OK, I'm confused. I'm building an electronic bias switch and vacuum relay
QSK into my SB-220, having finally been jarred out of procrastination by
the failure of the changeover relay this past weekend. In the process, I
have become aware of (apparently) wide variation in the bias voltages that
various modifiers recommend.
To recap, the standard bias source is a 5.1 volt zener. Harbach uses 8 x
1N4005s, back connected, to produce 6.8 volts. One mod I've seen uses an
8.2V zener for SSB and a 6.8V for CW, but the designer says that the 6.8V
makes the 3-500s too hard to drive, so he just uses the 8.2V position all
the time and runs in SSB position.
If the 5.1 volt original bias produces Class B operation at the higher SSB
plate voltage, what does 8.2V produce? Any difference in IMD, one way or
the another? What about for CW?
73, Pete N4ZR
Sometimes a tower is just a tower
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