SB-301 PS Filter Cap

[Mike]

I recently completely recapped an SB-300 receiver. Having the same problem
of locating a triple canned electrolytic capacitors, I simply did what Glen
Zook said, or something similiar but different.

There's not much room at the rear of the receiver to place the capacitors
near the original can. Therefore, I opted to move the electrolytic to the
front of the chassis, directly under the LMO. My initial thought was the
wiring that now ran along the bottom of the chassis and under the LMO could
possibly produce AC hum into the LMO and adjacent circuitry. However, after
temporarily installing the capacitors and resistors plus wiring at that new
location, I found no discerable hum was noticed.

The wiring that leads to the new capacitors from the rear of the receiver,
was twisted to further reduce an AC being radiated by the power supply
wiring. Furthermore, I used cable ties, small ones, to keep the wiring
tightly together and ran the wiring away from any adjacent circuitry.
This has worked very well and the hum that was present before capacitor
replacment has not vanished and the receiver works great. I did not have to
drill any additional holes since I used the hardware that holds the LMO to
the chassis. I further checked the receiver mixer and IF inputs with an
O'Scope and there was no AC showing on either of the inputs nor at any
other place in the receiver chain.

Another method would be to shield the wiring leading from the capacitors to
the rear of the receiver, grounding both ends of the shield. This can be
done using RG-8 coax braid, removing the inner conductor and running the
wiring inside the shield, grounding both ends of the shield to a ground
terminal.

73's,

Mike
W5RKL
w5rkl at yahoo.com

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