Golborne quiz

[Skywave]

Yes, Lawrence: I think we can be quite sure that H.V. R.F. current measurement is involved here: and R.F. at VHF, probably, too, looking at those two single-turn coils. The question is . . . . for what application?

Al. / Nov. 04, 2013 //

[Refugee]

the capacitor suggests that it is for some kind of pulse measurement but not high enough for radar.

[pwdrive]

I haven't a clue yet Al, the two loops just look like two shorted turns from the photo's, if so how would you induce a primary mag field if it was for RF and how would you convert such to DC for the meter, I'm assuming it's a DC moving coil meter, the diodes look like protection diodes.
It's difficult to see what's connected to what internally.
The brass socket thing intrigues me, quite a large diameter.
I shall await another clue.


Lawrence.

[Keithstv]

Well here's the schematic, very simple. I think you're on the point of getting it.

If it's not guessed by tomorrow I'll post one more clue.

Keith

PS it's a 1mA meter

[pwdrive]

From that can I take it that the socket is the input and the red cable is the output?

Lawrence.

[Refugee]

Would it be for checking for DC on an RF feed?

[Skywave]

Hmm. Well one thing is for sure: that 0.15 µF 250-v. by-pass capacitor rules out its possible use for doing anything meaningful at H.F. and up - so, just like a Hunts capacitor, 'pop' go my theories! The two diodes are for protection of the meter and the entire config. strongly suggests it is a current measuring device and that, with the thick cable, (which I note is red in colour) strongly suggests HV / EHT use. Conclusion: it is an EHT current milli-ammeter for TV CRT use. That 'fits in' with the meter FSD. Although why the two rings are included, I have no idea: I can only assume that they are there to provide a very low value of capacitance. And if so, why?
Having said all that, I'm really an R.F. man, (which kinda explains my original ideas) and am not a vintage T.V. enthusiast - which, as we know, Keith is.

Al. / Nov. 4, 2013 //

[Keithstv]

Well between them Lawrence and Al have it. If I told you it came from the company I work for in the most recent clear out and that the company is in the consumer electronics field (that was to have been the next clue) and at one point designed TVs. The one thing I didn't show was the connector on the end of the red cable - a connector for the EHT connection to a CRT. That would have been a bit of a giveaway.

So it's a meter for measuring the EHT current of a CRT. Well insulated to cope with 25kV or more and the 2mA FSD allows it to be used with colour CRTs. The socket is to accept the EHT connector of the TV with the EHT cable/connector connecting to the final anode of the CRT. The two loops are across the 68ohm resistor, I assume to act as a spark gap if the resistor fails.

So Lawrence and Al have the satisfaction of deducing the correct answer.

Well done

Keith

[pwdrive]

I was thinking along the lines of a eht/beam current meter a while back (honest) as I figured the input socket would take the claw plug on a eht cap from a tripler etc, it was the two copper rings I wasn't too sure about, originally I was thinking along the lines of equipotential electric field/anti corona but your description sounds more likely and simple.

Lawrence.

[Skywave]

The one thing I didn't show was . . . .
Keith

Exactly: I've learnt a valuable lesson here: information comes in two types: what you see - and what you don't see. The thought of "Err, wait a minute . . . he's displayed quite a lot of 'info'., but he could (possibly) have shown a bit more. So what is missing? And why hasn't that 'whatever' been shown?" never crossed my mind. Reminds me of that famous quote by Donald Rumsfeld: "There are the things we know we know, there are things we know we don't know, . . . . ", etc. It's having the appreciation that the full picture is made up of those two parts which can really help solve brain-teasers, but that latter part is frequently overlooked. Some might sum it all up as lateral thinking.

Anyway, thank you Keith: I enjoyed the challenge.

Al. / Nov. 5, 2013 //