Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mike_J on March 04, 2016, 11:39:51 am
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I have used an oscilloscope to mark the outside foil on the new PP caps for the one-channel AB763 build. Will use them in the reverb and vibrato sections of the amp. Not quite certain what direction to place the outside foil here however, Fender used ceramic caps in the reverb and vibrato sections of their AB763 builds so can't look at a picture to get any ideas there.
Can I make a general assumption that the outside foil should face towards a plate connection and away from a grid connection or is that too simplistic? If I can make that assumption then there are still two .1 and one .01 cap that aren't directly tied to either a plate or grid. Needless to say I am confused again. Any help would be appreciated.
Thanks
Mike
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Attached Doug's One-Channel layout with known outside foil locations marked with a red circle. This is based on photos of Fender chassis. Not sure about the rest of the caps specifically in the reverb and vibrato sections.
Thanks
Mike
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The general rule from what I've read is If it is going to ground foil side goes to ground. If it is going towards another stage, the foil goes to the previous stage. This means that any noise it picks up doesn't continue on to the next stage.
When I did any of mine that were coupling caps, I put the foil side to the previous stage as an example.
As a side note, some of them were really hard to determine, I'd have maybe a super tiny difference between orientation on my scope... but I figured that if the noise change was so nominal in those, it may not matter as much. Some were extreme though.
~Phil
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The general rule from what I've read is If it is going to ground foil side goes to ground. If it is going towards another stage, the foil goes to the previous stage. This means that any noise it picks up doesn't continue on to the next stage.
When I did any of mine that were coupling caps, I put the foil side to the previous stage as an example.
As a side note, some of them were really hard to determine, I'd have maybe a super tiny difference between orientation on my scope... but I figured that if the noise change was so nominal in those, it may not matter as much. Some were extreme though.
~Phil
Thanks Phil. Your comments make sense. As such the simplistic explanation of putting the outside foil towards the plate and away from the grid and otherwise towards ground probably is right. Have attached an updated layout that has the Fender outside foil directions in red and the others circled in blue. If anyone sees a problem with it would you please advise.
Thanks
Mike
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Yeah, now that I rethink what you wrote, it is absolutely identical to mine, I just didn't quite get it at first read (Engalish is hard mmkay). Yeah, the picture, imo seems right with respect to the OF side of the cap. Probably want more than just my opinion though :)
~Phil
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Maybe these will help:
http://www.aikenamps.com/index.php/where-to-connect-the-outside-foil-on-capacitors (http://www.aikenamps.com/index.php/where-to-connect-the-outside-foil-on-capacitors)
http://el34world.com/Forum/index.php?topic=11427.0 (http://el34world.com/Forum/index.php?topic=11427.0)
If I understand this correctly you want the outer foil towards AC-ground so either towards B+ rail or the ground, whichever has the least resistance on the way. :dontknow: