>
>Hello,
>
>I am in the process of putting together a 4CX1500 amp. Any input to the
>following would be greatly appreciated?
>
>1. Antenna switching ... Vacuum relays Vs pin diodes
? PIN diodes allow 100wpm cw. Vacuum relays can go about 35wpm or so.
Vacuum relays are simpler to use and they are less susceptible to damage
from high-swr and electrostatic discharges in the near field of the
antenna.
>2. Full break-in keying
? On my Web site, Fig. 7B shows a high-speed [2mS] switching circuit
with an EBS for cathode-driven amplifiers. By substituting the EBS for
grid-driven amplifiers circuit on my Web site, essentially the same hs
switching circuit will work with Class AB1 amps.
>3. Meter and protection circuits
>
? I would use a zener-string shunt screen regulator biased from the
anode supply through a suitable resistor/s, and a glitch resistor in
series with the pos. hv. To avoid vhf parasites
1. mount the grid term. R directly to the grid and triple-bypass the
cold end of the R to gnd. [the EBS feeds grid bias to the cold end].
2. Do not use a high vhf Q parasitic suppressor. (in other words, a vhf
suppressor that does not get hot on 28MHz is not going to do much vhf
suppressing)
3. If you have enough drive to develop c. 65v across 12.5 ohms
(c.170w-pep), a 12.5 ohm grid term. R [using 4/1 bifilar ferrite input
transformer] would provide better input swr above 14MHz as well as
better vhf stability.
- later, Joe
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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