Real world efficiency in class B is 60-65%, and 70-75% in Class C. You wont
be able to tell the difference between a Q of 10 to 14 with properly sized
components in the tank and wiring.
You are right in the middle so why bother for no real improvement.
Use a small fan if the heat bothers you plus it is a good idea anyway. The
graphite plate version of the 813 is highly
underated for Pd. My tests show it is more around 200W when comparing with a
USA made Cetron 572B.
With CW having a 50% or less duty cycle you havent come close to stressing
----- Original Message -----
From: "Steve Flood" <email@example.com>
Sent: Saturday, October 10, 2009 7:52 AM
Subject: [Amps] How high can I go with this amp?
> Can I get more output power/efficiency with a smaller inductance coil in
> my pi-net?
> Power supply is 2700v key-down and capable of 800mA (it is built around an
> SB-220 transformer).
> Ip meter max is 750mA.
> Amp is 3 x 813.
> Pi-net designed around RL of 2333 ohms. Pi tank is variable caps and
> fixed coil. Design Q is 12.
> Currently, my input power is 2700v x 600mA = 1620w.
> Output measured on scope is 1111w.
> Efficiency is 68-69%.
> Plate dissipation is 176w per tube.
> These figures are based on CW with adjustable bias set for 0mA ZSAC.
> Grid current is 150mA (50mA per tube).
> Drive is 100w through input pi net.
> What if...?
> I decrease the coil inductance to lower the RL to 1800 ohms.
> It seems this will allow me to generate higher Ip and input power - say
> 2700v at 750mA = 2025w.
> If I can maintain 68% efficiency, I could theoretically get around 1370w
> Or does the tank modification allow me to go well into class C - say 75%
> efficiency or close to 1500w out?
> Or will my drive power limit how high I can go?
> I'm just talking about CW here.
> What am I overlooking? I am trying to figure out what the amp is capable
> of. I know the extra power makes little difference on the other end, and
> I'll have extra heat and tube stress.
> Steve, KK7UV
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