In a message dated 11/18/03 7:13:14 PM Central Standard Time, r@somis.org
writes:
>
> >> ** The 4-400A and the 3-500Z use the same 5V/14.5A cathode and have the
> >> same peak-emission (c. 1.3A) , thus, the output Z of a 4-400A and a
> >> 3-500Z are pretty much the same if the anode supply potentials are equal.
^I don't know where you got your peak emission numbers from, but the
characteristic curves published by Eimac for both tubes show Ip as high as 2.2
amperes.
^ The only difference is that the 4-400A needed 500 volts on the screen to do
it.
^ (The 4-400 did the 2.2 amps Ip with an Ig of 200ma and an Iscn of 100ma.)
>
> ** Applying screen V to a tetrode with both grids RF-grounded does not
> change the amplification because screen-amplification only occurs when
> the the grid's RF potential differs from that on the screen.
^ Wouldn't you consider the RF riding on top of a DC potential of 500 volts
(or 750 volts) on the screen grid to be at a different RF potential than the RF
riding on the Grid which is at ground potential or somewhere very close to
it?
> > If he has less than 300 watts of drive available, (say only 50 to 100
> >watts), his power output would positively increase with 3-500Z's being
> >used
>
> 300W would drive 4 - 5, 4-400As in g-g with a 3500V anode supply.
^ Probably more like 6 or 7 if you use the 40 watt Max Sig drive figure
posted both by the ARRL and by Bill Orr for those tubes running in a Ground
Grid
configuration.
^ I'm saying that he would need 25% more drive to obtain 30% less output
power using 4-400s than using 3-500s.
^ If he only has 50 to 100 watts of drive available he should be able to see
1500 watts peak from a pair of 3-500Zs at 3KV. That number would drop to less
than 1000 watts, (probably more like 750 watts), if the same drive was used
on 4-400's running G-G at the same plate potential.
>
> With = anode voltages, a 4-400A in g-g has less ZSAC than a 3-500Z
> because a 4-400Ain g-g has more Mu.
^ I cannot argue that point because I have never seen any published figures
from Eimac or any other source stating what the Mu was for a 4-400A with both
grids tied together.
^ All I can say is that my own experiences have proven contrary to your
statements and are reinforced by what I have seen published by Eimac, Arrl, and
Bill Orr.
^ My personal experiences with replacing 3-500's with 4-400's in grounded
grid amplifiers have always resulted in significantly less power output for the
same drive levels and plate potentials, and I had to double or triple the drive
level to obtain the same power output I had with the 3-500Zs.
^ If what you stated is true, and the 4-400's had higher gain (Mu) and the
same plate voltage and peak Filament/Cathode emission capabilities, please
explain to me why Heathkit (and everyone else) switched to the more expensive
3-500Z tubes?
^ Regards,
^ Dennis O.
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