inexpensive/cheap cb amps . palomar/cobra vs. rm/kl

BOOTY MONSTER said:

if used just on cb and export frequencies whats your opinion of these amps ?

kl-300p Copper Electronics, Inc.
cobra 250 COBRA 250 BY PALOMAR-H&Y Electronics

H&Y Electronics

Click to expand...

Isn't the Cobra amp @H&Y a copy of the original?
Does it have the 1446's in it?

That 300P is a fine amp if not overdriven. Set DK to 1.5-2.0 watts and let it run. A single final radio is best for this amp, however I have used dual-mosfet radios with this too with success. If you could keep the radio PEP @ 25-watts or less, you'll be fine.

I think for what they are, a cheap cb amp those mosfet rm or kl or whatever amps are awesome... cheap, small make some watts.

H+y are doing the kl503 mosfet amp for the same price as the kl 300p listed under specials,can't be bad at that price.

Those blue face Cobra amps are supposed to be nice class AB amplifiers. If they could sell well on Evil-Bay I would love to buy 6 and sell 5, then mine is free.

kl503 with mosfets?

Are you sure the KL503 uses mosfets and not 1446's like the 500 and 501?
RM have not posted the diagram of the 503 on their website yet to check.

rgds,
Dave

I couldn't tell you what they are using in the KL-503. I sent RM Italy an email a couple weeks ago asking them, and here is their reply. Of course they are in Italy, and the English translation is not great, but here is what they said:


Dear sirs, we usede N.9 special transistors make for us!! Regards rm@rmitaly.com
------Messaggio originale------
Da: Jim
A:rm@rmitaly.com
Oggetto: KL-503
Inviato: 28 Set 2010 07:26

Hello,

I am interested in buying one of your new KL-503 amplifiers. Could you
please tell me what type of RF transistors are used in this unit, and how many?

Thank You,
Jim

KL503

You are right, They do use mosfets. an RM 4 driver and RM3's in the final.
A wild Arse guess is that the RM-3 is a re-badged IRF520 and they use 8 of them.
We will have to rip the lids off one of them and take a photo!

cheers,
Dave

So what do you think the actual output of the KL-503 would be using 8 mosfets? How is the performance of mosfets in these types of applications?

dd18 said:

Are you sure the KL503 uses mosfets and not 1446's like the 500 and 501?
RM have not posted the diagram of the 503 on their website yet to check.

rgds,
Dave

Click to expand...

Here is an link off the schematic.
http://cbradio.nl/rm/RM_KL503/Schema_RM_KL503.pdf.pdf

I like my RM KL503 i see 250W out of it on FM i still have not used it on SSB

Well.... put that baby on SSB and post the results!! Inquiring minds want to know!

i have owned a KL300p before and they are a "not bad" type of amp.

did about 150 to 180 watts PEP depending on input. it liked about a 1.5 to 2 watt deadkey.

they are class C, so SSB doesnt sound the greatest, and i found the SSB delay to be not quite long enough.

believe it or not, these things actually have a sub-par low pass filter built into them. not sure how well it worked, but it is there.

it did run hot, but never burnt out on me.

there is one MAJOR downfall to these amps IMO though.
the receive pre-amp is ON ALL THE TIME when the amp is on!
to me this was beyond annoying, as it ruined the great receive of my radio.
(we all know linear amp pre-amps are not the greatest)

i added an extra switch and made the pre-amp switchable, increased the SSB delay a bit, and the amp worked fine for me until i was tired of it and raped it for parts. LOL

the pre-amp thing alone would be enough for me not to recommend one to anyone.


i have not owned the cobra amp, but i would make damn sure its the class AB style with a built in low pass filter and not some cheap copy in the same case before i bought one.
(copper fooled quite a few people a few years ago with their palomar 225.
people thought they were getting a great deal on an AB box and ended up getting a bare bones class C 2x1446 amp)

if it is the "real deal" cobra AB amp, then its basically the same on the inside as the palomar 225 amp that you and i both have.

good luck,
LC

KL503

Without seeing the layout it does resemble a pair of KL203's with a driver.
I kl203 will do 160-200W PEP on SSB so I guess the KL503 should max out around 320-400 depending on frequency. Like the 203 it will probably only work well from 18-30mhz as on mine the input SWR rises to 2.5-3 to One on 14mhz.
Still put out some signal but it may affect the drive radio.
from 18mhz on up no problems.
cheers,
Dave

kl503 with mosfets

Could someone post a picture of the insides of this amp showing the transistor layout.
How does it go in SSB?
Anybody used them around 11m on SSB yet?
be nice to know cos they are a nice price.
cheers,
dave