1 new power tube red plating bias changed next day (HIGH!)

H

hammer jammer

New member
Anyone got any ideas, Bad power tube ? NEW matched Quad

Went to play it on second day after instal and the NEW power tube (1st outside power tube behind V1-Renegade Head) red plated when I turned on the amp making a loud howling...I turned it off immediatley and diagnosed the bias was way high (I had it set to 66/67 per specs the day I had installed and had checked periodically all night while playing it.)

after the redplate I reset the bias and it was fine for the rest of the night..

tonight third day after instal and it did it again, same tube same position red plated made a howling noise, I turned it off and reset the bias and its fine...

I decided to investigate further so I swapped the two outside power tubes around to see if it happens again on the same tube (figured a good sign its a bad tube) its cooling now, Im gonna let it cool off a fire it up and see if it changes or gets weird again.

BUT ? if its not and this happens again anybody have any ideas ?
 
Just a bad tube. Not unusual even though they are new. FYI, the bias control is adjusting the amp to the tubes, not the other way around. That bad tube was drawing too much current as it failed. You were sort of compensating for it by reducing the setting until the tube just failed completely. Also, even though a tube overheats, it can sometimes be the other one in the pair because the bad one is robbing bias voltage from the good one. Does that make sense?
 
Hey Thanks Bruce,makes sense I thought the same things after further reading, company I bought from is going to exchange them for me.
 
Just wondering after moving them around, I have them biased a little lower 64/65 on both sides and they seem to be running fine right now, should I still exchange them or is it possible that they settled in and will be ok ?

Or will it red plate again at a later date ?

just wondering what you would you do in a situation like this ? exchange the tubes or keep them ?
 
If they are offering to replace them, I would do that. The fact that they "nearly" failed once, I would expect it to happen again.
 
Yep Jennifer down at Amplified parts was very cool about it and replaced the quad with a new set and they sound killer, my Renegade is back in good order and sounding great, I am happy once again...

Gotta plug Amplified parts for being upstanding dealers and standing behind their products, I did everything right on handling, instal and bias of the tubes, just got a bad tube so kudos to those guys, I will buy again.
 
I had the same problem with mine. I changed the tubes, and everything was fine after that.
 
Most problems are simply replace a grid resistor or capacitor but wish I knew the symptoms .
Simple most times !
What is that amp doing !
 
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