Hi Oli, I guess I'm a 'never give up' on a valve type.
I have had "dead" valves come back to life simply by running them for a time.
Seems to allow an electron emitting surface to 're-activate' after being unused for decades.

Marc may have had some experience there or comment?

Also, I test such a valve in some sort of bench rig where I can easily meter what sort of current can flow from plate to heater.
I use a typical 385/385 power tranny hook it all up on the bench with series resistors in the plates and heater output into a load.
The voltage drops across the resistors then translate into Ma.
A common like PW10 x 100 ohm is a good value.

I've left valves sitting for hours hoping and praying and occasionally get a surprise.
The current drawn by the heater may also give a clue to the envelope being under vacuum.
If the current draws a value that then drops to a lower value once heated that could indicate 'normal' vacuum.
Unfortunately i've never had a large rectifier and done that test, just with 5y3 size.
I've 'resurected' filment output like 45 and cathode signal valves like 57.

A lot of trouble unless it's the last bottle 5AS4 on earth!

Fred.

Ian:
Thank you very much! I'd really appreciate that.

Fred:

I guess it wouldn't hurt to try to "rejuvenate" the valve by running it on around 10v on the heater?
But, like you said, a lot of trouble.

Really I just wanted a new (old) one!

Oli

I was rather lucky. Very early in what was then a hobby I scored a 1938 Paton VCT Valve and circuit tester 240VAC 6VDC. Since repairing its meter movement, it has been handy for years, as it can test valve radio tubes except miniatures. Caps resistors & also has a bonding meter.


Later I acquired a Tech that could test miniatures as long as you used an isolation transformer which I moved on, with warning, when a retired Radio guy I knew for ages gave me a 110V Knight 600 Tube Tester. I might run a tube for a while, but that's normally to speed up the Araldite curing when I re glue the base on a cold night.

Tip once you have run a bit of Araldite around the base. Use insulation tape, sticky side in to hold it in place; Until it finishes reacting.

The old "Radiotron Handbook" does not list 5AS4 as its a newer tube. However:-

5Y3 550V in 4μF 8k load is 72mA per plate good & 58mA at end of life.

A hefty 5U4 550V in 6μF 3550Ohms load 141mA per plate good and 113ma at end of life. 1000 ohms series, one volt across the resistor = 1mA

I glued the bases of the ones I have. GT & ST-14 envelopes.