Bad whisker! A cautionary tale...

King Fan

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Years back, shortly after I built my Princeton Reverb, it developed an occasional loud snap, crackle, pop. Someone smart suggested I should blast out the chassis with compressed air -- I'd used some shielded cable and they mentioned that stray whiskers of shield (but also solder blobs, or chunks of wire strand, or...) could cause intermittent shorts and snaps. I opened it up, shook it out, dusted it upside down with canned air, and the problem went away.

Just last week I was looking for something else and came across this pic, taken shortly after the build when I added a PI grid stopper — *and* two runs of shielded cable to a raw pot. Hey, chief inspector, get out your magnifying glass. As Helen Hunt says in 'Twister': "We have debris...."

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Moral of the story -- housekeeping. A dry acid brush, canned air, compressed air, invert and shake, etc. A clean build is a quiet (and safe) build.
 
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sds1

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FWIW I got one of these along the way, many years ago, possibly a gift, it's been one of those invaluable tools I didn't know I needed and now can't live without. There are many like it but this one is mine:

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I do use it to blow out amp chassis after I work on them. Those little wire snippets/whiskers don't always shake out on their own.
 

King Fan

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Workflow too. Ideally I should do prep work (like building shielded leads with braided shields) well away from the chassis -- and take revision work out too. Drill shavings? ideally you never have to drill or enlarge a hole in the chassis once the build actually starts -- yeah, right. It doesn't hurt (and has lots of other advantages) to populate the chassis walls (pots, jacks, etc.) and do all power, non-board, off-board, or under-board wiring before you put in the board (which is good at hiding debris). A small magnetic screw-retriever tool is handy for dropped washers and so on, but of course a tiny chunk of cut copper isn't magnetic, so I try to needle-nose it out of there before it runs off to hide.
 

johnnylaw

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Initially, I thought your band was Bad Whisker.
Thanks for the thread though.
I’ve been salvaging and stockpiling tid bits for a build, when and if I ever retire.
Oh, and Princetons are brilliant amps too!
 

Mongo Park

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A timely thread for me. The present build I am working on had this same problem, a first for me. I did a B+ check and while I was getting all the voltages and writing them down I herd a spark sound. So I shut off the amp. On close inspection a piece of resistor wire as a cutoff that must have flown away when it cut it was stuck unders some components and was just close enough to conduct a spark to the chassis. So go figure. Something new to add to startup before sending electrons through the maze
 

Bill Moore

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I built a 5E3 last year that the sound was low/distorted on startup. Voltage checks showed a short, upon further inspection, found a "whisker" of solder had shorted a turret to the chassis. A bent piece of wire swept under the board cleared it, and it sounds great!
 

King Fan

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For sure, stuff that 'hangs out' under the board is the worst. Bad enough if it's just hiding there, but worse if it's a stalactite 'hanging down' from the board. I like the old backing board plus eyelet board sandwich for that reason, but even with eyelets (which I find less prone to wick in excess solder), I've gone to standoffs.

In fact, I'm debating just this week between ¼" and ½" standoffs. Ah, the old tingle; I feel a new thread coming on... :)
 

Digital Larry

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The only tube amp maintenance I ever did was on a Webcor 5W tabletop HiFi thing. Even after recapping and lots of DeOxit it would crackle starting a few minutes after warmup. Finally in frustration I busted out the original phenolic sockets to replace them with ceramic ones I'd purchased. The internal layers were all carbonized. Those must be the cheapest sockets possible; they are one step above cardboard.
 




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