VGA cable - beware

[MontyS]

I am preparing to install an amplifier on my K3.  To get the ALC signal from the 15 pin DIN plug I was hoping to use a VGA cable, cut one end off, and wire it up accordingly.

 

Unfortunately pins 3,4,5,6,7,8 and 11 are all grounded in the cable.  There are 4 shielded wires in the cable and the ground foil on the outside.  So I will have to cut off the offending pins or spring for a male connector.

 

Monty K2DLJ

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[Jim Brown-10]

Modern power amps (built after about 1975) do NOT need AGC -- in fact, they often create lots of distortion (splatter, clicks, sideband noise) when you use AGC. The RIGHT way to control power (drive) is to use the power control on the rig that you're using to drive it. Simply bring up the power on the transceiver until you reach the desired power from the amplifier.

While many power amps include an AGC line, their manuals often tell you not to use it. The manuals for my Ten Tec amps (Titan 425, Hercules I, Hercules II) specifically tell you NOT to use AGC.

73,

Jim K9YC

--Original Message Text---
From: Monty Shultes
Date: Sun, 30 Nov 2008 10:02:50 -0500

To get the ALC signal from the 15 pin DIN plug I was hoping to use a VGA cable, cut one end off, and wire it up accordingly.



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[Jerry Flanders]

Your research is not complete, if you actually meant ALC. Yaesu's
Quadra uses ALC as an emergency shutdown method to protect the amp in
emergency situations. It  is REQUIRED.

I once had a flakey antenna coax open up when running full 1500 watts
on RTTY with an AL-1200 and blew up the output circuit. I was not
using ALC then. I use the Quadra now, and insist on using ALC per
Yaesu's recommendation.

You probably could not manually shut down drive fast enough in an
emergency to save the SS output devices if you were not using the
ALC. Tubes maybe. Either way, why risk it?

I agree that we shouldn't be trying to regulate power levels this way
- but as an emergency protective measure, it can save your butt.

Jerry W4UK

At 01:43 PM 12/1/2008, Jim Brown wrote:

>Modern power amps (built after about 1975) do NOT need AGC -- in
>fact, they often create lots of distortion (splatter, clicks,
>sideband noise) when you use AGC. The RIGHT way to control power
>(drive) is to use the power control on the rig that you're using to
>drive it. Simply bring up the power on the transceiver until you
>reach the desired power from the amplifier.
>
>While many power amps include an AGC line, their manuals often tell
>you not to use it. The manuals for my Ten Tec amps (Titan 425,
>Hercules I, Hercules II) specifically tell you NOT to use AGC.
>
>73,
>
>Jim K9YC
>
>--Original Message Text---
>From: Monty Shultes
>Date: Sun, 30 Nov 2008 10:02:50 -0500
>
>To get the ALC signal from the 15 pin DIN plug I was hoping to use a
>VGA cable, cut one end off, and wire it up accordingly.
>
>
>______________________________

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[P.B. Christensen]

> Your research is not complete, if you actually meant ALC. Yaesu's Quadra
> uses ALC as an emergency shutdown method to protect the amp in emergency
> situations. It  is REQUIRED.

That's a poor RF design strategy.  If a SS amp is so sensitive to input RF
drive level that it requires feedback from the exciter (of all brands) to
protect itself, then the amp should also be smart enough -- and fast
enough --to know when it's being overdriven.

Think about it.  Yaesu is relying on a complete unknown from a transceiver.
While they specify the use of ALC from the transceiver for use with their
Quadra amp, they have no idea about "Brand X transceiver's" ALC response
time.  A ca.1969 Heathkit HW-100 has an ALC circuit for connection to an
external amp.  Are we to assume that a 40 year-old transceiver will have
adequate ALC dynamics as do some (but not all) of the modern transceivers?

The only time that ALC could possibly make any sense is to use a like-brand
amp and transceiver (e.g., Yaesu FT-2KD with the Quadra).  This allows a
manufacturer of both the rig and amp to satisfy the proper ALC "meet me
point."

Paul, W9AC



 

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[Jim Brown-10]

On Mon, 01 Dec 2008 14:39:16 -0500, Jerry Flanders wrote:

>I agree that we shouldn't be trying to regulate power levels this way
>- but as an emergency protective measure, it can save your butt.

I agree, and have no problem with using it that way.

73

Jim K9YC


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