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I haven't made much physical progress since the last update, but still chipping away. I'm getting close on the preamp board design. One of the things I've learned through this process is that Boogie used plated through holes all the way back to at least the Mark IIB. This surprised me because...

The word bias refers to a DC offset between the cathode and grid that controls the plate dissipation at idle. The greater the offset, or distance between the points on the number line, the lower the idle dissipation will be. In Class AB, tubes are typically biased such that the plates dissipate...

Thanks for sharing! Looks like you have a single 33k the same place I do. Interesting how cold yours is biased. To check plate current, I measured the resistance of each side of the OT primary when the amp was off and charged down, and then measured the voltage drop when it was on. Then Ohm’s...

Yes, it was to determine the value of the fixed resistor, I replaced it with a 33k resistor. What resistor values do you have in yours? There should be two on the edge of the board, they are referred to as factory set on most drawings I’ve seen

Got the power amp wired and tested tonight, don’t mind the sloppy temporary wiring. Used JJ 6L6GCs for the test, getting 496 V on the plate at 40 mA plate current, leaving the tubes around 20 W at idle. Bias voltage was approx -51 V.

With your circuit, the darlington emitter should be half the supply and the base should be a couple diode drops away from the emitter. The differential amplifier emitters should also be approximately half the supply. Transistors are sensitive to both heat and incorrect voltage, they’re easy to...

Wiring has begun, will probably send another update when I’ve got the power supply, graphic and power amp wired and tested

It’s pretty close, but no. When I measured the slots on my IIB faceplate, I found that the graphic pots are not equidistant. I laid out everything equidistant for this build, and I have more chassis height so mine is taller as well

It looks OK on paper. I’d double check the transistor pinout, if that’s good check your DC voltages, and tracing the signal thru on a scope

The dark red are 47 and 100 nF, I believe both are 250V CDE DME series. I probably got them from Mouser

Their purpose is to reduce hum. The resistors create a virtual center tap for the heater winding and reference the circuit to ground. Check out The Valve Wizard Heater / Filament supplies on the net to learn more

Ready for install

Got the power amp and graphic PCBs finished and the graphic populated. Hopefully I’ll populate the power amp card tomorrow and can start wiring the amp.

Thank you for the kind words!

I can't see myself selling board sets as they're specific to the parts I have, my chassis design, any layout decisions I made, etc, not to mention the cost would be hard to justify. There are IIC+ board sets already available on the market, I even bought a preamp card from a kind fella on...

Got the power supply card done and drilled the tube socket holes in the power amp card. I haven’t installed any biasing resistors yet, will determine the values using a potentiometer when I get it all wired up

I gotcha. I have a IIB faceplate off an amp, but no access to a scanner that does 17”

Make reproductions of the faceplates?

Here is the EQ driver card completed Edit - the Darlington is installed backwards in this picture, I fixed it afterwards

Got the three single-sided boards etched today