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Standby without speaker


Magnus Ritland
Posted on Sunday, January 09, 2005 - 03:57 pm:   


I accidentally put my 65-amp on Standby without any speaker connected for about 10 seconds today.
It works OK, but I'm just wondering if this damaged the amp in any way?

I guess if I'd put it from Standby to On, I would really made some damage?

michael kaus
Posted on Sunday, January 09, 2005 - 05:31 pm:   

You didn't do anything. The B+ isn't going anywhere it can hurt anything. The only thing you had cooking were the heaters. Rock away! Mike.
Steve Kennedy (admin)
Username: admin

Registered: 03-2002
Posted on Saturday, January 15, 2005 - 09:32 pm:   

You probably wouldn't damage anything unless you tried to PLAY through the amp after taking it out of standby.

The amp circuits wouldn't know anything is amiss at the OUTPUT side of the transformer until some AC audio signal is generated and passed to the secondary of the transformer. When there is no speaker load, there is nowhere for the energy to go so it has the opportunity to arc-over internally in the windings inside the transformer. Also, the proper load impedance isn't "reflected" back to the output stage of the amp so you can fry output tubes in addition to the output transformer.

When you take the amp out of Standby, there is B+ voltage applied to the plates of the output tubes through the primary winding of the transformer. In this condition, the primary of the output transformer is simply a resistive voltage divider. It doesn't become a transformer (or a problem) until the output tubes are asked to produce big voltage swings into the transformer's Primary winding.