Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: trevorpowell on April 15, 2021, 12:07:21 pm
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Hey Everyone,
I just took my first crack at building an amp by following the Pro Jr build/conversion. I finished it up last night, but the fuse blew on the first power up just a second or two after flipping the power switch (no tubes in at the time).
Is there an immediate jumping off point for troubleshooting? Or am I looking at a laundry list of potential issues?
Thanks!
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Welcome!
Build a lamp-limiter!!
Disconnect parts of the power wiring in some logical order until the short is gone.
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Welcome!
Build a lamp-limiter!!
Disconnect parts of the power wiring in some logical order until the short is gone.
I'll give that a shot, thanks!!
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Well, before building a lamp-limiter I was able to track down some problem areas where components were touching the chassis beneath the board (rookie mistake not trimming those up properly). After correcting those, I tossed in the original fuse and the amp fired right up. The amp stayed on plenty long enough to check biasing, add in tubes (which lit up - the 12ax7's dimly albeit), and try to get sound.
However, I was only getting a very faint hum out of the speaker regardless of where the volume knob was set. I turned the amp off to double check components, connections, etc. then it immediately blew the fuse the next time I turned it on.
Obviously there is another undiscovered short, but are there specifics I should be looking at to resolve the no sound issue? Prior to the rebuild I had some bizarre issues with sound, so I'm wondering if I'm looking at some sort of transformer issue - again I'm awful green behind the ears, so it's all a mystery to me.
Thanks!
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follow this
https://robrobinette.com/Tube_Amp_Startup.htm