Problems With Obscure Russian Miniature Valves

I'm working on a circuit design just now, and am trying to use these as simple gain stages in triode mode:

http://lab.artematrix.org/electronics/datasheet/VALVE/1J24B.pdf

At the moment I am trying to run the valve on a 9V battery which I was using successfully with another low-powered valve - the 6418, so B+ is 9V and heater is 1.2V or so.

As it is just now, the valve is only passing a small distorted signal only when the input is high which sounds a bit like a valve which is biased too cold, or missing a grid-leak resistor for bias.

I've made the assumption that like the 6418, this valve is biased via the heater voltage since there is no separate cathode connection, but this is what I am wondering if I may be wrong. Does anyone have any ideas?

The fact that the datasheet is in Russian doesn't help me.

Roddy

Hi Roddy,

What's the circuit? Is there a grid resistor to ground or is it all relying on leakage paths like the Royer small diaphragm mic design?

z50

[quote author="zebra50"]
What's the circuit? Is there a grid resistor to ground or is it all relying on leakage paths like the Royer small diaphragm mic design?
[/quote]

Hi, no there is a grid-leak there, so it should work.

Here is is drawn in MSPaintCAD:



There's a possibility I may have omitted some parts. I also tried tying S and G3 to ground instead of f+.

Obvious first - DC offset fncking up the input bias? Maybe try a DC input blocking cap?

Bet you thought of that already. Dodgy tube?

[quote author="zebra50"]Obvious first - DC offset fncking up the input bias? Maybe try a DC input blocking cap? [/quote]

Well, source is a guitar pickup, so I don't think that should be a problem.

I may try another valve.

Have I understod the biasing correctly do you think? That it is fixed-bias at the filament voltage?

Cheers.

might the filament need to be connected with respect to the negative battery terminal instead of positive? With 800 R from battery neg to ground, rather than as drawn? Crackheaded thought....

[quote author="emrr"]might the filament need to be connected with respect to the negative battery terminal instead of positive? With 800 R from battery neg to ground, rather than as drawn? Crackheaded thought....[/quote]

Good point, but I did find this, and it appears that f+ is indeed positive:

http://joopmusic.de/hammond/diagrams/MIG-T/mig-t_diagram.pdf

Problem solved. I shouldn't have trusted the specs entirely for the valve - seems it wasn't happy with underheating. So, bias voltage was low, and heater wasn't hot enough either - which was causing more problems I'm not sure.

I may see if the others in the batch vary in their heater's current draw - this one didn't like my calculated heater supply.

> didn't like my calculated heater supply.

My calculation says 600R, not 800R.

And ~~80% of battery money is going up as heat in that resistor. One AA-cell is the right voltage, no waste, also much cheaper per watt-hour.

[quote author="PRR"]
My calculation says 600R, not 800R. [/quote]

Yep, I didn't bother swapping the original value I was using with my previous circuit with different valves.

And ~~80% of battery money is going up as heat in that resistor. One AA-cell is the right voltage, no waste, also much cheaper per watt-hour.

Click to expand...

True, although I'm trying to keep things simple. I did consider using a current-doubler DC/DC converter to step down the 9V, but I think that is maybe over-complicating still.

Try connecting G3 to F-, or to G2.
Shield should go to ground.