• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

I put a bad ouput tube in my amp, did I hurt it?

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I did a dumb thing...

I got a 6AS7 off of ebay, tested it and it only posted like 10 on a scale of 0-120. I wanted to see if I could hear anything out of it anyway so I put it in my Van Waarde design headphone amp flicked the power switch and plugged in my good headphones like an idiot.

I got a load hum out of the left channel and nothing out of the right.

I unplugged the headphone and checked the output with a meter just to make sure that I didn't send a stupid amount of DC to the phones, nope just 20 mV I think

It was at that time that I noticed some noise coming from the choke in the PSU. One side of it was hot to the touch and the other side was cold. I cut the power and pulled the tube.

I put the good tube back in and everything sounds normal but I only listened for 10 minutes so I don't think it had much time to warm up yet.

Do you guys think I hurt anything?
 
Here's something I've always wanted to know - how do you know when a choke is faulty? I hear of chokes becoming 'oversaturated', what happens then?

depends on the fault!

If the choke overheats or the back EMF is very high you can get shorted turns this means your power supply will become noisy due to lower henrys. (Hum). If you get a short to Gnd then the B+ will either blow a fuse or if no fuse then rectifier or HT winding on power Tx will fail.


Regards
M. Gregg
 
If a saturated choke sits around for a long time the magnetic field will diminish. It also drops a bit just about every time you power it up. So if you don't notice any hum, you got an almost free lesson.

Now you can place the same tube back on eBay and honestly say you tried it and did not like it!
 
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