>
>> >>In all this discussion, nobody has mentioned the bias switching. IMO,
>> >>the amp should not be biased on until all the relays have closed and
>> >>must be biased off before any of them open.
>> >>
>> >
>> >/\ Please explain why.
>> >tnx
>>
>> _________________________________________________________
>>
>> It will make it impossible for a tube to be momentarily unloaded, either
>> at the input or output.
>
>Bill, What actually
// (key word)
>...will happen ios the tube becomes a dc cathode
>follower, and the cathode voltage easily pumps up a bit higher than
>you might expect.
>
// The 3-500Z filaments/cathodes connect directly to the +110vdc PS
whenever the T/R relay bias contacts open. In a g-g 3-500Z, running at
3kV, cathode current is essentially cut off with c. +23v on the cathode
because the grid looks 23v negative with respect to the cathode . At
+110v, the tube is undoubtedly cutoff.. How can zero cathode current
"pump up" anything? It seems to me that someone is pumping blarney.
>Then the relay has to discharge any capacitors,
/// The relay NC contact is required to instantly charge the 2x 0.02uF
of filament winding bypass-C to 110v whenever the T/R relay switches to
receive.
>plus handle some
>instant peak anode current while bouncing.
>
>That might wear on the relay, but I'm not sure at all it is any worse
>than a small RF spark on the input relay.
>
>My gut feeling is it is better long-term to not close the input relay
>early or open it late...compared to the output relay. But that is only
>a gut feeling.
// ... that is seemingly not based on logic.
>73, Tom W8JI
>W8JI@contesting.com
>
cheers
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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