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LA-3A Problem .. lightbulb keeps going out...
Old 11th June 2006
  #1
Gear Addict
 
🎧 15 years
LA-3A Problem .. lightbulb keeps going out...

Hi guys,

I have a vintage Urei LA-3A... and when I bought it (used) about a year ago, the lightbulb was not working. So I took it to a guy in Los Angeles, who repairs them. I originally took it there for him to do the noise floor mod... but he also replaced the bulb and changed the caps, etc... and it worked fine... But since then, the bulb went out again (twice). I just changed it about a month ago, and now it's out again. And I hardly used the LA-3A lately.... (I haven't been that busy).

Any idea what the problem might be? The bulbs I bought are #1819 (Bayonet), from Radio Shack.

Thanks for any help....
Old 11th June 2006
  #2
Lives for gear
 
No4PCs's Avatar
 
🎧 15 years
Cool Mercenary audio

Quote:
Originally Posted by Rockman
Hi guys,

I have a vintage Urei LA-3A... and when I bought it (used) about a year ago, the lightbulb was not working. So I took it to a guy in Los Angeles, who repairs them. I originally took it there for him to do the noise floor mod... but he also replaced the bulb and changed the caps, etc... and it worked fine... But since then, the bulb went out again (twice). I just changed it about a month ago, and now it's out again. And I hardly used the LA-3A lately.... (I haven't been that busy).

Any idea what the problem might be? The bulbs I bought are #1819 (Bayonet), from Radio Shack.

Thanks for any help....
Hi, i heard about mercenary audio tech person do good job.
Old 11th June 2006 | Show parent
  #3
Gear Maniac
 
🎧 15 years
You could see about the purple audio light kit. I have those in my console VU's and my 1176 and a few other thingies that I got tired of replacing bulbs in. Bright, good looking LED light that is multi segment... It will probably outlast me!

They are awesome. Contact purple about it.

purpleaudio.com
Old 11th June 2006 | Show parent
  #4
Gear Addict
 
🎧 15 years
Thanks guys... I guess I could do that... But I was just curious... is this normal? Replacing a bulb every month? it doesn't sound right to me.... I wonder what could be causing this...
Old 11th June 2006 | Show parent
  #5
Lives for gear
 
brianroth's Avatar
 
🎧 15 years
It might actually be the socket. Did you check the lamp itself with a VOM to be sure the filament is actually open?

Bri
Old 11th June 2006 | Show parent
  #6
Gear Addict
 
🎧 15 years
Thanks for the reply. Well, I just checked it.. and it was the bulb indeed.

But...

I think I might have just figured something out. Maybe I had the wrong kind of bulb in there... ?

The old bulb that was in there was much brighter. There are 2 sockets in the LA-3A (for 2 bulbs).. I think that one of the bulbs was burned out... and the other one was burning relatively bright.

The model number of the 2 bulbs were: N239 and 1818

I replaced both bulbs with #1819 bulbs... They both work now... but they are both very dim. You can barely see the lighting at all... (but maybe it's because I got so used to the brighter bulbs).

Do I have the right bulbs in there? Anyone?
Old 11th June 2006 | Show parent
  #7
Lives for gear
 
🎧 15 years
Hi
Small bulbs typically have a short lifespan so should be run with about 20% less volts than rated on the bulb. Some can be only 1000 or 2000 hours at full supply.
I don't know your unit but if the bulbs are fed from an unregulated supply and your mains is a bit high normally then they will be stressed. If you have 2 bulbs as you say then the two should probably be same type and vintage otherwise they may not share power equally, appearing to blow prematurely.
Good luck
Matt S
Old 12th June 2006 | Show parent
  #8
Lives for gear
 
brianroth's Avatar
 
🎧 15 years
I just checked a LA-3A manual, and the correct bulbs are 1819. They are wired in series, so if one bulb burns out, neither will work.

An 1819 is rated for 28V, so a pair in series would require 56V for full brightness. Since these are wired across the secondary of the power transformer, I'm guessing only 40V or so is available, which means the 1819's *will* run dim...and for much longer than their specified 3000 Hours.

Bri
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