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Single Ended: the pentode retaliation
Single Ended: the pentode retaliation
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Old 11th June 2021, 02:59 AM   #71
smoking-amp is offline smoking-amp  United States
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Might be interesting to use external grid 2 drive exclusively, with series grid 1 Fdbk. Darn curve tracer had to crap out just when it was getting interesting.

Then make a P-P with the new type of roll-over on one side and the old type on the other side, using the internal triode for that. Definitely a new type of SE like sound. Rock n' Rollover.

Last edited by smoking-amp; 11th June 2021 at 03:13 AM.
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Old 11th June 2021, 03:16 AM   #72
SpreadSpectrum is offline SpreadSpectrum  United States
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A note on my feedback divider choices:

I wanted to compare the series vs parallel feedback separate from the screen voltage modulation effect so I adjusted the parallel feedback resistor divider until the gains were equal between the CED with constant Vg2-k and the parallel feedback case.

Then I changed to a ground referenced supply for the screen in the CED configuration to examine the screen voltage modulation effect separately.

Also, I used the somewhat heavy feedback in zintolo's original schematic in this thread. One could try various percentages and see how that affects things.
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Old 11th June 2021, 06:45 AM   #73
zintolo is online now zintolo  Italy
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Quote:
Originally Posted by Bandersnatch View Post
Ultimately it could be that I will take a very mild Schade applied to a medium sized transmitting triode I want to use.
[omissis]
From zero bias on the triode I need about +/- 35V of swing...
[omissis]
...leaves the grid at ~28V...and so I'll need a bit of MOSFET headroom.
So you are hyper-triodizing a triode? Just ground the pMosfet and guive its gate a bias higher than +28V (how much depends on the triode you are using as a power tube). Just note that you'll need to drive that stage with 70Vpp plus 4.8% of the total swing of the anode of the triode. If you supply it at 600V and it swings EG 1kV you'll need around 120Vpp to drive it to g1=0.
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Old 11th June 2021, 06:49 AM   #74
zintolo is online now zintolo  Italy
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Quote:
Originally Posted by smoking-amp View Post
Looks like one wants to keep Vg2 to K more close to constant for better triode emulation.
This brings back from chthonian abyss of my memory Wavebourn suggesting to have a very low AC impedance between g2 and k, and the importance to have them follow each other. I don't remember if it was here talking about GU50 or on his (unfortunately now dead) forum.
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Old 11th June 2021, 06:53 AM   #75
zintolo is online now zintolo  Italy
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Originally Posted by SpreadSpectrum View Post
I thought it was very interesting how the normal CED curves without the floating supply had less rollover at high voltages than at lower voltages.
Thanks for sharing and for the hack! I'm intrigued by these new considerations on further possible improvements and possible developements.
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Old 11th June 2021, 07:03 AM   #76
zintolo is online now zintolo  Italy
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Originally Posted by smoking-amp View Post
Might be interesting to use external grid 2 drive exclusively, with series grid 1 Fdbk.
In parallel I will do some simulations driving g2 through a common-collector BJT with the base driven by pentode's cathode, g1 still driven through the voltage divider and the pentode driven through the pMosfet on its cathode. Everything fixed, just changing what signal is imposed to g2.

Quote:
Originally Posted by smoking-amp View Post
Then make a P-P with the new type of roll-over on one side and the old type on the other side, using the internal triode for that. Definitely a new type of SE like sound. Rock n' Rollover.
😍
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Old 11th June 2021, 07:07 AM   #77
zintolo is online now zintolo  Italy
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Quote:
Originally Posted by SpreadSpectrum View Post
I used the somewhat heavy feedback in zintolo's original schematic in this thread. One could try various percentages and see how that affects things.
Reading George's previous fireworks experience (thanks for sharing and saving me from possible injuries!) it is probably too much feedback for nowadays available components, and it would be needed to drop it to around 10%. It's a pity, because I liked the balance I got from the available clean swing of the driver and the performance of the KT88 with this amount of feedback.
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Old 11th June 2021, 08:12 AM   #78
Bandersnatch is offline Bandersnatch  United States
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Quote:
Originally Posted by zintolo View Post
So you are hyper-triodizing a triode? Just ground the pMosfet and guive its gate a bias higher than +28V (how much depends on the triode you are using as a power tube). Just note that you'll need to drive that stage with 70Vpp plus 4.8% of the total swing of the anode of the triode. If you supply it at 600V and it swings EG 1kV you'll need around 120Vpp to drive it to g1=0.
This pup will start at grid=0V. Class A, PP HY51A from about a 600V/100 mA idle point. 10k a-a OPT. :It was going to be cathode driven anyway, grid grounded, and bias adjusted with a variac on the plate Iron's primary.

It occurs to me that the grid current is not going to like the FBK resistors.
cheers,
Douglas
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Old 11th June 2021, 03:25 PM   #79
SpreadSpectrum is offline SpreadSpectrum  United States
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Originally Posted by Bandersnatch View Post
It occurs to me that the grid current is not going to like the FBK resistors.
You'd probably have to buffer it with a mosfet which if I remember correctly you are trying to avoid.

I've had good luck doing it, though. My 826 SE amp with a mosfet grid driver makes 19 watts but distortion is at .063% at 10W. The step in load doesn't seem to be much of a problem for the mosfet in my experience.
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Old 11th June 2021, 07:48 PM   #80
Bandersnatch is offline Bandersnatch  United States
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This tech is getting me slightly nutty...and contemplating an all-ss variant of it. TX coupled like a tube amp tho...

Could be likely powered by a packaged DC switcher...it is just a matter of heatsinks weighing more than PS irons...LOL
cheers,
Douglas
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