[Test-Equipment] AN/PRM-10 Question

[Richard Knoppow]

----- Original Message ----- 
From: "Brooke Clarke" <brooke at pacific.net>
To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>; "Discussion 
of Electronic Test Equipment" 
<test-equipment at mailman.qth.net>
Sent: Sunday, October 30, 2011 1:25 PM
Subject: Re: [Test-Equipment] AN/PRM-10 Question


> Hi Richard:
>
> Is it possible that there's a short somewhere else that's 
> in parallel with the choke?
> Did you check with the tube unplugged?
> If you have a digital camera try taking some close up 
> photos of the area from different angles an look at them 
> on your computer monitor, i.e. use the camera as a 
> microscope.
>
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com
> http://www.End2PartyGovernment.com/
>
>
     Thanks for the very quick response.
     This little choke is connected between the ground side 
of the filament and the cathode of the 955 oscillator. 
Physically it goes between the filament clip of the base and 
a collett type connector for the cathode pin so it can be 
pulled off and measured directly. When connected the tube 
acts like its running with no bias because the B+ gets 
pulled way down. If I lift the choke the plate voltage goes 
way up. To me that indicates the tube is either drawing no 
plate current or too much plate current. I will try a 47 ohm 
resistor in place of the choke to see what happens as  a 
trouble shooting tool (not sure I have a resistor of the 
right value).
     I've done a visual inspection of the choke using a 
strong LED flashlight and magnifying glass but can not find 
the fault. Its possible its not a single layer, I will 
inspect again. I can't understand how falling a couple of 
feet onto a thick carpet could have damaged something that 
can't move but who knows. The unit was intermittant when I 
got it.
     I would really like to either obtain a replacement 
choke or at least to know what its inductance is supposed to 
be so I can make one if necessary.

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