I just pulled this guy out of my pile of mystery, and I am wondering, is it any good for an amateur like me, and is there any chance of finding a crystal probe for it?its a 240 volt (plug in) with valve circuitry. Cool, I thought! I bought off eBay so long ago I forgot, it was untested and has no probe. I seem to remember it was in a lot with another old piece of kit, an “Avometer”

Maybe one could build a probe?

Photo uploaded.

Personally, having had dealings with old meters including an AVO 7X. I would be inspecting it to see what sort of capacitors it has, and the general condition. If it has any Electrolytic caps, they will have likely lost polarity, if its been stored for several years.

If it has Wax Paper caps they will likely leak. There is no place for leaking non polarised caps in a test instrument & I do not care where they are. I have a surplus Leader SG-11 Signal Generator, it had an axial oil filled type, I ended up tossing the lot, they seem to be as bad as Wax paper & actually may well be that.

So on that basis I would not go plugging it in: I wouldn't

Hi, I agree with Marc, your first job would be to replace all caps and any carbon resistors with new, plus checking any other resistors for value. And put a new power cable and plug!!! I have a similar meter and the proble is just a shielded cable 1:1 to a plastic prod.
I would remove the old style screw on connector and replace it with a BNC socket. Then you can make up a straight 1:1 probe cable or use a store bought cable. I know its then not original but usefull.
Anybody else agree?
Fred.

Yep Fred.

I used to use one of those at Cumberland in the late 60s. Nice to look at but quite irrelevant to use these days with cheap higher performance DVMs available.

AWA were using polyester caps when this model was made, in my experience. I'd dim-bulb it first and see how you go. Bring it up gently and it might be OK.

The ones we had at Cumberland had plastic insulated power cables and I note the power plug is not the suicide variety (all enclosed) so even that might be OK.

Ok, thanks for the input. I’m a sucker for old stuff, so I might put this back away for another day. I need to learn a bit more before I tackle that. I’m looking at a variac, to buy, it’s probably a bit premature, but it’s the right price..

The AWA 'VOLTOHMYST' seems to be a re-branding of the RCA 'Senior Volt Ohmyst', as they call it, (pic) which also has 'Acme' type probe connector.

I use its bigger brother the 'Master Volt Ohmyst' for measuring high voltage on electrostatic speakers which have very high source impedance and the Volt Ohmyst + its HV probe is about the only thing that has absolutely no loading to get an accurate reading.

When you find these, they have a 'D' cell battery holder in them and you might find a 40 year old battery in there! - better hope it's a "guaranteed-never-to-leak" Ray-O-Vac!

Photo uploaded to Post 7.

It would actually pay to check it for a battery. Found a "York" cycle (bias) battery in a Seyon. Its warranty expired in 1927. It was under voltage so needed replacing. I have seen the floor & walls damaged in one coffin set. The contents of the cells dissolve wood. I had to treat it to kill any residue.

I gave up on Duracell, the Mexican ones seem to be ok, but I had a run of Chinese ones, that didn't wait to go flat before leaking.

Probably a worthwhile exercise to restore it. It always pays to have an analogue meter, especially when you have valve equipment & old cars. Some DVM's have issues with RF and because of the way they analyse & display they can be hopeless with dirty DC.

DVM: Sample / Average / Display, the speed of the process is the "Sample Rate".

It is often cheaper to buy a "suicide cable" with the moulded plug on it. There are a thousands of homeless computer IEC cables out there: Cut the IEC plug off & use it.

I dug out another Senior Volt-Ohmyst which also had the associated probes (HV & AC-DC, but no RF probe found so far.)

It had corrosion migrating to outside of cast alloy back case, but upon opening was relieved to see it was from a previous cheap battery which someone neglected to treat, because its present battery is an ENERGISER brand which, though measuring only 0.2v, is not leaking!

The Ohms 'D' cell battery is held in with a spring clip and wires are soldered on for reliability when changing.

Power consumption is rated at 6 watts as it has a small 6.3v transformer plus direct-to-AC selenium and 10μF 200v electro for B+.

Resistors inside are precision/selected and there are ceramic caps, so no parts to change. There is an RCA 12AU7 & 6AL5.

Would be interested to know what brand of 12AU7 & 6AL5 are in the AWA and how they dropped the 240v for B+?

I eliminated the battery in my Voltohmyst via a simple rectifier arrangement off the filament supply.

I have the same meter 1A56074 with the standard 1R50675 probe.
I have the manual for the 2A56074, seems to be a very similar unit.
Can scan the manual and upload it.

Normf,

That would be handy if you could!

NewVista, I will open it up and have a look when I get a second. I need to check the battery thing anyway.
Murray

Normf,

That would be handy if you could!

NewVista, I will open it up and have a look when I get a second. I need to check the battery thing anyway.
Murray