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RM KL503 & SSB compatibility

Discussion in 'General CB Services Discussion' started by Dereka5, Jul 29, 2021.

  1. Dereka5

    Dereka5 Member

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    I've got a RM KL203P here for the Car, & thd audio reproduction on SSB is pretty good.



    I'm thinking about getting the KL503 for the Car, so can any users tell me if they sound OK on SSB please?
     
    #1 Dereka5, Jul 29, 2021
    Last edited: Jul 29, 2021

  2. ForestRunner98

    ForestRunner98 917 SoCal

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    I have the same 203 and it’s great on SSB as well. I am also in the market for a 503 or 506 and I have read that they both work well on SSB.
     
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  3. BigLou

    BigLou Active Member

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    I have one 503 it work,s fine on SSB.
     
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  4. Dereka5

    Dereka5 Member

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    @BigLou

    Do you have the HD version, or the Blue standard one as per the image?
     

    Attached Files:

  5. 9C1Driver

    9C1Driver Sr. Member

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    Either will work fine on SSB.
     
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  6. Dereka5

    Dereka5 Member

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    I've just been doing a bit if reading around, and some say audio on SSB is dismal without a mod' - others as per this thread say it's fine.

    Does anyone know what the modification is?
     
  7. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    You able to understand schematics?

    upload_2021-7-29_20-11-50.png

    In the above, locate J13 and J14 - SSB Delay...short to enable.

    Locate J17 and J18 - POWERS SSB MODE - changes BIAS from Class C to AB.

    J9 and J10 - APPLY power for BIAS - provides power to J17 so J18

    Note the J3 and J8 are INPUTS for a Resistor Padding section that affects the level on INPUT power - this is controlled thru the front panel of the Amp but you may need to tweak resistor values to make this concept work.

    Found Schematic here...
    https://www.rmitaly.com/wp-content/uploads/2018/10/834_Manuale_Tecnico_KL_503_rel_1.2-1.pdf
     
  8. Dereka5

    Dereka5 Member

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    This is really helpful, so many thanks for this.

    Am I right in thinking I should bridge (short) J9 to J10, and also bridge J17 to J18? Then that way it will be class AB.

    I can sort of read schematics.

    I presume the "J" denotes pads on the PCB?
     
  9. 9C1Driver

    9C1Driver Sr. Member

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    For best SSB audio and performance a class AB amplifier is preferred. Class B will also work well like the old Magna Force and TnT line from X-Force. Many amplifiers are class C and the builders add either an auto or switched SSB delay to them. They work on SSB but some people will say they can sound crunchy on SSB. If you are looking for an amplifier for SSB most of the time I would just buy a class AB amplifier.
     
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  10. Dereka5

    Dereka5 Member

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    Thank you for the explanation.

    Upon reading mixed reviews about the KL503, I instead amended my order to a KL505.

    There's not a lot of information around about these, but from the little I've read, it seems to be the better choice.

    Here is the schematic for the KL505...
     

    Attached Files:

    #10 Dereka5, Jul 30, 2021
    Last edited: Jul 30, 2021
    Handy Andy likes this.
  11. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    If you run strictly 10M - this amp is ok - but the problem begins when you go out of band.

    See that Schematic? That "input" side RTX (L1 thru L4) is what is called an SWR block - it a notch filter - designed only to pass 10M and 12M and below - but BLOCKS 11M operation - sends it to ground - and causes a High SWR condition.

    To defeat that - refer to the schematic. There are two caps - choose wisely.
     
  12. Dereka5

    Dereka5 Member

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    Hi Andy,

    With regards the notch filter Capacitor's blocking 11M, are you referring to C3, C4, and C5 or some others? Also, what alternative values would you suggest, please?

    Here in the UK, I use frequencies 27.555 to 27.99125 - so do you think as it is, in stock form, it would completely block this range of frequencies?

    Do you think I've made the right decision buying this as opposed to the KL503?
     
  13. secret squirrel

    secret squirrel Lustrous Potentate

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    Recently picked up a KL503 HD. I had Dave from DTB put it on Spectrum Analyzer with my Texas Ranger FD-1 driving it with 6.5 swing to 30 watts PEP. It was putting out just shy of 200 watts with the cleanest signal at setting 4 SSB, and setting 5 AM. His bench is at 14.3 volts. I was pleased to have about 200 watts clean with the KL503 HD.
     
  14. Dereka5

    Dereka5 Member

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    I've been told in a couple of places now that the KL505 works fine on 11M (CB frequencies) out of the box, but post #11 says otherwise.

    Many say the KL503 sounds pants on SSB, others say good, so I guess I'll have to buy & try the KL503 at a later date.

    My new KL505 is due here on Monday, so I'll report my findings as to whether or not it will work on 11M out of the box.
     
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  15. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    I cannot guarantee with your location being off shores to the USA. The Wave trap is specific for CB band.

    You're situation and location is different for your purchase and point of origin you may not receive such a unit.

    However - ones sold around here in USA - you have to disconnect C1 and L4 - to take out that 11M wave trap. C2 then took over the powering of the "sense" and Key relay. Refer to the schematic - you being regulated/licensed by some other country regulated by ITU versus FCC - may not have to worry about the wavetrap and SWR problems and should operate normally - here in the States, it's different.

    You asked earlier - the KL503 - a little brother to the 505 - more for Class C means AM or FM limited uses - but SSB can be setup to work - you just have to set it up for the effort to work for your situation. The clincher is the effort and dedicated the amp to your setup. 503 is more of an add on accessory than a dedicated equipment setup - but 505 should deliver good results but you're stuck if the Wave Trap is in there.

    The 505 - being more dedicated to 10M - is optimized more for Amateur for the level of filtering - which you will need to use Low-Pass filters for other bands. The 503 was/is geared for those that want a quick and easy add-on to their radio for CB - not the level of performance the 505 would have - but again basic entry versus Amateur equipment.

    I wish you well in your endeavor, I hope the Amp doesn't give you any troubles - but due to the nature of the beasts belly I live in (being the USA) the challenges around here are different.
     
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