[Icom] 765 output spike

Wed, 05 Jun 2002 10:39:21 -0700

Hi Floyd,

This initial output spike is caused by an excessively long ALC attack time; a
similar problem exists in the IC-781.

From a look at the schematic, I believe that you may be able to decrease the ALC
attack (and decay) times by reducing the value of C92 (now 1 uF). You could also
increase the value of R149 (now 100 ohms). Refer to IC-765 Service manual, p.
9-1, MAIN Unit.

If you do not have a service manual, I can scan the relevant pages and e-mail
them to you.

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/
Note new e-mail address:
mailto:[email protected]

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Floyd Sense
Sent: Wednesday, June 05, 2002 06:44
To: [email protected]
Subject: [Icom] 765 output spike

I've seen this problem documented for other HF rigs, but have been unable to
locate anything for the 765.  Has anyone found a cure for this ?

Problem: In SSB mode with the power control at maximum, keying the PTT
switch results in a short output spike of around 50 watts as seen on a peak
reading wattmeter.  The 765 power meter shows only about 10 watts owing to
the short duration of the spike.  This occurs with no audio input, mic gain
at full CCW.  Reduction of the spike appears to be relatively linear as the
power control position is moved CCW.

I've read through the mods for the 765 and found nothing describing this
condition, although there is one item that addresses  improved T/R
switching.  Any ideas greatly appreciated.

K8AC