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JackButler
10-27-2007, 02:11 PM
Other player in my band, JCM900 he retubed (with used cheapo tubes) about 6 months ago went dead last night. Sure enough one of the tubes was arcing like mad! It is the 100w model and has the bad tube warning indicator light thing on back. He pulled the bad tube and the partner to try and run just two tubes and the indicator light was still on and cranked there was a wee faint sound.

So, would something else have went bad besides tubes? I have some decent ones I am going to throw in it for him and bias, but I don't want to blow one of them if there might be something else happening or bad. He checked and said the fuses looked good, but I'll obviously check them before messing with it.
Thanks for any help or comments:)
PRNDL
10-29-2007, 08:36 AM
I'll check my Oija board.
TopBooster
10-29-2007, 09:29 AM
If a warning LED is on, that means the associated fuse is blown. Even if it looks OK, it's likely blown if the light is on...

Aside from that, you should be OK with putting new tubes in and rebiasing, although you might as well check the screen grid resistors while you're in there...make sure they're dropping evenly and aren't "charred" or "browned" in appearance.
TopBooster
10-29-2007, 09:49 AM
He pulled the bad tube and the partner to try and run just two tubes and the indicator light was still on and cranked there was a wee faint sound.

Was it the two outer tubes or the two inner tubes that were pulled? (He didn't pull one side, right?)

Also, did he set the amp to half of the cab impedance during this test?
Hipster Dofus
10-29-2007, 05:50 PM
Fuse inside?
JackButler
10-29-2007, 06:30 PM
Thanks guys. I a'm going to help him this weekend.
Appreciate the info
JackButler
10-29-2007, 08:39 PM
Got it.
Fuses are fried! I can't make out what they are.
Really small fuses, "T500250V" is all I can make out on them. I figured they would be slo blo, but guess they aren't?
TopBooster
10-30-2007, 09:18 AM
Yes, you're going to want a 500mA 250V Time Delay 5x20mm fuse (http://www.mouser.com/search/ProductDetail.aspx?R=BK%2fGDC-500MAvirtualkey50400000virtualkey504-GDC-500MA) for this position. Radioshack Slo-Blo would work...