Hi Neil, Yes. Scott Zimmerman and I have successfully modified several 110 watt Micor PA's to produce a 10 watt driver or IPA. I apologize that I haven't had the time to write the modification up and present it as a webpage yet, but I'd offer the information to anyone wanting to do it. I basically saw the board in half (yes literally) and wind a new output coil. It's more involved than that, but that is the basic concept. All filtering and Power Set functions still work as original.
The modification is shown on this site as the modified board is used to drive a 330 watt GE tube PA: http://www.shol.com/kuggie/ahra/hmftinfo.html (Let the pictures load) Kevin Custer Neil McKie wrote: > Kevin, > > Have you or anyone else figured out where to cut a Micor PA board > and modify for a 50 ohm output what is remaining to be able to use > the same board but at a lower power? > > Ie: take a 100 watt PA Board, cut off the 4 transistor finals and > use the driver stage? > > Neil - WA6KLA > >Kevin Custer wrote: > > >>In Class C operation, especially when considering repeater operation, >>its way better to run an appropriate sized amplifier full bore than it >>is to run a bigger amp at 1/2 or 1/3 its rating. Class C amps run >>cleaner when properly (over) driven, as they will get spurious when >>under driven. Typically, the smaller amplifier will run more >>efficiently (more power for less or same amount of heat) then its big >>brother throttled back. The efficiency rating of a power amplifier will >>vary to some degree in relation to how hard the amplifier is driven. >>Usually the amp will be more efficient when properly driven. >> >>The text below is a generalization of what can happen when commercial >>radios are tuned to the ham bands and are not being driven correctly. >>My example below is from the Motorola line, but, this can happen with >>GE, Motorola, or whatever. >> >>Poor efficiency is what kills power amplifiers. Too many folks believe >>its better to run an oversized amp at 1/2 its rating to make it last. >>Lets take the Motorola Micor 100 watt UHF mobile for example. The >>amplifier in this mobile throttled back to say 50 watts of output will >>require about 12 to 15 amps of DC current. A 45 watt model running full >>bore (45 to 50 watts out) will require 6 to 8 amps of current. The 45 >>watt mobile radio will produce about 45 to 60 watts of wasted heat that >>is dissipated by the heatsink. The Micor mobile heatsink is rated at >>around 40 watts continuous dissipation, so we are close to being able to >>run it continuous duty, and can likely stretch that extra 5 to 20 watts >>of dissipation if a fan is used. Now lets take the 100 watt mobile that >>is throttled back to 50 watts. Its dissipating 117 watts of heat, and >>won't matter how many fans you blow on it, it's going to eventually burn up. >> >>What I'm driving at here is *Dissipation* and *Efficiency* are words >>that we as repeater builders need to understand. >> >>In my opinion, its better to appropriately size the power amplifier and >>save the additional money on the electric bill then to be replacing the >>PA every 6 months due to heat failure. >> >>Kevin Custer >> >>georgiaskywarn wrote: >> >> >> >>>Good Morning Tom, >>>I would have to run the driver just about on full bore though. >>>(because of the 30 in 100 out amp...again only running it right now at >>>75 watts) I am a little nervous on running it like that. I wonder if >>>anyone else is running the driver that hard and getting good results?? >>>Thanks, >>>Robert >>> Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
