Single Ended Amps - Opinions

[Littlewyan]

This is really cool guys, I didn't realise there were so many Single Ended builds around.

Phil S - Going by the 6V6 datasheet, with 285V HT the Plates and Screens will draw 105.5mA at full pelt, which will increase a bit with 340V HT. I did use this PT for a 6V6 Push Pull build originally and it sagged a lot at full load. I recall I only got about 12-14W clean (Fixed Bias) and the PT ran warm. I then replaced the PT and can now get 20W clean. Granted the HT also increased by about 30V but I don't think that would account for a 6-8W increase.

I think it should handle a Single Ended EL34, as long as I bring the HT down a bit. Which I'll do with a CRC filter.

[statorvane]

I have no clips. I recently put in a SS effects loop. I'll have to get some.

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For all things SE there is a pretty good forum here: http://www.sewatt.com/forum Initially it focused on mods and upgrades to the Epiphone Valve Jr., an off=-shoot from https://www.18watt.com/. Some every cool projects over there.

[wpaulvogel]

This is really cool guys, I didn't realise there were so many Single Ended builds around.

Phil S - Going by the 6V6 datasheet, with 285V HT the Plates and Screens will draw 105.5mA at full pelt, which will increase a bit with 340V HT. I did use this PT for a 6V6 Push Pull build originally and it sagged a lot at full load. I recall I only got about 12-14W clean (Fixed Bias) and the PT ran warm. I then replaced the PT and can now get 20W clean. Granted the HT also increased by about 30V but I don't think that would account for a 6-8W increase.

I think it should handle a Single Ended EL34, as long as I bring the HT down a bit. Which I'll do with a CRC filter.

That’s the rating for 2 tubes push pull class A. Single 6v6 single ended is probably about 1/2 or 55mA. A single EL34 is up there at about 120 mA.

[Littlewyan]

For all things SE there is a pretty good forum here: http://www.sewatt.com/forum Initially it focused on mods and upgrades to the Epiphone Valve Jr., an off=-shoot from https://www.18watt.com/. Some every cool projects over there.

Yeah I found that forum, doesn’t seem to be very active anymore though. I’ll make sure I post my build there when I do it, try and bring it back to life!

That’s the rating for 2 tubes push pull class A. Single 6v6 single ended is probably about 1/2 or 55mA. A single EL34 is up there at about 120 mA.

Yeah that’s what Phil S was talking about. I can’t remember exactly what the EL34 datasheet said but I think my PT will just about handle it, as long as I bring the voltage down a bit.

[Phil_S]

That’s the rating for 2 tubes push pull class A. Single 6v6 single ended is probably about 1/2 or 55mA. A single EL34 is up there at about 120 mA.

Yeah that’s what Phil S was talking about. I can’t remember exactly what the EL34 datasheet said but I think my PT will just about handle it, as long as I bring the voltage down a bit.

Maybe I don't quite understand this...I don't think I'd look to reduce plate voltage. EL34 is a robust tube that should be able to handle quite a bit of voltage, so that's not a concern. What I figure is that there is an inverse relationship between voltage and current. Higher voltage will draw less current. I'd treat the vacuum tube as a fixed value component (not entirely true) in terms of watts. Remember, watts = voltage x current. Am I missing something?

[Littlewyan]

I could just reduce the current and it would work, but the operating point would be wrong. Who knows, it might sound great, but it could also sound bad. So I’m just going to play it safe and bring the voltage down. It’ll likely still be higher than the recommended 265V for Class A but won’t be as bad as 340V.

Personally I think a lot of guitar amps have too high a HT voltage and I don’t understand why. You don’t really gain anything by doing so. The tone may not be as good and you can end up with shorter valve life.

[brewdude]

My take on the trend, higher voltage translates roughly to cleaner louder, generally useful to marketing regardless of whether it sounds better.

[ViperDoc]

Assuming the correct power tube voltages were managed, is it possible to run a parallel SE amplifier with dissimilar power tubes off of individual OTs? Like one OT drives an EL34 and the other a 6V6?

[Synchu]

I don't see why it wouldn't work, besides you'll need to consider the (potentially) different driving requirements, depending on the power tubes combination used.

Niki

[katopan]

I don't like the overdriven tone from a SE power stage anywhere near as much as a PP power stage. Two reasons:

I like PP amps with a healthy amount of screen compression best. It effects not just the tone but also the dynamic feel of the amp. SE can only ever have that on one side of the waveform.

SE also has no current flow at clipping on the cut-off side, which means no magnetic field in the OT at that time, which means no field to sustain the voltage/current to the speaker at cut-off clipping. Ever noticed on a CRO (or shots someone else has posted) how a PP clipped waveform sustains the flat peaks between cycles, but SE always has one side sustained flat and the other side sloping or dropping away significantly? The slope on the grid clipping side (with current flowing) always matches what you'd expect from the inductance of the OT, but the cut-off side has a way steeper drop off. That difference in waveform you can see with your eyes is also a difference in tone you can hear with your ears. It's also a tonal difference that over the years I've decided I don't like so much.

[bepone]

6V6 S.E can work very nice with 300-340VDC
bias in class A can be at 80% to preserve tube life so, 12W/340V=40mA max
in class A one can find sweet spot from tube graphs, lower voltage is better for S.E ofcourse, it is more linear area.


distortion from class A amp, one tube, is better to make in preamp, so one wants more preamp stages.. distortion from one device in output just sound not ok, or limited, compared to PP amps. i did many.. i prefer stronger tube when going this way , 2xKT88 SE in paralell, it was a beast

[bepone]

https://www.youtube.com/watch?v=5CDivirjQNY
here is some ultra lo fi record years ago from this creation, but sound was strong ad powerful 2xKT88 SE

[bepone]

another one with pulled one tube out, so 15W on small combo with cheap tube 10 celestion driver.. sing can be heard
ultra lo fi clip again recorderd with potato
https://www.youtube.com/watch?v=4qqA4Gzn1yY

[JD0x0]

Single ended class A tends to have more asymmetrical clipping than PP. If you've ever messed with clipping diodes in a distortion pedal, you can hear the difference. Assymetrical tends to be more aggressive and prone to fizz, but you can deal with it in the same way as a pedal. Cut some highs in those fizzy frequencies. Take a look at the 'Texture' circuit on the VHT special 6 ultra. It shaves highs at the OT so any power tube clipping will get smoothed out.

FWIW I have a singled ended 6CM6 amp with two channels. On the clean channel you can set it up so there's no preamp clipping, and then push the power amp into clipping. It sounds good IMO, even without shaving highs.

[wpaulvogel]

I just got this one running last night. It’s KT88, 6550 or EL34. With KT88 it’s making 18 watts clean and EL34 makes 16 watts clean. Running 405 volts on the plate and 215 volts on the screen. Sound testing this afternoon.