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jarthel 24th October 2006 11:29 PM

tube for a shunt voltage regulator
the schematic is from raleigh audio:

can I use any type of triode? daydreaming that I have a box full of WE 300b, can I use it for this application?

if not all tubes are suitable, can you give examples?

thank you.

Wavebourn 24th October 2006 11:36 PM

Western Electric 274A tube early globe style may work well.

Also, you may use Telefunken ECC83 in parallel. 20 of matched pairs for the best sonic results.

ray_moth 25th October 2006 06:01 AM

Jarthel, the type of tube needed for shunt regulation is dependant upon the current demanded by the load. The shunt tube will have to adjust its own current so that the sum of shunt current + load current is constant. It's easiest to assume that the shunt tube could have to draw the full current, if the load is open circtuit, and choose the shunt tube accordingly.

You certainly could take the approach recommended by Wavebourn but I think 20 pairs of ECC83 might be an expensive, unsightly and very space-consuming solution.

Geek 25th October 2006 07:14 AM

Just triode a TV horizontal sweep tube and call it a day :)

Wavebourn 25th October 2006 07:28 AM

By the wey, a light bulb may be used instead of CCS. In such case we have already one glowing beauty, so a shunting regulator may be made from one HEXFET and a gas discharge tube between drain and gate, with a resistor between gate and drain.
Simplier, chiper, and more cool different glowings.

mach1 25th October 2006 08:15 AM


Just triode a TV horizontal sweep tube and call it a day
I was rather partial to the idea of 20 matched pairs of Telefunken 12AX7 or even a few WE 205D.

Geek 25th October 2006 11:53 AM


Originally posted by mach1

I was rather partial to the idea of 20 matched pairs of Telefunken 12AX7 or even a few WE 205D.

Lemmie get those on Ebay first, then I'll back you up on that ;)

SY 25th October 2006 12:11 PM


Originally posted by Geek
Just triode a TV horizontal sweep tube and call it a day :)
As long as the voltage is below 250-275V. Otherwise, it won't work.

David Davenport 25th October 2006 12:19 PM

Hi Jarthel,

There are two considerations when choosing a pass tube for the regulator.

First, as Ray mentioned, is to pick a tube that is capable of carrying the full current provided by the series element. You can use two halves of a dual triode in parallel.

Second is to make sure that the tube is capable of the plate-to-cathode voltage that it will see. To be safe, I always assume the full B+.


kevinkr 25th October 2006 05:17 PM

Another consideration is that the tube chosen should bias in the active region without exceeding the voltage rating of the TL431.

Also true that the bias needs to be above the minimum required for the proper operation of the TL431 as well.. :D

Seems like a nice solution. Suitable tubes could be ones like the 6BQ5, 12B4, 12BH7, 6BX7, 6CK4, etc. EL34 could be rather marginal at higher voltages. 300B, 6L6, and 6550 will exceed the 36V rating of the TL431..

I have used tube shunt regulators with zeners on the cathode as well - works ok with higher mu small signal triodes, and low currents only. Zener voltage was about 1/3 - 1/2 of the target voltage. (mu >20) The TL431 solution will perform a lot better where it can be used.

You can do something similar with higher bias types using a zener, npn transistor, tube cascode. Some additional gain will be provided by the npn depending on the pass tube's internal cathode resistance.

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