Warming-Up Amps w/o Inputs or Speakers Attached

Thanks; I like the idea of the dummy load resistors. Will definitely get a set of those.

FYI for anyone interested

I will not be drawn into some endless debate but Mr Rodman is wrong on most counts. Kijanki is correct. SS voltage sources don't care if they have a load or not.

Transformers do indeed store and release energy. That is why tube manufacturers caution you to always have a load connected. That is why many guitar amps have spike protection across the output tubes in case there is a voltage kickback from the inductance in the transformer.

Radio Shack has 20W 8 ohm resistors which are plenty for the purpose of protecting the output tubes unless you want to drive the amp with an input signal

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Herman,

Even when driving input 20W should be enough since average music power delivered to speakers is only a few percent of peak power.

Herman is correct in referring to inductive kickback that will occur in the output transformer of a tube amp in the absence of a load, and Rodman is correct in that damage is unlikely to occur in the absence of an input signal.

However, "unlikely" does not mean that the chances of damage in the absence of an input signal, when there is no load, are zero. Depending on the specific design it is conceivable that transient "signals" which the amp's circuitry may create internally at turn-on or turn-off will induce significant inductive kickback, which could cause damage cumulatively over time.

The most significant concern is not damage to tubes, but the possibility of damage to the transformer itself, due to the extremely high voltages that can be briefly produced when the current through an inductance changes abruptly.

Concerning SS amps, my understanding is also that in most or all cases the absence of a load will not be harmful.

Regards,
-- Al

What Al said. Most tubes are cheap compared to the price of good output transformers.