feedback in Shindo pushpull amp

[hooman]

original circuit of AP-80 Mono Block 6550

 

[jhstewart9]

Same internal negative FB hookup as seen in several of the later RCA Receiving Tube Hand Books.
For example in RC30, refer to schematic 29-11. This on also has a small amount of Schade FB included.
Who knows why the extra, just another unnecessary frill. 😀

 

[Chris Hornbeck]

It's very tempting to include DC blocking capacitors in these two-stage feedbacks, but it probably shouldn't be done automatically. The extra zero complicates things for low frequency stability, so needs to be somewhere far below the dominant pole. Even more challenging, the dominant pole needs to be somewhere else than at the clipping point, the output valves' grids (where it would ideally be for best overload recovery time) because clipping changes the open-loop response in a less stable direction.

All good fortune,
Chris

 

[6A3sUMMER]

As I always say:

"If you have an RC coupled circuit, and you turn the signal up enough to draw grid current . . .
Then turn the volume down . . .
Or get a more powerful amplifier."

The exception is: you are a guitar player who purposely wants grunge and distortion.

Just my opinions

 

[hooman]

Harman Kardon itation II

 

[zintolo]

Can I ask what is the point?

 

[hooman]

​

yes....
The point is .... simple. But there is a big difference between a professional amplifier and the things that everyone makes. Unfortunately, there are no schematic from Shindo amps. The difference is not only in output transformer and capacitors... it is in the type of feedbacks. When There are two local feedbacks on 12bh7 as a phase splitter... do you know how its circuit is? I am looking for someone who knows.

 

[Bigun]

Like many De Forest did not invent the triode, he stumbled on to it, His PhD thesis covered conduction in flames.
He got a vacuum diode & his tech stuffed in another wire, on the other side. The result did some strange things.
When it worked as a detector of sorts it was very unstable, De Forest thought his thing had to contain a gas to operate.
The opposite was true & had to wait for a way of creating a better vacuum was found.
And Deforest was never able to properly explain the function of the result.

For a very good account of De Forest's lurching along to the triode from conduction in Bunsen Burner gas flames, get yourself a
copy of Gerald F Tyne's book Saga of the Vacuum Tube. The most important work came later in the labs of GE & Wesitinghouse
were better methods of pulling a good vacuum on an industrial scale & cathode materials that were efficient & dependable.

Another famous stumble was the XRay. But Roentgen was careful, He did more work before letting the World know of his discovery.
Roentgen was on the level, De Forest was not. De Forest had his lawyers chasing Edwin Armstrong, a for more knowledgeable inventor.
De Forest claimed the Superhet receiver & sued. A lawyers free for all was the result. David Sarnoff of RCA got in the middle,
Armstrong committed suicide. But his wife eventually prevailed.

And the lawyers always win.................................win or lose by the players.

At HP the corporate legal team spent a lot of time & resources to educate us in terms of legal matters that might effect the company
When you get big all kinds of people are nipping around the edges hoping for a big payout.
America is a litigious society,😈

De Forest may have received more credit than due on the invention of the triode but he was a clever guy nonetheless and I heard that he likely invented the regenerative receiver before Armstrong but it’s hard to change popular opinion.

 

[hooman]

this is another power amp from shindo lab...please looke at 2 local feedback from plate of output tubes to srp phase splitter circuit .

 

[hooman]

 

[directdriver]

It's easiest to visualize the way 50/50 anode/cathode loading can be 50% partial triode with G2 at signal ground by making two drawings.

Would that be similar to a split-load/cathodyne/concertina phase inverter circuit with a gain of 2? That's how I visualize it whenever plate and cathode have same resistance value and, in this case, same inductance value. Due to the low gain in the power stage, is that why most Mac amps have high driving voltage?