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  1. I've made it a habit to do some additional...

    I've made it a habit to do some additional forming on CE Distribution can capacitors before installing them, which I do with an ancient Heathkit Condenser Checker that I've modified slightly to give...
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    In the Hammond world, we tend to acknowledge the...

    In the Hammond world, we tend to acknowledge the necklace reverb as the best-sounding spring reverb, but its drawback is that it's so sensitive to any motion around it like someone walking past the...
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    Yes, I'm a Hammond tech, so I know the whole...

    Yes, I'm a Hammond tech, so I know the whole story going back to 1939 and the oil-tube (not oil can) spring reverb units with their crystal pickups. The necklace style spring reverb appeared in 1959...
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    FWIW, 1122 is Hammond Organ Co.'s EIA code. I've...

    FWIW, 1122 is Hammond Organ Co.'s EIA code. I've seen people on other sites confused by that number.
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    Magnatone M15A original speakers

    In the late 1965 M15A I'm working on, someone replaced one of the original 16Ω Jensen C12P speakers with an 8Ω Oxford.

    I removed the remaining original C12P and found it was a version of the C12P...
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    I saw that picture of the M15. The M15A cabinet...

    I saw that picture of the M15. The M15A cabinet is different, having an angled piece of wood between the amp and the speakers. Looks like whatever held the reverb tank was mounted vertically to the...
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    Interesting. In the M15A I'm working on, the tank...

    Interesting. In the M15A I'm working on, the tank was simply banging around under the amp in the cabinet. You can see where it had very old (now extremely deteriorated) adhesive foam applied to the...
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    In terms of the reverb tank, it would be great to...

    In terms of the reverb tank, it would be great to find someone with an M10 and original reverb tank to see exactly what was in there.

    These were the very early years of reverb tanks. They were...
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    I'm sure you found the 38W figure on the...

    I'm sure you found the 38W figure on the Magnatone site. I read the same thing there. It probably came from Magnatone's original marketing. The thing is, back in those days, the rules about stating...
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    In terms of output power, the specs you are...

    In terms of output power, the specs you are quoting are misleading. There is no way you can get 38 Watts from a pair of 7189A run ultralinear (or pentode). You might be able to get a brief transient...
  11. I could try the lamp limiter circuit. I'm a...

    I could try the lamp limiter circuit. I'm a Hammond tech, so I actually keep the #12 lamps in stock. After years of use, they do burn out.

    There are screw-base lamps with the same filament specs...
  12. The M15A uses two channels, each with one pair of...

    The M15A uses two channels, each with one pair of 7189A running ultralinear fixed-bias -- or rather a hybrid fixed-bias since each pair has a 100 Ohm cathode resistor in addition to a negative grid...
  13. Yes, I think this one will end up being the...

    Yes, I think this one will end up being the 4AB3C1C, vertical-mount.
  14. Yes, I have the March 1965 to January 1966...

    Yes, I have the March 1965 to January 1966 version in which the tank's output transducer appears to function as the cathode resistor for the first recovery stage.

    Looking at the schematic glued...
  15. Magnatone M15A speaker-driven reverb tank?

    I'm working on a late 1965 Magnatone M15A amp, and the output transducer on the presumably-original Gibbs spring tank is open. On this amp, the tank is driven in series with a 100 Ohm resistor from...
  16. Thanks for posting the review. It's always seemed...

    Thanks for posting the review. It's always seemed strange to me that Fender does not sell replacement PCBs for these amps since they do fall apart over time. I've seen some that have been repaired...
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    Are you sure it isn't the same amp? ;-) Two...

    Are you sure it isn't the same amp? ;-) Two Gibsons exactly the same is actually suspicious.
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    Reading photos can be tricky, but that kind of...

    Reading photos can be tricky, but that kind of looks to me like someone made a new speaker baffle for this cabinet. Also, I just googled it again and saw one photo of this cabinet with the back off...
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    That layout is for the third version of the...

    That layout is for the third version of the GA-40, while yours is the second, so there are some minor differences in wiring of the volume pots and tone control.

    Further down that thread is a...
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    I can see the photo now. Same version I just...

    I can see the photo now. Same version I just worked on. All the electrolytic cathode bypasses are on the back side of the board. This thing was not built to be service-friendly.

    I moved the...
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    Your image link doesn't work. I ended up...

    Your image link doesn't work.

    I ended up doing a complete rebuild on this GA-40 because it was a basket case. All the board components were way out of spec, most over 20%, many close to 40%. Even...
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    With a little more digging, I think I've got the...

    With a little more digging, I think I've got the sequence better figured out.

    First you had the first version of the GA-40 with 6SJ7 input tubes and a very different amp circuit from the...
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    Gibson GA40 Les Paul versions

    I'm just finishing up a restoration of a late 1956 Gibson GA40 Les Paul amp, a real basket-case, so I've had to get deep into the details. As with almost all Gibson amps, there are variations from...
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    One tweak I read about was changing the Master...

    One tweak I read about was changing the Master Volume pot on this series from a linear to an audio taper pot to make it more user-friendly. I noticed that the MV pot is pretty abrupt on this one.
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    Hot Rod Deluxe service points

    I'm working on a MIM Hot Rod Deluxe (2002 board) and have dealt with the standard problems with the resistors that cook the board, solder joints, B+ caps, jack contacts, and so forth. It's for a...
  26. One of the ways a voice coil dissipates heat is...

    One of the ways a voice coil dissipates heat is by radiating it into the top plate; the metal edge of the cap actually conducts heat away from the coil better than air. With square waves, the coil...
  27. I saw a Blues Deville 4x10 with similar speaker...

    I saw a Blues Deville 4x10 with similar speaker damage, but the owner knew what happened. One of his friends tried using it as a bass amp, and, being a bass player, he cranked the bass in an...
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    Magnetic tape history

    I was watching a TV show recently set during WWII that featured people on the British side (not at the top ranks of military) using a reel-to-reel tape recorder, and I started wondering if this...
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