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CB amplifiers RM-Italy KL203P

iz oos
 

There are some reasonably priced CB amplifiers on the market that maybe could be hacked for HF use, provided you add lowpass filters and make other mods. One of this is the RM-Italy KL-203P that is meant for SSB with an input power less than 20w and should work as is from 18 to 30Mhz (if you add the low pass filters). This amp also has a switchable receiving amplifier and totally RF sensed (no need for PTT). I know that these should not be over driven and do not represent the best example of linearity but has someone tried one of these?

Richie Chambless
 

I’ve thought about these amplifiers, also. Despite the negativity around them, I think the only thing that’s missing is the low pass filters (the ones biased for linear operation). I’m thinking they all use RF transistors, but I could be wrong.

iz oos
 

On their website you can download the schematic. They are a bit obscure on the mosfets, it seems they are four MS1307. As said they lack of any lowpass filters so as such they do not comply to the FCC rules.


Il 11/giu/2018 15:48, "Richie Chambless" <rchambless7@...> ha scritto:
I’ve thought about these amplifiers, also. Despite the negativity around them, I think the only thing that’s missing is the low pass filters (the ones biased for linear operation). I’m thinking they all use RF transistors, but I could be wrong.

iz oos
 

The MS1307 seem similar to the IRF520 btw


Il 11/giu/2018 18:39, "iz oos" <and2oosiz2@...> ha scritto:

On their website you can download the schematic. They are a bit obscure on the mosfets, it seems they are four MS1307. As said they lack of any lowpass filters so as such they do not comply to the FCC rules.


Il 11/giu/2018 15:48, "Richie Chambless" <rchambless7@...> ha scritto:
I’ve thought about these amplifiers, also. Despite the negativity around them, I think the only thing that’s missing is the low pass filters (the ones biased for linear operation). I’m thinking they all use RF transistors, but I could be wrong.

Valentin Braescu
 

I use the CTE Booster 747 amplifier modified like this : www.radioamatoripeligni.it/i6ibe/pdf/cte747.pdf

It works well , up to 80w on 40meters . I only need some ebay hf lpf's .


On Mon, Jun 11, 2018 at 19:47, iz oos
<and2oosiz2@...> wrote:

The MS1307 seem similar to the IRF520 btw


Il 11/giu/2018 18:39, "iz oos" <and2oosiz2@...> ha scritto:

On their website you can download the schematic. They are a bit obscure on the mosfets, it seems they are four MS1307. As said they lack of any lowpass filters so as such they do not comply to the FCC rules.


Il 11/giu/2018 15:48, "Richie Chambless" <rchambless7@...> ha scritto:
I’ve thought about these amplifiers, also. Despite the negativity around them, I think the only thing that’s missing is the low pass filters (the ones biased for linear operation). I’m thinking they all use RF transistors, but I could be wrong.

iz oos
 

I have checked the schematic and both the kl-203P and the CTE seem similar. Is the cap necessary or just a jumper would suffice to lower the frequency of operation? Would a mod at the input to keep the SWR acceptable be necessary? How much power you would use? Maybe a 6db attenuator at the input would be a solution, as the Ubitx provides over 10w at the lower frequencies and you might overdrive that amp in the lower bands.


Il 11/giu/2018 18:51, "Valentin Braescu" <valentin_braescu@...> ha scritto:
I use the CTE Booster 747 amplifier modified like this : www.radioamatoripeligni.it/i6ibe/pdf/cte747.pdf

It works well , up to 80w on 40meters . I only need some ebay hf lpf's .


On Mon, Jun 11, 2018 at 19:47, iz oos

The MS1307 seem similar to the IRF520 btw


Il 11/giu/2018 18:39, "iz oos" <and2oosiz2@...> ha scritto:

On their website you can download the schematic. They are a bit obscure on the mosfets, it seems they are four MS1307. As said they lack of any lowpass filters so as such they do not comply to the FCC rules.


