I just received my amp a RM Italy KL-503 for $130.00 I am getting an unbelievable 500 watts on high setting on am dead key. My base station is powered by a MEGA-WATT 33 amp switching power supply. I have checked this with THREE DIFFERENT meters all showing the same approximately. I checked my 148GTL wattage it showed a five watt dead key and swinging to about fifteen watts I turned it down to one watt dead key but unbelievably still swinging to fifteen watts the strange part is I only get barely eighteen watts on ssb peaks. Now I get about two hundred twenty watts dead key with the amp set on high but amazingly with audio peaks on am four hundred eighty watts. The only thing that I did to my Cobra 148GTL was clip just one of the audio limiters and turned the alc to it's max and added a Workman DM5000 echo power mic which does not seem very noise canceling as it picks up noise anywhere in the room like my old Silver Eagle did. I got several radio checks from the only ten CBer's near me which are all fifty to sixty miles away they told me to turn that echo down! When I came back after tuning it way down they recognized now who I am and got really good comments of how good my radio sounds strong signal, great forward swing, loud audio etc. The Workman DM-5000 is the only power mic that has worked on my 148 all the others squealed at the lowest setting. Just wanted to let some of you guys that are on a limited budget like I am get out there and sound like a BIG radio station. All my equipment comes from eBay some new some used and the amp from H&Y electronics. Any comments welcome especially from the experienced and seasoned techs appreciated.
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Cobra 148GTL RM Italy KL-503
- Thread starter hammer0630
- Start date
It is unbelievable to get 500W with a 33A PS.
33A*14V=462W. That's with an imaginary 100% efficiency amp.
Something is wrong.
33A*14V=462W. That's with an imaginary 100% efficiency amp.
Something is wrong.
Mega Watt 33 amp power supply
RM Italy KL-503 web site does state it needs I forget the amps needed on low but I do remember what the input amps needed on high is 30 amps. The Mega Watt power supply does state 33 amp surge and 30 amps continuous. I did have the 148 powered with the KL-503 together on the same power supply and it did seem to over tax the supply. When I keyed my 148 with the amp on high the meter light on the 148 would get brighter with audio instead of getting dimmer only on the last two high settings on the amp. I separated the 148 to it's own power supply. Now I get reports of forward swing on all power settings except on max high they said there needles stay even (don't move either way) with dead key and with audio what is strange about this report is on my meter I am swinging several hundred watts forward swing. This switching power supply is strange to me how it works when pushing the amp on high my desk lamp dims when I speak but their is no sign of the amp seeming to be working any harder as compared to power supplies that use a transformer. As you can tell I use very primitive techniques to go by for lack of diagnostic equipment and mostly not knowing how to use it if I had it. By the way I used a PDC 600 meter 1000 watt scale max, a Para dynamics meter, and a brand new Workman HP201S 1-KW to test my wattage output. According to reports from fifty miles away my bare foot signal compared to my amplified signal is dramatically different
RM Italy KL-503 web site does state it needs I forget the amps needed on low but I do remember what the input amps needed on high is 30 amps. The Mega Watt power supply does state 33 amp surge and 30 amps continuous. I did have the 148 powered with the KL-503 together on the same power supply and it did seem to over tax the supply. When I keyed my 148 with the amp on high the meter light on the 148 would get brighter with audio instead of getting dimmer only on the last two high settings on the amp. I separated the 148 to it's own power supply. Now I get reports of forward swing on all power settings except on max high they said there needles stay even (don't move either way) with dead key and with audio what is strange about this report is on my meter I am swinging several hundred watts forward swing. This switching power supply is strange to me how it works when pushing the amp on high my desk lamp dims when I speak but their is no sign of the amp seeming to be working any harder as compared to power supplies that use a transformer. As you can tell I use very primitive techniques to go by for lack of diagnostic equipment and mostly not knowing how to use it if I had it. By the way I used a PDC 600 meter 1000 watt scale max, a Para dynamics meter, and a brand new Workman HP201S 1-KW to test my wattage output. According to reports from fifty miles away my bare foot signal compared to my amplified signal is dramatically different
A KL-503 won't key anywhere near 500 watts or do 500 watts peak swing either.
If you turned a Cobra 148 GTL from 5 watts key to 1 watt, unless an NPC mod was done, there is no way the swing will remain the same.
P=IV so there is no way a 30 amp power supply would handle 500 watts key...that would take 36 amps at 100% efficiency.....so your wattmeter needs calibration or adjustment.
