[ICOM] IC-746PRO with Ameritron Amps

[Alan Zack]

Several of us with Ameritron Amps have been experiencing keyup 
problems when using IC-746PRO's.
I tried searching the archives on the 3 IC-746 related lists but could 
  not find any info on this problem.

Here is the situation:
IC-746 and Ameritron Amp combo works fine on AM, FM, CW, and RTTY.
On SSB there is SOMETIMES, not always, a slight delay to see power out 
when keying.  For example, my call is K7ACZ.  I can push the PTT on my 
mic, say K7ACZ but only the ACZ gets transmitted.  The amp relay 
clicks in fine with the PTT being pressed but does not show power out 
until after a slight delay.
Looking at the IC-746's meter when this happens I observe the Po not 
showing power out on my first word or so, the SWR is at minimum and 
the ALC goes full scale, past the normal range.  After a short delay 
everything is normal.
Operating conditions:
1.  Does this regardless if the ALC line is connected between the 746 
and amp or not.
2.  Does it at all power levels of the 746.  Have tried from 10 watts 
to 100 watts, no difference.
3.  Does it on all bands.
4.  Does it regardless if the 746PRO auto tune is on or off.
5.  Hitting the 746PRO TUNER button (to force the 746 to tune to the 
amp's input circuits) does not help.
6.  Tried doing a steady AHHHHHHHHHHHHHHHHHHHHHH into a dummy load, 
hitting the PTT on and off, and watching sometimes full power as soon 
as the PTT is pressed and other times a slight delay.  Each time there 
is a delay the 746PRO meter shows no Po and max ALC for a second.
7.  As expected, VOX cannot be used as each time VOX drops out and 
then kicks back on you may or may not be putting power out.

Have tried different coaxes, went direct into a dummy load, different 
antennas, no change.

Keying circuit is a direct connection from 746PRO's SEND jack to Amp's 
RELAY jack, no buffers or extra keying circuits.  Ameritron says their 
amps will not damage the 746PRO's keying circuits by using a back 
pulse canceling diode in the AL-80B I have.

Has anyone else experienced this?  On the Ameritron Amp reflector it 
seems only a few of us see this, and only with the 746PRO.

I have just purchased this amp Friday from AES and am ready to return 
it if I can't figure out this keyup problem.  I am a contester and 
want to use my VOX, which I can't do with this amp.

TIA & 73
-- 
__________________________________________________________________________ 

Alan Zack
Amateur Radio Station K7ACZ
Las Vegas, Nevada, USA
Quality Engineer, The Boeing Company, Retired
Aviation Chief Warrant Officer, U.S. Coast Guard, Retired
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