1. You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
    Dismiss Notice

Receive transistor in amp - same/same?

Discussion in 'CB Radio Modifications' started by Robb, Oct 1, 2016.

  1. Robb

    Robb Yup

    Joined:
    Dec 18, 2008
    Messages:
    10,581
    Likes Received:
    2,267
    20161001_134528.jpg



    Working on a local op's 'King Bee 150/250' amp. The receive amp doesn't work; receive goes dead when switched on. What transistor is used? What substitutes can be used? Schematic for this amp available/link? Possible biasing mods?

    Don't usually work on CB amps, just radios. Turned down the AM carrier to 2w to keep it from splattering. ANY/ALL info appreciated and welcome, as I can't seem to find much info at all about it.

    Thanks.
     
    #1 Robb, Oct 1, 2016
    Last edited: Oct 1, 2016

  2. 222DBFL

    222DBFL Sr. Member

    Joined:
    Jul 28, 2013
    Messages:
    3,301
    Likes Received:
    1,290
    Let me post a pic of the inside of my Palomar amp that looks similar. The switches are different, but the case looks identical to the one I have. Might help. Not sure. But here are some pics to compare. Again, not sure this will help, but here goes.
     

    Attached Files:

    BBB likes this.
  3. 222DBFL

    222DBFL Sr. Member

    Joined:
    Jul 28, 2013
    Messages:
    3,301
    Likes Received:
    1,290
    If you need more pics let me kmow. I tried to get as many as I could.
     

    Attached Files:

  4. 222DBFL

    222DBFL Sr. Member

    Joined:
    Jul 28, 2013
    Messages:
    3,301
    Likes Received:
    1,290
    Couple more, might be some repeats. Sorry if it doesn't help Robb. I tried man.
     

    Attached Files:

  5. 222DBFL

    222DBFL Sr. Member

    Joined:
    Jul 28, 2013
    Messages:
    3,301
    Likes Received:
    1,290
    Some more pics
     

    Attached Files:

  6. 222DBFL

    222DBFL Sr. Member

    Joined:
    Jul 28, 2013
    Messages:
    3,301
    Likes Received:
    1,290
    Last ones. Hope they might help.
     

    Attached Files:

    Robb likes this.
  7. ExitThirteen

    ExitThirteen Grumpy and Cranky

    Joined:
    Apr 18, 2008
    Messages:
    1,626
    Likes Received:
    886
    Usually, a 2N2905 or a 2N2222 is used for the preamp transistor in an amp of that era.
    You can substitute a 2N2907 in for the 2N2905. All are cheap and readily available.


    ~Cheers~
     
    222DBFL and Robb like this.
  8. 2RT307

    2RT307 Sr. Member

    Joined:
    Nov 22, 2011
    Messages:
    2,300
    Likes Received:
    722
    Hey Robb, just curious... what's in the thing? MRF 455's?

    73,
    Brett
     
  9. Robb

    Robb Yup

    Joined:
    Dec 18, 2008
    Messages:
    10,581
    Likes Received:
    2,267
    Yup.

    Correction:
    MRF454's
     
    #9 Robb, Oct 2, 2016
    Last edited: Oct 2, 2016
    2RT307 likes this.
  10. Robb

    Robb Yup

    Joined:
    Dec 18, 2008
    Messages:
    10,581
    Likes Received:
    2,267
    Don't know much at all about amps; so bear with me.

    When the amp is off, I am seeing a 1 1/2 watt carrier loss thru it into the dummy load. IOW, 3w in to the amp, and 1 1/2w out of the amp when turned off. I'm sure this can't be correct.

    BTW - what is the proper input power to mrf454's?
    5w or 10w/each?

    Took out the mrf454's and tested them. They tested OK with both the diode test and resistance test. Also not seeing anywhere near 200w out of it, so I am at a bit of a loss to figure out why this amp isn't working as it should.

    What could be causing this? Bad relay? Bad coupling caps?
    Again; working w/o a schematic has been difficult.

    Also the original receive amp transistor is marked:
    "034
    MPS
    5172"
    So I have NO idea what part is in this thing.
    Any ideas?
    2N5172- maybe?
    Translates to equivalent 2N2904.
    Perhaps a suggestion for a replacement trans that has low noise/clean output?
    Like a 2N5088?

    blue_thunder_200_inside.jpg

    BTW 2222DBFL, this pic is similar to the inside of this amp and your amp; could you take a closeup pic of the small transistor near the very front of your box (circled in red in the pic), and can you read the numbers on the face of it and its orientation? That may help me figure out what transistor I need to get this amp fixed and off my bench. Much appreciated!

    Thanks
     
    #10 Robb, Oct 3, 2016
    Last edited: Oct 4, 2016
  11. bob85

    bob85 Supporting Member

    Joined:
    Mar 30, 2005
    Messages:
    2,896
    Likes Received:
    632
    10w drive should make about 200w output with a pair of 454's on 13.8v,

    i have come across amps that have high vswr and attenuate your power in bypass mode, cp163's do it,
    sometimes a trimmer cap from the bypass side of the relay to ground will tune out most of the mismatch.
     
    AudioShockwav and Robb like this.
  12. 222DBFL

    222DBFL Sr. Member

    Joined:
    Jul 28, 2013
    Messages:
    3,301
    Likes Received:
    1,290
    Robb here is that part I think. The numbers on it are as seen on the pic below.
    Part #
    MPS2
    222A
    M594
    This is the part number I see. I hope this is what you are speaking of. I am no amp expert by any means either!! Again, hope I got the correct part for you.
     

    Attached Files:

    Robb likes this.
  13. Robb

    Robb Yup

    Joined:
    Dec 18, 2008
    Messages:
    10,581
    Likes Received:
    2,267
    Seeing about 1/2 that - about 100w on AM.
    Transistors are out now and tested OK.
     
  14. 222DBFL

    222DBFL Sr. Member

    Joined:
    Jul 28, 2013
    Messages:
    3,301
    Likes Received:
    1,290
    That bottom row of numbers may be different than what I posted. Hard to tell. Here is another close up pic of it.
     

    Attached Files:

  15. 222DBFL

    222DBFL Sr. Member

    Joined:
    Jul 28, 2013
    Messages:
    3,301
    Likes Received:
    1,290
    I'll see if I can find my magnifying glass and look closer at it as well. Give me a few as I am headed to the store now.
     

Share This Page

  • About Us

    The WorldwideDX Radio Forum was originally established in 2001. We pride ourselves on welcoming Radio Hobby enthusiasts of all types, while offering unbiased, informative, and friendly discussion among the members. We are working every day to make sure our community is the best Radio Hobbyist's site.
  • Like us on Facebook

  • Premium VIP Member

    The management works very hard to make sure the community is running the best software, best designs, and all the other bells and whistles. Care to buy us a beer? We'd really appreciate it!

    Donate to us!