Joe,
The original design (black drawing) came from a Russian website or some place
like that as I remember seeing it elsewhere. It was a working amp and can see
easily what they done. Only thing though is that it uses a series regulator for
the screen. The schematic on down the page I guess is by the author, and is
totally different. It looks to me like someone went wild using chokes for
everything and put them where they wasn't needed. In other words like a choke
was added on every source. If you notice, they put a choke in series with the
attenuator resistor to ground on the input and that wasn't needed (here you
want some RF to go to ground as that's its purpose, a voltage divider. Same as
the cathode choke and screen grid circuit choke, why? The capacitance of that
bypass in the control grid circuit looks to me to be a perfect RF short to
ground at say 160-10 meters. At 10 meters, heck a couple hundred pF would be a
killer. There he has a 1000 pF which is what most use as a by
pass at a tube pin, or behind a choke on the supply side. At 160-10 meters,
that's correct for a coupling cap too. Also, look at the inductance of the
plate choke. It's only 40 uH total, and that's pretty small to be operating at
the low frequencies. The only chokes that looks right to me is the RF safety
choke off the Load C, and the one off the control voltage at 200 uH. I may be
wrong though.
Best,
Will
*********** REPLY SEPARATOR ***********
On 1/30/06 at 9:01 PM John Popelish wrote:
>Will Matney wrote:
> > On 1/30/06 at 8:37 PM John Popelish wrote:
>
>>>Is it possible that these chokes and capacitors you mention are pars
>>>in a peaking circuit, to push the frequency response of the amplifier?
>>>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.
>
> > The link is below. No, at the valuse there, it don't make sense
> > at all, or to me I can't see it. I've never seen anything
> > set up that way.
> >
> > http://www.angelfire.com/nb/ni4l/gu84b.html
>
>Thanks for the link. Here are some of the numbers:
>The cathode LC resonance (just the 15 uH and .01 uF) produce an
>impedance peak at .41 MHz.
>That would notch out frequencies near that (a little lower because of
>the cathode capacitance).
>On the grid, the 22 uH and .001 uF would peak the grid voltage around
>1 MHz. But the Q is very low because of the resistors in the grid
>circuit.
>
>Very strange. Anybody have a spice model for this tetrode? I would
>love to frequency sweep this circuit and see what all is going on
>inside it.
>
>
>
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