle presents a good appearance.

I'm not a headphone person, but I think for someone considering a headphone amp, the SimpleSE with 6G6G might be worth considering. Their modest power would not be an issue in that application. Regardless, a pair of 6G6G are happily driving my 87db-ish speakers as I type this.

I gave away almost all of my new production 6V6 but I picked up a pair of the 6V6 EH and I believe their claim that they stand up well to high voltage. They had no trouble with 400 volts. Based on my recollection of the JJ 6V6S, I think it would have no trouble with higher voltages as well.

I breadboarded this SimpleSE design awhile ago and used some junk box 6V6s with about +325V B+ and a pair of Hammond 125ESE trannies. My impression was that it did sound very good at mid and higher frequencies but the low end had severely rolled off. I was in triode mode only and did not think of using any feedback (I should have at least tried it but never did). I did try to vary my B+ and play with the cathode resistor values but did not find any combinations that would bring up the low end. I gave up after awhile and went on.

My question is do you think that my 125ESE were the problem or did I build it wrong? Would some feedback helped a bit here? The circuit is easy enough to rebuild and I could try again if you think that I built it wrong but if my OPT is the limiting factor then I'll wait till I can get something better.

Your thoughts?
RockysDad said:
My impression was that it did sound very good at mid and higher frequencies but the low end had severely rolled off.

I have the 5k:8 Transcendars on mine. Within the power limitations of the tubes, there may be a little less bass compared to say, a GE or Tung Sol 6550, but I would not describe it as severe.

I have some 125ESE but I have not played with them all that much.