Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: walkman on April 29, 2020, 08:25:40 am
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Hi All,
Looking for some advice about building a 'Micro' Marshall in the style of https://robrobinette.com/RR2104_Master_Volume_Micro.htm#JCM800_Micro (https://robrobinette.com/RR2104_Master_Volume_Micro.htm#JCM800_Micro)
I'm thinking of using a power transformer that will supply around 110-130v when rectified.
Partly this is due to some parts i have and partly due to wanting to keep the output power in the rang of 1/2 watt - 1 watt
I found reading http://coolwire.co.uk/tube-amps/as-quiet-as-a-very-noisy-mouse/ (http://coolwire.co.uk/tube-amps/as-quiet-as-a-very-noisy-mouse/) interesting
and may end up doing something more like Phil Crooks 'Little One' http://www.coolwire.co.uk/littleone/images/LittleOne1.3.gif (http://www.coolwire.co.uk/littleone/images/LittleOne1.3.gif),
however with a different small signal pentode and a single tone control.
If i were to stick to a Marshall theme then i'm thinking a JTM45 preamp or Plexi preamp would work better as with the low output its not going to be a clean amp mostly and it will perhaps be more suited to the lower voltage than the 800 preamp.
What do you think? I know that small signal pentodes should be able to handle lower voltages ok.
That brings me to the phase inverter and push-pull 12ax7 output? will the values need to be scaled to work alright, or will a 12at7 do better in the LTPI? with HT about 100V ?
As for the OT PRR indicates that a 12K OT would do the job. However with lower voltages perhaps it could be as low as 6k for a tad more power and more distortion as he suggests https://el34world.com/Forum/index.php?topic=16536.msg163056#163056 (https://el34world.com/Forum/index.php?topic=16536.msg163056#163056)
At this stage just conceptual, what have others found that works for bedroom friendly dare i say Beano territory (duck and run from the "it won't sound the same" comments, of course it won't).
As long as it ends up sounding 'good' at these volumes is the point and of course the fun of design and build.