In article .com,
"terryS" in rec.radio.amateur.boatanchors
writ:

On Mar 4, 8:57 am, (Chris Suslowicz) wrote:
In article .com,

"terryS" wrote:
Came across a couple of those RF antenna current meters. Typical they
have a scale up to three of five amps. One is US and other is UK war
surplus.
AIUI the meter movement is driven by a small DC current produced from
the output of the thermocouple.
The thermocouple being heated by the RF current. Looks like the meter
itself is a one or five milliamp movement. Can anyone comment/advise?
Thanks.

The British ones (black bakelite cases) almost always have the thermocouple
built into the meter. They will usually be marked "Thermocouple" or "For
Radio Frequency Only" on the dial, and the resistance is usually shown
as well.

Be careful: the thermocouple is *VERY* delicate and will not stand up
to overload - the nichrome wire melts and it's useless thereafter.
(I've blown up an ex-Admiralty plug-in meter that was scaled 0-500mA
but had "requires x20 shunt" pencilled very faintly on the back.)

Chris.

Thanks Chris and others. Part of what I was wondering is a seemingly
'dud' RF ammeter. The movement might be OK and could be, say, 1 or 5
milliamp etc. fsd.

When I was a kid there were thermocouple ammeters ex T1154 etc on the
surplus market, usually at about 25% of the price of a normal surplus
meter. So, snip out the thermocouple and get a cheap voltmeter. Not
so, the meter relied on the low Z of the thermocouple for damping.
10 to 20 seconds of oscillation before a stable reading if used as a
voltmeter, about passable if used with a 20A shunt.

jww.