Dear Mr. Williams,
As a graduate of the Marconi Technical school I may be able to offer some
little knowledge to your project.
1. The Positive (+48V) Battery Return may be an integrated ground,
meaning that
some internal components may seek a Battery return through the frame
and through
their individual Battery return cables, so be sure to include your
power supply
Positive Battery Return (+48V) in the connection to the Ground Buss
where you
establish a polarizing Frame Ground (Trip Ground) with reference to
the amplifier
frame.
2. Be sure to use the same size, or larger diameter conductor for your
Trip Ground
as the Battery Supply (-48V) and Battery Return (+48V) so that
integrated
Ground currents do not suffer a voltage drop in the loop from supply
to appliance.
3. Do not tie the filter signal ports together. Their paralleled
impedances may detune
the entire frame. A B&W 6-position coax switch in the input and
output can
select the proper filter.
What kind of power supply (e.g., amperes DC, etc.) are you running your
amplifier
with, and do you use a battery as a noise sink, filter and power supply
reference
voltage?
Respectfully,
Hal Mandel
W4HBM
On Sat, 2 Oct 2004 00:14:53 -0400 (GMT-04:00) Web Williams
<kr4wm@earthlink.net> writes:
> This is a question about a Marconi Canada commercial HF
> amp, -NOT- a CB-type amplfier. It is a model BL-100 (not
> a Courier BL-100 tube CB amp).
>
> This amp uses four modules to generate 1KW of RF. All
> the amp modules are in a bottom enclosure, then a large
> rack of cooling fans is in the middle, then the top rack
> enclosure contains massive brute-force bandpass filters.
> There is a single coax input, but multiple coax outputs
> which are switched in and out by relays on the filter board,
> depending on which band you switch to (I guess the
> assumption must have been that if you had enough money
> to buy this amp, you have enough real estate for separate
> antennas for each band). This behemoth takes a 48VDC
> supply, which I was lucky enough to locate with battery
> backup! (Thanks TELCO!). (Yes, I realize it's positive
> ground, but I can make it work, I'm fairly certain.)
>
> I'm not going to use the original exciter, so this amp is
> not going to have the capability to switch between the
> different outputs (unless I can design some manual
> switching arrangement).
>
> My question is this- in the group's opinion, would the RF
> follow the path of least resistance if I just tie all the filter
> inputs and outputs together (sort of like installing multiple
> Hustler loading coils on a mobile antenna), or must the
> various filter combinations be switched in and out as band
> changes occur? I guess I -could- run it without the filter
> board, but it probably would no longer meet spectral purity
> requirements, which is why the engineer put the filter
> board there to start with. I want to use it if I can.
>
> Any ideas? Is anyone on the list using one of these, or
> have any experience with them?
>
> Thanks, -Web Williams in Myrtle Beach, SC
>
> Kind regards, -Web Williams in Myrtle Beach, SC
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