KA7OEI did a repair on his amplifier. He documented the whole process on his blog:
Earlier this year I picked up a Heathkit HL2200 amplifier (the newer, “brown” version of the SB-220) at a local swap meet for a reasonable price. What made it particularly attractive was that it not only had a pair of new, graphic 3-500Z tubes in (Chinese-made, but RF-Parts Inc. tested/branded) but it also had a Peter Dahl “Hypersil” tm power transformer rather than the “just-adequate” original Heathkit transformer and an already-installed low-voltage keying circuit which meant that rather than nearly 100 volts on the keying line to operate relays there was only a few milliamps at a few volts.
More details at KA7OEI’s blog.