>
>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.
>
? The ZSAC (zero signal anode current) matters more than the actual bias
voltage. In a 3-500Z, IMD goes up rapidly with a ZSAC of less than
65mA, I like to use between 75 and 100mA,
- If an electronic bias switch is always in sync with the RF relays, the
tubes will always be biased for linear operation whenever the relays are
in the transmit position. (see Fig 7 on my Web site) However, with
RF-derived bias switching, the tubes rapidly switch in and out of linear
bias during normal speech when the relays are in the transmit position.
This causes additional distortion during soft syllables and at the
beginning of syllables. .
>......
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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