[Hallicrafters] SX-101A Motorboating.

[Waldo Magnuson]

Mike Langston wrote:
    I've heard the term "motor-boating" used before but I'm not sure what
circuit is susceptible to it or what it sounds like. The reason I
mention it is that with a steady carrier, it sounds like an outboard
motor idling.

    Mike, quoting from Marcus and Levy "Practical Radio Servicing": "The 
most common cause for a complaint of hum, squeal, or motorboating is an 
open filter capacitor in the power supply. -- With such complaints in a 
transformer type power supply, prepare a test capacitor of about 40 
mfd, rated at 400 volts. -- connect the negative lead of your test 
capacitor to the common negative terminal of the filter and the 
positive lead of the test capacitor to each positive terminal and when 
the best capacitor bridges the open unit, the hum, squeal or 
motorboating will stop or diminish."
    There are four other references to motorboating in the book on where 
to look for the trouble.  Its a fairly good book for beginners or for 
review for those of us who have forgotten.  If you can't find a copy I 
have an extra copy for $10 plus postage.

73,  Skip  W7WGM