[AMPS] Re: regulator mu

Sat, 14 Jun 1997 09:42:17 +0000

> From:          Rich Measures <measures@vc.net>
> To:            <amps@contesting.com>
> Subject:       Re: [AMPS] splatter etc
> Date:          Sat, 14 Jun 97 04:27:27 +0000

> Perhaps it does not make sense to you, but most of the tube-type 
> regulator designs I've seen use a pass element that is voltage driven as 
> opposed to current driven.  The only types of triodes that can draw their 
> rated anode current with no grid current are Mu of less than about 3 
> types such as the 6080 and 6336.  

You seem to be (as you commonly do) saying because you haven't seen 
something it must not work.

For example, look at the 3CW5000 tube family. The low mu F1 type is 
listed as a audio amplifier or modulator. The high mu F7 is listed 
for voltage regulator applications.  

I also notice you and others equate mu to gain in a PA, claiming 
tubes with high mu have higher gain (that's part of your parasitic 
conundrums). Now in direct conflict to you parasitic tendency claims, 
for the regulator you claim low mu tubes have MORE power gain.  

Which claim is correct? Do high mu tubes have more gain, or do low mu 
tubes?

The truth is the regulator tube selected depends on the application. 
If the supply to output voltage difference is low, a low mu tube is 
useful. If the regulator requires excellent stability a high mu tube 
makes the associated circuitry less complicated.

Mu has nothing to do with grid current. The electron stream is 
controlled by the electric field surrounding the grid. Grid current 
is caused by the grid wires being in the path of the electron stream.

For example, an 8877 tube has very little grid current and very high 
gain, and very high mu. That's because the grid wires are not in the 
electron stream. The 8877's grid current is zero Ma at 1500 volts 
anode voltage and one ampere. 

The high mu 3CX3000F7 requires less driving power than the low mu 
3CX3000F1 for the same output power. Which is it Rich? Do low mu 
tubes require less drive power (have more gain) or do high mu 
tubes?

You "assume" the use of low mu triodes for regulators has something 
to do with grid current, but the real reason they fit SOME 
applications is low mu tubes often, but not always, have lower plate 
to cathode voltage drop than high mu triodes.

If we have a series regulator and wiggle the anode voltage around 
with a fixed grid voltage, a high mu triode produces  more stable 
cathode voltages. It also does not need "high grid current" to 
operate, as you claim. The high mu tube certainly does not 
require more "drive power".

73, Tom W8JI 

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