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Tube Amp #2 - Check That Speaker Connection!

Solid state amplifiers can be damaged by a speaker cable that is shorted or when too many speakers are hooked up. Solid state amplifiers are very forgiving when operated without a speaker connected; in this case, the output transistors simply don’t produce any current.

Tube amps are the opposite. A tube output transformer can be ruined permanently if the amp is played without the speaker hooked up. On the other hand, the output transformer in a tube amp can withstand heavy loads or short circuits for short durations.

The output transformer secondary must be under load in order to work within it’s design limits. Without a speaker load, voltage in the transformer can surge to tens of thousands of volts. In essence, an unloaded transformer secondary becomes a spark coil.

Tens of thousands of volts in the transformer secondary can burn through internal insulation, causing intermittent internal shorts. A damaged output transformer might exhibit poor sound, low power, with pops and clicks as voltage arcs across the damaged segments of wire. This condition is hard to diagnose and expensive to repair.

If you fire up your amp and hear no sound, stop playing immediately and check to be sure the speaker is hooked up. Once you’re sure the speaker is hooked up and there’s a little bit of amp hiss, then you can play while checking other things like master volumes, channel switching, hookup cables, pedal arrays, etc.

A high quality speaker cable in good condition is always a good idea. Worn and torn speaker cables should be replaced as a safety measure. If a solid connection to the speaker is lost during a blazing solo, not only have you lost the glory of the moment, you may have also lost a power transformer.