[Collins] Test

Wed Apr 8 21:55:01 EDT 2009

Greetings all,

A nice tutorial thread! Ah, yes, the 30L-1 power switch replacement  
challenge. Not easy. About a year ago Mr. Dennis Brothers told me me  
how he does it. I have notes from the telephone conversation, but I am  
not sure I can articulate it in writing well enough to be worthwhile,  
even though I think I can do it now, if forced to. He described the  
power switch replacement as the "most difficult repair to do on a  
30L-1". I believe I read a recent post indicating that he is a CRA  
guest speaker at Dayton this year. If someone going to Dayton could  
corner him and get a good description of the procedure, IMO, it would  
be a great subject for the "Journal".

Bob, KF6BC

Brian - I am glad to hear you have things under control now.

Bob, KF6BC
On Apr 8, 2009, at 4:44 PM, Dr. Gerald N. Johnson wrote:

> 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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>>>
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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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