28-29 amps is on the high side. Are you using the amp at more than maybe 5
MHz or so from the original frequency? Some of the Milcom/Crescend amps are
tunable, but many used fixed-value metal-clad mica capacitors in the base
and collector matching. The values of the caps and/or their placement along
the microstrips is varied depending on frequency.
While you could experimentally determine the right values/placements using
common sense techniques, it's probably easier just to send it to Crescend to
have them move it to your frequency. I have a 350 watt Vocom UHF amp that
had the same issue - fixed caps. After counting how many caps I'd have to
futz with, I concluded it was cheaper to send it to them and letthem do it
for $200. They turned it around in about a week.
If you need 250 mW in and 100 watts out, a Mastr II PA would do you nicely
(and cheaply!).
--- Jeff WN3A
> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com
> [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Adam Feuer
> Sent: Saturday, June 05, 2010 11:35 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: Re: [Repeater-Builder] Re: Milcom International UHF PA
>
>
>
> Hi Alex,
>
> Thanks for the reply! Your description of the pots was great but I
> don't see ANY tuning caps on any boards in this amp. There's a 10watt
> board that feeds a 65w board. Then, this 65w board gets split to feed
> two more 65w boards which get combined as the final output.
>
> I can easily set R10 to 100 watts but I would like more info on the
> tuning caps if it's applicable to this amp. At 100 watts the amp is
> drawing about 28 to 29 amps. I may be incorrect but I thought
> some of my
> other 250mw in 100w out PA's only draw 22 amps.
>
> Thanks again!
>
> Adam N2ACF
>
> On 6/5/2010 6:04 PM, opelgtalex wrote:
> > Adam-
> > R10 controls the bias voltage to the first stage driver-
> this sets the power out of the amp. Turn this pot down (lower
> the PA output) peak out all tuning caps starting at the 1st
> stage, then the 2nd and on to the 4 driver boards. Once all
> tuning caps are adjusted for peak output, then adjust R10 for
> the amplifiers rated power out (100W in your case).
> >
> > R9 controls the foldback power in case of a high temp
> condition the power output is cut by 3dB- the thermal switch
> is located just below the control board.
> > As per manual R9 is adjusted by removing power from the
> cooling fan, key the RF source, wait for the unit to reach
> 135deg F and adjust R9 for 3dB below rated amp output- this
> is per manual.
> > Hope this helps,
> > Alex
> >
> > --- In Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com> , Adam
> Feuer<feu...@...> wrote:
> >
> >> Hello All,
> >>
> >> I have a Milcom International UHF PA on the bench. Model number is
> >> P12-O5HA1-C1 rated at 250mw in with 100w out. I'm trying
> to identify
> >> what two pots (R9& R10) do on a board that "seems" like a control
> >> board. Both pots appear to vary the output power and current draw,
> >> although one does it more dramatically than the other.
> >>
> >> Anyone have a manual or information for this PA? Any help would be
> >> greatly appreciated.
> >>
> >> Thanks!!
> >>
> >> Adam N2ACF
> >>
> >>
> >
> >
> >
> > ------------------------------------
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
>
>
>
>
>
