Dual Recto Problem: Loud POP sound and then nothing

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YellowJacket

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Hi Everyone,
I just sold my Rev F Blackface Dual Rectifier and it was running fine when it was shipped. Furthermore, I have a clean bill of health from a very capable tech as of a year ago. I wasn't having any problems before shipping the amp and I've really never had any issues at all beyond minor tube problems. I usually hear when something is amiss and switch it before there are any real problems. So, I got an email from the buyer today and I found it to be somewhat surprising. I offered advice to him but I am curious about what you guys think as well. Here is a copy of the email:

so I got the amp and am having some issues. Everything arrived ok and it looks great. However the rectifier tubes were loose, just rattling around in the head. So, I put them back in place and started up the up. The other tubes all lit up but not the rectifier tubes, there was no glow or warmth from them. It sounded like there was a lack of gain also but I can’t really judge this as I have nothing to compare to. After messing around a bit I heard a loud pop and the amp turned off. I think it blew a fuse because it won’t power on now. I don’t know too much about tube amp repair etc so I just wanted to see if you have any advice.

I told him to pull the amp from the chassis and inspect it. If there are no signs of problems with screen resistors, filter caps, or burn marks on the PCB, I told him to remove the rectifier tubes and run the amp on the silicon diodes. Replace the fuse.

Power it up and see if it makes noise.

I said to check v1 for the 'weak distortion' problem since it may just be that I abused my v1 preamp tube too much with OD pedals haha.

I also said to roll power tubes to see if the amp starts running better. I haven't really ran the Dual Recto hard in a decade but even if the amp was in good shape, the transport can induce vibration or impact which can damage the tubes.

I also advised he call Mesa. Just gotta check everything after trusting your amp to a courier haha.
 
So apparently, the amp was running on the silicon diode rectifiers but he flipped the switch to the tube recifiers at which point the fuse blew. Sounds to me like bad rectifier tubes. I have instructed him to replace the fuse, the rectifier tubes, and v1. I think the v1 may need to be replaced.
 
YellowJacket said:
So apparently, the amp was running on the silicon diode rectifiers but he flipped the switch to the tube recifiers at which point the fuse blew. Sounds to me like bad rectifier tubes. I have instructed him to replace the fuse, the rectifier tubes, and v1. I think the v1 may need to be replaced.
Interesting. The rectifier tubes are always in the circuit, regardless of the rectifier select switch, which simply brings in the silicon diodes in parallel to the rectifier tubes. If a rectifier tube(s) is 'bad' I would be inclined to believe the fuse would blow at power up regardless of the rectifier select switch. Did he flip the switch while the rectifier tubes were out?

Regardless, if the amp runs fine without the 5U4GB's, I would think you found the issue.

Dom
 
Update: buyer says that the rectifier tube had no Keypins on them so he installed them with the pins in the wrong place. This is why the fuse blew. He tried to install new rectifier tubes and the Keypins broke off of these new tubes.

Rectifier tubes were loose and rattling around in the head with no Keypins when the amp arrived.

I told him that the rectifier tubes were installed before the amp shipped and I am now wondering if there was an impact during shipping that broke the Keypins and knocked the rectifier tubes out of the sockets. Are the Keypins still in the rectifier tube sockets?
 
I'll bet the keypins are still in the holes and he broke off the keypins on his new tubes trying to force them in.

Have him remove the chassis so that he can get a better look at what's going on
 
cyber104 said:
I'll bet the keypins are still in the holes and he broke off the keypins on his new tubes trying to force them in.

Have him remove the chassis so that he can get a better look at what's going on

That is precisely what had happened and what I suspected as well. He had a tech look at it and everything else survived shipping. It was just tube problems.

After the tech visit and the Keypin extraction, the amp was humming really loudly so I explained how to test tubes. The guy swapped out v2 and a duet of power tubes and the beast roared to life.

Case closed.
 
Yep, my first thought was "bad rectifier tube". I can't count the times I've had a rectifier tube show up busted, separated from the base, etc. I bet I've had to toss out at least 8-10 over the years that were knocked out in shipping. Glad it's resolved!
 

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