Low Voltage Valve/Tube Buffers/Hybrids/Amps

Graham Slee wrote: My Junior's teacher once brought in some batteries for us to experiment with. One was a 90V HT battery!!

Have I got my A B C s mixed up?

Isn't that where we got "B+" to mean the high voltage power supply?
 ... 90 volt HT battery was called the "B" battery, as I recall.

An "A" cell was the grid bias battery?

A "C" cell was the filament ? 


Edited by BAK - 27 Jan 2016 at 3:32pm

Indeed! If we could just get all the injury lawyers to visit each other's offices, fall over and sue each other... perpetual inflation.

US Patent 5450034 looks interesting and reached its 20 years last September, so it will be turning up in all sorts of valve hybrids soon (if not already).

http://www.google.co.uk/patents/US5450034

It's called a Reflected Plate Amplifier and is very similar to the two transistor stage used in many a transistor preamp circuit.

It suggests the use of one half of a twin triode, but the other half couldn't be used for the second channel (because of crosstalk) and would be wasted.

It gave me the idea to try making a differential input stage which would use both halves and traditional negative feedback could be applied in a more predictable manner (I do so hate wasting time and components on "what if's").

At least the invention could make use of the same plate voltage used in a class-a 90V HT supply circuit using just 45 volts for its supply, as there is no conventional plate (anode) load. Therefore the valve's designed characteristics would be met.

I will try and draw up the basic circuit and present it here, and if it succeeds you never know, the stage could be offered as a kit...

We'll see.