Valve testing a 4212
 

I have recently acquired a very large valve - a 4212H, I believe.
Is it possible to test one of these huge valves ?
It is undoubtedly beyond me !
I have ascertained the filament has continuity and thats me done!
Is this a service that is provided by anyone ?
Many thanks

Re: Valve testing a 4212
 

One of these: https://vintage-radio.net/forum/showthread.php?t=40716

Re: Valve testing a 4212
 

Hi Tinker, you should be able to run the filament supply up and then connect a voltmeter between cathode and grid. If the valve has emission you should get a small voltage reading.
Then you can think about other power supplies to try it in anger.

Ed

Re: Valve testing a 4212
 

Yes - thats the one.

Well - I have a voltmeter so thats a step in the right direction - but as to connecting up the filament I would have no idea what kind of voltage to apply and would be terrified of doing the wrong thing - I am led to believe this valve has a fair value, so it might well end upon ebay...

Re: Valve testing a 4212
 

So - reading the link above it seems the filament runs at about 14v ?
If I apply that to the filament with a variac and connect a voltmeter to the other two pins I should get a reading .....
Am I on the right track ? I shan't do anything just yet .......!!
Thanks for the help:)

Re: Valve testing a 4212
 

There was a similar thread to this a few weeks before Christmas. See "Search". Also, I actually tested one a couple or so years ago, using a bespoke DC Rig, plus produced a Ia/Vg Graph which I could compare with an actual STC graph. Sourcing a high current heater voltage is the awkward bit.

Regards, David

Re: Valve testing a 4212
 

14V @ 6A would be the easy part for me.

Re: Valve testing a 4212
 

Car battery? With ln line fuses of course! Not quite 14V, but should suffice for testing.

CB radio PSU?

Re: Valve testing a 4212
 

Wow thanks Station X -
Car battery - I have several of those hanging about.
So connect that to the filament terminals and measure the other 2 with the voltmeter to see if there's any voltage .....
That's tomorrows project sorted

Re: Valve testing a 4212
 

Don't forget the fuses or you could find yourself doing some involuntary arc welding.

An alternative would be to connect to a car's cigarette lighter/accessory socket which will be fused within the vehicle.

Re: Valve testing a 4212
 

Ok - fuses at the ready !
I will report back tomorrow

Re: Valve testing a 4212
 

The National Valve Museum website for 4212 gives a PDF data sheet link

Re: Valve testing a 4212
 

Aye Tinker, you'll be needing hefty Va & Vg supplies plus being able to measure in the region of 160mA Ia. Way beyond the VCM's & Valve Testers we all know. Plus you'll need to make a bespoke valve holder with sturdy valve pin connections. Don't be tempted to use cheapo crock-clip leads.
Jesus, was it all that long ago - 7th Oct.2015 was my "Testing the STC 4212D Triode" Thread.
My 4212D drew 6.3A at 14V Vh. And with 500V Va drew 160mA at -5Vg, but I started out gently at -50Vg. If you look at the STC family of Gm curves, you'll see that these fearsome valves were happy working in the 1KV Va region. Running Vh at 12V off a battery might do just to see the thing glow, but 14V would be needed to get comparisons with STC's data.
Caution - if your valve is a decent NOS one, it could be worth a few hundred quid, so don't phook it.

Regards, David

Re: Valve testing a 4212
 

If this were mine and I wanted to sell it, all I'd do would be to test the heater for continuity and state that it had continuity in my eBay listing or W.H.Y.

That's what I did with a load of 4CX250B's a few years back.

Re: Valve testing a 4212
 

Thanks everyone for the advice - I have already tested for continuity of the filament and it is good.
I think on balance I shall leave it there and sell it as is.

Re: Valve testing a 4212
 

Not quite, there won't be any voltage, you have to apply some and measure the current.

I'm just wondering how low a voltage you could use, and see some current and diode effect on a multimeter? Would a 9V battery be too low? Would -9v from a second battery be expected to cut the valve off or at least reduce the current?

More a classroom demo than meaningful testing, but it would prove there was some vacuum and emission.
(posts crossed)

Re: Valve testing a 4212
 

The OP was referring to the advice in post #3. ie measure the cathode to grid voltage.

Re: Valve testing a 4212
 

That's interesting, I don't suppose you could detect the space charge with an AVO 8 though...

Re: Valve testing a 4212
 

Now on eBay: https://www.ebay.co.uk/itm/293434534649?ul_noapp=true