sl250dx linear amp .not a kit but would like to add a ptt on the back if pos

Discussion in 'Homebrew and Kit Projects' started by 2E0OKC, Jun 26, 2014.

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  1. 2E0OKC

    2E0OKC Ham Member QRZ Page

    hello all i have a flex1500 qrp setup . at times i just need that little extra power so i got a solid state sl250dx linear amp . (dam mist out on a yaesu one )
    its all fine in digi modes but wonting to use ssb with no talking the relay chatters so too speak, can a ptt input be added you think ,
    and to let the flex1500 do the keying instead of the rf sensor .
    im not that tec minded , still learning for my last licence

    i not sure if i have put this in the right place of qrz. tc all 73 andy
     
  2. G4COE

    G4COE Ham Member QRZ Page

    These are HF CB linears.....er, burners! How linear it is remains to be seen.

    I do hope you are using a harmonic filter on the output.... you need one for each band you operate on, otherwise you will be emitting all sorts of chaff!!!

    It ought to be simple wiring a PTT line in instead if using the RF sense changeover.... I have the amplifier which was given to me but never studied the circuit, I did try it on a dummy load for laughs, lo and behold it had the last one - it worked! Just that I was expecting 'sizzle, sizzle burn, burn' because it was an ex cb'er that give it to me, must say it looks as though it's never been used.

    All you need is to disconnect the input to the base of the relay driver transistor insert say a 1.5K to the PTT line, I don't think the bias is switched in these, if it is this would have to be switched as well.

    Remember when you measure RF power you need to know what power you are measuring, RMS or peak, I wouldn't take too seriously what it say's on the meter regarding the power rating, the PA transistors are certainly not going to run 200W AM as shown on the meter... think about it? Many a rig that churns 100 Watts SSB out will only run about 25 Watts on AM.

    Dave
     
  3. K8JD

    K8JD Ham Member QRZ Page

    Since you have to modify your CB amp with a number of lowpass output filters anyway, why not just add a large value capacitor across the T/R relay winding to tame it for SSB operation !!
     
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