Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Foreplay III => Topic started by: arveedub on March 05, 2011, 11:57:06 AM

Title: Adding C4S boards to a FPIII
Post by: arveedub on March 05, 2011, 11:57:06 AM

I have some old C4S anticipation upgrade boards from a FPII that I'd like to use to load the CF stage in my FPIII. I was hoping that somebody could check my math on the values for R1 and R2.

The FPIII's B+ is 150V. In order to bias the LED's to 1mA R2 would need to be 150K. I should use at least a 1/2W resistor.

As near as I can tell, the FPIII's CF passes 3.4mA. This should give a value around 300R for R1.

Am I correct on any of this? Thanks!

Title: Re: Adding C4S boards to a FPIII
Post by: Paul Joppa on March 05, 2011, 06:19:01 PM

Yes, we use 150K for R2. We use 237 for R1, which is about 3.8mA with the current HLMP-6000 LEDs. The older LEDs would take a bit more resistance, so 300 is a good starting point. It's not too sensitive for the CF load.