Glow Tube Voltage Droppers

If they glow, this is the place to be
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Cressy Snr
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#1 Glow Tube Voltage Droppers

Post by Cressy Snr »

Providing you accept what voltage comes out, these things seem to be great for low current applications when placed in series with the B+

I've been playing around with the test monoblocks, running 6V6s at 43mA using the existing series reg for the front end and just using a 75C1 direct off the end of the PSU, before the series reg, to drop the volts to the output stage.

I got the idea when looking for 6V6 single ended amps on the web.
Part of the PSU for the Decware Zen Mini Torii 6V6 amp uses glow tubes in series with the B+

Steve Deckert claims excellent sound using glow tubes as voltage droppers. OK we have to beware of vested interest here, but after having tried them in my amp, it would appear that he has a point.
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Cressy Snr
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#2

Post by Cressy Snr »

here's the 6V6 amplifier.

Image

The 6080 is dealing with the input stage only; dropping and regulating the PSU output voltage of 400V to 300V at 12mA (gross waste of a 6080 but whatever) :)

75C1 glowing in background is dropping the power supply output voltage, from 400V to 325V at 43mA to feed the 6V6 output stage.
This is nice. It sounds like a proper valve amp :) widescreen, in the nicest way.
I like 6V6s, even modern production JJs.
For me they have a 'rightness' about their sound that allows one to listen for hours on end with no fatigue.
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Mike H
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#3

Post by Mike H »

I'm trying to think why using a reg. tube as a dropper might not be a good idea. Is this 325V rail decoupled to ground at all?
 
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Cressy Snr
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#4

Post by Cressy Snr »

I'll put a block diagram up after lunch Mike
:)
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Mike H
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#5

Post by Mike H »

Okey-doke. :D
 
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Cressy Snr
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#6

Post by Cressy Snr »

Here's my implementation

Image
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Cressy Snr
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#7

Post by Cressy Snr »

To give an idea of how easy to use these VR tubes as voltage droppers are, I changed the output valves in the test monos from 6V6 to 6P25.

Image

All it required was a change of bias resistor to 200R and a simple change of dropper tube to 0A2 (150V)
This gave 240V at the plate of the 6P25 with 40mA current.
Just about cock on for this nice little KT61 equivalent by Mazda.

This, in the tradition of old English valves, sounds mighty fine. I'd forgotten how good these old Brit valves can be :)

6P1s, PEN45s, I feel a British valve extravaganza coming on.........er....Steve...where are you?
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Mike H
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#8

Post by Mike H »

Ah right OK ~ was wondering where the source was coming from for the dropper tube, but it's a regulated rail. Fairy nuff
 
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steve s
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#9

Post by steve s »

[quote="SteveTheShadowThis gave 240V at the plate of the 6P25 with 40mA current.
Just about cock on for this nice little KT61 equivalent by Mazda.

This, in the tradition of old English valves, sounds mighty fine. I'd forgotten how good these old Brit valves can be :)

6P1s, PEN45s, I feel a British valve extravaganza coming on.........er....Steve...where are you?
[/quote]
I'm here....
that is a pen 45 with a 6 volt heater, it will also do nearly a couple of watts in triode mode... the pen 45 is always was shown as a triode as well as pentode when lots of valves were not... must be a good reason for that..?

250 vt, -9,8v,35m/a,280 ohm Rk 3.500Rl 1.7 watts

worth a go steve.?
cheers
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#10

Post by Cressy Snr »

Definitely worth trying out.
The 6P25s put out around 4.4wpc in ultralinear mode and sound quite enchanting. It's a very involving, musical sound, brimming with vim and vigour but not in the least bit hard or strident.

As you know Steve I have been wanting to play around with some British low powered pentodes for the last few years but seem to keep getting distracted. And whaddya know, the first time I do it I get a great sounding amp.

What I like about the old Brit pentodes is that apart from the usual suspects, ie KT66/88 EL34/37 they are relatively cheap to buy, for now.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
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