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[AMPS] Henry 2kd classic

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Subject: [AMPS] Henry 2kd classic
From: (Tom Rauch)
Date: Wed, 12 Sep 2001 10:22:48 -0400
> Hmmm, if there are no good rules of thumb and no peak current/energy
> ratings for anode supply components, how does one go about sizing
> the glitch resistor? 

I'd just make it as big as I reasonably could, depending on plate
current. There really isn't any reason to dissipate more than a 
percent of the output power in the resistor from I^2 R losses, and we
don't want to noticeably reduce HV regulation.

> BTW, speaking of grid components, how come Drake grounds the grids
> on the L-7 thru a parallel combination of RF chokes and capacitors? 

That is a mistake that was promoted by Bill Orr (now SK). Bill 
talked Heathkit into doing it also, as well as other companies. The
original idea came from the 30S1 where it worked quite well. The 
is you form a capacitive voltage divider between the cathode and
ground and tap the grid up on that divider to make the amplifier less
sensitive to drive power.

 It works perfectly in the 30S1 because it is a grounded-grid tetrode
that draws no grid current. The screen shields the input and output,
and since the divider is lightly loaded by a very high grid impedance
the division is the same from band-to-band.

The moment the 30S1 draws grid current, the impedance between 
cathode and grid drops like a rock and the grid is "tied" to the
cathode. While this produces distortion when grid current appears, 
does prevent hurting the tube from excessive grid current. It also
increases driving power requirements. So it was an excellent idea in
the 30S1 because it was an AB1 TETrode!

The results are different in a triode, because there is no shield
between the anode and cathode other than the control grid. Also, 
the tubes generally draw considerable peak grid current the grid
voltage waddles all over the place on SSB. This causes increased 
and the gain varies from band-to-band.

This is a good example of what happens when people try to apply a 
idea in one application to other systems without understanding how
they work. Every system is different, and should be evaluated on its
own merits.

That system actually moves the amplifier towards LESS stability 
and poorer IMD if it is a GG triode!

73, Tom W8JI 

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