[Kenwood] ALC with Kenwood TS-830S

[ken.d.brown at hawaiiantel.net]

Hi Steve,

I think using the ALC to keep the power output down to 5 Watts on a 
system that normally puts out about 100 Watts is not likely to work very 
well. I had difficulties just trying to reduce drive to 50 watts on a 
100 watt radio. A very different radio, but I'll tell you the story 
anyway.

I was using a TS-440 (yes I know a solid state PA not tubes like the 
830) to drive an SGC SG-500 amplifier. The SG-500 needed to have about 
50 to 60 watts of drive. Anything higher would make the SG-500 
protection circuitry switch in it's own internal input attenuator. Of 
course you cannot have the protection circuitry switching in the 
attenuator at the beginning of every transmission. That would no doubt 
make the leading edge of the first dit or dah sound really weird and 
probably wear out some relay contacts pretty quickly.

I thought I could just turn down the TX power with the front panel knob 
on the TS-440 and everything would be fine. I did that, and it seemed 
like it was working, until Mort W6JU (SK) told me there is something 
funny about my signal. I couldn't hear the problem on a receiver, 
because the signal was just too loud locally. I had to look at my signal 
on an oscilloscope to see what was happening. What I discovered was the 
when I turned to TX power down on the TS-440 the keying envelope 
changed. The rise time of the CW waveform got longer and the leading 
edge of the envelope not as steep as it should be. It gave the signal a 
very "soft keyed" kind of sound and probably reduced the useable keying 
speed significantly. By the way, the TS-440 did this all on it's own. It 
didn't matter whether it was driving the amplifier.

I tried some adjustments in the ALC circuit, I found I could set it up 
so that the keying envelope was normal at 50 or 60 Watts output, but 
then I could not get full 100 Watt output from the TS-440. I considered 
leaving it adjusted this way and having a TS-440 that wouldn't put out 
full power. I didn't really like that idea and settled on building an 
attenuator to put between the TS-440 and the amplifier. The 2.5 to 3 dB 
attenuation would never be noticed on receive, at least not on the lower 
bands. I also had separate TX and RX antennas and did not necessarily 
listen on the antenna connected to the amplifier. That is a different 
story.

In your case having to reduce the power from 100 watts to 5 watts will 
require a 13 dB attenuator, and that amount of attenuation in the 
receive signal path may be objectionable. You may need rearrange your 
T/R switching so that the receive path is not through the amplifier 
internal T/R switching system and not through the attenuator.

Have fun DE N6KB

On 2021-03-29 07:23, Steve H wrote:
> Trying out this alternative to using an attenuator
> with my 830S and an older linear that only needs 5-10W to excite.
> 
> Was told to get pin 6 on the remote connector din and get a 9v battery 
> with
> a 225k potentiometer on it and feed the wiper as per the attached
> illustration.
> 
> Thats seems to be for the 520/820s now that I notice. Turns out all the
> hybrids use pin 6 for the alc, but I notice they are putting the gnd 
> into
> pin 4 on this diagram.
> 
> https://www.mediafire.com/view/5sf9ovlmvhvkqjv/alc.jpg/file
> 
> 
> I had tried this but used the chassis ground and pin 6
> thinking that would work, but it does not have any effect. Pin 4 on the 
> 830
> is to the NO contact of the control relay, so I dont think this will 
> work.
> 
> Has anyone used the ALC on their 830 to limit input to their linear?
> 
> 
> 
> Steve
> KA2PTE
> 
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