Archive for May, 2010

B15VB Schematic (2010)

May 15th, 2010 No comments

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.

B15VB Schematic 5/10 (PDF)

Categories: Schematics Tags:

Voltage issue corrected

May 15th, 2010 3 comments

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:

B15NC Voltages (PDF)

Categories: Ampeg B15NC Project Tags:

Hum issue – solved!

May 15th, 2010 No comments

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 Tags: