Problem with RM KL 805 Linear Amp!

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Rusty_Cockroach
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Problem with RM KL 805 Linear Amp!

Post by Rusty_Cockroach »

My son bought me this amp for my birthday...

I not sure I have a problem with the amp or my setup...

If I input more than 10 watts from the radio the SWR rises and the amp shuts down, due to high SWR.

In normal operation the SWR is 1.0:1 on channel 19 UKFM, on both Channel 1 and 40 UKFM the SWR is 1.2:1. So the SWR is low on all UKFM channels.

The SWR rises to over 2.0:1 if I increase radio wattage over 10 watts. This is when the amp shuts down.

My setup...
CRT SS 6900N
RM KL 805 Amp (24v, powered by two 12v car batteries i.e. outputting 24v)
Home Made 6M Vertical, end fed antenna, with three 65cm ground planes and a bottom loaded coil (1.7 microhenry ).

In all other aspects the amp seems to be working fine and does output 350 watts @ 10w input.

I'm not worried about out putting loads of watts, 100 is enough for me, but would like to know why this is happening!

Thanks for any ideas!
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ch25
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Re: Problem with RM KL 805 Linear Amp!

Post by ch25 »

Test on dummy load and report results.
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Rusty_Cockroach
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Re: Problem with RM KL 805 Linear Amp!

Post by Rusty_Cockroach »

Thanks ch25... I'm getting a dummy load to test further!

Things have improved somewhat!

I dug out my old variable 50 Amp PSU (12v to 24v).

If I use the two 12v batteries to power the RM amplifier I get the result as my first post i.e. radio output more than 10w, with the amplifier on high power, it shuts down due to high SWR.

With the PSU set to 24v, the amplifier will run at high power with 15w input, although the SWR does rise.

My results...
@ 10w input
L - 80W - 11A - 1.0:1 SWR
M - 200W - 18A - 1.0:1 SWR
H - 350W - 25A - 1.0:1 SWR

@ 15w input
L - 125W - 14A - 1.0:1 SWR
M - 295W - 22A - 1.0:1 SWR
H - 430W - 30A - 2.1:1 SWR (48W Reflected)

So, with the PSU instead of the batteries the amplifier doesn't shut down and will output more power. But the SWR still rises to a steady 2.1:1 on full power @15W input. With the batteries I'm not sure how high the SWR goes before it cuts out, I suspect more.

Maybe the amplifier has a fault or with the coax/antenna. But I didn't think the batteries would have an impact.
Rusty_Cockroach
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Re: Problem with RM KL 805 Linear Amp!

Post by Rusty_Cockroach »

OK... I fixed the problem with SWR rising on high power...

I made a 1:1 balun/choke aka like in this video...
and attached it to the base of my vertical antenna.

Now, my SWR stays steady (1.0:1). @ over 800w SSB/500w FM. Even when the SWR is not perfect i.e. 1.2:1 (channels 1/40 FM) the SWR doesn't flutuate at high power.

I suspected it maybe could be! common mode returning from the antenna along the coax. In any case my problem is fixed.
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astradyne
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Re: Problem with RM KL 805 Linear Amp!

Post by astradyne »

Rusty_Cockroach wrote: 05 Sep 2021, 04:44 OK... I fixed the problem with SWR rising on high power...

I made a 1:1 balun/choke aka like in this video...
and attached it to the base of my vertical antenna.

Now, my SWR stays steady (1.0:1). @ over 800w SSB/500w FM. Even when the SWR is not perfect i.e. 1.2:1 (channels 1/40 FM) the SWR doesn't flutuate at high power.

I suspected it maybe could be! common mode returning from the antenna along the coax. In any case my problem is fixed.
Great news! It's always good to hear a happy ending.
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Buick Mackane
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Re: Problem with RM KL 805 Linear Amp!

Post by Buick Mackane »

TRX Bench is a good channel. Peter certainly knows his stuff.
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Rusty_Cockroach
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Re: Problem with RM KL 805 Linear Amp!

Post by Rusty_Cockroach »

astradyne wrote: 05 Sep 2021, 09:55 Great news! It's always good to hear a happy ending.
Yes indeed, always nice to solve something technical, even with my limited knowledge. The PSU v battery testing results (as above in previous post) was a red herring, one of the batteries was faulty. So the power source didn't impact the problem. The faulty battery couldn't handle the amperage.

Hopefully my fix will be helpful to others who have a similar problem. I have read elsewhere on the interweb, instances of people saying SWR is a problem at high output with this and similar amps. I suspect in most cases its not the amp that's at fault.
Buick Mackane wrote: 05 Sep 2021, 16:02 TRX Bench is a good channel. Peter certainly knows his stuff.
I watch TRX Bench quite often and Peter is great at explaining stuff. I've made and repaired a few things now. Including repairing my old Harrier CBX, which is now in tip-top condition.
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Re: Problem with RM KL 805 Linear Amp!

Post by cb4ever104 »

Rusty_Cockroach wrote: 14 Aug 2021, 00:31 My son bought me this amp for my birthday...
My kids bought me socks. I'm going to have to have a word with them :lol:
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