Gareth Magennis wrote in message
...

"N Cook" wrote in message
...
Ron(UK) wrote in message
...
N Cook wrote:
What happens if in process of owner stowing away or pulling out the
cables ,
foot switch etc from that convenient stowage box next the speaker, he
unknowingly pulls out the internal speaker plug.
Turns the amp on and tries turning up the wick to get some output.
With no speaker plug inserted the 8 ohm line from the o/p
transformer,
it is
grounded via the built in switch contact in the socket like an input
socket..

In that case very little will happen, the switched socket shorts out
the
output. However if the socket or speaker cable were open circuit then
there`s a good chance that the output tranny, valves or valve bases
would flash over.

How much does the matching transformer heat up with a direct short ?

What happens to the output valves, droppers etc I can't believe they are
self limiting ?

Years ago someone asked me to repair a Selmer valve amp that he'd
shorted
the speaker lead on and the primary side, high impdeance side, of the
o/p
transformer went o/c , but I never asked how long it was "running" like
that.



If I were you I would take some time and do some research about how valve
amplifiers work, you clearly have little idea. A short circuit is way
safer
than an open circuit. An open circuit feeds up to twice the HT voltage
back
into the output valves and can destroy them and lots of other stuff in an
instant. A short circuit will take much longer to do any real damage,
generally longer than a guitarist will spend playing his guitar with no
sound coming out of his speakers.

Get yourself a book on valve amplifiers and read it, you will be amazed
about how different the discipline is to solid state. It's never too late
to
learn.


Gareth.




Left to me I would have been perfectly happy leaving valve stuff back in the
fifties and earlier.
But these musicians and HiFi nuts will keep buying the stuff and then expect
people to repair mid 20th century technology that is unbelievably still
being made in the 21st C.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/