Construction tip - LEDs on nine pin socket

[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

[Deluk]

I recently had one of mine "pop" off the centre connection. Being a bit hidden away I didn't notice that the solder connection was minimal but under tension. Reflowing fixed it but bringing up this thread makes me think I should get a some spares. Being in the UK makes it easier/cheaper to get them locally. Does this eBay link show the correct ones? Note it says that the picture is for illustrative purposes only. Says to check the specs. Are they correct/the same as the ones supplied for the Crack?
http://www.ebay.co.uk/itm/5-X-LED-SUBMIN-RED-Part-HLMP-6000-/351609648339?hash=item51dd9174d3:g:HvYAAOxyd8NSa78D

Thanks in anticipation.

[Doc B.]

Yes, that is the same part.

[lthomash]

Dan, out of curiosity, is there a less fragile substitute, cost is not a consideration in this question.

[Paul Joppa]

Unfortunately no, there is no substitute. It's an old design and an inefficient light source - but it has a very low effective resistance, and is very quiet. Used to be made in a sturdier package, but this seems to be the only format still available.

[Deluk]

Thanks Doc.

[Natural Sound]

I suppose you could mount the LED's on a small piece of perf board and run wire to the socket. However, Doc's suggestion of a little sag in the lead dress seems more than sufficient IMHO.

[lthomash]

Paul, do the original LED's have the same spects as the HLMP being used today?  I still have a couple of dozen of the originals.

[Paul Joppa]

Paul, do the original LED's have the same spects as the HLMP being used today?  I still have a couple of dozen of the originals.

The current/voltage plot in the spec sheet is clearly identical; however the measured voltage drop seems a bit smaller than the measured originals, at least for the few times I've taken measurements. So I am not sure what to think. The chemistry ("Standard Red") is the same. Note that the HLMP-xxxx family includes seven different chemistries, three of which are reds. Only this one, which I believe was the first red LED chemistry, has the low dynamic impedance.

[adydula]

I was able to install with long enough leads to help prevent. But I am now reminded not to wiggle the tube in the socket if at all possible...I think the idea of soldering the led to a perf board and then wiring it to the pins is a good idea...you could easliy hot glue a small board next to the tube socket...voila issued resolved.

Alex

[John EH]

I've built three Cracks and on the last two I installed the LED's as the first step of the kit.   Get them right on the top of the pin with just the smallest bit of solder holding them.  Then later when working on that socket I just used some stats to hold them in place and act as a heat sink when soldering the rest of the wires in.   Not totally necessary but if you have the tools, why not?