On Jan 30, 2006, at 5:37 PM, John Popelish wrote:
> Will Matney wrote:
>> What I looked at in the schematic didn't make one lick of sense
>> to put a cathode choke to ground on a grid driven amp,
>> then place a shunt resistor across the choke
>> (especially that high of value).
>> The resistor wouldn't serve any purpose unless the choke opened.
>> And if it did, you'd really be better off not to have the resistor
>> so the tube would not conduct at all.
>> Also, the choke isn't needed as there's NO RF there to block
>> from ground. He also put a RF choke across the attenuator resistor
>> going to the control grid.
>> That don't make sense to me. I would think you would use two
>> non-inductive resistors. (Rich will jump me for calling them
> that). > He also has a choke in series with one of the attenuators
> resistors
>> going to ground which would raise the impedance there too.
>>
>> All I've ever seen here, for an attenuator, is a couple of
>> non-inductive resistors.
>>
>> Why put a choke in series with the screen lead? All that's needed
>> is a bypass cap at the tube socket pin. Here, the cap is on the
>> other side of the choke where it's shouldn't be.
>> Last, there's a 0.001 bypass cap hooked right from the control grid
>> to ground on the wrong side of the RF blocking choke.
>> The RF will go to ground and not to the tube!
>>
>> Am I missing something about this?
>
> Is it possible that these chokes and capacitors you mention are pars
> in a peaking circuit, to push the frequency response of the amplifier?
John -- My guess is that the designer would do well to take a course
in alternating current circuit analysis.
end
> That would explain the high value parallel resistor (limiting the Q)
> and the cap on the tube side of the grid choke (to form part of a
> resonance, not a bypass). I am afraid I have lost the original link
> to the schematic, so I can't easily look if this explanation is
> reasonable or silly.
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>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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