If you turned a Cobra 148 GTL from 5 watts key to 1 watt, unless an NPC mod was done, there is no way the swing will remain the same.
P=IV so there is no way a 30 amp power supply would handle 500 watts key...that would take 36 amps at 100% efficiency.....so your wattmeter needs calibration or adjustment.
Frequency 20-30 MHz
Supply 12-14 Vcc
Input energy/power 12-30 A
Input power 1-6 W
Input power SSB 2-12 W
Output power 250 W Max
Output power SSB 450 W PEP Max
Mode AM-FM-SSB-CW
Fuse 3x10 A
Output power level 6
Size 170x295x62 mm
Weight 1.5 Kg.
Antenna preamplifier 26 dB
www.rmitaly.com
To be perfectly honest, I see a lot of puzzling things about this setup you posted.
AS mentioned, you cannot get 500 watts of power - SSB or AM - from a 33 amp supply. You would be lucky to see 300 out of it. For 500 watts out, I would choose a 60 amp supply. However, that amp is only rated for 450 watts peak power on SSB; not AM. There is DEFINITELY something wrong if you are seeing 500 watts!
Even if you used three different meters, unless they are tech grade meters, take any reading from the meters you used with a grain of salt.
RM amps are notorious for blowing up because of too much input power.
Big numbers output truly fail to impress unless it is relatively clean output.
No one likes to hear massive signal distortion, unless someone taught you incorrectly.
You removed the AM regulator; did you also disable the 54mhz trap filter in the radio as well? If you did; then you made two major mistakes. Only forcing the radio to have massive harmonics that are going anywhere but the freq that you are on. Basic CB Radio 101. Crap out of the radio amplified by an external amp will only ensure that you will have amplified even more crap out.
A radio with massive output distortion is only harder to read from a receiving station.
Think about it.
Just the facts, ma'am . . .
Supply 12-14 Vcc
Input energy/power 12-30 A
Input power 1-6 W
Input power SSB 2-12 W
Output power 250 W Max
Output power SSB 450 W PEP Max
Mode AM-FM-SSB-CW
Fuse 3x10 A
Output power level 6
Size 170x295x62 mm
Weight 1.5 Kg.
Antenna preamplifier 26 dB
www.rmitaly.com
To be perfectly honest, I see a lot of puzzling things about this setup you posted.
AS mentioned, you cannot get 500 watts of power - SSB or AM - from a 33 amp supply. You would be lucky to see 300 out of it. For 500 watts out, I would choose a 60 amp supply. However, that amp is only rated for 450 watts peak power on SSB; not AM. There is DEFINITELY something wrong if you are seeing 500 watts!
Even if you used three different meters, unless they are tech grade meters, take any reading from the meters you used with a grain of salt.
RM amps are notorious for blowing up because of too much input power.
Big numbers output truly fail to impress unless it is relatively clean output.
No one likes to hear massive signal distortion, unless someone taught you incorrectly.
You removed the AM regulator; did you also disable the 54mhz trap filter in the radio as well? If you did; then you made two major mistakes. Only forcing the radio to have massive harmonics that are going anywhere but the freq that you are on. Basic CB Radio 101. Crap out of the radio amplified by an external amp will only ensure that you will have amplified even more crap out.
A radio with massive output distortion is only harder to read from a receiving station.
Think about it.
Just the facts, ma'am . . .
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My base station
The 148 I am using was made in Malaysia it came in the original box all Styrofoam plastic bagged owners manual etc. It did have signs of being taken out of the box so I am not sure of it's history. I snipped one of the audio limiters which CB radio magazine.com they recommended if you really feel the need to get louder audio you could remove R-33 marked on the circuit board and this would not effect your audio on ssb (warble) The power supply I have was purchased to power a RM Italy KL-203 which burned out with my wife's long key downs and driving it with what I know now was five watts dead key it was putting out eighty watts swinging to one hundred twenty watts. The one watt I now have on the 148 is as low as I can set it at and my meter on the 148 now the needle only moves about one third of the way up dead key and pegs the needle all the way with audio. I am not really a skip talker but now conditions are everyday sun up to sun down it wasn't like this when I last used a CB back in the eighties with this KL-503 I can get out or get back to almost everyone on am or ssb. Despite popular belief the the audio is clean almost overwhelmingly loud and with the KL-503 in gear the output signal is everywhere I could not reach before. For you guys that want a good sounding station with out spending a fortune the Cobra 148GTL $70.00 used/Mega Watt 33 amp power supply new $55.00/KL-503 amp new $130.00/New Workman DM5000 echo & talk back & down loadable sound byte power mic $39.00/New Patriot antenna $49.00/New Workman HP201S 1 KW watt-swr illuminated meter $37.00/ 50' large diameter coax $25.00/Jumpers amphenol connect $10.00 each/RF Limited antenna matcher new $37.00/Two 5"X5"cooling fans with guard $29.00 new/Motorola ext.speaker used $10.00/ eBay everything except amp H&Y electronics.
