[DIY] OT: Tube amp disaster

[René Schmitz]

At 13:36 15.08.00 +0100, Tony Allgood wrote:
>Hi all,
>
>Is it possible to destroy a tube amp by running it at the wrong output
>impedance? I have just got an amp that was run with a 8 ohm speaker in
>its four ohm output socket for about a week. Then it started to smell
>bad and started to oscillate. When I turned it on, after connecting the
>output correctly, it then started to smoke. I haven't turned it on
>again.

I doubt that the tubes are the cause, they don't smell or smoke.  
(Besides there are only two ways to damage them electrically: 
Overpowering until the plate turns red-glowing - the glass will 
melt and the vacuum "evades". Or burnout the heaters. )

Its most likely the output transformer. The too high impedance did not 
damp the transformer enough, so there may have been some arc overs, 
either between some turns of the transformer or at the tubes sockets.
In a class AB push-pull stage one tube cuts off completely, so that the 
inductance of the transformer can generate some high voltages. Like a 
flyback circuit.

Bye,
 René 

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159