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Tony King - W4ZT
Hello Thomas,
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A couple of suggestions for your amplifier... First, I would float the B- to make metering of plate and grid current readily available to you. It takes no more than two resistors and a few diodes to protect the metering to make this big improvement. Second, I would suggest that you do not do T/R keying of the bias the way that is shown on your schematic. That method is similar to the Clipperton L and a few others. The flaw is that during the transition of the contacts the cathode will rise to near full anode potential and when you make contact with your bias circuit, you are hitting it with a very high voltage at that moment. A simple cure for it without changing the circuit entirely, and this applies to the Clipperton L as well, is to place a jumper across the wiper and the normally closed contact of the keying relay. That will keep the cutoff resistor in the circuit all the time and prevent the cathode voltage from soaring. I would also place a fuse in series with your bias circuit rated at just over your maximum expected plate current. Also, a Metal Oxide Varistor or an NE-2 neon bulb in parallel with the bias circuit will help protect it against transient voltages. You may want to increase the value of the cutoff resistor to about 20K to minimize the current in standby. 73, Tony W4ZT la3pna wrote: Hi group. |
