[Test-Equipment] TEK 494AP Gain problems

[Fuqua, Bill L]

  Entirely possible, once I have time to get into it I will take a look.
They use PIN diode attenuators and variable gain stages which are
voltage controlled and possible that the control voltages are fluctuating.
  I have to get time, ie get other projects for other folks, out of the way
before I can get inside. This is the best spectrum analyzer I have. I have
a 494P and a 495P as well. I sold my 496P sometime ago and now wish I
had kept it for parts. 
  Thanks for the email, I appreciate the suggestion. Once I pin down exactly where
the variation is taking place I can then track down the specific source. 
   thanks again es
73
Bill wa4lav

________________________________________
From: test-equipment-bounces at mailman.qth.net [test-equipment-bounces at mailman.qth.net] on behalf of Alan Melia [alan.melia at btinternet.com]
Sent: Thursday, December 12, 2013 1:26 PM
To: test-equipment at mailman.qth.net
Subject: Re: [Test-Equipment] TEK 494AP Gain problems

Hi Bill I have one of these here but with a major PSU  problem ....I can
even think of RF problems
:-((

At the risk of "insulting" your technical skill :-))  I must say that, being
kit of "a certain age" it feels awfully like a sort of power supply problem
.......probably not the main supply itself but maybe an electrolytic
decoupler or two. It is these sort of symptom I have seen in receivers where
the emitter decoupler is "dry" leading to negative feedback on that stage
(lower gain) this slowly recovers some capacitance after power is applied,
and the gain comes back. Tacking a new cap across the installed one is a
quick way of checking.

That may be totally off beam but it may trigger someone to respond telling
me I am totally wrong ang giving you the correct diagnosis :-))  I dont mind
sticking my neck out if it helps in any way.

Good Luck with it.
and Best Wishes for the Holiday Season
Alan
G3NYK



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