Hi Alex, > "kq2h" <[EMAIL PROTECTED]> wrote: > Skipp, the PA modules did not work at 29 MHz, tested individually > into a dummy load. I had a chance to play with them yesterday, > and as it turns out, there is no need for additional transformer > cable length.
Which is what I would have expected... The difference in the two VHF Low Band frequencies is not enough that I would suspect the xmfr core material or the winding value to be the big frequency selective player. Mostly how some of the supporting components would "set the operational range. > I got each module to put out close to 300 W while drawing > just under 7A of current per transistor, without any bias. I > added an inductor in parallel with a 75 pF capacitor across > the drains, and increased the coupling capacitors to 1500 pF > from 1000 pF and added 130 pF (25%) to the transformer input. > That was it!!! Excellent'e..! From past examples I would suspect the xmfr input capacitor value increase was a fairly large part of the picture. Once you arrived at some x-minimum value changes the amplifier would probably have started to really get with the program > Hopefully the combiner and low pass filter will work. The > amplifier control board has problems that I'll have to tackle > after getting the PA working on > 10 Meters... Alex Great to read your project is moving forward... keep up the good work. cheers, skipp > > > --- In [email protected], "skipp025" <skipp025@> > wrote: > > > > > > Based on what I've seen for Quintron Glenayre Equipment I would > > question if you really need to rewind the xmfr for that > > relatively short distance from 36 MHz. > > > > If the manual doesn't have different part values for the low range > > split I'd take a careful look at the circuits after the xmfr. A > > case can be made where a non 180 degree filter after the PA would > > echo larger problems back at the xmfr. > > > > Did you measure the pa operation before the frequency change? > > > > You might also consider joining the yahoo rfamplifier group where > > a number of folks migh help you sort through this conversion > process. > > > > http://groups.yahoo.com/group/rfamplifiers/ > > > > cheers, > > s. > > > > > "kq2h" <kq2h@> wrote: > > > > > > Perhaps a little off topic subject.... Does anyone know of a > source for > > > 25 Ohm, 0.10" diameter flexible coax cable? I am in the process of > > > converting a 500 Watt Quintron QT-7095 station to 10 Meters. The > RF > > > amplifier uses four 28V MOSFET's matched to 50 Ohms with a > Guanella 4:1 > > > transmission line transformer. Unfortunately, the amplifier is > tuned to > > > 36 MHz. The Guanella transformer gets very hot at 29 MHz while > output > > > power is low. It looks like I may have to rewind it, but am > unable to > > > find a source for 25 Ohm mini flexible cable. The closest thing I > can > > > find is semi-rigid, which is no good for this application....Alex > > > > > >
