[sdiy] Tube amp problem

[John L Marshall]

You might want a current limiting resistor in the plate circuit as well.
Personally, I don't like running all that DC current through a transformer.
The transformer has to be really big to avoid saturation. I would
capacitively couple the transformer and let the DC component warm a big
resistor and your room. It is terribly in efficient, I know. But class A is
always horribly inefficient. less than 16%? There must be a reason that
push-pull, class B amplifiers are more popular.

Take care,
John

Take
----- Original Message -----
From: René Schmitz <uzs159 at uni-bonn.de>
To: Justin Herrmann <herrmann at eecs.ku.edu>; <synth-diy at dropmix.xs4all.nl>
Sent: Friday, May 03, 2002 1:27 PM
Subject: Re: [sdiy] Tube amp problem


> Hi Justin!
>
> To me this sounds like you didn't connect any load to the amplifier.
> In that case the tubes can arc over from large inductive kick from
> the output transformer. That would explain the blue light and the
> buzzing sound.
>
> Cheers,
>  René
>
>
>
> At 14:36 03.05.02 -0500, Justin Herrmann wrote:
> >Hi, my senior design lab final project is to design a vacuum tube guitar
> >amplifier.  The output stage uses two EL34's.  The first time we
> >(our project group) powered it up, one of the tubes made a buzzing sound,
> >then it made some popping sounds and emitted flashes of blue light, at
> >which point we turned the power off.  We rechecked all the connections,
> >put in two new tubes (or valves), turned the amp on again, and one of the
> >tubes made a hissing sound, so we turned the amp off before anything
could
> >blow.  I really have no idea what could be causing this.  Does anyone
have
> >any suggestions?  You can see the schematics for all the parts of the
> >project at http://people.eecs.ku.edu/~herrmann/sdl/tubeamp.html
> >
> > -Thanks-
> > -Justin Herrmann-
> >
> >
> >
> --
> uzs159 at uni-bonn.de
> http://www.uni-bonn.de/~uzs159
>
>
>