B15VB Schematic (2010)
May 15th, 2010
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Here is a schematic of my B15NC amp project. It is based on the Ampeg B15NC schematic but reflects changes I have made to the circuit.
Categories: Schematics
Archive
Archive for May, 2010
Voltage issue corrected
May 15th, 2010
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I finally got around to addressing the high voltages I was showing in my amp. After considering a few potential fixes (some internal and some external) I decided on a relatively cheap and simple internal solution involving the use of Zener diodes (1N5347BG’s) in the PT secondary center tap lead to reduce the B+ voltage.
String of Zener diodes
Since I had room at the end of my turret board, I opted to use five 10v, 5w Zener diodes to drop the voltage. I used 1/16″ slugs of copper, 3/4″ square, as heat sinks for each diode. I get a voltage drop of 38.4v across the string of Zeners, which has brought my other voltages much closer to where they should be. Here is a chart showing the voltages I was measuring before and after the fix:
Categories: Ampeg B15NC Project
Hum issue – solved!
May 15th, 2010
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Okay, it’s been so long since I’ve posted an update it’s taken me awhile to remember how I was doing it! The strong hum issue with the amp has been fixed. Someone much more observant than I pointed out an apparent problem with my tube socket wiring. According to the schematic, pins 8 of V4 and V5 should be tied together. If you look at pin 8 of V4 in the following photograph you will notice that something is missing:
Power tube wiring
Since correcting the problem the amp runs much quieter! I’m glad the problem was discovered but I also feel kind of stupid. I supposedly did thorough double-checks of my wiring and yet I still managed to miss something this obvious!
I’m happy with how the amp sounds now, but I still plan to correct some lead dress issues with my AC lines feeding from the power cord socket.
Categories: Ampeg B15NC Project