Don, John, ???does the “common ground return” mean any old connection to a “ground wire” scheme, or is it a specifically designed wiring scheme ?

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We sometimes forget that a chassis is often a high-current AC conductor, sometimes carrying several amps of tube heater current.? To Don’s comment, bonding to a single common chassis point often reduces or eliminates induced hum and buzz.?

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Someone mentioned using balanced heaters and a hum control balancing pot.? That’s excellent advice, but during production, manufacturers would typically wire the heater bus first, then overlay additional wiring like laced cable harnesses.? In many transceivers with dense wiring practices, it’s a real challenge to replace heater wiring with a twisted pair without disrupting components and existing wire runs, even if attempting an overlay.? I once tried to balance a Collins KWM-2A’s heather string but gave up: a point was reached where collateral damage started to occur owing to under-chassis packaging density.?

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On a positive note, I replaced the AF amps in my Drake R-4B and R-4C receivers.? The goal was to get hum/buzz down to zero with the AF control wide open.? With a screwdriver connected to the AF amp’s ground lead, I wiped across the chassis in search of the lowest hum/buzz level.? I found several points that met this criteria.? Once found, a hole was drilled in the chassis and a solder lug added for the ground connection. ?At these points, AC heater ground current is minimal, sometimes cancelling altogether.?

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Paul, W9AC

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