When I worked with 2nd harmonic cancellation on a 6P41S amp several years ago (I eventually built three of them), I found that if I suppressed 2nd too much the amp began to sound harsh. I also found it was very difficult to maintain the cancellation over time and had to re-adjust the circuit over times. The circuit was also "tube specific". Changing output tubes required an adjustment to the driver tube (6J9P Triode connected). This may have been specific to the tube combination I was using, however I gave up on distortion cancellation after that and instead worked on overall distortion reduction with orderly decreasing harmonic content.
As soon as I see GZ34 I think - it isn't for poor men. 😆 TV Damper diodes (2x 6ax4 or similar) are a nice alternative. 😉
Nice work on the Mains Transformer though. It really needs a cover.
BTW - ALL distortion simulations are suspect! Don't trust them. I only trust measurements...
Nice work on the Mains Transformer though. It really needs a cover.
BTW - ALL distortion simulations are suspect! Don't trust them. I only trust measurements...
Regarding artosalo's Post # 39, which I gave a "Like" to:
Global Negative Feedback, either how much, or how little, has to work harder (struggle more), if the No-negative feedback open loop design of the amplifier already has lots of problems:
With distortion (harmonic and intermodulation),
With frequency response
With lots of Hum, Noise, and Hash
Fix the open loop performance first, and then apply global negative feedback, if you wish.
Global Negative Feedback, either how much, or how little, has to work harder (struggle more), if the No-negative feedback open loop design of the amplifier already has lots of problems:
With distortion (harmonic and intermodulation),
With frequency response
With lots of Hum, Noise, and Hash
Fix the open loop performance first, and then apply global negative feedback, if you wish.
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Cancelling H2 usually increasing H3. If H2 decreased, the H3 will be dominating.
No free lunch.
IMHO any cancellation is a different kind of harmonic distortion.
Are you sure, that this amplifier working well?
Channels harmonic structure differs in both connection (triode, UL), mainly at higher power.
Try to swap power tubes and repeat measurements.
Channels harmonic structure differs in both connection (triode, UL), mainly at higher power.
Try to swap power tubes and repeat measurements.
I completely abandoned UL connection, triode is the way to go. Maybe I will try some global NFB. We will see.
250Vac is a standard value in the US for two phase line. Other standard voltages are available, including 380 for Y connections IIRC.
Does anyone build a genuine 300B SE amp?
It will be nice to see some measurements for comparation with GU50.
Or my amp is the most well documented amp on this forum?
It will be nice to see some measurements for comparation with GU50.
Or my amp is the most well documented amp on this forum?
hello, after building this :
https://www.diyaudio.com/community/threads/how-might-a-6gm5-do-tied-as-triode.361182/post-7555142
I want to try now a SE with the gu50 .
Anyone as tried the pentode mode ?
How its sounds ?
I have tektronix power transformers who can allow it and 4K output transformers.
The picture shows what i get with the Vtadiy simulator.
THD pentode mode give more power and less THD, but more 3rd Harmonic distortion than triode mode.
After few reading ultralinear mode doesn't work well.
Any reviews,please ?
Regards
https://www.diyaudio.com/community/threads/how-might-a-6gm5-do-tied-as-triode.361182/post-7555142
I want to try now a SE with the gu50 .
Anyone as tried the pentode mode ?
How its sounds ?
I have tektronix power transformers who can allow it and 4K output transformers.
The picture shows what i get with the Vtadiy simulator.
THD pentode mode give more power and less THD, but more 3rd Harmonic distortion than triode mode.
After few reading ultralinear mode doesn't work well.
Any reviews,please ?
Regards
Attachments
For pentode mode you will need some kind of negative feedback. The Vtadiy simulator only takes into account the tube (output one in this case) curves, that's it. The input stage matters, feedback etc.
Yes ! I agree with you.
I noticed two fact:
1) for the same output voltage swing 3rd HD fail to 1.13%
2) the pentode mode requires only a small input signal, which allows a negative feedback.
With a nice pentode at input stage , a 10 dB negativ feedback should be possible.
I noticed two fact:
1) for the same output voltage swing 3rd HD fail to 1.13%
2) the pentode mode requires only a small input signal, which allows a negative feedback.
With a nice pentode at input stage , a 10 dB negativ feedback should be possible.
Attachments
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