Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: labb on June 02, 2016, 12:58:45 pm
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The schematic for the tube pre amp shows a 470k resistor in series with a .047 cap that connects pin 2 to pin 1 of V2-A. This is not shown on the lay out. Is this a mistake on the schematic?
(http://el34world.com/projects/images/TubePedalSchematic.gif)
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It appears on Doug's build pic, so yes, trust the schematic
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The schematic for the tube pre amp shows a 470k resistor in series with a .047 cap that connects pin 2 to pin 1 of V2-A. This is not shown on the lay out. ...
You should see the schematic as "V2-pin1 direct connection to V2-pin7" and the 0.047uF and 470kΩ as running from V2-pin1 to V2-pin2 (negative feedback).
I see what I believe is the 0.047uF cap in the photo of the point-to-point version (http://el34world.com/projects/tube_box_4.htm) (no layout provided; must compare the schematic to the picture).
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Here's the 2 layouts from the library...neither show the NFB.
Maybe it was a late build tweak that he squoze in there.
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Thanks all for the help. I intend to build one of the tube pre amps. Not going to try to put it in a pedal box. Not sure I have the skills to work in that small an area. Instead I will put it in a 1U chassis. I intend to change up the power supply to a small toroidal transformer instead of the back to back 12 volt arrangement that Doug shows.
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Thanks all for the help. I intend to build one of the tube pre amps. Not going to try to put it in a pedal box. Not sure I have the skills to work in that small an area. Instead I will put it in a 1U chassis. I intend to change up the power supply to a small toroidal transformer instead of the back to back 12 volt arrangement that Doug shows.
This one should get you close to his 280V B+
http://www.antekinc.com/as-05t200-50va-200v-transformer/ (http://www.antekinc.com/as-05t200-50va-200v-transformer/)