On Aug 25, 2004, at 3:24 PM, Harold B. Mandel wrote:
Dear Sirs,
In reading about how the SB-220 will be used on AM I wonder
if any of the '220 users out there have connected a known-good 50 ohm
dummy load AFT of the amplifier and a known-good Reflected RF Power
meter between the exciter and amplifier and measured what the
amount of reflected power is with and without the amplifier on line.
Is it not true that the SB-220 pass-through circuitry and the
input tuning circuitry sometimes displayed greater than ten percent
reflected power with the amplifier in STBY and an equivalent amount
of reflected power while keyed?
Depends on what band. 10m is typically the worst on standby/bypass.
Adding c. 30pF across the output connector will cancel the L in the
relay. The SWR of the input can be corrected by raising the Q of the
Pi tuned inputs to c. 2.
In developing an A-M signal and worrying about the ability of
the amplifier to withstand prolonged keying, is it not wise to
determine
if an inherent defect of design is adding to the problem?
An additional cooling option is available at Max-Gain on the
web.
They sell a Tarzan fan that can be bolted to the exterior of the '220,
doing away with the internal fan altogether. The Tarzan fan is much
more
robust and coupled with the dual-level airflow in the '220/'221 series,
should provide more than adequate cooling for long key-down times.
The only other issues to tackle are the anode and filament
transformer capabilities.
Respectfully,
Hal Mandel
KA1XO
Only problem is, my screen mod ARC-5 setup can
only muster about 25 watts so I don't have any good way to tune
up at the SB-220's full capabilities. -Charles
Charles--- If you have a xcvr capable of 100w output, tune the
final for full pwr out. Then switch to the Arc 5 and drive with the 25
w out
from it. that will give you the 4 x head room normally required for AM
operation. BUT you need to be sure the amp is robust enough to opr at
this level
key down.------73 john WA4TT
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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