SB-200 on AM:

[Joe Cro N3IBX]

Regarding the question about running a SB-200 (or any other class A/B) linear
on AM I use the following formulae:

Whatever your PEP from the amp is you want to throttle back the drive to no
more than 25 percent of that figure. For example, if your PEP is say 800 w
atts on 75 meter SSB; 1/4 of that would be 200 watts. To play it safe I
wouldn't drive it any harder than say 100-150 watts. The plate supply in the
SB-200 (or any other class A/B amp) wasn't designed for a 100 percent duty
cycle. The same rule would apply for using a solid state exciter or amp on
AM. If your solid state tranceiver develops 100W PEP, keep the drive down to
an absolute maximun of 25 watts. Your final transistors will thank you for
it.

When modulating the amp (SB-200 or other) you want to disable your ALC if
possible. A slight forward blip of the wattmeter should occur when modulating
your adjusted carrier. A wattmeter inserted between the exciter and the
amplifier, and then another between the amp and the antenna would be a great
idea as well. You'll be able to see if you have any reflected power between
the exciter and amp (as with many solid state rigs). It will also enable you
to know just what your exciter drive power is.

When using the amp notice the color of the PA tube plates. If they turn
yellow they are at or near full plate dissipation. If they turn red they are
being overdriven and need time to cool down. If you're running non-USA made
572-B's in your SB-200, the grids will sag and actually touch the plates due
to fatigue from exceeding rated plate dissipation. OUCH - you don't want that
to happen.

I hope this helps. Good luck and hope to hear you on the bands.

Mod-U-Later,
                                                                         Joe
Cro N3IBX

Joseph Cro N3IBX




Collins, Heathkit, Hallicrafters
Drake, National, and General
Boatanchor language spoken
here: <A HREF="http://hometown.aol.com/yardleyite/index.html">N3IBX Basement of Boatanchors</A>

        <A HREF="http://members.aol.com/yardleyite/collect/index3.htm">N3IBX Boatanchor Website</A>
        <A HREF="http://www.geocities.com/n3ibx/N3IBX.html?1000084610680">N3IBX AM Studios:</A>
Collins Radio Association Member # 122
AM International Member # 1280

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.asp?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://interactive.tempe.gov/archives/HEATH.html