guitar speaker / was Re: Tube challenge!

patchell patchell at
Thu Nov 25 17:01:00 CET 1999

    When I used to service amps (both tubes and solid state), I used to use a 200
watt, 10 ohm resistor for a dummy load.  It had a variable tap on it so I could
set it to 8 ohms, by putting the tap in the middle and connecting the two ends I
could get 2.5 ohms (two 5 ohms connected in parrallel), etc.  On some of the
bigger amps I could really get that sucker hot.


DCMagnuson at wrote:

> In a message dated 11/25/99 7:28:18 AM Eastern Standard Time,
> Juergen.Haible at writes:
> > While it's well known that an *open* output can cause some damage on a tube
> >  power amplifier, I nver heard of a constant load resistor instead of a
> >  speaker
> >  would cause any problems. Is this really true ? And if so, why ?
> I was speaking to my service tech that retubed and biased my guitar amp, and
> he said he uses a bunch of high wattage power resistors as a dummy load while
> doing his repairs.  I'm not sure exactly what he uses, (whether or not he
> adds some inductive load or not), but he seems to have no problems doing
> this.
> Perhaps some types of output configurations cannot be run like this (Class A,
> etc), but my push-pull amp works fine in this case.
> Dave Magnuson
> Independent Music Site


More information about the Synth-diy mailing list