[Collins] Test
Dr. Gerald N. Johnson
g369n849j at weather.net
Wed Apr 8 19:44:03 EDT 2009
On Wed, 2009-04-08 at 09:06 -0700, Brian Harris wrote:
> The bridge I am talking about is the one that is used for tuning the
> plate tank, not the DC metering. This bridge is supposed to be a
> factory aligned thing that you don't touch but I know it's off because
> when I adjusted the amplifier according to the manual, the plate
> tune/load settings were not optimal. I think I will determine the
> optimum plate/load setting for each band and then attempt to tune the
> two bridge controls (an R and a C) so that the meter indication is
> correct but not before surfing the web to see if someone has a better
> way of doing it.
>
> {the manual I have shows an adjustment technique}
>
> Brian Harris phone 214-763-5977 email cosmophone at yahoo.com website
> www.myhamshack.com/wa5uek
>
> --- On Wed, 4/8/09, Dr. Gerald N. Johnson <geraldj at storm.weather.net>
> wrote:
>
> From: Dr. Gerald N. Johnson <geraldj at storm.weather.net>
> Subject: Re: [Collins] Test
> To: "Brian Harris" <cosmophone at yahoo.com>
> Date: Wednesday, April 8, 2009, 10:43 AM
>
> On Wed, 2009-04-08 at 08:00 -0700, Brian Harris wrote:
>
>
> > Most definitely the list is working.
> >
> > {But only when I use a different address than the one I'm
> subscribed
> > with.}
> >
> > I have been working on the 30L-1 with the weird output tank
> behavior
> > and found the problem yesterday. A terminal on the
> bandswitch that
> > shorts the various tank coil sections as you progress from
> 80 to 10
> > meters was cracked to the point of no continuity. This lack
> of
> > shorting is what I figured the problem was but I expected
> the culprit
> > to be one of burned contacts rather than a broken terminal.
> Anyway,
> > because of this, as you went up in frequency, you always had
> the
> > entire tank coil present although the loading capacitance
> decreased in
> > large steps as it should.
> >
> > {That sure explains the tuning you saw.}
> >
> > In addition to this easy fix and the missing T/R relay,
> there were
> > other problems the previous owner left me (some people
> should just not
> > work on electronic equipment). The three screws that hold
> the
> > aluminum panel that divides the RF section from the power
> supply to
> > the inner rear panel were missing along with two of the four
> 1/4" tall
> > metal standoffs that hold the loading capacitor away from
> the front
> > panel. By the way, you cannot remove the front panel on a
> 30L-1.
> > It's spot welded to the aforementioned divider panel.
> Perhaps that's
> > why nobody ever responded to my question about its
> removal...either
> > how to or you can't. To remove the bandswitch you have to
> back it out
> > after you have removed the tubes and various other things
> that are in
> > the way. By the way, the reason the bandswitch terminal was
> broken is
> > because the former owner mishandled it as he/she took it out
> so he/she
> > could replace the On/Off switch. This person apparently
> failed
> > Soldering 101 as they did a lousy job of replacing the
> switch also.
> >
> > {There is that unfortunate characteristic amongst some
> Collins
> > collectors.}
> >
> > Today I will reinstall the tubes, replace the missing
> standoffs and
> > see how it performs after I align the tuned input circuits.
> I am
> > fairly certain the metering bridge circuit needs tweaking.
> I don't
> > know of a procedure for doing this but I'll figure one
> out.
> >
> > {Last time I did that to a Dentron, I unhooked a wire here
> or there
> > and inserted my "standard" meter for current. Voltage was
> easier, and
> > the resistors had all drifted. You could check them with a
> good
> > ohmmeter and simply replace them all with 1% film resistors
> and have
> > confidence in the metering.}
> >
> > P.S. As a newly retired (laid off Nov 2) EE with a
> background in RF,
> > Analog, Digital and Software Design, I really enjoy posts
> from you and
> > a few others on the list that are also technically strong.
> >
> > 73,
> >
> > Brian Harris, WA5UEK
> >
> > email cosmophone at yahoo.com
> > website www.myhamshack.com/wa5uek
> >
> > --- On Wed, 4/8/09, Dr. Gerald N. Johnson
> <geraldj at storm.weather.net>
> > wrote:
> >
> > From: Dr. Gerald N. Johnson
> <geraldj at storm.weather.net>
> > Subject: [Collins] Test
> > To: collins at mailman.qth.net
> > Date: Wednesday, April 8, 2009, 9:15 AM
> >
> > CQ CQ is this list working?
> >
> > --
> > 73, Jerry, K0CQ, Technical Advisor to the CRA
> > All content copyright Dr. Gerald N. Johnson,
> electrical
> > engineer
> >
> >
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> >
> I'm an EE because I was a ham first. I started out at a time
> when
> everything was tubes, but in college power was tubes, small
> signal was
> germanium transistors, ICs hadn't yet been invented. I worked
> at Collins
> my first job with BSEE in broadcast, very high power with
> people who did
> the ham gear earlier. I didn't worship Art and didn't
> appreciate his
> treatment of hired slaves and took a leave of absence for
> graduate
> school and haven't been back.
> --
> 73, Jerry, K0CQ, Technical Advisor to the CRA
> All content copyright Dr. Gerald N. Johnson, electrical
> engineer
>
>
>
I have downloaded 30l-1-_5th-ed-06-02-sec4.pdf. In section 4.7 it
describes how to set the capacitor.
What this is is a pair of volt meters, one on the filament for the input
voltage, and one on the plate through the plate to grid capacitances (as
described in section 3.8). The voltmeters have opposite polarity and so
when the voltages seen by the diodes are the same (taking into account
the voltage dividers on both) the meter shows zero and the stage gain is
as designed. If the plate load Z is off a little as you run the drive up
the PA will clip and that will show on the meter. If the PA isn't
resonant, the voltage gain will be low. If the loading isn't right the
gain voltage will be off.
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