Hi Jason,
> I just looked at RF Parts. They have a matched pair of 3-500ZG
> (3-500ZG RFP) for about $255. I think that they are Svetlana tubes.
As far as I know, Svetlana never made and production 3-500Z
tubes. As I recall they re-labelled some Chinese tubes,
accidentally stamping "made in USSR" on them.
> The price is excellent. Are these good tubes? They also had some
> Amprex but at a much higher price. How about Taylor 3-500s? Where are
> these tubes made?. A pair of these is even cheaper ($238).
There are a half-dozen sources in China. Some are reasonably
good, some are junk. You have to ask the vendor hat his most
reliable brand is.
Amprex tubes seem to be the most reliable, other than a tendency
for about 1 out of five to develop a grid-filament short.
> I understand that the graphite plates will dissipate more power. If
> one gets these tubes, does one increase the plate current to match the
> increased dissipation? That assumes that the stock power supply will
> handle the increased power. From some of the comments, I think that
> it might not. What is an HB supply? Is it a brand or a design that
> one home brews? Jason
Graphite anodes have more thermal lag, so they handle short-term
overloads better. They take longer to heat, they take longer to cool.
You generally never want to run the tube at maximum dissipation.
This is especially true with a poor cooling system like the L4B.
There simply is not enough airflow across the tube seals for 500
watts dissipation in each tube. Even if you found a 700 watt
dissipation tube, you would still only have the airflow to move 300
or so watts of heat from each tube.
A given physical size and style tube ALWAYS produces the same
heat for the same actual dissipation. The temperature does not
"drop" and the tube does not run cooler just because it can
dissipate more power.
You will have multiple problems trying to substantially increase the
output of an L4B, not just power supply issues. If you did NOT have
multiple problems, then obviously Drake did not engineer the PA
well and they wasted money on things that were needlessly large.
73, Tom W8JI
w8ji@contesting.com
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