Wednesday, March 21, 2007
815 Xmtr - Safety mods
Someone asked me about modifying a vintage design in the name of safety. Sounds like a good idea to me. I already modify vintage receiver projects to keep B+ out of the headphones ( see http://www.io.com/~nielw/onestep/onestep.htm ). I also try to keep transmitter B+ away from accidental touching. This design, unfortunately, has 500 VDC exposed on the final tank coil and C2. I plan a couple of things to to help. First a front panel. I'll probably use a piece of masonite painted wrinkle black. As a bonus this gives me room for a plate current meter should I decide to add one. The second modification is to move the crystal socket to the front panel. No need to be reaching around behind the front panel to change frequency. The rest needs to be handled by being careful. Obviously power down when changing bands and short the tank coil to ground before touching it. Not so obvious is the key. Cathode keying allows one side of the key to float to B+. Usually one side of a key is more protected than the other. Connect this side to R1 and don't diddle with the key contacts with power applied.