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View Full Version : Help - Blowing Fuses!


Rick1114
08-22-2008, 04:24 PM
I have a 1957 GA-5 I recently aquired. Of course I been experimenting with tubes and such for it and last night it started sounding a little funny and then wham - it just died. I smelled the scent of burnt components, although no actual smoke or anything.

To make a long story short I replaced all the tubes and the the amp still blows the fuses a second or two after power up. I opened it up & It looks like the amp had a cap job at some point because I saw those shiny blue & white electrolytics in there(actually they were pretty old looking too, but not "vintage"), but noticed the big 'ol 20uf cap said "mallory" on it - that can't be good. Nothing looks "burnt up" though, although I'm going in for a closer look later - it was pretty dark at the time.

Can anyone tell what the next troubleshooting step is? If it's the tranny I'll bite the bullet and go to a tech, but if it's not, this amp is so so simple, I might try this one myself. But I'd like to determine that part first before making a decision.

Thanks,

Rick

skipm45
08-22-2008, 05:13 PM
Hey Rick,
remove all the tubes and connect a light bulb current limiter in series with the power cord.
http://i246.photobucket.com/albums/gg106/skipm45/VVR/Lightbulb_Limiter.jpg

Power the amp on. The bulb should initially be bright and then go dim. If it stays bright ..Short circuit!

If it stays bright, disconnect one power supply stage at a time until the offending stage is isolated.

If all stages are disconnected and the short is still present, it's the PT or a bad switch / pilot light.

HTH

Skip
www.skipzcircuits.com (http://www.skipzcircuits.com)

Rick1114
08-22-2008, 05:47 PM
Thanks for the advice skipm45 - I've read about those in Gerald Webers's book as well. Unfortunately, I don't have a light bulb current limiter to work with. I have a decent multimeter though. Anyway here are some pics I just took. Nothing looks overtly cooked and my suspicion is the burning small came from one of the transformers getting too hot - doesn't mean it's not some other components fault though yet I guess?

Here are some pics - let me know if anyone has any ideas!

Thanks,

Rick

http://i6.photobucket.com/albums/y235/Rick1114/AMp002.jpg

http://i6.photobucket.com/albums/y235/Rick1114/AMp018.jpg