I have a Mark III Combo w/ 6l6/EL34s. One of the EL34s will glow and the amp starts humming. Once I turn it to standby and back on it goes away. Its happened twice now in the last couple of weeks. Could it be just the power tube going bad or something else?
Glowing Power Tube & Hum
- Thread starter Goldtop
- Start date
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JOEY B.
Well-known member
Do you mean the orange glow of death? Shut'er down. Get a new set of outer tubes and give it a whirl. 
tony777
Well-known member
Goldtop said:
ABSOLUTELY!
That's the glow of death, replace them as quick as you can.
I would replace all four power tubes, but you NEED to replace both EL34's since they should be matched.
Before you replace the tubes you should pull the chassis and check the resistors on the power tube sockets . I found one burnt after the symptoms you described , called boogie and they shipped to me within days no charge .
Even replaced the tubes !
Even replaced the tubes !
Boogiebabies
Well-known member
Yeah, the longer they glow the harder they are on the components. It's not bad enought to pop the fuse, but every second it red plates you loose a weeks worth of tube life. In many cases the heater filament wire lays against another internal component and the tube freaks out.
Both EL-34's need to be changed. For the screen grids to blow, it's usually a violent tube failure. One that just red plates too fast to catch before the HT fuse can blow. the tube blows and takes the screen grid with it, then the fuse pops. Out of all of the MK series amps I have seen, oddly the only blown screen grid resistors were on the inner two sockets.
Both EL-34's need to be changed. For the screen grids to blow, it's usually a violent tube failure. One that just red plates too fast to catch before the HT fuse can blow. the tube blows and takes the screen grid with it, then the fuse pops. Out of all of the MK series amps I have seen, oddly the only blown screen grid resistors were on the inner two sockets.
6L6C
Well-known member
Probably the tubes as everyone has already stated but to make sure it is not anything else. Remove the EL34’s put in the 6L6’s run class A and see how they do. If your III is like a IV it will run with just 2 power tubes.
Then spring for a whole new set, treat yourself, live a little!
Then spring for a whole new set, treat yourself, live a little!
Thanks for the input guys! I when out to store and bought a set of Mesa Boogie EL34s. Popped them in and let the amp warm up a bit and there I was back with the same glowing tube again. Its only on one of the EL34s, the rest of the tubes are fine. I haven't had a chance to look inside yet, but plan on taking a peek tomorrow. Its done this about 2 times over the last week or so and I guessed it was probably time to change them. When it did this I could turn the amp to standby and flip it back on and it would be fine. Any more thoughts on what I should look for inside and how expensive of a repair would this be? Thanks.javascript:emoticon(':lol:')
