RM KL203-P

[9C1Driver]

The KL-200 is a class "C" single bipolar and really sound like crap on SSB.

Yea I dug out an old H & Y flyer and it was the KL-200p with a single 1446 final. Adding a P to the end of the KL-203 fooled me.

 

[William C. Colvin]

Hey, Dr DX.....

If you haven't already bailed on this thread, here's my take on your question. I have done this on a lot of amplifiers, especially solid-state mobile amplifiers from the 70s and 80s. Mostly, we would leave out the "high" switch since we were simply making the amplifier compatible with a radio that's just too big for it.

To do what you ask requires breaking the connection between the antenna relay, and the amplifier circuit. This is the circuit path feeding your radio drive into the amplifier circuit.

This will require finding the correct foil trace on the circuit board that carries this circuit and cutting a gap in the foil. The simplest of all methods is to wire a resistor across the cut in this foil trace. The resistor will now turn some of the radio's drive power into heat, and the remaining wattage will be what drives the amplifier.

Two problems with this approach.

First one is that you can't accurately calculate the resistance value of this resistor in advance. To get the desired drop in power will require what's commonly called a "cut and try" method. I would start with a 22 ohm resistor and see how much the power is reduced. If it's not enough, a higher value gets tried. And if it gets cut down too much, a lower value.

Now for the other problem. The amplifier must fool the radio into operating as if it were connected to an antenna. The amplifier's input circuit should have an impedance that is nearly the same 50 ohms as a properly-adjusted antenna. You check for this by putting a SWR meter and an additional coax jumper BETWEEN the radio and the amplifier. You key the radio with the amplifier set to operate, and measure the SWR as if it were an antenna. If the amplifier's input circuit is well designed, you'll see a reading under two to one. And if it's a sloppy design, this reading will be higher.

The "one resistor" method of reducing the amplifier's drive will change this "input-side SWR" reading. If it pushes the SWR too high, you need a more-complicated type of solution called an attenuator. The one we use in the Pride DX300 amplifier to cut the drive level in half uses three resistors. If you have a high input-side SWR with the single-resistor solution, you will need at least one other resistor that connects to ground to remedy this issue.

The wattage rating on your single resistor, or on the three we use in the Pride must be large enough to absorb the radio drive power without overheating.

If I were to try this, I would probably just use the "Preamp" switch on the front of the amplifier, taking it loose from the preamp function and rewiring it to simply short across the single-resistor setup. That would restore your normal (original) drive level. There is no good place to drill a hole and mount an additional switch on this amplifier.

But this would be a design project. Nobody has done this modification and posted it for us to copy that I know of.

73

If you lower your mic gain it will also lower your output power - or it does if using an old D-104 Power mic and gets rid of background distortion.

 

[old goat 321]

The 203p does have a pre amp and it does seem to work well..I used this amp for about 3 months mobile and now use it on a power supply on my base.

Hey Bamm, what size amp do you need to run your 203p?

 

[9C1Driver]

Hey Bamm, what size amp do you need to run your 203p?

Hmm, the kl203p is an amplifier. Low powered radio is plenty of drive for that amp. I would not run an amp into a kl203p.

 

[old goat 321]

Hmm, the kl203p is an amplifier. Low powered radio is plenty of drive for that amp. I would not run an amp into a kl203p.

I'm sorry for the misunderstanding what I'm talking about is an AC to DC power supply that would be sufficient to run the small amp.

 

[Tallman]

I'm sorry for the misunderstanding what I'm talking about is an AC to DC power supply that would be sufficient to run the small amp.

A fifteen amp power supply would be plenty for radio and amp. The KL-203 is fused for 12 amperes.

 

[old goat 321]

A fifteen amp power supply would be plenty for radio and amp. The KL-203 is fused for 12 amperes.

Thanks Tallman..

 

[radioreddz]

It amazes me how many will bash this amp or any product that they deem to. If you read the reviews on this amp about 90% of them are positive...yes it's a LOW drive amp, yes the pre amp amplifies EVERYTHING and yes I honestly have and use one! Am I embarrassed to admit it? Not at all, as a matter of fact I have recommended this little disposable amp to many..why you ask? Because it's a cheap way to get 100 watts and living in the Chicago area theft is common plus if it burns up your out like $50! I keep hearing people that have never used one say how terrible they sound yet I have had nothing but positive comments. I drive mine with 1.5 watts AM and about 8 watts on SSB and I see 80 ish watts AM and around 115-120 On SSB..I'm not saying this is the best amp ever but how are you going to comment on something that you have never used? I know...unless it's FCC approved ham gear it's not good enough for some...

Well said I love mine have 3 great way to get that first 100 watts

 

[old goat 321]

I brought in my 980 and rm 203p in from the pickup and hooked up to a new Megawatt p/s. Have it running into an a99 for a temporary base. The amp works on am and ssb both regardless of which mode is selected. From my trusty MFJ 872 swr/watt meter, looks like 50 dead key on am and swinging 90. Ssb is 100 or so pep. I dont have to flip the switch between am and ssb. Just wondering if anyone else has experienced this. Also, i have never done any thing to lower the dead key on the 980. It looks to be 3 watts. I use the amp rarely and when i do its not for long or sustained conversions.

 

[dave457]

50 watt dead key coming out of this amp is to high

 

[CB590]

Deadkey should be 25-30w and swing up from that. Most set the radio to 1.5w-2w..

Others have ran 3w and stock 980 and it is probably swinging to say 7 or so.. hence the 90w out.. which is good.

If you can find the right pot to turn it down a tad.to get the 30w you would be good and last longer.

 

[BammBamm]

Hey Bamm, what size amp do you need to run your 203p?

I have it on a old pyramid 35 watt.

 

[9C1Driver]

I have it on a old pyramid 35 watt.

35 amp.

 

[2NC995]

Somewhat of a hijack..but is anyone running one of these on SSB?

Wanting a cheap amp for my son to pair with a 980. This might be the ticket, if it’s acceptable on SSB.

 

[CB590]

Somewhat of a hijack..but is anyone running one of these on SSB?

Wanting a cheap amp for my son to pair with a 980. This might be the ticket, if it’s acceptable on SSB.

I ran mine with my Ranger 296DX that has a 16w pep on sideband. I was seeing 120-140w with the RM 203 all day. My avg voice was 75-100w or so. Definitely a little more umphh when shooting skip from my pickup.