Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: nico3las2003 on June 29, 2016, 11:15:25 AM

Title: Replaced broken LED with jumper cable
Post by: nico3las2003 on June 29, 2016, 11:15:25 AM

Hey all, I built my crack two weeks and it has been amazing! However, today while shuffling it around -  the LED on pin A8 snapped off and I promptly soldered a jumper cable in place.

This may be a really stupid question..but do these LEDs alter the sonic sound in any way, or are they just a diagnostic tool to check for bad solder joints, etc. ?

Title: Re: Replaced broken LED with jumper cable
Post by: Doc B. on June 29, 2016, 11:38:44 AM

The LED sets the bias for the tube to 1.56 volts. That is good. A piece of wire sets the cathode bias to 0 volts. That's not good. Best practice is to replace the LED. Second best is to jumper A8 to A3 so that the LED at A3 sets the bias on both triodes in the 12AU7. That is a kludge, but it will work.