SW-717 Hum

[Gordon Brandly]

Thanks very much for that useful information. I'm in the middle of restoring
my SW-717, and this hum had me very puzzled since I had already tried the
capacitor fix and probed around with my 'scope. I was thinking of next
replacing that regulator, so now I won't bother -- thanks!  :-)


-----Original Message-----
From: Heathkit Owners and Collectors List
[mailto:HEATH at LISTSERV.TEMPE.GOV]On Behalf Of Harvey A. Kader
Sent: September 8, 2000 5:56 PM
To: HEATH at LISTSERV.TEMPE.GOV
Subject: SW-717 Hum


The SW-717 hum was always present on my unit from day one. A visit to a
Heathkit center resulted in the technician stringing FOUR voltage
regulator transistors in series(instead of the required two). That of
course did not work. So the unit was sent to Heathkit's Canadian head
office. They removed the four voltage regulator transistors, and
replaced them with the required two.

Now, I was back to where I started from. Then Heathkit sent a
replacement power supply electrolytic capacitor(can type). Replacement
with this component had no effect.

So, I thought it must just be the design. Probably needs more power
supply filtration, or better ground terminal connections. Some receivers
hum more than others. Just like some PLL receivers hiss alot, whereas
other hiss hardly at all. It all has to do with the design.

Harvey.

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