JTM50 1986 new build

Discussion in 'Building the Classics' started by StingRay85, Mar 23, 2020.

  1. StingRay85

    StingRay85 Active Member

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    Decided to build this amp as the next project. I think it will a good match for the early 70s Drake iron I have lying around from a Carlsbro TR60 chassis. PT gives high voltage on the plates, and is center tapped with diode rectifier. Drake OT for 2x EL34 and a choke. I will just build it into the Carlsbro chassis, and see what happens.

    The layout I just make based on the past experiences. I'll raise the heaters of the preamp tubes, move V1 as close as possible to the inputs. And then have a center ground buss in between preamp valves and pots, and run the components next and over it to make the signal path as short as possible, and ground the buss close to the PT ground. Last build had virtually no hiss or hum, without using shielded wire.

    Is this the schematic to follow?

    1986jp.gif
     
    Kelia likes this.
  2. South Park

    South Park Well-Known Member

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    That drawing does not have the right diode bridge pack. The star grounding works great on those amps. Hoffman amps has a wire layout that is easy to follow . Rock on
     
  3. StingRay85

    StingRay85 Active Member

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    Thanks brother
     
  4. neikeel

    neikeel Well-Known Member

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  5. MickeyJ

    MickeyJ Well-Known Member

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    zero consideration to cost - maximum consideration to tone.
    building like this takes a lot more time, but uses far less 'antennas' so you get less transmissions of everything into your amp from sources you don't want.
    Consider this, when you build an amp in the conventional manner, not only are gird wires flying everywhere, but ground paths are made with a wire going to 'somewhere'. More wire.
    True PTP is better, quieter. However repairing the amp is harder. Everything is hunched close around those sockets.
    When you think that this gentleman built this device as his first amp, and it sounds as it does..extraordinary.

    What I like doing is making the chassis, drilling all the holes for sockets etc, and then using a gas torch to pool solder wherever I need a ground connection.
    Then paint the chassis.
    This gas torch thing is another blast from the past, and it is superior.
    Before I bought a gas torch, a pissy little one from the hardware store..i used to put the chassis on the hotplate in the kitchen and warm them up that way before pooling the solder.
    dodgy but it works.
    When you make pools of solder like this, and the solder really bites onto the surface of the chassis metal, it is very easy to solder a wire or component to it..and it simply never goes bad, In 100 years that ground connection is still solid.
     
  6. MickeyJ

    MickeyJ Well-Known Member

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    And yes, it wont work with aluminium, but amps built with ally have a sound to them, it's so fast..I'll get there too one day, i'd love to make a jtm45/100, I have some very appropriate iron, already tone tested, and the signal caps.
     

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