At 11:22 PM 5/2/99 -0500, Jon Ogden wrote:
>
>>What's all this about parasitic oscillation, etc, with the SB-220 and do I
>>really need to worry about it?? Any other things I need to ask the current
>>owner if I find one I'm interested in?
>
>Horsepucky. If the amplifier is working, don't mess with it. If it
>ain't broke; don't fix it!
Amen ... my SB-220 has been unconditionally stable. However, these were
built as kits, and there could be a certain amount of variation in layout
under the chassis that could affect VHF stability. I would not assume that
it will have problems.
>
>>
>>Do I need to worry about whether the ALC is compatible with my rig, or do I
>>just throttle back the output power so as to never overdrive the amp? ...
>ALC is likely compatible. However, if you set your rigs max output for
>whatever is the max input of the amp, you shouldn't need ALC since that's
>what it does.
I have never run ALC with my SB-220/TS-930 combination. I can just about
get rated grid current, properly tuned, on 80--20 meters.
>
>>Rich pointed out that since my FT-920 has fast T/R switching, that I *do*
>>need to take the QSK capabilities of the amplifier into consideration. ...
>IMHO, I wouldn't worry about it. Some say that with the TX speed of
>modern rigs, you need it so you don't hot switch. However, when you key
>down with SSB you don't generally start talking in a couple of
>milliseconds. Again, I wouldn't worry about it and I would only make
>whatever modifications you deem necessary after having the amp and
>working with it for a while.
Here, I disagree, at least in part. I have experienced T/R relay sticking
in my SB-220 due to hot switching, in both phone and CW. If you rely on
the vox to switch from receive to transmit for either phone or RTTY, your
radio will probably deliver RF to the amp's relay before it's ready. If
you use a footswitch, probably not. Fortunately, I've been able to burnish
the contacts and restore proper functioning. Most of my operating is in CW
contests, and TR Log has a neat feature that keys the PTT line with a
programmable delay before the first character is sent. That has cured my
sticking relay problems, but I still plan to install a vacuum/reed relay
combination to ensure reliability.
73, Pete Smith N4ZR
n4zr@contesting.com
Loud is.
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