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RCA PA MI-38103
RCA PA MI-38103
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Old 1st January 2018, 11:10 PM   #11
famousmockingbird is offline famousmockingbird  United States
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Join Date: Dec 2010
Location: Nottingham, NH
First wave of mods are completed and I am very happy with the results!!!

For 'microphone 3' I disconnected the ground from cathode (V2 pin 3), I also disconnected the .047uF at the grid (V2 pin 2) coming from the step up transformer.

I took the shielded cable from the 'phonograph' input jack and disconnected it from the 'phonograph' potentiometer. I then connected it through a 27k grid stop resistor to V2 pin 2. With 140v B+ and 180k plate load resistor I decided on a 3k cathode resistor and bypassed it with 22uF at V2 pin 3.

I left the 6AU6 wired as a pentode and I think it will leave it that way.

The gain is perfect and the amp sounds amazing wow!! I figured it would work and sound decent but I wasn't getting my hopes up for magical but it's magical.
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Old 2nd January 2018, 01:57 PM   #12
jazbo8 is offline jazbo8
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RCA PA MI-38103
Glad to hear the mods are working out well - magical is always a good result...
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Old 2nd January 2018, 05:47 PM   #13
famousmockingbird is offline famousmockingbird  United States
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Quote:
Originally Posted by jazbo8 View Post
Glad to hear the mods are working out well - magical is always a good result...

Hahaha I know 'magical' sounds cheesy but I was very impressed. It has enough accuracy where it allows the tone of the guitar to be heard but also just enough warmth and coloration to not sound too boring like most SS guitar amps. The low end is clear and well defined. She is a keeper and I am really happy I picked her up. I couldn't stop playing it last night, a true toe tapper

Thank you Jazbo for finding me the schematic and I thank everyone else for contributing. There is still a lot of room to tinker, maybe the other 7025 can be used as a "high gain" channel or something but for now I am pleased with the tone. I got band practice tonight so I will see how it does in a band situation with a drummer and some pedals cranking away.
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