2 power tubes glow?

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100watt

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I have a BE100 running into a Friedman 4x12 impedance switch set on 16ohms... the two power tubes to the left started glowing bright red and had a loud hum with almost no volume. I pulled one of the power tubes that was glowing put it so both the glowing tubes are on the outside of the 4. Turn the amp back on and everything is working great, tube are back to normal. Is this possible the EL34s are going bad or maybe something else? Tubes are original ARS EL34s and had the amp for about 1 year. Please help...any ideas what might have happen.
 
The bias readings I got from left to right 33.5 33.6 36.0 37.1 are these good readings for a BE100?
 
You should swap the 2nd and 4th tubes and rebias. They should be balanced pairs, inside pair and outside pair..
 
If I adjust the hottest tube at 37.1 down to 32mV and all the over tubes will fall under that, it would be good? my other tubes would be closer to 28 or 27mV all my tubes are the original tubes
 
That is correct. You should bias to the hottest tube.
 
Had a new set of matched tung sol put those in and was able to get 32mV across. I hope this helps with the 2 tubes that glowed bright red and had a loud hum coming from the speakers. It had happen twice but when I let the amp cool and restart the problem had gone away. Back to rockin. I have a few high end amps but this HB100 I use for everything to bedroom volume practicing to turning it up with the band. I love this amp!!!!! Thanks to Dave Friedman for turning these things lose on the world.
 
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