Power control with a VVR on G2 - what do you think about ?

[kagliostro]

I was looking for a PT at TubeTown and I've seen this circuit (only for cathode bias amps)

a VVR to be used as to control power

regulating G2 voltage instead of plate voltage

http://www.tube-town.net/diy/tt-needfull/03-ttvoco.html

http://www.tube-town.net/ttstore/product_info.php/info/p5651_Kit-TT-VoCoM---Variabler-Spannungsregler.html

that is new for me

what do you think about this way of power regulation ?

Thanks

K

[DummyLoad]

seems like it would work...

something similar - just not setup for variable power output control.

http://www.el34world.com/Forum/index.php?topic=13634.0

[Willabe]

They say it's good to up to 600 dcv. I wouldn't trust putting 600dcv on that circuit kit/mod.

IIRC, an alpha pot has a 350dcv rating for the resistive track and a 500dcv ark over from track to case? I know the current is very low but still 350dcv to 600dcv is a pretty big leap. They also talk about using their kit for the power tubes plates.

If more heat has to be dissipated; for example, if the plate voltage of the power tubes is to be regulated, then the BUZ90 could get quite hot, and the small heat sink.

A PEC (2w mil. spec.) pot has a 500dcv rating for the resistive track and a 900dcv ark over from track to case. Which is why KOC used them on the early Power Scale kits (VVR), with a PSU limit of 500dcv. Later PS kits have a different circuit and can use any style/rating of pot.


                                  Brad      
                              

[kagliostro]

DummyLoad

Thanks for the info

Willabe

I can agree with you about voltage excess on the pot

about the use for plate regulations, instruction report to connect the BUZ90 to the chassis as you can see also on the photo

----

About this way of regulation (G2 voltage regulation) it will be interesting to know tone response

if this way of regulation give good results I think it will be interesting to be used in high power amps (100W or more) as if we want to regulate plates voltage we need a high spec mosfet

however the fact that the most part of high power amps use fixed bias instead of cathode bias will be a problem

K

[Willabe]

about the use for plate regulations, instruction report to connect the BUZ90 to the chassis as you can see also on the photo.

I know the current is very low but still 350dcv to 600dcv is a pretty big leap. They also talk about using their kit for the power tubes plates.

I sorry, I was not very clear, I was trying to say some would say you can get away with using that pot with 600dcv on it with only the screens 5 to 10mA's of current. But they also seem to be saying you can run 600dcv on the pot with the full PP output tubes plate current which is around 10X the screen current.          All you have to do is use the chassis as a heat sink. But that has to do with the mosfets raitings, not the pot.


                          Brad               

[kagliostro]

But that has to do with the mosfets raitings, not the pot.

yes, I agree with you about voltage excess on the pot

K

[PRR]

In a cathode-bias amp, varying G2 voltage does change max-power 100% to about 10% without large change of gain or distortion shapes.

I don't think it is "The Same" as dropping plate voltage, reducing OT size, etc; but it sure is simpler than carrying all different size amps.

[DummyLoad]

They say it's good to up to 600 dcv. I wouldn't trust putting 600dcv on that circuit kit/mod.

IIRC, an alpha pot has a 350dcv rating for the resistive track and a 500dcv ark over from track to case? I know the current is very low but still 350dcv to 600dcv is a pretty big leap. They also talk about using their kit for the power tubes plates.

If more heat has to be dissipated; for example, if the plate voltage of the power tubes is to be regulated, then the BUZ90 could get quite hot, and the small heat sink.

A PEC (2w mil. spec.) pot has a 500dcv rating for the resistive track and a 900dcv ark over from track to case. Which is why KOC used them on the early Power Scale kits (VVR), with a PSU limit of 500dcv. Later PS kits have a different circuit and can use any style/rating of pot.


                                  Brad      
                              

use a high quality multi-turn this one has a 1000V rating and is a 3 turn...

http://www.bourns.com/data/global/pdfs/3547.pdf

--DL

[DummyLoad]

this one is single turn with a 900V rating.

--DL

[kagliostro]

PRR

..... without large change of gain or distortion shapes ..... I don't think it is "The Same" as dropping plate voltage ....

do you mean that probably the use as to reduce power will have good results but we must not expect to have the sound of a cranked amp at low power levels ?

DummyLoad

Both are interesting components, the second also has 1/3 of the price or the first one

thanks to both friends

K