Fwd: [Premium-Rx] HP8640B

[jeffa at ix.netcom.com]

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

CFAH> _______________________________________________

CFAH> Premium-Rx Mailing List
CFAH> To Post: premium-rx at ml.skirrow.org
CFAH> For Info: <a target=_blank
href="http://ml.islandnet.com/mailman/listinfo/premium-rx">http://ml.islandnet.com/mailman/listinfo/premium-rx</a>


_______________________________________________

Premium-Rx Mailing List
To Post: premium-rx at ml.skirrow.org
For Info: <a target=_blank
href="http://ml.islandnet.com/mailman/listinfo/premium-rx">http://ml.islandnet.com/mailman/listinfo/premium-rx</a>
>