A simple Valve Test Jig

[AlanBeckett]

Recently I had to test a Valve. I did this by using my HV PSU and a couple of Meters, plus wires tacked on to a Base - not very convenient, especially as it was a Triode Pentode. I have a couple of Valve Testers, and a couple of historic ones, but I figured it would be more trouble to get one out and make sure it was doing the right things than knock up a Jig to allow more convenient connections to my PSU etc, and anyway I'd have it for the future.

So, usual Plan, a Drawing first:-

   

I had a piece of 2mm Aluminium Plate so cut it out and mark up:-

   

Drill some Pilot Holes and cut out the Corners:-

   

Cut out the IO Hole - that's the tricky one because I had to do it with a Fly Cutter:-

   

Seems OK so Drill the other Holes and bend up the Sides:-

   

Strip off the Plastic and clean up all the Burrs - looking promising:-

   

To be continued ....

[pwdrive]

Alan, are you going to use the same type of terminals as what your tapped HT Load unit was fitted with?

Lawrence.

[AlanBeckett]

Next mount the Valve Holders properly and the Terminals.They were meant to be all mounted with the Index 'Down' but the B7G didn't clear the IO so they're all to the Right:-

       

Now a bit of scruffy Wiring and some Cable Ties to make it look civilised:-

   

The Eagle-eyed will have spotted by now that there's an extra Terminal. It dawned on me that I'd nowhere to park a Top Cap Lead so added one in
I figured it was a bad idea to have the bottom open as I was bound to pick it up Live one day so a bit of MDF and Feet fills it in.

       

It Buzzes and Meggers OK.
Finally some Labels for when I forget which way round the Terminals go, and a coat of Laquer to make sure they stay there:-

   

 So, best try it. I have half a dozen EL42 which claim to be NOS but who knows.
The easy way to try them was to tack in a couple of Resistors as per the Data Sheet and measure the Anode Current.

   

The Sheet says 26mA and that's what they all measured, at least within the limits of my Tests.

Onward and upward

Alan

[pwdrive]

Spot on.

Lawrence.

[Ed_Dinning]

Hi Alan, it may pay to slip some ferrite beads over each of the leads at the valveholder ends. This will stop any instability with high gain valves and long leads.

I think I'll build one of these, I have some nice top hat section that will do nicely.

Ed

[AlanBeckett]

I did consider it Ed but I haven't got any and I only propose to do DC Tests with Low Impedance PSUs.
Still, it's a good point and I'll keep an eye out for any strange results.

Alan

[Radio Fixer]

Well you could use it to measure and keep a "Standard Valve" for an AVO tester which to me is a good test that my MK 2 is working correctly then just get that out. Saves all the connecting and PSUs IMHO.

Gary

[Alan Douglas]

100 ohms in the control-grid lead should stop most parasitic oscillations.

[AlanBeckett]

Sorry Lawrence, I missed your Post. I should look because you always seem to manage to slip one in between my Posts, no matter how fast I am
I intended to use the same Yellow Terminals but found I hadn't got enough, so I used what I had. Anyway, having the Colours in Threes makes it easier to count round.

Alan

[pwdrive]

No worries Alan, that EL42 test checked out good, I noticed the value of the cathode bias resistor in a data sheet I found for that valve but no value for the grid resistor, just wondering what value you used?

Lawrence.