>> Subject: Re: [AMPS] Single supply -Multi-amo help
>
>hi rich, jordan, et al.
>
>> >> Are these amplifiers going to be in simultaneous use?
>
>great question!
>
>> >No they would be run one at a time ...
>
>great answer.
>
>> Then one supply would do.
>
>yep.
>
>> >I see a ckt in QST where they
>> >just remove the screen voltage to the unused amps...
>>
>> . When the normal cutoff bias is applied to the grid, the tubes draw no
>> current. The presence or absence of screen voltage matters not.
>
>it's best to "remove" the screen voltage by grounding (or returning
>to ground through a low-value resistor) the screen. that is, don't
>let it just "float" because it might wander up near anode potential,
>and take out the screen bypass capacitor.
Wandering is not likely if the screen is fed from a shunt zener-string
regulator, biased through a suitable power resistor connected to the
anode supply. When zeners fail they short. For 4cx250Bs, a shunt screen
regulator looks like a good solution. To adjust screen potential,
progressively short/unshort individual zeners with a rotary switch.
Rich...
R. L. Measures, 805-386-3734, AG6K
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