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| | |-+  jtm50 blowing fuses		 « previous next »
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Author Topic: jtm50 blowing fuses  (Read 6376 times)
72fetter
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« on: January 21, 2009, 09:04:54 PM »
alright so here be the issue.
my jtm50 has started blowing output fuses. In the tests...the v4 power tube starts glowing really hot and then the fuse blows.

what the hell do i do?
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wyatt
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« Reply #1 on: January 22, 2009, 03:14:43 AM »
Constantly blowing fuses is a common sign of a bad power tube.  It would seem the other symptom points this way as well. 

If you have a backup set of tubes, this would be a good time to test them out.
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72fetter
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« Reply #2 on: January 22, 2009, 04:47:52 PM »
if i switch out the tubes and it still does its thing...do i got a bad output trannie? Undecided
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wyatt
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« Reply #3 on: January 22, 2009, 06:30:06 PM »
I would highly doubt it's the OT.

If it still does it after swapping tubes, then I would have a tech look at it.  It would probably be something as simple as a bad resistor at the power tube that's arcing. 
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cmoore
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« Reply #4 on: January 25, 2009, 03:06:15 AM »
Did you try a new/different rectifier tube?  When you put in the new tubes did V4 still red plate?  Have you checked the bias, maybe a bad plate resistor?  Those are a couple things to check.
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Roe
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« Reply #5 on: January 26, 2009, 04:12:53 PM »
retube, install 1k screen resistors on v4-5 pin 4 and 6. install 5k6 resistors on pin 5 on v4-5
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72fetter
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« Reply #6 on: January 27, 2009, 07:36:55 PM »
I converted the rectifier to a solid state silicon diode but it did the same thing. I just got back in town and will try the new tubes at practice and I will see if this resolves the issue.
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