OK, exactly why don't trannies (on valve amps) like it being run without a
load?

It's not like they are going to burst open, is it??

Also does quick 'hot-swapping' speakers while an amp's hurt it any? (Oi dun
a lot o' thaat in tha parrst.... ;-)

Keith G wrote:
OK, exactly why don't trannies (on valve amps) like it being run
without a load?

I think it has something to do with the xformer's secondary trying to drive
a very large impedance (ie, open circuit). I think this translates into
excessive current in the primary (but I could be wrong).


--
Wally
www.artbywally.com
www.wally.myby.co.uk

Keith G wrote:
OK, exactly why don't trannies (on valve amps) like it being run without a
load?

It's not like they are going to burst open, is it??

Also does quick 'hot-swapping' speakers while an amp's hurt it any? (Oi dun
a lot o' thaat in tha parrst.... ;-)



Well it starts with load lines and reflected loads and goes on from
there. how far back do you want to go ?

--
Nick

"Nick Gorham" wrote in message
...
Keith G wrote:
OK, exactly why don't trannies (on valve amps) like it being run without
a load?

It's not like they are going to burst open, is it??

Also does quick 'hot-swapping' speakers while an amp's hurt it any? (Oi
dun a lot o' thaat in tha parrst.... ;-)



Well it starts with load lines and reflected loads and goes on from there.
how far back do you want to go ?


Wot ho Nick, that wuz quick!!

OK, not too *deep* but more along the lines will it damage the amp if a
speaker swap is quite quick (while it's *on* - omitted that in the original
post)...???

Perhaps I should say will it damage the transformer?

"Wally" wrote
Keith G wrote:
OK, exactly why don't trannies (on valve amps) like it being run
without a load?

I think it has something to do with the xformer's secondary trying to drive
a very large impedance (ie, open circuit). I think this translates into
excessive current in the primary (but I could be wrong).

I'd have thought quite the reverse; usually, I'd have thought the
primary current would decrease when the load was removed from the
secondary.

Mind you, if there's feedback and so on happening round it all, goodness
only knows.



Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

"Keith G" wrote in message


OK, exactly why don't trannies (on valve amps) like it being run
without a load?

There is a possibility that the output transformer(s) will arc over
internally and be permanently damaged.

Fleetie wrote:
"Wally" wrote

Keith G wrote:

OK, exactly why don't trannies (on valve amps) like it being run
without a load?

I think it has something to do with the xformer's secondary trying to drive
a very large impedance (ie, open circuit). I think this translates into
excessive current in the primary (but I could be wrong).


I'd have thought quite the reverse; usually, I'd have thought the
primary current would decrease when the load was removed from the
secondary.

Yes, it will, without the reflected load the primary reverts to
effectivly choke loaded. But the secondary is still a inductor, and so
does what comes naturally to it.

Think about how ignition coils in cars work, its the rapid di/dt that
causes a high voltage.


Mind you, if there's feedback and so on happening round it all, goodness
only knows.


Its not a feedback issue, just inductors at play.

--
Nick

Keith G wrote:

OK, exactly why don't trannies (on valve amps) like it being run without a
load?

Because with no load on the secondary, the primary of the transformer just
behaves like a huge choke.


It's not like they are going to burst open, is it??

The current swing can cause huge 'back emfs' that can damage both output valves
and the transformer itself.


Also does quick 'hot-swapping' speakers while an amp's hurt it any? (Oi dun
a lot o' thaat in tha parrst.... ;-)

If there's any significant signal, the damage can occur.


Graham

On Thu, 04 Nov 2004 19:25:34 +0000, Keith G wrote:

OK, exactly why don't trannies (on valve amps) like it being run without a
load?

It's not like they are going to burst open, is it??

Also does quick 'hot-swapping' speakers while an amp's hurt it any? (Oi
dun a lot o' thaat in tha parrst.... ;-)

If you want to do some speaker swapping turn the volume right down
or, better, switch to standby (HT off) while you do it. That way the
output stage won't be driving into the open load and it will be ok.

Running a signal into an open load can do a few things:
1 - nothing (quite possible as some circuits put sufficient load on
anyway, or you may have insufficient signal to cause a problem).
2 - internal arcing in one or more valves - usually ok.
3 - insulation breakdown on one or more turns on the output transformer
primary. If this causes one or more shorted turns (quite possible) then
the tranny is usually dead. If it causes an open circuit then it is
definitely dead! It probably won't look damaged though.

--
Mick
(no M$ software on here... :-) )
Web: http://www.nascom.info

On Thu, 04 Nov 2004 20:50:43 GMT, "Fleetie"
wrote:

"Wally" wrote
Keith G wrote:
OK, exactly why don't trannies (on valve amps) like it being run
without a load?

I think it has something to do with the xformer's secondary trying to drive
a very large impedance (ie, open circuit). I think this translates into
excessive current in the primary (but I could be wrong).

I'd have thought quite the reverse; usually, I'd have thought the
primary current would decrease when the load was removed from the
secondary.

Mind you, if there's feedback and so on happening round it all, goodness
only knows.

Flippin' 'eck, I thought you guys were supposed to be the experts on
valve amps! What happens is that you have a situation similar to that
in a car ignition system. A transient hits the primary, it gets
transformed massively in the secondary, and the energy has to go
somewhere when the magnetic field collapses, so the secondary arcs
over, damaging the insulation and destroying the tranny in quick time.
--

Stewart Pinkerton | Music is Art - Audio is Engineering