The 148 I am using was made in Malaysia it came in the original box all Styrofoam plastic bagged owners manual etc. It did have signs of being taken out of the box so I am not sure of it's history. I snipped one of the audio limiters which CB radio magazine.com they recommended if you really feel the need to get louder audio you could remove R-33 marked on the circuit board and this would not effect your audio on ssb (warble) The power supply I have was purchased to power a RM Italy KL-203 which burned out with my wife's long key downs and driving it with what I know now was five watts dead key it was putting out eighty watts swinging to one hundred twenty watts. The one watt I now have on the 148 is as low as I can set it at and my meter on the 148 now the needle only moves about one third of the way up dead key and pegs the needle all the way with audio. I am not really a skip talker but now conditions are everyday sun up to sun down it wasn't like this when I last used a CB back in the eighties with this KL-503 I can get out or get back to almost everyone on am or ssb. Despite popular belief the the audio is clean almost overwhelmingly loud and with the KL-503 in gear the output signal is everywhere I could not reach before. For you guys that want a good sounding station with out spending a fortune the Cobra 148GTL $70.00 used/Mega Watt 33 amp power supply new $55.00/KL-503 amp new $130.00/New Workman DM5000 echo & talk back & down loadable sound byte power mic $39.00/New Patriot antenna $49.00/New Workman HP201S 1 KW watt-swr illuminated meter $37.00/ 50' large diameter coax $25.00/Jumpers amphenol connect $10.00 each/RF Limited antenna matcher new $37.00/Two 5"X5"cooling fans with guard $29.00 new/Motorola ext.speaker used $10.00/ eBay everything except amp H&Y electronics.
none of the meters you have mentioned are known for accuracy, which also if i'm not mistaken is being compounded by the measurement being taken into a reactive antena and not a resisitive dummy load.
as others have pointed out that amp will never do 500w, on 11m anyway, i think robb might be closer to the mark at 300, but even that is probably ambitious, especially knowing rm's and zetagi's concept of what a watt is, in italy 2w = 1w everywhere else.
as others have pointed out that amp will never do 500w, on 11m anyway, i think robb might be closer to the mark at 300, but even that is probably ambitious, especially knowing rm's and zetagi's concept of what a watt is, in italy 2w = 1w everywhere else.
Dummy load vs. active antenna
That is an interasting point I haven't completely thought of before. I have never invested or really thought of investing in a dummy load and kind of puzzled that there is a market for this and it is rather expensive. I kind of thought that these are more for radio techs that often are testing radio equipment to invest in one who might merely be checking for audio squeal or swr's briefly on the air seemed not worth spending that kind of money.
That is an interasting point I haven't completely thought of before. I have never invested or really thought of investing in a dummy load and kind of puzzled that there is a market for this and it is rather expensive. I kind of thought that these are more for radio techs that often are testing radio equipment to invest in one who might merely be checking for audio squeal or swr's briefly on the air seemed not worth spending that kind of money.
How has the amplifier been performing and holding up??
An Update would be nice.
Thanks
I have all my ducks in a row and I just barely touch a 300 reading on the LP100a with an Astron RS70. Nothing but glowing audio reports using classic gear on SSB.
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It's been really great so far. I have invested in several meters since then and a higher amp power supply. I have my 148 set now at two and a half watts which is giving me two hundred fifty watts dk on high and swinging to about three hundred forty five watts audio on AM. My 148 swings about twelve watts with it's original dynamic.
That's a 1 driving 8 mosfet amp, I think it runs rebadged irf520 mosfets
That being said you would really need to be careful on how much power you are running into it
Is your power supply this one? http://www.12voltpowersupplies.us/ the s-350-12?
That being said you would really need to be careful on how much power you are running into it
Is your power supply this one? http://www.12voltpowersupplies.us/ the s-350-12?
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