[Test-Equipment] AN/PRM-10 Question

[Richard Knoppow]

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: <anchor at ec.rr.com>; "Discussion of Electronic Test 
Equipment" <test-equipment at mailman.qth.net>
Sent: Sunday, October 30, 2011 10:09 PM
Subject: Re: [Test-Equipment] AN/PRM-10 Question


>
> ----- Original Message ----- 
> From: "Al Parker" <anchor at ec.rr.com>
> To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>; 
> "Discussion
> of Electronic Test Equipment"
> <test-equipment at mailman.qth.net>
> Cc: "Brooke Clarke" <brooke at pacific.net>
> Sent: Sunday, October 30, 2011 2:04 PM
> Subject: Re: [Test-Equipment] AN/PRM-10 Question
>
>
>> Hi Richard,
>> I have a PRM-10, that I haven't used for 6-8-10 yrs.  I
>> could pull it out, open it up, & ck anything (later
>> tonite) if you run out of things to do.
>> 73,
>> Al, W8UT
>
>     I may have misled myself about the choke. I've found
> something else that seems wrong and will follow it up and
> post here. Thank you all for being so helpful. I am off to
> work (graveyard shift) shortly so will work on the GDO
> tomorrow.
>

     Turns out I DID get mislead. After doing some more 
measurements I discovered that one stator of the tuning cap 
was grounded. The cap is part of an assembly with the dial 
and tube held to the case of the probe by several screws. I 
loosened all and wiggled the assembly around, then tightened 
it again. That fixed it! I don't know what was causing the 
short. The box shows lots of signs of having been worked on 
before so there could well have been some solder chips or 
something else of the sort in there. I also discovered that 
there may be a missing spacer for the coil mounting 
insulator (not sure this is the right description). I will 
see about replacing this later.
     Now, I have to track down the problem I had originally, 
namely that the audio oscillator stopped working. It was 
working when I received the rig but stopped after I did a 
frequency alignment. I have yet to measure all the voltages 
and resistances. It may turn out to be simple.
     Another problem is that the lowest frequency coil stops 
oscillating near its lowest frequencies. The others are 
strong all over. I don't know if this was a problem on 
reception or something else that happened while trouble 
shooting other things. I don't think its a weak tube because 
the tube tests good and is strong on the highest frequencies 
where one would expect a weak tube to have trouble. 
Nonetheless, I think I have another and will double check. I 
also need to make sure the compensating pot is really 
aligned correctly since that also could have an effect. 
However, if it was off by much the end stops would be 
affected and that would be obvious.
      FWIW, the value of resistance shown for pin-3 of the 
955 tube is wrong. Chart says 42 ohms, it should be 0.42 
ohms. I think there is also an error in the method of 
aligning the tuning cap and compensating resistor but will 
have to double check that.
     More when I have more and, again, thank you so much to 
all on this list who helped both on the list and via private 
e-mail.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com