Not having (anywhere close to) the technical knowledge of some -
However, it seems that the L-4B deck WAS comparatively overdesigned for
what was the legal limit (about 600W output) when it was designed.
Compare the tank components to the SB-220 that has well over 3,000
volts. At any rate, with additional cooling, about 3,500V, and bias, I
get 1500W out in a 48 hour contesting environment. Of course I am
eliminating the normal tuning errors by carefully tuning it up on a
single band in mulit-multi environment (no fast band switching and
tuning). For those of you who operated the CQWW CW Test and know what
happened to the propagation on Sunday afternoon, you will enjoy the
caption on the picture of my power supply that had two 115V primary
transformers in series/parallel (mistake) when it smoked. That was
4200V which was indeed too much. The amplifier is much happier now with
3500V...
See picture at http://cooldude.com/k5go/new/cqwwcw00/mvc-101f.jpg
Stan
Tom Rauch wrote:
>
> 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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