Valve testing/matching rig question

[frankmcvey]

Hi, David, good to hear from you again.

I'd briefly considered the valve panel from an old Avo 2 or some-such - you regularly see them coming up on Ebay, some pretty shot-up and all at daft prices! Since this is as much about the building - and the quality of the build - for me as the eventual use it'll see, I thought I'd stick with all new components. You guys at Cosford did a good job of drumming into my thick head that a bit of kit shouldn't just work right, it should look like a good craftsman-like job as well! And while I'm not in the happy position of saying that money is no object, I'd rather spend a little extra to get something I'd be happy to live with and take pride in. Time isn't really a factor either for me when it comes to something like this - I don't mind the fannying about!

Thanks for the advice re ferrite beads. I'd been swithering over that one, but your comments have convinced me. I'd very much appreciate any other pointers and advice over specs. While I hadn't really envisaged running an 807 at 600-700V (yet!) some degree of future-proofing would be a good thing.

For example, I have plenty of 7/0.2 hookup wire, but that limits me to 1.5A or so - what wiring do you use in your rig?

I'd also appreciate your comments regarding wiring layout, given that it's a DC tester. How critical? For example, since most pins on most holders are potentially heater pins, we can't do the good thing of making a nice beefy dedicated twisted pair to carry the heater current and hiding them in a corner. Is it worth going down the road of using DC heaters?

Funny how such an apparently simple job raises so many questions!

Looking forward to hearing from you, and thanks to everyone else who has contributed their thoughts.

Cheers,

Frank

[Dekatron]

You can look at the two modern valve testers, the uTracer by Ronald Dekker here: http://www.dos4ever.com/uTracer3/uTracer3_pag0.html and the RoeTest by Helmut Weigl here: http://roehrentest.de/ to get some ideas on how to build a valve tester that is connected to a computer.

I own both of these and really like them both, the uTracer is a lot cheaper than the RoeTest but on the other hand the RoeTest can test tubes that require higher voltages/currents. Unfortunately both need to be hooked up to a computer as there is no standalone mode (yet).

The RoeTest use a 12 pin DIN41622 contact and a small plastic box which is mounted so that it slides into position and is kept down by the edges by two "rails". You can read the latest manual here: http://roehrentest.de/construction%2...%20english.pdf.

/Martin

[Radio Tech]

Hello Frank

Have a go at the one I rebuilt, the design was in a practical television mag of which I have the detail, it will more than cover the range of valves you wish to test. I can if you wish send you the detail.

Regards

Ken

[David Simpson]

Hello again Frank,
I was dead jammy in acquiring a duff, bodged AVO VCM Mk1 with a pristine top valveholder panel with the thumbwheel switch assembly & all it's wiring intact & in good nick. However, some years back I remember stripping down an old Jackson valve tester, and thinking at the time that it's valveholder panel would come in handy. But I then passed it on to someone who was renovating one.
I do have some spare Septar ceramic valveholders(for QQV06-40's etc.) if you need one.
Your hook-up wire, or 2491X (0.5mm sq), or similar would do for most of the circuitry. Again, I've been lucky, in acquiring some ex oilrig hi-spec sections of looms of MV wiring of a similar cross-section, but tinned. Having a selection of colours, I was able to follow the old Cosford(now not PC)colour-code mnemonic in connecting additional valveholder's pins or building beaded plug-in extensions.
Valveholder connections that end up being used for heaters or anodes can get a bit warm, so best avoid running any looming close to those bases used for O/P valves.
If you cannot acquire an ex AVO panel, you'll need to find Nine 10way hefty Yaxley type rotary switches. Some old makes of Decade Resistance Boxes have some lovely bespoke h/d wafer or rotary contact switches, designed for multi-repetitive switching & HV rated(for when they are used in substitution mode in live circuits). They can be picked up quite cheap at sales.
A decision you'll need to make initially is - what shape & size of cabinet do you want to use. Ergonomics, I think is the term used. Do you want to stand up at a bench & look downwards at something like an AVO CT160 ? Would you like to sit down & work something sloped like an AVO Mk 3 or 4? Or perhaps something upright like an AVO Mk1 or 2? I ended up choosing the latter, having acquired a decent empty Marconi TF995A/2 cabinet. What you'll need to avoid is reaching past or over the valves - to reach & adjust switches/pots/etc.
Should you decide to use external power supplies for HT, -ve Vg, Heaters, - bring them in at the back. Use banana plugs, Jones Plugs, Plessey Plugs, whatever. As long as you keep the frontage of your tester free of several cables going hither & thither. You'll need that space on your workbench for valve data books, A4 graph paper( for drawing up Ia/Vg (Gm) graphs), & so on.
Finally, to avoid cooking any size of valve, or whanging your display metering to bits -consider applying Va & Vs(for a shorter period as is convenient) via a H/D double pole relay controlled via a spring operated toggle switch.

Regards, David

[frankmcvey]

Hah - talk about great minds thinking alike; except that my virgins have become puritans!

The wire I was considering using is around half the area you recommend, so I'll get some heavier stuff.

Thanks for the recommendations; I particularly like the relay idea. More food for thought!

Cheers,

Frank

[JacKam_]

Frank,
FYI: I found an old tube tester on Allegro, (Polish Ebay).
http://allegro.pl/miernik-lamp-elekt...671310529.html
Hope it will help you to design the front panel for your tester.

[Ed_Dinning]

Hi Jac, that's the old US WW2 tester, quite a useful bit of kit, but you need to have the handbook with switch settings to go with it. Also note that they were 110v supply.

Ed

[David Simpson]

There is a school of thought which holds Hickok valve testers in the same reverence as AVO ones. I've never used or worked on one, but the pictures I've seen & past comments made on this & other forums would indicate that they are really decent pieces of kit.
To acquire one just to strip out it's valve holder panel, might attract some adverse comments from purists. This was a worry to me when I stripped down an old AVO Mk1.
Talking of AVO's, there is a huge amount of spare space within the cabinet of the Mk3's & 4's. I'm sure that some enterprising Forum guy could fit modern smaller rectifier & filtering circuitry for DC conversion. Without spoiling the external appearance & integrity. Just a thought.

Regards, David