QROKING@aol.com wrote:
>
> Ok fellas, lets let Heath, Ameritron and kenwood off the hook for a moment
> and lets look at the Drake L4-B. My guess is that this unit can easily
> handle 4000 volts on the plate instead of there mere 2600 that is stock.
I note you used the word "guess." I would not make that presumption.
Going from 2500 to 3000 V--maybe a bit more--seems reasonable, but do
you KNOW that the plate cap, RF choke, bypass and blocking caps will
take the strain of 4 kV--which exceeds datasheet maximum? If you presume
1500 W out at 60% efficiency, that is 1000 W plate dissipation. Unless
you remove it and measure its output, is there any reason to think that
the blower is adequate for moving that heat? And, of course the power
supply requires a total rebuild; if you do it, be sure to replace the
diodes and caps as well as the transformer, and add step-start and maybe
some air.
> I am thinking of doing this, but I think their method of bias is not
> appropriate for the high voltage, they do not use a zener diode, looks like
> put 125 volts from the bleeder string.
When I read this, it makes me nervous about your tinkering with 4 kV.
That 125 volts is cutoff bias, not operating bias! Zero-bias operation
is appropriate for 2500 V operation--see the Eimac data sheet--so no
zeners were necessary. At 3500 V--maximum data sheet rating--15 V bias
is recommended. This reduces conduction angle and zero-signal plate
current. A zener with a power transistor can provide this value, and an
optoisolator in series with the zener can function in lieu of the cutoff
bias from the bleeder string.
--
Garry Shapiro, NI6T
Editor, "The DXer," newsletter of the NCDXC
Visit the Northern California DX Club 50th Anniversary page:
http://www.aa6g.org/ncdxc50.html
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