The LeyMarcAVO DC-VCM

[Herald1360]

There's some nice silver coloured laser printable adhesive plastic label material available- we use it on in-house test boxes at work. It's something like this:

http://www.ebay.co.uk/itm/10-A4-Meta...item5af02c44b7

though I don't think that's the same make.

[David Simpson]

Thanks Herald1360 for the tip.
I just have a cheapo inkjet printer. I think I'll try & draw gradated dials first freehand, then print onto some inkjet friendly acetate sheeting or thick photo paper.
Someone told me that "Hobbycraft" have some etching kits. So will pop into Aberdeen & see what they've got.
I'm getting close to wiring everything together, but as space is taken up, there is less room to work with. Shooting persuits & outside work is taking a toll on time available for electronicing.

Regards, David

[Herald1360]

These days I'm not sure that "cheapo" and "inkjet" go together any more unless it's a colour printer.

Laser is certainly cheaper to run on consumables for general B/W printing.


I would think that any basic graphics program would give a better than freehand result for graduated dials- even wordart in Word......

[David Simpson]

Its just a cheapo Brother colour inkjet printer I have. Yep, Microsoft Word is another option. Although I must admit to having very little experience or skill computer graphics-wise. The computer is just a communications tool for me, emails & exchanging info/diagrams/pictures. Multimedia/graphics/modern jiggery-pokery - - I'm just not interested in.
Will certainly have a go at MS Word, but dont expect too much. I'd much rather use my drawing board & my old set of Rotring & Staedtler pens & stencils.

Regards, David

[Herald1360]

Ahh, proper "freehand" then! If you've got that sort of kit and the skills to go with it I'm sure the results will be just fine. If you can still find Letraset transfers they're useful too. ISTR the D.O. doing it that way at Racal in the '70s.

[David Simpson]

What I aim to replicate is the lettering & numbering on the Marconi VVM which takes up thr r/h/s of the valve tester frontage.
Thankfully, the Levell meter(-veVg), and the two Ernest Turner meters(Ia & Is), have existing scales which lend themselves to little alteration. Shant touch the VVM's meter scale at all. As the volts ranges(AC & DC) are ideal. Just the ohms ranges will be redundant, but might give thought to using them at a later stage if I can work out suitable aditional switching for resistance testing between valve's electrodes.
Havent done much today on the project. As my old r/o mower needed cleaning & greasing up prior to being put into winter hibernation.

Regards, David

[Pamphonica]

David, you might try:
http://tonnesoftware.com/meterbasicdownload2.html (free meter scale software)
or more recently I have been using the amazing free GALVA software.
http://www.f5bu.fr/wp/?page_id=13
It can do scales, panels, circular sliderules - the lot! But is hard to drive as it uses a sort of simple text-based parameter list, rather than interactive controls. But I have never seen anything as capable.
For what you want to do, use MeterBasic, I think! The attached photo is the front panel of my as yet incomplete Sussex valve tester!
I have the full version of Meter and it can do virtually any scale you want, colour, everything.
I print on sticky-back transparent laser labels, or on OHP (Overhead Projector) laser foils with spray glue.
PM me for more details.
- Jeremy

[David Simpson]

Many thanks Jeremy for the info. Your Sussex certainly looks a treat. What I have in mind are are back laminate plates similar to the ones in the accompanying pictures. They are secured by the pot/switch lock nuts. The big 343's plate is actually brass, but thin laminate ones that size would be ideal for my two big ex Leybold voltage pots. The smaller one would be an ideal size for other switches & the Vg pot. Back plates(On/Off etc) for the toggle switches can be sourced online, but I'm sure I've a couple spare somewhere.

Regards, David

[Pamphonica]

Yes, you can certainly do those sort of dials using MeterBasic. You can reverse print onto film then glue it onto aluminium or plastic or whatever print side down with spray contact adhesive. That way the text is protected. That's the way I did it for the Sussex front panel, and for a new dial for a KW2000A which was glued onto thin white plastic card.
- Jeremy

[David Simpson]

Thanks again Jeremy for your helpful advice. I'm just in the final process off connecting the new front panel & close to powering up. I think I'll just temp fit cut-outs made from thin white card & mark out the actual switch positions & pot values etc as neatly as possible with drawing pens. Due to the big pots & the meter taking up approx 2/3 of the panel(rear-wise), the switches & Vg pot had to be spread out as economically as possible, but this will mean that the radii of the card or laminate circular cut-outs will vary slightly.This'll give me a reasonable idea of what I'll need permantly using decent laminate or film as you suggest.
Isn't electronicing fun ?