Il 11/giu/2018 15:48, "Richie Chambless" <rchambless7@...> ha scritto:
I’ve thought about these amplifiers, also. Despite the negativity around them, I think the only thing that’s missing is the low pass filters (the ones biased for linear operation). I’m thinking they all use RF transistors, but I could be wrong.

Dennis
 

I have been using a RM Italy HLA-305v for a year or so. Passes the US requirements and was favorably reviewed by ARRL. I hooked up the uBitx to it and had no issues.

73, Dennis
W7DRW

Roy Appleton
 

A little pricey at $730!


On Mon, Jun 11, 2018, 5:54 PM Dennis <dennis@...> wrote:
I have been using a RM Italy HLA-305v for a year or so. Passes the US requirements and was favorably reviewed by ARRL. I hooked up the uBitx to it and had no issues.

73, Dennis
W7DRW

Jim Strohm
 

Iz,

If you have questions about solid-state (SS) amp topologies, please know that the RM-Italy amps (as do darn near every HF SS amp ever made since 1970) closely follow the Helge Granberg designs for Motorola, starting about 1968 and continuing well past 2000.

These designs are easy to find on the internet.

But as to your questions, it's difficult to get much more than a decade (e.g., 3 - 30 MHz, or 10X) of bandwidth using the older designs.  To go lower than 3 MHz, you'll need more rust in your ferrites -- that is, larger cores -- in both the input and output, and that tends to limit your high-frequency usability.  Especially w/ those RM-Italy amps.  Just adding a capacitor won't do it -- you can pull the input down in freq., but you'll lose at least the same comparable bandwidth up top.

If you look at the Jerry Sevick (SK) W2FMI books, you'll find some ways to stretch your bandwidth.  They're pretty simple to achieve once you know what you're doing, and not too expensive, but take a great deal of study at first.  And these books aren't cheap.

My recommendation?  Pay somebody who's already mastered the techniques for their expertise and finished products.

I have a few funny stories about making bootleg SS CB amps from the early 1980s.  Based on those experiences, I suggest people BUY these amps new or used, or at least buy dead ones from the ham radio flea market, and then resurrect them. 

Dead ones usually go for about USD$5 or $10, and the parts needed for resurrection are easy to determine, source, and replace.

Yes, you still need lo-pass filters.

73
Jim N6OTQ

Russ KG0BK
 

I ordered one just to have some more "fun" with.
Being a broadcast engineer I love to rework something to make it work with something else,
The one I ordered says from 20 mhz to 30 mhz it will do 250 watts.
Power output drops down below 20mhz.
Should be fun to play with.
Should have it by Friday the 15th.
I'll play with it over the weekend and post comments.

Russ     KG0BK

ajparent1/KB1GMX
 

Richie,

Its not so much what they use but how they use them.

I have a Silconix 100W SS (literally CB) amp.  Got it cheap for modding.  Base design is
EB63/Granberg with shortcuts and omissions.   Only a few things wrong with it.  Class B
zero bias (no bias circuit at all) so it had serious crossover distortion Add a regulated bias
and that cleans up. Then it needed varying drive depending on frequency and a seriously
bad input SWR at all frequencies from 3-30mhz.  New ferrite, equalization network plus
a 2db pad to keep it under 1.7:1.  Remove a half dozen mica caps factory installed to
try and calm the amp, added feedback.  Remove the useless RX preamp as it was
noisy and excessive gain.   Add switched LPF.

So why buy it?  The transistors were good (MFR454s), the heatsink and board were good,
and the TR relay worked.   Use it as was, not on a bet (it worked but RF dirty!).   Once I got
done it was a nice clean 13db amp that could run at 100W easily with 5W drive.

Way to many out there like that.

Allison

Richie Chambless
 

Thanks Allison! I’ve seen these amps used on EBay and thought they could be repurposed. This sounds like a cheaper and easier alternative to scratch building a 100 watt amp.

Sajid Rahum
 

I did get the KL203; not bad of course low pass filtering is required.  It works with 20m up. power mod is required and will make it once i get the caps 1200pf/50v for C14.

For softrock no lock; SSB output is too low to trigger it; not sure if anyone has thoughts to make the input power mod?