Fwd: [Premium-Rx] HP8640B

[Carcia, Frank A. HS]

	Hi Jeff,
	You hit the nail on the head. I turn it on and it kind of works over
part of the tuning range. Then after a while the power drops very low. I
wonder what
is on the inside surface of the cavity 
and slide. I wonder if it needs to be cleaned? The frequency was drifting
around but I thought it was just warming up. I have that child urge to take
it apart now.      TNX,
				fc	  

-----Original Message-----
From: jeffa at ix.netcom.com [mailto:jeffa at ix.netcom.com]
Sent: Friday, March 14, 2003 11:22 AM
To: premium-rx at ml.skirrow.org
Subject: Re: Fwd: [Premium-Rx] HP8640B


One problem that can happen with the 8640B is that, over a long time (years)
moisture can accumulate in the cavity, de'Q'ing it enough so that it stops
oscillating.  Symptoms include failure to oscillate when power is applied,
to oscillation stopping some time after power up and/or at band edges.

A solution that seems to work is to remove the oscillator assembly from the
unit and place it in a warm oven for half a day to a day.  Before placing in
oven, though, loosen up the "fine-tuning" part of the assembly that is
attached to the cavity - this will reveal a hole into the cavity, and it is
through this hole that the moisture can escape.  Make sure this hole is
exposed.

Also, make sure the cavity is tuned to its lowest frequency so that the
entire area of the cavity is exposed.

Let us know if it works for you!

- Jeff, WA6AHL

-------Original Message-------
From: Christine <christine2001_579 at t-online.de>
Sent: 03/14/03 07:59 AM
To: premium rx <premium-rx at ml.skirrow.org>
Subject: Fwd: [Premium-Rx] HP8640B

> 
> Dear Frank,

i  have the manual for the HP8640B (and have two of them for all kinds
of   rx-testing  (mainly  NF, IP2 + IP3, sensitivity, etc. etc.) and i
had a similiar problem with one of mine. this was a contact problem in
the mech. cavity-tuning, i solved with a lot of work ...

yours, Christine

ps thanks, Baruch, for the nice complement ...


>>       hi All,
>>       I just bought a broken HP8640B off Ebay.
>>       There appears to be a problem with the Cavity.
>>       The output drops very low after it has been
>>       on for a while. I have the procedure for setting
>>       the two levels. I wonder if anyone has ever 
>>       taken one apart or ever seen this problem.
>>       The power supply voltages appear normal.
>>       I wonder if there is a feedback probe   adjustment and the
>> transistor type used 
>>       in the oscillator. This was to be a hanger      queen but looks
>> clean with no cracked gears.
>>       It is the early model with wafer switches.
>>                               TNX,
>>                               fc

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