Boat Anchor Grounds
I purchased a restored Heathkit HW-101 & HP-23C Power supply this year. I subsequently purchased an old Astatic hi-impedance dynamic microphone for SSB operation. Well, consistently I received reports of an "ac-hum" in my audio. I decided to rebuild the HP-23C power supply using a kit from K8GNZ who owns "Old Heathkit Parts". The rebuild/conversion up-grades the HP-23C with new heavier duty capacitors, resistors & diodes. The kit is well documented & is an easy & fun conversion to make. The HP-23C is now known as an HP-23D.
I also examined the grounding on the HW-101 which I determined to have suffered from the ravages of "old age"! The HW-101 has several printed circuit boards in which the ground circuit of each relies on mechanical fasteners (screws, star-washers & nuts) to "transmit" the ground throughout the rig. Old age has caused "floating" grounds. So, instead of replacing all the fasteners I simply ran a ground strap from each board to the frame of the rig and then cleaned & re-tightened the fasteners to which the various aluminum frame components are attached.
I then inspected & tightened the female microphone connector on the HW-101, and re-installed the male connector on the microphone.
Once completed, my SSB signal from the HW-101 has gotten excellent reports from fellow hams. I am well pleased with the outcome.
The moral of this story is: when refurbishing, modifying and or upgrading an old boat-anchor be carefully to inspect all ground connections; especially if the rig uses printed circuit boards. Even if it does not use PC boards, inspect all ground connections to ensure there are no bad solder joints, corrosion problems or loose connectors.
Boat anchor rigs are so much fun to refurbish, maintain & operate. We are maintaining and operating an important part of the history of Amateur radio.
In addition, we learn so very much from working on these rigs.
Best 73s - Ken
I "fix" at least 90 percent of the "screwball" problems in "boat anchor" equipment that I work on for others simply by tightening all of the machine screws and nuts that go through the chassis. In most equipment all of the grounds are made through these connectors.
If you tighten all of these connectors it really is not necessary to add ground straps which can, in certain circumstances, cause problems, especially on the higher frequencies. Basically, tightening the connectors lasts for at least 10 years and often more. However, over the years the connectors do work loose and/or build up corrosion.
Those poor chassis to pc board to chassis ground returns are a common problem in older Heathkit gear. The first time you try to figure out what is going on is an adventure! Congrats on getting her going!
I'd also note that it isn't uncommon to find rivets on terminal strips or saddle sockets ground returns also becoming noisy or high resistance. Directly soldering the tabs to the chassis is good practice in many cases.
Not only a problem in Heath equipment, poor grounding of circuit boards is very common in the newer equipment made by Kenwood, ICOM, and Yaesu. When all else fails, tighten the machine screws!
One should NEVER use a star washer against a PC board or anything soft or with low compression strength. It is the exactly wrong part to use.
The washers against a circuit board should be stainless, lightly coated with silicon dielectric grease, and the washer should be a spring type on the fastener side of the buffering washer. The board should be clean and shiny and the washer tightened down solidly.
Putting a star against a PC board is asking for problems.