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Gray Electronics Three Hundred Bi Linear into needed

Discussion in 'General CB Services Discussion' started by towerdog, Feb 27, 2013.

  1. towerdog

    towerdog one-niner-seven

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    I brought back into service an old Gray Electronics amp, looks like someone hooked it up backwards and burned traces off the board and then cannibalized the switches, but its fixed now. I cannot find any information on it, would like to know how much current this thing will draw on max power.
    I know it is late 70s early 80s vintage, switch for low-med-hi-max, rcvr amp, ssb-am/fm. It sounds awesome on SSB, I suspect its class-AB biased. Was told not to hook it to anything more than 5 watts key. It uses 4 MRF492 - 231
    I really just want to know max power I can drive this thing, and how much current it will draw. I like it and dont want burn it up.


     

  2. Shockwave

    Shockwave Sr. Member

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    It should never draw more than 40 amps with those transistors. That's where they will burn up.
     
  3. Rb30

    Rb30 43WR30

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  4. gamegetter

    gamegetter Well-Known Member

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    i still have an original one from back in the day...i have not run it in a long, long time but on am i would do about 210 watts IIRC, and that is about where I wanted to be. good little amp but I have not used on the sideband.
     
  5. towerdog

    towerdog one-niner-seven

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    Motorola be telling some bus man of deadkey like 300 swinging to like 2 kw
     
  6. towerdog

    towerdog one-niner-seven

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    All I really used it for was ssb . No more than maybe 18w drive or it distorts and clips . Heard somewhere if the transistor base is to inductor iz class ab. 280 pk am wpld be pretty much honest I try to bprrpw meter this wkkened
     
  7. Shockwave

    Shockwave Sr. Member

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    1 person likes this.
  8. TonyV225

    TonyV225 W9WDX Amateur Radio Club Member

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    I believe I have one of these in a base version its black with red writing and says GB 300 on the front and also has the 4 position power selector. This base version also gets distorted and funky sounding if pushed past 15 watts input drive on SSB otherwise its a good sounding amplifier I could never find info on it otherthan its also running the 4 x MRF-492 configuration for output transistors. I just assumed the GB stood for Gray Base.
     
  9. crunchybobjones

    crunchybobjones Active Member

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    You have to remember the Gray 300 came with the MRF455.. 50 watts at 30 mhz ,
    The MRF492 is rated at 70 watts at 50 mhz.. the gain is much higher at 30 mhz on the 492.. If driven right it should do 300+ watts on 10/11 meter
     
  10. bassman21

    bassman21 Active Member

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    Old thread, but what the heck..... A local guy used to sell these and I knew several CBers and hams that ran them in the late 80s and early 90s. Pretty much everyone in our group either had the Gray 300 or Blue Thunder 200 in their mobile. The Gray's are good amps that will do more than they are rated. Like Crunchy said it should do 300 watts pep easily with no issue and they can do more. Just don't try and volt it, they are not built for more than 14 volts. You shouldn't have any issues with a stock alternator unless you have a really small car and I don't see you needing more than a 50 amp power supply for it.
     
    crunchybobjones likes this.
  11. psycho

    psycho Running a special on our rooms!

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    The Gray 300 is fused at 40 amps and put a 2-3 watt key into it.
    The reason why all Gray 150 or 300 amps seem to have the case rivets drilled out is because of overdriving and burning up the power stage resistors.
    I owned one and burned the low and med stage resistors using 9 watts on SSB.
    300-350 watts peak is normal for these gems.
     
    #11 psycho, Apr 5, 2017
    Last edited: Apr 5, 2017
  12. nomadradio

    nomadradio Analog Retentive

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    My experience with the Gray 300 was that it had Billy D. Ward's bogus "neutralizing" link to stop it from oscillating.

    Trouble was, that didn't work. This makes it incredibly touchy about small differences in SWR and jumper-coax length. Had a tendency to oscillate and hold itself keyed up when you let off the mike. Things get hot fast when it's doing this, so if you don't have a way to pull the plug on the main power, it can toast itself this way even if you are totally sane and responsible with your drive power.

    There's a bonus. No bias for sideband. Never mind the "SSB" switch. All it does is slow down the relay to keep it from chattering. Just because you see a switch marked "SSB" on the front doesn't mean that it's suitable for clean sideband audio. The Gray will sound like doo-doo on sideband.

    It can be salvaged with negative feedback and by adding in input-matching circuit to get the SWR on the input down to an acceptable level. More like a rebuild than a repair. And that's if the transistors haven't already been toasted.

    Finding one that has not already done the "mushroom cloud" dance would be the hard part.

    Even then, it's still an AM-only box.

    73
     
    LeapFrog likes this.
  13. Robb

    Robb Yup

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  14. bassman21

    bassman21 Active Member

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    I run my Dave Made M400 on SSB. I just turn it back to about 200 watts and back off the modulation, works great. I've done recordings and while you can tell I'm running an amp it doesn't sound bad at all. Not ideal, but proof that class C can work on SSB with a good amp properly ran.
     
  15. WHEELS

    WHEELS Member

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    I am actually looking to purchase this exact amp from a neighbor. If I'm reading correctly. Are some people saying you can't you this amp on SSB, or any amp. I am just now getting back into cb'ing. After taking a 20 yr. break. Thanks ahead for any info.
     
    crunchybobjones likes this.

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