You have one or more bad connections. In the SB and HW series of Heath transceivers the bandswitches have contacts on both sides of the switch wafers. The two sides are wedged together and the "connection" becomes intermittent with time. This causes the lower level and driver stages to "drop out" of resonance. The coils in the circuits are additive, in other words the 10 meter coils are first, then the 15 meter coils are added in series, and then 20 meters etc. This can be cured by applying a soldering iron and solder to the wedged connection. You have to remove the shields and it is difficult to get to the wafers. A good deal of heat is needed to make the solder flow. There are probably more bad connections and bad solder joints. Some kit rigs where not properly assembled and may never have worked correctly. You have to go back through and make sure that all the parts are correct (like resistors in the wrong place etc.) and are still good. It takes time and careful work to restore these rigs.
The situation where the voltage rises with key down (170 volts key up and 240 volts key down) means that the tube is being cut off. With no current flow the plate voltage rises.
It takes a lot more skill and effort to troubleshoot and repair old equipment than it would to build a kit from scratch.
Allen KA5N
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