• 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.

Triode Pentode Switch vs Sound Quality

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to Binary: do you know the % of THD at 10 watts?

When you drive positive the grid you are going inside a non linear field; the driver need to give current so you are a risk of great THD mainly odd; with feedback, in this case you may have an increment of distortion.

Here's the project in breadboard form: CatSkin Class A2 SET with Secondary Flux Cancellation

The 10W figure is for limiting just visible on the scope, so probably near 3~5% THD. There is no notch in the distortion residual waveform as grid current begins to flow. This was achieved with a semiconductor grid drive buffer.

TV sweep tubes in audio service can be safely pushed pretty far past their dissipation specs -- perhaps as much as 40%, according to some sources (John Stewart).
 
It just it? This video is a collage of images, there is no camera moving into the room and the sound is direct from the CD player.
Any link to Ebay?

No, the sound IS NOT direct from the CD player. Don't you hear speakers & room acoustic? However, what the amp adds to it, is so negligible, so you can't hear any coloration...

The amp is on top of the rack, and he shows it in a separate picture, time to time.

Here is my record, this time with my speakers that are worse than his...

https://www.youtube.com/watch?v=y7oxwdSgUs8&t=9s

Speaking of eBay, it is too late, as I already explained. You are deciding too long. 🙂
 
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Here is one more record, with the same relatively cheap JBL-990 monitors, but a different pentode amp. Not just pentode; 2 pentodes with nested feedback, but different kind of pentodes. No, I am not selling it yet. It is a prototype that I use now to show to potential partners and customers.

https://www.youtube.com/watch?v=526Q-xiqpkU&t=18s
Great room acoustics, I liked that amp.
Nice looks, very Russian looks.
 
I fail to hear the room acoustics, my PC speakers are small.
I see that amp on top the rack, what are the tubes?
Any photo under side?

Not anymore. Stay tuned; may be while you are deciding what to put inside of your amp I will have some more prototype for sale. ;-)

I also sold one triode push-pull amp prototype, 10 W per channel, also with nested loops, 2 of them were positive feedback loops by current.

As usual, the sound is recorder in the room on my iPhone, it is not a CD track 🙂

https://www.youtube.com/watch?v=qsb2Hzq7sD8

https://www.youtube.com/watch?v=iZ4BDSrHkxI
 
The GK71 amp sounds great congratulations.

The 4П10C tube is so rare GSTubes dont have any.
Do you sell that tube?
Any datasheet in English?

Thank you! Yes, GK-71 are great tubes.

https://www.facebook.com/Wavebourn/videos/1541634742561488/

4П10С are sometimes on ePay. And yes, I can sell them. I bough some from a British lady.
No datasheets are available, in any languages, just test conditions for military users. They forgot to de-classify them, like US and British military sweep tubes VT-127 and CV-1127. But you can use datasheets for Pen-46 tube that was used as a prorotype for them.
 
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