Road King 1 tube looks like plasma globe, lightning

[jmp22684]

Welp... this is turning into a journey. I ordered some tubes from Eurotubes.

Order details:

1 Mesa Boogie Road King Series I Custom Re $0.00
King Custom)
CONFIGURATION
Custom Kit: Custom Kit Included
Power-Tubes: 5881 Matched Quad $80.00
Power-Tubes: EL34II Matched Pair $36.00
V1: ECC83 MG Gold Pin $22.00
V2: ECC83 MG Standard $12.50
V3: ECC83 MG Standard $12.50
V4: ECC83 MG Standard $12.50
V5: ECC83 MG Gold Pin with Balanced Trio $24.50

Ran them for about a week without a problem, then out of the blue the amp started making pretty bad popping and crackling noises.

So I pulling the chassis dabbed a little rubbing alcohol on a could old tubes and slid them in and out of the sockets a few times hoping that would help clean them up. Waited a bit for any extra alcohol to dry up, and then I retentioned all the sockets. Long tedious work.

Kicked her back on and noticed the same noise.

Wiggled around the preamp tubes to see if that would have any effect, nothing.

Thought I would see if I could isolate it to a power tube and started switching the progressive linkage. At this point one of the tubes lit up like a lightning storm was going off inside. I immediately shut down the amp.

I popped the old tubes back in, REALLY old tubes, and the noise and such was gone. I haven't had a chance to run it for a while like this yet. I'll do that today.

I just wanted to poke around for ideas from the community.

Thanks!

 

[IronSean]

You might have just got a dud in that power tube. They're still fairly delicate and finicky things. Just because they tested well at the factory/store doesn't mean during shipment a part of the power tube shifted and started shorting.

I'd contact the store you bought them from, let them know one was a dud, and see if they'll send you a replacement.

 

[jmp22684]

That's what Eurotubes said as well. They sent me another el34ii.

Ran daily for about a week.

Last night... snap, crackle, pop, boom... again....

Popped a fuse.

I don't know what's going on here. I haven't had a problem yet with the stock tubes; though, I dont think I've run them as long as I have the new JJ's. They are pretty old, the guy I bought it from said they were the original tubes.

I know it's a fixed bias amp, but am thinking about popping my probe on, and if I can get her to fire up long enough to get a reading see what these things are biased at. I'll do the same with the stock tubes.

This kinda bites. I feel like I just wasted $200 in tubes.

 

[jmp22684]

Got her to run for a bit with the probe on. She climbed to 60 and started to pop, managed to get to the power before it blew the fuse.

Popped the original el34s in. Bias held steady at 28.3.

Though the original tubes are a bit noisy.

 

[domct203]

Sounds like its the JJ tubes giving you the problem.

Did you throw the bias probe on all 4 output tubes? Make sure that all four are showing bias current. I had a power tube blow in my Roadster once, replaced the fuse, and threw my old set back in. I thought all was good, but after a week or so I felt the amp didn't feel right. I put my bias probe on the amp and found out one of the positions was dead, no bias current. I pulled the chassis to find a blown screen grid resistor on that tube position.

Had the resistor changed and the amp has been fine ever since.

Dom

 

[jmp22684]

Haven't had a chance to pop the probe on every socket yet.

I did pull the chassis expecting to see something.

Everything is as clean as can be. No burning or scorching around any of the resistors or sockets. All caps look nice and happy. Thing looks like it came off the factory floor yesterday in there.

I'm going to order a set of mesa tubes. I'll send all the tubes I have back to JJ, tell them I don't have any use for them and hopefully get some sort of a refund. Outside of that... these things are popping like crazy and they're the only tubes giving me grief. So ... if I get something back, cool... if not. Whatever. Cut my losses. I'm spending more time on this than playing at the moment. Time to worry about something else when it's obvious.

Mesa tubes = happy amp
JJ tubes = blown up amp

Not going to keep stressing a costly amplifier.

 

[jmp22684]

So checked the bias on both el34 sockets. The same.... though today a different reading. Both sockets, swapping tubes, 20~21.

Now.... when I selected the rectifier instead of diodes... 10~11?

With diode selected and triode selected... 40.

 

[bandit2013]

I personally have had no luck with JJ tubes. Had a set of 6CA7, they sounded awesome but had one with intermittent failure after the tube warmed up it would cut out. Problem followed the tube when I swapped its position with the other tube in the inner sockets. Shortly there after I went back to stock tubes and then I lost two screen resistors. Seemed to be the two sockets I had the one bad tube installed in (original position and then when I swapped places). Perhaps it was coincidental or not. I did try the other tubes that were in the outer positions of the amp in my Mark IV (replaced the EL34 I was using at the time, worked for another week then they burned up with a cool arcing jumping around the pins and metal ribbon connections. Did not damage the amp but the tubes were toast. First and last experience I will use JJ power tubes for me. Preamp tubes are great and never had issues with those (Mesa branded or JJ branded).