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Bassman Micro transformer question.

Discussion in 'Shock Brother's DIY Amps' started by Moodivarius, Jan 19, 2021.

  1. Moodivarius

    Moodivarius Tele-Meister Silver Supporter

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    I’m looking at building a Bassman Micro.

    Just finished an AX84 P1eX. Awesome amp.

    The Bassman calls for a 270AX and a 125B. I can pickup a used 269EX & a 125A.

    Would theses be sufficient?


    Scott
     
  2. Nickfl

    Nickfl Friend of Leo's

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    The 125A is rated for 3 watts vs the 5 watt 125B, otherwise they are the same. A bassman micro isn't putting out more than 3 watts anyway so I doubt there would be much difference there and it should work fine.

    The PT is more of a problem, the voltage is going to be quite a bit lower (around 70 volts less) than it would be with the correct transformer. You can work around that but it would potentially require changing some component values and would possibly change the sound of the amp a bit.
     
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  3. 2L man

    2L man Tele-Meister

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    I use toroidal power transformers because they are cheap, small, light and radiate less electromagnetic "hum". Here in Europe we have good availability nut in USA I know only AnTek. Their 50VA tube PTs are $30 and 50W is good for up to about 8W amp. DVNator is very innovative amp designer and he uses AnTek but despite that his page is more than worth visiting. HiFi builders use AnTek and othet toroids much more than instrument amp builders who seem to appreciate vingage.
     
  4. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    What Nick said re the OT. For the PT, if you want to use the 269EX, look at Rob's new EF80 pentode version. Rob says, "The Bassman Micro LTP EF80 below uses 290 plate and 285 screen volts using a Hammond 269EX 190-0-190V power transformer. The 269EX is a good choice for any amp using an EF80 power amp but it does not include a 5v secondary so use an EZ81 (6.3v) tube or solid state rectification."
     
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  5. robrob

    robrob Poster Extraordinaire Ad Free Member

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    ^What Nickfl and King Fan said. The 125A will work just fine but I would go with the EF80 with that power transformer. You can use that transformer in the Bassman LTP 12AU7 version but use the voltage dropping resistor values from the EF80 version to maximize the voltage available to the preamp.
     
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