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From: "W2XJ" <W2XJ@W2XJ.NET>
Sent: Friday, September 24, 2010 12:38 AM
To: "Jim Thomson" <jim.thom@telus.net>; <amps@contesting.com>
Subject: Re: [Amps] Pulse tuning
> This discussion pertains only to poorly designed AMPS. There should be no
> voltage sag and the amps should be ccs at 1.5 kw out (in the US). If
> digital
> modes are contemplated, 5 to 10 KW amps in class A mode are necessary.
### 1.5 kw out requires at least a 3.5 kva CCS xfmr. Ten Tec claims their
centurion, with the
2 x 3-500Z's has a 3.5 kva CCS xfmr, then further blathers on abt '7 kw
IVS' which is a throw back to
orr's books. [ Int Voice Service]. Fact is the centurion is capable of
1300w pep out and that's it. It doesn't
have anything anywhere near close to 3.5 kva. It's well under 1 kva. A
buddy tried a brand new 46 lb mag cap
xfmr on a 1 x gs35b, 6m amp... fed with 12 ga wire. B+ sags 800V.
Switched to a 2 x gs35b 6m amp [diff amp]
+253 lb dahl xfmr, and 2 ga wire, and B+ sags 50 vdc. [4.4 kw cxr, 50.125
mhz].
## Why do digital modes require class A ? Bill tells us the amp does not
have to be linear for RTTY,
and that class C is just fine. That assumes you are using FSK, and not
AFSK. I have zero experience
with digital modes.
## somebody mentioned abt anode diss. You won't get 1 kw of ccs anode diss
from any sb-220, or
drake L4B any time soon. Neither blow enough air to do the job. If you
expect 1.5 kw CCS anode diss from
a 8877, you better have enough air flow. The L4B, stock, with zero bias,
idles at 600W. Key the amp, with no drive
applied, and let it sit for 5 mins. You will burn your hands on the top
lid. It doesn't help that the top lid restricts the air
flow.
## Re duty cycle on SSB. If you are referring to the plate current, a lot
of that depends on how much idle current you draw.
That alone, will skew the average a bit. I tune for 800 ma cxr. On SSB,
average plate current is aprx 275-375ma. [1235 pep out]
Using both a bird and a Coaxial dynamics meter, [in average mode], on ssb,
it averages out to 250 w out. Average Po is
only 1/5 the pep out, on the power out end of things. On the dc plate
current end of things, average is 34-46%.
Jim VE7RF
>
>
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