"N_Cook" wrote in message
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Arfa Daily wrote in message
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"N_Cook" wrote in message
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Arfa Daily wrote in message
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"N_Cook" wrote in message
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Arfa Daily wrote in message
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"N_Cook" wrote in message
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I have one in front of me labelled
UTM 210-9 25435,3 watt probably Russian and can find no info
Like the standard pillar white/grey ceramic resistors but instead
of
the
wire returning down the flute of the ceramic there is a sprung
join
set
in
the flute with bismuth solder or something. Anyone know a generic
name
for
this type of thermal cut out resistor or a maker name ?
Other than the opening temperature must be greater than the
sustained
power
rating temp of the resistor and lower than standard solder,
anyone
know
what
sort of safety cut out temperature?



Back in the day when I was a TV engineer, they were very common,
and
known
as 'spring-off resistors'. Often used to be used in the feed to the
HOP
stage, and would spring open when the HOP valve failed. They were
usually
re-soldered with what we knew just as 'high melting point solder'.
I've
no
idea what actual temperature the stuff was, just that it was issued
to
us,
a
few feet at a time, for re-soldering these devices. The Adcola
irons
that
we
used (about 50 watts, as I recall ??) struggled a bit with it, but
were
ultimately capable of making the joint quite nicely.

Arfa


Are you saying it was somehow solder that needed a lot of heat
rather
than
a
lot of temperature?



Dunno really. No. I think I mean that it needed a lot of temperature.
The
Adcola, with its solid copper bit, certainly produced enough heat at
the
tip to handle a small job like resoldering that spring, but it did
have
a
little difficulty taking the solder to a 'full flow' consistency, so
probably didn't have quite the temperature required. Remember that
this
was
nearly 40 years ago, when a TV engineer's soldering iron was little
more
than an electric poker ...

The solder was just designated "HMP" for high melting point, and as I
recall, was a little greyer looking on the reel than 'standard'
solder.

Arfa



So a more sophisticated version of the aluminium foil and nail for a
fuse
replacement ?



No, I would say not. I worked for Rediffusion, and they were one of the
best
'technical' rental companies in the business. Their training and
attention
to detail, was second to none, and they used these resistors in their own
TV
set designs, so if that's what they said was the right way to handle
remaking one of these devices after it had sprung off, then you can be
pretty sure that it was right. There was never any question of the
resistor
having to be replaced because it had sprung open ...

Arfa


I must be missing something here , what is the point of the spring off
disconnect?



It opens the resistor, and removes power from the overload condition that
it's there to protect against ...

Arfa