OT-Help me (noob) find this diode??

Hi,
First let me say I know very little about electronics but I might as well start learning something.

I found an old Vega Soundservo audio compressor from the 60's on CLfor $10 and am playing around trying to get it operating. It powers up, the transformer seems to work (9VDC), pots do there thing, etc... but no effect on the output. Two issues pop out while I was poking around with my multimeter. Looking at the board it looks a little discolored where the two parts I am describing below solder on.

(Sorry about the crappy iPhone photo, I can get a better one when I find my camera if it helps. Diode doesn't photograph well alone, but I'd guess you know what they look like.)


The first obvious problem is that a diode was looking a little burnt where it solders onto the board. So I removed it to test it and managed to break of one leg. I have so little knowledge that I don't know how to compare its specs to what it on the market today. Everything I see has a PIV spec. This is what I can find about it:

Semcor LMZ9.1A - printed on it so that much is known.
This is off the web:
LMZ9.1A
General Purpose Reference Regulator Diode
Various
V(Z) Nom.(V) Reference Voltage=9.1
@I(Z) (A) (Test Condition)=55m
Tolerance (%)=5
Temp.Coef. (pp/10,000) Max.=6.8
Z(z) Max. (Ohms) Dyn. Imped.=2.5
P(D) Max.(W) Power Dissipation=2.0
Status=Discontinued
Package=DO-41
Military=N

Issue #2 is a resistor that tests a little out of spec, if I am understanding the band colors on it right. It looks like it is a 100ohm carbon composition resistor, with a 5% tolerance. It ohms out at 109 ohms, slightly beyond tolerance. Is this something that I ought to replace while I am at it? Can I use a more modern 100ohm resistor? Something from Radioshark for instance...

While I am asking for help, anyone got any idea what the sealed white rectangle is? I have heard it might be a LDR but I don't know if that guy was just guessing.

Thanks for any help,
Andrew

OK, so 2 votes for zener. Thanks for the help guys!

After googling for a few I have a very basic idea of what a zener diode does, and it makes sense with how the traces on the board seem to be laid out. Makes me hope that I am on the right track. If that particular piece is no longer available, what other options are there?
The local RS offers a 12v 1w zener (1N4742A), if I substitute something like that will that allow voltage to pass through at 9v? Or is it likely to just burn up due to a lower wattage rating?

As to the white plastic thing on the board. Any thoughts on why a light dependent resistor might be in an audio compressor?

Thanks
Drew

Ok, thanks alot! I really appreciate it. I'd have stuck a regular diode in there and had no idea what I had done wrong. I'm obviously way over my head even at this basic level. Oh well gotta start somewhere...

So now I just need to find that zener diode and then I can move on to the next thing I mess up! Do you have a online source for small numbers of this kind of thing? From ON semi 5 would cost $11.00 which seems steep.

Just to make sure I understand, this zener diode is there to ensure that the circuit it feeds only gets 9.1v regardless of what the transformer may put out?

If you're not tired of my questions yet, why use a LDR instead of a pot to vary resistance?

Thanks again
Andrew

Thanks for the lesson, now I wait a few days until I find out if that diode was the problem. There's lots to play with in the mean time; I've been trying to figure out how to check the 6 transistors as well.

I'll update this when the diode comes in and let you know how it came out.

If something inside that LDR is not functioning I'll give up and cut it open just to see what's in there! This project has set me off on reading all I can find about how this stuff works so no matter what happens I'll at least have learned a little.

Thanks again,
Andrew