>
>Hello,
>I am building a 6M amp and currently deciding on a bias
>switching scheme. I note in the SB-220 they use a rather
>high resistance in the zener bias circuit and switch the
>relay from the 110 (or so) VDC bias line. I see on other
>amps that the relay is used as the series dropping resistor.
>It seems to me the latter is more efficient though it
>requires a higher wattage zener. Are there any other points
>to consider?
>Art K3XF
>
Zeners are not adjustable. They usually don't survive a glitch. A
string of foreward biased diodes is Way cheaper than a zener and they are
adjustable in 0.7v steps. // With V-cutoff bias, there is a danger of
burning up the cutoff-V power supply if a tube shorts (SB-220, TL-922).
Resistor-cutoff bias has no problem with a shorted tube.
cheers
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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