Regards, David

[David Simpson]

Well, fingers crossed - have powered up this thing and everything seems to be working OK so far.
Static internal voltages for Va,Vs & Vg meet expectations of 330V,330V, & -33V max resp. The external connections can give give higher Va if required, and up to 60V for either Vg or Vh from a DC bench PSU.
Have just started Ia/Vg testing with a couple of 76 triodes. One was duff, but the other compared favourably between the LeyMarcAVO & my CT160. So will get out some graph paper & compare the curves.
Niggles - Although the Turner Ia & Is meters gave spot on 100mA fsd readings when I tested a 6U4 Diode, the 5mA ish readings for the 76 needed an AVO8 shoved in the Anode Link terminals to get accurate readings. So will fit a wee c/o switch to alter the multiplier/shunt arrangement to give an alternative fsd of 10mA, say.
My arrangement of switches & their sequence of opperation whilst reading the Vg meter & then the Ia meter at first seemed a bit clumsy compared to being used to rotating RV1 on a CT160 then just looking for a "Green Zone" reading on the meter. However, after a few tries, things got a lot simpler. And as I said some time ago - just the same as AVO asked us to do when testing transistors in a CT446. There is no fancy telephone dial type RV1 or fancy coloured meter zones. You just have to work out beta or alpha in your head , so to speak. Only takes a few seconds. The same with Ia/Vg.
I'm glad to see that others are also into homebrew valve testers. I'll echo FrankB's comments about old VCM's giving up their Heater transformers for constructing a PSU source. Guess that'll be the fate of the AVO VCM Mk(?) 1/2 I've mentioned in another T/Eq thread. Now that it's lost it's VBU to this L/M/A project.

Regards, David

[David Simpson]

Grotty weather has driven me inside. So reckon I can close the lid on my LeyMarcAvo project thread.
Further to my last posts(16th & 20th July) in Mike-repairman's thread "Valve testers, the best ?", in which I mentioned my L/M/A homebrew valve tester - - I guess I've come to the end of my AC signal testing set-up experiments. It has been working successfully as a pure DC valve tester(Static) since last year, but I was determined to examine it's potential for putting a valve in an amplification mode(Dynamic). And, its been successful also.
No - having given recent advice in other folk's threads on soak testing powerful valves, or prolonged testing of TV l/o/p valves - I shant be shoving 1KHz at full whack through 807's,TT22's,PL504's, etc. But, I expect that most "middle of the road" o/p valves can be tested & analysed signalwise, and their waveforms scrutinised as well as their mu & G calculated.
Quick-check scoping can eliminate poor performing valves from a batch of the same type. Then tabulations, formulae & graphs will determine very closely matched pairs for example.
Yes, simple matching can be done with any of the AVO VCM's & Testers, but you are fannying about with imaginary "DC" values, when in fact they are all unsmoothed 50Hz 10mS pulses.
So, no more banging on by me on self-built DC valve testers. On to pastures new, project-wise. Yes, some final touches to the paintwork, and I must make some permanant meter scaleplates & switch range plates.
Thanks to all the folk who contributed data from their VCM's & Testers for my L/M/A - EL37 , and my L/M/A v Sussex graphing Ia/Vg projects. I'll try and post copies of the results this wintertime.(Should've done them last year, my apologies).
Fed up of seeing the purchase price of AVO VCM's & Testers rocketing to sky-high levels - - thanks to speculative audio-phools & mercenary internet wheeler-dealers ? Then build your own !
I've copied an email to a close electronics pal, which has some details on testing for "G".
Hats off to "Woodchips" and a small handfull of builders of homebrew DC valve testers. Great projects.
All folk need to do is look at AVO's diagram for CV455/491 DC Standardizing Circuit which is in most civilian & military VCM manual versions, and let your mind expand the concept.

Regards, David

[Dan Payne]

Great project Dave, I like the recycled items. I picked up an old radio cabinet at a surplus shop last winter, had planned to make a small retro guitar amp. I think it is really destined for something else now!

Cheers, Dan