Hi all,
I have two new 6AX4GT's which show some cathode-heater leakage.
One is about 10 meg, the other about 7 meg.
What is an acceptable level of leakage with these valves?

I have a third which measures perfect at >25 meg on the same tester tia

What did you measure that with and what is it going to be used for? That's a fairly hefty damper diode.

Hi Marcc, At first I was puzzled by your question as to what I made the measurement with, then looking at my post again, realised that part of my post had gone missing???

The tester is an AVO CT160.
The valve usage is the boost diode in the obscure b/w TV of my late brothers.

I was a little perplexed as to where that was going.

The maximum rating Heater to Cathode:

Heater Neg: In respect to cathode 900V
Heater Pos :In respect to cathode 100V pulse around 300V

Refer "Franks electron tube pages". At the high voltages I would have concerns with 7-10 Meg.

Some one out there will know. I do little in the way of TV servicing.

Did you post in the TV section?

I can't advise as to what the maximum allowable leakage would be but it would need to be fairly low. In typical TV damper applications the cathode has a fairly high (100's of volts) pulse voltage on it with respect to ground. The heater is normally grounded at one end in most applications.

In the real world, the valve will either work or not work in the set. H-K leakage would not have been measurable by the average serviceman in the 1960's and 70's so valve substitution was the fault finding method of choice.

Thanks for the replies, will try them all in the set and see what happens.