Re: {Collins} KWM-380 and Alpha 76A



Butch,

A less invasive way to limit power to the Alpha amp is to ground Pin 25 of the rear panel Control Interface connector, provided:

  - your KWM-380 is equipped with the Control Interface option,
- Service Bulletin 17 (SB-17) has been performed or already cut into production, and
  - the Control Interface board is Rev H.

I know, a lot of if's. But if your rig is so equipped, dropping power to a safe level for the Alpha is made easy.

Pin 25 is the "TUNE POWER" input to the power amplifier ALC circuitry. If the amp ALC is set up correctly (i.e. ALC limits max power out to 90-100 watts), grounding Pin 25 will limit power output to about 30 watts, which may be sufficient and safe to drive an external grid-driven amplifier. However, when the TUNE POWER input is brought low, the rig's power output meter will still indicate near its normal reading (100 watts) and the ALC meter will read similar to what it does with Pin 25 ungrounded (maybe a little more). Therefore, your only indication that max power output is at the TUNE POWER level would be an external power meter.

In later production radios and those modified with SB-17 and having the Rev H Control Interface, the TUNE POWER connection from the PA was brought out to the rear panel for use with the CU-380 Antenna Coupler, so that the coupler can tune itself at reduced power output from the radio.

If you are currently using the Keypad attached to the Control Interface connector, you will have to bring out a flying lead connected to Pin 25 of the Keypad connector for external control of TUNE POWER such as with an external switch. Or, if the Alpha amp can provide a contact closure to ground when turned on, the reduction of KWM-380 power output to the TUNE POWER level can be automated.

Jerry Kessler,
N4JL


----------

At 05:39 PM 2/7/2010, Torrey Mitchell wrote:
My 380 has the modification where the power switch is replaced by a rotary
switch plus a variable pot resistor which varies the ALC.  This allows me to
cap the power as low as about 40 watts.  The mod was part of a general
make-over by Bob Struk, KX6K.

Torrey N9PY

-----Original Message-----
From: collins-bounces+torreym=mchsi.com@xxxxxxxxxxxxx
[mailto:collins-bounces+torreym=mchsi.com@xxxxxxxxxxxxx] On Behalf Of Butch
Schartau
Sent: Sunday, February 07, 2010 4:27 PM
To: collins@xxxxxxxxxxxxx
Subject: {Collins} KWM-380 and Alpha 76A

Is anyone using the above combo and if so, how do you keep the KWM-380 from
over driving the Alpha?

Butch K0BS
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_______________________________________________
SHARE THE FUN: JOIN THE COLLINS COLLECTORS ASSOCIATION TODAY !
http://www.collinsradio.org/membership/

 NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific
  SUNDAYS: 14.263 MHz-2000 UTC  +  AM Net: 29.050 MHz-1200 Central
  1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)

LIST HELP?  ADMIN EMAIL:  collins-owner@xxxxxxxxxxxxx
This ONLY goes to the list admins and does not post to the group!






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