F-50 red plating brand new tubes

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seabeesw2

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Hey all. I'm new to this forum, and to the Mesa world in general.

I recently picked up an F-50 combo in a trade, and I absolutely love the sound of it. I brought it home, gave it the compulsory warm up time, and ran it hard for a good 45 minutes. It performed flawless, with the exception of a little hum from the reverb (which I've read is kinda normal).

I decided after playing it that I would go ahead and retube it, as it still had the stock Mesa 6l6GC STR 430s in it, which I was told have been out of use for about 8 years. I ordered a set of STR 440s, got them, popped them in, warmed them up for about 20 minutes, and went to town. About 15 minutes in, my low end dropped out completely. I checked the tubes (with the amp on) and the leftmost (not sure of position) of the pair was completely red. I immediately turned the amp off and contacted Mesa, who said they would ship a new set.

After the amp had cooled, I removed the new tubes and replaced the old. No issues. Let the amp sit idle for a good half hour with no issues. Played for another half hour with no issues. Tried the "bad" tubes again to see if I could recreate the problem, nothing.

Anyone ever have this happen with a new set of Mesa tubes, or have any suggestions?
 
seabeesw2 said:
Hey all. I'm new to this forum, and to the Mesa world in general.

I recently picked up an F-50 combo in a trade, and I absolutely love the sound of it. I brought it home, gave it the compulsory warm up time, and ran it hard for a good 45 minutes. It performed flawless, with the exception of a little hum from the reverb (which I've read is kinda normal).

I decided after playing it that I would go ahead and retube it, as it still had the stock Mesa 6l6GC STR 430s in it, which I was told have been out of use for about 8 years. I ordered a set of STR 440s, got them, popped them in, warmed them up for about 20 minutes, and went to town. About 15 minutes in, my low end dropped out completely. I checked the tubes (with the amp on) and the leftmost (not sure of position) of the pair was completely red. I immediately turned the amp off and contacted Mesa, who said they would ship a new set.

After the amp had cooled, I removed the new tubes and replaced the old. No issues. Let the amp sit idle for a good half hour with no issues. Played for another half hour with no issues. Tried the "bad" tubes again to see if I could recreate the problem, nothing.

Anyone ever have this happen with a new set of Mesa tubes, or have any suggestions?

A mild short in a tube is not a physical short, but rather due to electrons getting over-excited and crossing over, making an electrical short. It can be temporarily interrupted by switching the amp off, but can be a sign that the tube could soon fail. The other possibility is that the tube was not seated properly in the socket - or that there is some corrosion on the pins, etc. During our phone conversation you mentioned that the tube base had melted somewhat, and also maybe the tube socket. If this is the case, I would take caution using those tubes again, and wait for the replacement pair. Thanks!
 
The first thing I do to any used amp I buy is to completely clean it, including the tube sockets. Spray a little De-Ox-It on the pins of a tube and work that tube in/out of the socket a few times, wipe off the pins and repeat with the next socket. Let the whole thing dry for 10 minutes, re-install all the tubes and rock on!

I will also tighten up the contacts in the powertube sockets a little. I use a round toothpick. If you're new to tube amps I would leave that one to a tech. There are leathal voltages stored in the amp that could kill you, even when it is unplugged.

Just be sure the amp is unplugged, and that you do things gently.

Dom
 
Update: I got my second set of tubes from Mesa yesterday. Put them in, warmed them up, gave them a good 45 minutes of play time and they work just as they should. So I'm going to say, tentatively, problem solved. Thanks for the replies, and thanks Mesa for getting my replacement tubes out so quickly.
 

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