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Found a 1962 Gibson GA-79RVT

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  • Found a 1962 Gibson GA-79RVT

    A young guy at work told me his dad had an old Gibson amp in the attic that hadn't worked in years and almost
    caught on fire last time it was plugged in. When he described it and said it was kind of wedge shaped I tried to
    act disinterested.

    A couple weeks later I bought it for $100

    The upper 200Ω 10W resistor and 25F capacitor were burnt to ash and the power supply choke smoked.
    I replaced those parts and totally rebuilt and rewired the power supply.
    Next power up the resistor burnt and the new cap exploded.

    THEN I realized the 7199 phase inverter tube had been replaced with a 12AX7 with no rewiring of the tube
    socket. Bought a 7199 tube and all or the other eight tubes and the next power up was much more successful
    but a lot of loud hum.

    More investigation showed the earlier tech had replaced the original 20/20 450V audio cap with a single
    40F cap and combined the circuits. I replaced that with two new 20F 450V caps on separate circuits.

    22 days after purchase and $380 in parts later I have a vintage tube amp that sounds like a 1960s amp
    is supposed to with no noticeable background hum buzz or hiss.

    This could be my highest profit turnover ever.
    I don't see that happening.
    Being they only made about 1132 of this model I'm thinking this one is keeper

    Picture red arrows point out the bad or failing parts. Other picture is the repaired chassis.
    I think I'll leave the tolex and grill cloth just as it it.
    I'm two years older than this amp and that look just fits me!


    Click image for larger version

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    Many of life's greatest adventures begin with the same four words:
    HERE, HOLD MY BEER

  • #2
    How did you spend $380 in parts? Seems high, Unless you had a choke professionally wound to original specs.

    Comment


    • #3
      He mentioned a re-tube. Maybe NOS?
      "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

      Comment


      • #4
        Tubes were the majority of cost.
        The 7199 was a little over $70 and the the three 6EU7s totaled $77
        It does add up quickly.
        Many of life's greatest adventures begin with the same four words:
        HERE, HOLD MY BEER

        Comment


        • #5
          Wow. Last 7199 i bought 2 years ago was $20, RCA brand new in the box. 6eu7 not sure on the price. You could have bought the 6gh8 adapter and rewired the 6eu7 for 12ax7. Does that model have the field coil speaker? I had a GA75 way back when.

          Comment


          • #6
            Great find and well done!
            I’m perplexed why a light bulb limiter wasn’t used to bring fault current down to safe levels when powering it up, especially when warned it smoked the last time it was used?
            My band:- http://www.youtube.com/user/RedwingBand

            Comment


            • #7
              Originally posted by mozz View Post
              Wow. Last 7199 i bought 2 years ago was $20, RCA brand new in the box. 6eu7 not sure on the price. You could have bought the 6gh8 adapter and rewired the 6eu7 for 12ax7. Does that model have the field coil speaker? I had a GA75 way back when.
              Wish I could fine them for that price.
              I did consider the 6gh8 adapter but wanted to keep is as original as possible.
              Many of life's greatest adventures begin with the same four words:
              HERE, HOLD MY BEER

              Comment


              • #8
                Originally posted by pdf64 View Post
                Great find and well done!
                I’m perplexed why a light bulb limiter wasn’t used to bring fault current down to safe levels when powering it up, especially when warned it smoked the last time it was used?
                Certainly should have but didn't.

                Several years ago I refurbished a 1978 Fender Deluxe Reverb. Smoked components in it too on first power up.

                I'm thinking a Variac may be added to my bench if I find another project.
                Many of life's greatest adventures begin with the same four words:
                HERE, HOLD MY BEER

                Comment


                • #9
                  My variac is a little used boat anchor, whereas my light bulb limiter ranks about#2 item of useful things. Not up there with a multimeter, but in terms of earning its keep / bench space / avoiding magic smoke release, to not have one seems remiss.
                  My band:- http://www.youtube.com/user/RedwingBand

                  Comment


                  • #10
                    I had built one many years ago. No idea what ever happened to it.
                    Maybe time to build a new one.

                    I do get lax sometimes.
                    Just like I'm constantly preaching the hazards filter caps, yet I still get the occasional knuckle numbing myself
                    from not discharging the caps.

                    I know better.
                    Many of life's greatest adventures begin with the same four words:
                    HERE, HOLD MY BEER

                    Comment


                    • #11
                      Originally posted by rake411 View Post
                      A young guy at work told me his dad had an old Gibson amp in the attic that hadn't worked in years and almost
                      caught on fire last time it was plugged in. When he described it and said it was kind of wedge shaped I tried to
                      act disinterested.

                      A couple weeks later I bought it for $100

                      Picture red arrows point out the bad or failing parts. Other picture is the repaired chassis.
                      I think I'll leave the tolex and grill cloth just as it it.
                      I'm two years older than this amp and that look just fits me!


                      Click image for larger version

Name:	20200520_080619.jpg
Views:	169
Size:	161.4 KB
ID:	907154 Click image for larger version

Name:	ChassisProblwms.JPG
Views:	114
Size:	329.4 KB
ID:	907155 Click image for larger version

Name:	ChassisFixed.JPG
Views:	115
Size:	182.4 KB
ID:	907156
                      I remember this amp, having seen one at Saul Benton's shop in Hollywood back in the mid-60's. Back in the era of Gibson's Titan and Mercury series amp/cabinets, and around when the Firebird and Thuderbird came out. Very cool amp.
                      Logic is an organized way of going wrong with confidence

                      Comment

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