How to evaluate RF tubes for power and fidelity?

[thadman]

I'm interested in purchasing a quantity of Russian military surplus vacuum tubes for an amplitude modulated 27Mhz RF amplifier. How can I evaluate the power and fidelity (linearity) of the tubes or differentiate between them? I'd prefer a minimum of 1kW. However, 10kW would be best.

Here is a list of Russian military surplus vacuum tubes that are available for broadcast.

STC NavigatoR / Tubes / Broadcast

If you are familiar with any of the models, I would greatly appreciate a recommendation.

Thanks,
Thadman

[bob91343]

It's patently illegal to do what you are planning.

[Arnulf]

Originally Posted by bob91343

It's patently illegal to do what you are planning.

He wants to create a tube-driven plasma tweeter.

@thadman: tubes capable of handing such high power will require forced colling, usually water colling. No if, no buts, anode voltage in kilovost range + plumbing to get water to the anode coupled with lack of experience is a recipe for disaster. Needless to say the power supply would have to be enormous (and expensive).

You were given a link to a project that different people have completed. Why not complete that first before setting out to do something as outlandish as multi kW tweeter (what's the point of that anyway - to run a concert ?).

[tubesteve]

my best advice: if you already ask how to evaluate these tubes, then best is for you: keep the fingers of that, besides the legal problems.

[danzup]

Originally Posted by thadman

I'm interested in purchasing a quantity of Russian military surplus vacuum tubes for an amplitude modulated 27Mhz RF amplifier. How can I evaluate the power and fidelity (linearity) of the tubes or differentiate between them? I'd prefer a minimum of 1kW. However, 10kW would be best.

Here is a list of Russian military surplus vacuum tubes that are available for broadcast.

STC NavigatoR / Tubes / Broadcast

If you are familiar with any of the models, I would greatly appreciate a recommendation.

Thanks,
Thadman

By constructing and see how it is working ???

[thadman]

Originally Posted by bob91343

It's patently illegal to do what you are planning.

Could you expand on this?

[thadman]

Originally Posted by Arnulf

You were given a link to a project that different people have completed. Why not complete that first before setting out to do something as outlandish as multi kW tweeter (what's the point of that anyway - to run a concert ?).

Arnulf,

It was previously suggested to use an adjustable gap. An Air-Core transformer could be used to step-up the voltage to the required levels for a 15cm gap (225kV/electrode). I'm concerned I won't be able to maintain the "holding current" required for a stable plasma with such high voltages.

Correct me if I'm wrong, but 225kV @ 1kW = .004 amps

[bob91343]

My error; I thought you were building a transmitter.

In any case, watch out for unwanted radiation or you could get into trouble with FCC. Worse, an army of angry CB operators may descend on your place.

The Russian tubes appear to be good. Many hams use them with good results. What types are you considering?

[kavermei]

It's not easy to make a transformer (air core or other) that will handle 225kV... arcs will fly all over the secondary, punching holes in the insulation of the windings...

[jrenkin]

Originally Posted by kavermei

It's not easy to make a transformer (air core or other) that will handle 225kV... arcs will fly all over the secondary, punching holes in the insulation of the windings...

A long time ago, when I worked in lasers, we had a 50KV transformer made for an experiment we were performing. We had to submerge it in insulating oil and the power wire coming out of it, insulated in one inch of silicone would have blue fingers of electricity radiating from it. Arcing was frequent to anything else. You couldn't point your finger at it from less than a couple of feet. The l;ab smelled of ozone. It is amazing we survived. Truly these voltages need to be in well controlled environments and most home work areas just wouldn't be safe.