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What electronics have YOU fixed lately?

Discussion in 'CB Radio Modifications' started by Robb, Dec 3, 2018.

  1. Robb

    Robb Yup

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    Hope this thread gets a lot of play on the forum . . . but it is meant as an example for whatever electronics you may be working on . . it can be anything . . .

    Got a Gibson Falcon tube guitar amp built around 1968-9. Got it for a song, around fifty bucks. Since it is getting into winter proper, I thought it would be a good time to work on it as a project while stuck indoors.

    The person I got it from had gone into the amp to repair it, and what a mess he made of it. Hence the cheap price. The power supply section was completely bonkers. Fortunately, all three transformers (power, output, and reverb xformers) were tested and are OK.

    Bought a complete set of Sprague 'orange drop' capacitors to replace all of the passive caps and a few silver mica caps to replace all of the old disc caps. Still looking at all of the resistors to see what needs to be replaced, but the ones in the PS section were all cracked due to the person who tried to fix it. The main filter cap had to be replaced too, since someone had replaced it with the cap with all of the wrong values.

    I cleaned the pots, but have not otherwise tested them yet.



    The connective wire used in these old amps are the cloth type; need to locate a source for it so I can rewire it too.

    Had to replace the neon power indicator or 'pilot lamp'. It is in the mail to me ATM.

    Had four of the six tubes (three 12AX7's and one 12AT7), so I ordered the two EL-84/6BQ6 to complete the lineup.

    The amp also was missing its reverb tank and foot switch.

    The speaker that came with it is a ceramic magnet 12"; but unfortunately it is a 4 ohm bass speaker. Not the original speaker. So I will need to hunt down an 8 ohm Celestion, Eminence, or Jensen brand speaker that has an Alnico magnet from that time period. Might be a little tough to get that piece; but there are enough other things that still need to be done in the mean time.

    The amp cabinet had loose back cleats to hold the open back boards in place, so they were already re-glued and clamps/fixed. The rubber feet were worn out, so I installed a set of Fender bottom glides. The handle. grille cloth and vinyl box covering are all in good shape. But the back covers are completely missing, so I will need to fabricate those as well.

    Sooo; what have you worked on lately?
    Or what are you planning to work on?
    Doesn't have to be radio related, but it helps . . .

    Pictures are not mine, I found them on the 'net. But that is what it looks like:

    falfr2.jpg
    Gibson-Falcon-1969 back panel.jpg



    Schematic of the amp
     

    Attached Files:

    #1 Robb, Dec 3, 2018
    Last edited: Dec 4, 2018
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  2. sp5it

    sp5it Master of puppets

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    BT controlled dildo.
    Customer was really happy about that :D
     
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  3. TheRealPorkchop

    TheRealPorkchop Certified Sith Pimp

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    OMG haha Hahahaha
     
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  4. Martian

    Martian Well-Known Member

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    Personal or work related?

    Nothing radio related unless I go to a friends' house but he has been really sick lately so no radio fun.

    Work related... some rework on prototypes because the board house swapped a couple of reels and installed a cap where a resistor should have been and vice versa.

    Personal stuff.... repaired my kids' monitor a couple weeks ago.
    Just needed to be recapped. Either it was dead, would lock up, or the backlight would shut down. Typical bad cap symptoms.
     
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  5. TM86

    TM86 I fix what the snake breaks

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    Fixed two radios a few weeks back, but these were easy.

    First radio, the long suffering Adams. Speaker was physically too small.

    Second radio, PC-122 XL. Speaker was dead.

    Swapped the speaker out of the Adams into the the PC-122 XL and put a new speaker in the Adams. Two repairs for the price of one.
     
  6. 338_MtRushmore

    338_MtRushmore Well-Known Member

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    I wish I could say this, but it ain't fixed 20181203_211321.jpg
     
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  7. fourstringburn

    fourstringburn W9WDX Amateur Radio Club Member K5KNM

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    Nice old tube amp!

    The schematics shows 4-12AX7 tubes but doesn't tell which one is for the preamp, tone, or driver, etc.

    Typically 12AT7 tubes have a lower gain than the 12AX7 tubes.

    The old stuff is so much easier to work on and it's fun to play around with different tubes to get different results!
     
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  8. Robb

    Robb Yup

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    Yeah, the 12AT7 is the reverb driver/amp tube; the schematic shows it as a 12AX7. But using a 12AT7 in the reverb spot gives the reverb a better tone.
     
    #8 Robb, Dec 4, 2018
    Last edited: Dec 4, 2018
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  9. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    I have also seen 12AT7's be used as a phase inverter in some amps as well.

    I'm boring, I'm just doing re-cap jobs on old CB's for people. I haven't fixed a guitar amp in a while.... maybe I should go find me a Fender Champ or a Band Master or something to fix/restore.

    TM86, I really like those little Uniden PC-122XL's... let me know if you ever decide to part with it.


    ~Cheers~
     
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  10. autotuner

    autotuner Supporting Member

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    Mostly work related audio amps. Usually bought at a low dollar value and left running 7x24x365 (schools, users too lazy to switch off) but common problem of capacitor failure on power rails. I know they are built to a $$ level but cap ratings 1volt over rail voltage is inbuilt failure.....
     
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  11. sunbulls

    sunbulls Well-Known Member

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    Those old school tube amps are great. As you know, they're highly prized for their tonal quality. Ask Eric Clapton...The only thing that bugs me is, after searching for hours for a schematic, the only one that can be found is copy taken from some old FAX machine. I really have been spoiled viewing quality PDF's that I can zoom. FAX is one older technology I'll never revert back or ever miss.

    I've been refurbishing a Realistic TRC-451. So far I replaced the Din jack with a 4 pin, unlocked the clarifier, and replaced the heat-sink compound on all the power components. I just started the recap job at the rate of about 5 caps per day. The radio should be completed within 2 weeks depending on the honey dew list.
     
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  12. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    Interesting that old Falcon amp isn't running a rectifier tube, most amps from that era usually run a rectifier tube, such as a 5U4, 5Y3, 5Y4, or similar.

    Sunbulls,
    those Realistic TRC-451's are amazing radios. You will not be disappointed when you finish it.

    ~Cheers~
     
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  13. sunbulls

    sunbulls Well-Known Member

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  14. Robb

    Robb Yup

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    My first Fender amp was a Band Master. I busted it when doing a Peter Townsend/The Who medley. I fixed it myself; had to replace the filter caps and the bias cap. Came back up sweet; sold it a couple of years later.

    Finding one of those old Fenders is hard to do - and pricey. Even getting this Gibson amp was just a stroke of luck too. Did it to learn more about tubes, and learned a bunch from it - and still am. Hope you get one; let us know.
     
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  15. Rwb

    Rwb Well-Known Member

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    Put new parts in a turner plus 3b mic last week
    Hobby for myself
     
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