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Loading Tube Equipment for Audition/Comparison

Hello. I'm at one of those "accumulation points" where I have a bunch of equipment that I need to sort through and make some decisions on which to keep. I'd like to listen to amps and preamps back-to-back for the purpose of comparison, and I'd like to keep the equipment warm so I am swapping in a warmed up piece of gear during the comparison. I know some pieces of equipment can be unstable if they are not attached to some sort of load. Here are my general questions:

1) Is this true at all with preamps? I heard that tube preamps are typically stable whether loaded or not. In that case, I can keep both preamps on during the comparison. Just turning them off to swap out cabling.

2) What "side" do amps need to be loaded on - inputs or outputs? If a tube amp is connected to speakers (or some other load), does it alo need loading on its input - or is loading generally just needed for the output.

3) Is there a way to load the output of an amplifier with just a simple resistor? Can one get an 8 ohm resistor that handles high watts to provide the load. If so, what are the approprirate specs and where would one find such a resistor.

Thanks very much for good input. Peter
peter_s

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peter_s OP
1,348 posts
 
Thanks Ralph! A few specific followups:

1) Is it correct to say that if you DO have an amplifier loaded on the outputs, you don't have to worry about the inputs (you can have nothing on the jacks)? I'm also asking because I want to test for the source of hum on a tube amplifier.

2) One can easily make a shorting plug with a cheap RCA patch cord by cutting off the plugs and soldering the two wires together just above each plug, correct?

3) When checking the amplifier with a DVM set on AC voltage, do you do this with the speakers hooked up, so you don't endanger the amp if it is unstable without a load?

Thanks again. Peter
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