[Test-Equipment] AN/PRM-10 Question

[Richard Knoppow]

----- Original Message ----- 
From: "k2cby" <k2cby at optonline.net>
To: <test-equipment at mailman.qth.net>
Sent: Tuesday, November 01, 2011 9:46 AM
Subject: [Test-Equipment] AN/PRM-10 Question


> It has been my experience that  wide range RF oscillators 
> (i.e., Grid Dip
> Oscillators and Signal Generators)  that use
>
> large value variable capacitors tend to poop out at the 
> low end where the
> capacitive reactance is lowest and the
>
> feedback demand is highest.
>
>
>
> The cure is usually a friskier oscillator tube.
>
>
>
> As a first step, be sure the oscillator has the proper B+ 
> voltage.
>
>
>
> After that, you might want to check component values of 
> the feedback
> network.
>
>
>
>
>
> Miles B. Anderson, K2CBY
> 16 Round Pond Lane
> Sag Harbor, NY 11963
> Tel.: (631) 725-4400
>
> Fax.: (631) 725-2223
> e-mail: k2cby at optonline.net
>
     Well, I've made some progress, or rather non-progress. 
The reason the oscillator is not putting out properly is due 
to a wiper that connects the rotors to ground through a 
resistor. It just doesn't make contact and nothing I can 
discover will make it do so. The wiper is a spring mounted 
contact on the top of the capacitor assembly that contacts 
the drive gear of the rotor through a hole in the frame. It 
just won't reach and pushing on it makes it short to the 
frame. Its mounted on a small bakelite insulator which, in 
turn, is mounted to the frame. You really have to see it to 
understand the problem. The rotor can't be moved because it 
is centered correctly in the stators and they are soldered 
in place to the frame. How the heck this thing ever work? 
The clearance between the end of the contact and the gear 
wheel its supposed to ride on has to be nearly a millimeter, 
if I push on the spring enough to make it touch it also 
touches the frame. Someone may know a trick for getting this 
right (I hope). Other problems I've found: the 6005 
(ruggedized 6AQ5) was dead. Replaced it. This tube serves as 
a series valve voltage regulator and also as part of the 
audio oscillator system. I've also found a couple of 1 meg 
resistors that have become 500K resistors. I will replace 
them. Usually composition resistors go up in value but I've 
found that often high value ones will go down. I still have 
not gotten the audio oscillator to work although it did when 
I got the box originally. Its a simple phase-shift 
oscillator so should not be too difficult to fix. I am 
disappointed that I will probably not be able to get this 
thing working as it should. My research shows it to be the 
most sophisticated of the GDOs, the Measurements Corp Model 
59 does not have the voltage regulated power supply and I 
think I prefer to have the indicator and dial on the same 
box. In any case, any help will be appreciated. I am not 
quite ready to give up on this thing but am getting close.


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