I had fixed (by fixed I noticed a loose lead not connected to the volume pot) a small 60s tube amp, but upon fixing it I wanted to add a fan bc it seemed real hot. No speaker load was connected, and I had the amp running so I could figure out exactly the DC voltage being output after rectification (I dropped it down for the fan). I fired it back up and my fan ran, but I had no output.
Where should I start looking for errors and could anyone guide me on how to troubleshoot without a schematic. I've been reading on tubes, but still haven't exactly pinned down their biasing techniques (FYI in case it matters).
Is it possible to send in a constant signal (music from my computer) and trace it with leads connected to a boombox? I figure this way I can check the signal at every stage by hearing the music on my boombox. However, I've always done low level signal levels, and I figure this wouldn't work after the power stage, but what about after the only preamp stage?
Thanks.
plz im a noob
The danger of running a tube amp without a speaker load connected is that any sort of crackle or pop that gets amplified can cause enormous voltage spikes (>10KV) in the primary winding of the output transformer (due to the "flyback" action of the induction coil, much like the coil that develops the voltage to fire the spark plugs in your car.) The high voltage can perforate the insulation in the winding and short it out. Sometimes it'll also damage the output tube or socket.
If you're lucky, there's just a connection loose or something.
NEVER turn on a tube amp without a speaker or resistance load connected to the output. You can even short the output for a brief period. But leaving it open is very risky.
Check here for lots of good practical info on tube amps, including necessary safety precautions and troubleshooting: http://geofex.com/gtramps.htm
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