LED retrofitting in audio gear

Relax in southern comfort on the east bank of the Mississippi. You're just around the corner from Beale Street and Sun Records. Watch the ducks, throw back a few and tell us what's on your mind.
Post Reply
brianroth
Posts: 91
Joined: Mon Jun 17, 2013 2:11 pm
Location: Salina, Kansas
Contact:

LED retrofitting in audio gear

Post by brianroth »

I was going to write a longer post, but it's getting late <g>.

Long story short, in the past 2-3 months, I've had to deal with multiple pieces of old gear with various burnt out incandescent bulbs. Illuminated switches, indicators on panels, VU bulbs, backlighting for console faders (!), you name it.

In most cases, I just threw up my hands and found suitable replacement incandescent bulbs due to lack of time for "Alice to go down the rabbit hole" and do essentially re-designs of the gear in order to substitute LEDs. Finding a LED which mechanically fits is the least of the problem. It's the rest of the process, including proper dropping resistor values for both current requirements of the LED as well as desired brightness, proper color of the LED, the "polar pattern" of the LED (MAJOR issue when trying to light most VU meters), deciding what to do with the existing bulb sockets, etc.

While there are various (usually EXPENSIVE!) screw-in/snap in/whatever retrofits for a number of popular incandescents, they almost always have "gotchas" of one sort or another.

Just thought I'd start the conversation here in the "Pink Ranch" section of the forum and see what the brain-trust has to offer.

As far as "maybe drop-ins", I do see a growing variety of choices at Mouser with less than stupid prices:

http://www.mouser.com/catalog/catalogusd/647/161.pdf

Perhaps the most interesting one there is what appears to be a potentially useful replacement for the famous #47 lamp:

http://www.mouser.com/ProductDetail/JKL ... hEVw%3d%3d

Runs on DC....or AC! Need to order one with my next Mouser order and see if it is useful behind the jewel on a Fender guitar amp!

Anyway, just starting the discussion.

Bri
Professional audio and video systems design/installation/maintenance.
www.BrianRoth.com
User avatar
mediatechnology
Posts: 5442
Joined: Sat Aug 11, 2007 2:34 pm
Location: Oak Cliff, Texas
Contact:

Re: LED retrofitting in audio gear

Post by mediatechnology »

The #47 replacement is a good find.

I have used the early LED replacements for slide-based lamps in the SSL and they worked pretty well visually.
They still burned out - just not as fast.
I have a friend that maintains a large number of modern Wheatstone control surfaces using LEDs and he still has burn-out issues.
I think the really small lamps assembled from die in a small form-factor have heatsinking issues since they don't have the lead-frame of both through-hole and SMT LEDs - just bond wires.
Lighting a VU meter that used incandescents with LEDs does seem like a challenge since they point the wrong way.
brianroth
Posts: 91
Joined: Mon Jun 17, 2013 2:11 pm
Location: Salina, Kansas
Contact:

Re: LED retrofitting in audio gear

Post by brianroth »

While recently working in Omaha restoring "serial #2" (of 2! lol) of the desk I designed back in 1977:

http://brianroth.com/pix/mb77-june2014/ **

...I tried various schemes to replace the incandescents in the VU meters with LEDs and it was "a Fool's Quest". The Dixson VU meters (similar model used in the original Ampex 440 machines) used lamps that slide in from the rear, with the lamp body perpendicular to the body of the meter. Needless to say, no standard LED will work in that situation since all the light output blasts directly into the inside/rear of the meter's front escutcheon!

What we need is a "side-firing" LED with a 360 degree dispersion pattern.

However, that same Omaha studio also has a SSL desk which uses the identical illuminated EAO switches as I used for mutes, etc. One of the techs there had actually taken a pile of dead slide base incandescent bulbs, removed the glass, and soldered a pair of resistors to the metal pieces and then onto a standard T 1-3/4 LEDs to make a homebrew replacement. Wish I had taken some pix.

Of course, you have a 50-50 chance getting the replacement to light up when you slid the lamp into the switch body since it is polarity sensitive.

Bri

** My Desks' back story here: http://brianroth.com/projects/m77/m77.html
Professional audio and video systems design/installation/maintenance.
www.BrianRoth.com
User avatar
JR.
Posts: 3700
Joined: Sat May 24, 2008 7:21 pm
Contact:

Re: LED retrofitting in audio gear

Post by JR. »

While this may involve too much design work and impractical for multiple units, but I have seen LED based night lights that use some clear plastic (plexiglas) as a light spreader to take concentrated white LED light and re-radiate it as a diffuse light source.

Do any 3-d printers support clear media? That would be interesting.

JR
Cancel the "cancel culture", do not support mob hatred.
brianroth
Posts: 91
Joined: Mon Jun 17, 2013 2:11 pm
Location: Salina, Kansas
Contact:

Re: LED retrofitting in audio gear

Post by brianroth »

mediatechnology wrote:The #47 replacement is a good find.

.
One of those JKL "47" bulbs hitched a ride in my recent Mouser order. Worked without problems in a Fender Deluxe and a Pultec DIY clone.

Nitpicks. There isn't a long glass envelope to hold when installing/removing in a "front panel loading" socket with a colored jewel. And, the color is very blue-ish, making the color through the jewel shift a lot. We have three Pultec clones here in the outboard rack, and the color through the red jewels are identical with incandescent #47 bulbs. With the JKL, the color shifted from red to orange-ish.

Bri
Professional audio and video systems design/installation/maintenance.
www.BrianRoth.com
Post Reply