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Construction tip - LEDs on nine pin socket

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Doc B.:
When it's time to install the LEDs on the nine pin socket, notice in the picture in the manual that they "sag" between their leads. When tube rolling 12AU7s the pins in the socket can move around a bit. If the LED leads are pulled tight between the tube pin and the center post you can end up breaking the lead right where it connects to the LED body when changing a tube. So curve your leads before you install the LED, either so that the LED hangs down between the leads as shown in the manual or so it sits centered at the top of an arc created by the leads, thus allowing the leads to adjust with any pin movement.

Tom620:
Thanks for the tip, I ordered a couple of these to resolder later.

Just curious, what is their function in the amp?

Doc B.:
They are used to bias the tube at 1.56 volts or thereabouts. The HLMP-6000 LEDs have a very stable voltage drop with varying current and this gives them some advantage over using a resistor to bias the tube.

Tom620:
That makes sense. Thanks for the explanation Doc!

adydula:
After trying to figure out why I kept getting  loud popping sound from one side of my headphones and watching one of the leds going on and off as I slightly moved the small tube around in the socket...I saw this thread and ordered and replaced both of the leds!  Using the leads as suggested to help the strain on these little devices.

The one that was cutting in and out actually fell apart as I removed it.

Problem Solved.

Alex

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