[Jukebox-list] Fw: Question

[Ron Rich]

Hi All, 
I just had what I consider a very strange thing happen. I re-cap'ed a Seeburg MRA-5 amp and started to test it. I normally stick a light bulb in series, but this time I forgot. I did, however plug it into my amp meter, which is CB protected at 5 amps.
I flipped the switch on and it was drawing the normal 1/2 amp, until the 5U4 tube heated up--then it "pegged" my meter, and poped the CB on the meter.
I went into "duh" mode--looked at that thing for an error, tested the transformers, and could find NOTHING--I then re-tested all the tubes (including the 5U4, which was brand new). NOTHING--all good no shorts.
So, I took it for a ride to my friends house. He looked at it--did probably the same tests that I had done, except for testing the tubes. ( I went inside the house and talked with his wife, so as not to "influence" his thinking) He said that there was no reason it should not work. So, he applied power--blew the 2 Amp CB installed in his test rig.
It NEVER blew the 2a SB fuse in the amp--fuse is the "original" put in it at the factory.
He said "it's gotta be a bad 5U4"--He installed a new one and we had music!  
My question is--why didn't the amp fuse blow?  It's in the transformer primary for the 5U4 tube? I would have taken that bad tube home with me, to test it again for shorts, when warm in the tester-- except that it rolled off the table onto the floor--just broke the glass---
Any ideas ??
Ron Rich


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