Re: Super Reverb Question, Take 2

[The Bernadettes <mdestefano@xxxxxxxx>]

IronMan Mike Curtis wrote:

> Hi Chris;
>
> Just curious as an electrical engineer - what potential problem would there
> be with pulling one tube of a push pull pair?

With one tube pulled less current is drawn from the power supply.  This causes
the voltages and current to the remaining tubes to then jump up, especially the
remaining power tube.  With the remaining power tube now pulling more current
and recieving higher voltages, the bias to that tube is now way off.  Especially
in a SF Super Reverb which has pretty high plate voltages and a high current
power transformer, the remaining power tube is probably dissipating way more
wattage/heat than it's designed to, especially since it's now running class A.
Result, a possible blown tube.  Also the output transformer may not be up to all
that extra current running through just one side.  You can do it but have to be
aware of these considerations.  Rebiasing the remaining power tube is a must
(remember to use class A calculations, not A-B push pull), also probably using a
less efficient rectifier to reduce power supply voltages would be a good idea.

> I know a few guys that pull half of the push pull amp to get a rather
> peculiar type of distortion.  I also played through an old Silvertone bass
> amp with one half of the power amp blown (output transformer) for a number
> of years, with no pyrotechnics.

Maybe the previous owner tried running a single power tube and blew one side of
the output transformer! :-)

Don D.

>
>
> Of course a Silvertone isn't a Super ;-)