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-   -   GAS VR Tubes on B+ (http://www.diyaudio.com/forums/tubes-valves/76926-gas-vr-tubes-b.html)

skip_scratch 1st April 2006 05:30 PM

GAS VR Tubes on B+
 
I have all the parts pretty much to build an RH84 as pictured here (see link) except a low enough value power transformer. So I was thinking to lower the B+ by designing in VR tubes on the B+. This brings down the voltage and provides some regulation. However, one seldom sees VR regulation in amp designs, any bad things sonically etc happen with doing this?

http://www.diyaudio.com/forums/showt...highlight=rh84

Zen Mod 1st April 2006 09:09 PM

just look at current range of any VR tube...
I doubt that you'll find any capable do feed even just one channel of even flea power amp......

most VR tubes are good to max 30mA
that's good for load current of some 20mA max......

Miles Prower 2nd April 2006 12:01 AM

Re: GAS VR Tubes on B+
 
Quote:

Originally posted by skip_scratch
I have all the parts pretty much to build an RH84 as pictured here (see link) except a low enough value power transformer. So I was thinking to lower the B+ by designing in VR tubes on the B+.
How much extra voltage do you have? It just might be better to use the VR tubes in an electronic voltage regulator.

Quote:

This brings down the voltage and provides some regulation. However, one seldom sees VR regulation in amp designs...
They were too cheap "in the day" to use them. You don't see them too often because we basically inherited all those circuits from the 1950s.

Quote:

any bad things sonically etc happen with doing this?
No. In fact, the noise that VR tubes produce is a good deal "softer" than what zeners (or any other reverse current across a PN junction) produce. Use them right, and this is not a problem.

lndm 2nd April 2006 08:15 AM

Quote:

Originally posted by choky
just look at current range of any VR tube...
I doubt that you'll find any capable do feed even just one channel of even flea power amp......

most VR tubes are good to max 30mA
that's good for load current of some 20mA max......

I assume the VR will be used as a shunt regulator, with a series resistance and the VR in parallel with the load. In this case the VR needs only to pass a current such that it can vary up and down by the current delta (total swing) of the load. A class A stage (or stages) draw a more or less constant current and are a good candidate here, even though they need regulation less than Class AB.

For class AB, I agree with Miles about the active regulator as a good way to use the VR.

PS, you could use your raw supply for your output and the VR in shunt form to power your earlier stages.

Eli Duttman 2nd April 2006 05:30 PM

Skip,

Have you considered a pseudo choke I/P filter? If the 1st cap. in CLC filter is held under 1 muF., behavior is primarily choke I/P. Experiment with the value of the 1st cap. to get exactly the rail voltage you need.


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