I’ve been working on the color preamp over the last few days as I’ve had time. My volume control and output capacitors are supposed to arrive today so it shouldn’t take too much longer to finish it up. However working inside the small chassis is a challenge.
I’ve got the entire power supply wired up with the exception of a dropping resistor. Here’s how it looks so far.
The power supply uses a 33µf first capacitor followed by an 2H/47µf LC filter stage followed by a 1kΩ/47µf RC filter stage. The power supply should have about 20dB of margin over my desired -90dB ripple level. However the voltage will likely be a little high. I was targeting a B+ of about 300V but I’ll have to see what dropping resistors I have available. The 6CA4 drop is only about 10V at the low current levels. A 1kΩ resistor drops ≈13v at this current level. My power supply calculations show about 316V with no dropping resistor so I may just use another 1kΩ before the choke to get me close to the 300V B+ I want.
I also had to turn the choke around to make room for a convenient location to mount the dropping resistor. This also gave me a nice spot to mount the 499kΩ PS bleeder resistor. With the power supply essentially complete, I can now start focusing on the audio side of the circuit. I get the feeling that things may get a little cramped before I’m done.
As always, questions and comments are welcome.