[Amps] Centurion cooling improvement ideas for AM service

[R.Measures]

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