[HAM] Motorboating Not the Scanner!

[Scott Hawthorn]

A cautionary tale for you do-it-yourselfers:
That pesky "motorboating" sound is not always a vibrato problem, and I have 
the repair ticket to prove it. The first thing I did to this customer's 
A-100 was, while it was running and it was making the bad noise, I put my 
finger (inside a shop rag) on the flywheel and slowed it down. The noise 
did not slow down in frequency. I stopped the generator with the organ amp 
still running, and guess what? Motorboating! ("BUP-BUP-BUP-BUP.")

Snooping around inside the amp revealed that the high-voltage (B+) supply 
was fluctuating everywhere in the amp, at just the same speed as that 
noise. Fix? New filter caps. And let that be a lesson to you, as it was for me.

I hate to see people rebuilding scanners unnecessarily.