[DIY] OT: Tube amp disaster

[Don Tillman]

   Date: Wed, 16 Aug 2000 23:36:39 -0700 (PDT)
   From: Eric <synth at metasonix.com>

   >> 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. 

   If the amp is operated within its rated power, it will not
   be damaged. But this being a guitar amp, it was "abused".

Also, for the original poster, note that speaker impedance is not
constant; it varies all over the place with frequency.  Like over a
20-to-1 range or so.  It's actually pretty hard for the amp to tell
what impedance its running into.  So merely twice the impedance is
barely noticible.

Hey Eric, since we've got you here, and we're so far removed from the
topic anyway...  

I've noticed that most, or maybe all, tube guitar amps have a shorting
speaker connector so that the output transformer is shorted when there
is no speaker connected.  Can you tell us why this is?  I'm guessing
the effects of running a tube amp into a short are less harmful than
running into an open, but what are those effects?  One would think
that running into a short would be bad for the transformer.

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com