guitar speaker / was Re: Tube challenge!

Paul Maddox Paul.Maddox at unilever.com
Fri Nov 26 13:35:59 CET 1999


MC,

  The problem with Transformers with open secondarys mainly
comes from the effective resistance that is presented to the 
primary, you effectivly get a massive standing wave problem and
a tonne of relfections and if its too bad, say good by to the
thing driving the primary. (wow look ma, I used my transmission
line/transformer theory I leant at college!!!)

  Paul

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-----Original Message-----
From:	Martin Czech [SMTP:martin.czech at intermetall.de]
Sent:	Thursday, November 25, 1999 12:57 PM
To:	cstoel at stack.nl; synth-diy at mailhost.bpa.nl; Juergen.Haible at nbgm.siemens.de
Subject:	RE: guitar speaker / was Re: Tube challenge!

:::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 think the transformer without load makes a resonator (winding
inductance and capacitance). Thus the isolation of the windings
can be dammaged due to very high voltages. A resistive load
will damp this completely.

AFAIK it is only dangerous to run without any resistive load,
or too high resistance value. The order of magnitude is important,
there is no exact value of resistance.

I once killed an old mono record player (Dual) with this,
the output transformer made nice sparks without the load,
then ... holy smoke ...


m.c.





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