LDR's for LA-4 repair?

Can someone suggest suitable replacements for silver face LA-4 LDR's?

Thanks for any advice!

Anybody? Advice appreciated.

Buy you a beer? (in Osaka japan)

Hi there,

I posted a similar question, and got no reply, just an eery hush. I guessed that you need two similar to those needed for a T4b, which might explain the radio-silence. I have replaced two missing from my (fire-damaged- the only thing that got any corrosion was the lead-in wires of the LDR's) La4 with two from a T4b, and it is super smooth. MUCH better than my other one! I am thinking of replacing the audio path op-amps in it with discrete op-amps to really make it sing. There are no markings on them, and they are very small. They appear to be very, v-e--r----y slow on the release. Someone eventually suggested a silonex dual (NSL-39V62?) but I cannot see how to make this work meself, being a something of a simpleton. If you find out anything further, please let me know!

All the best,


ANdyP :thumb:

here are the ldrs for the t4b opto ,

http://www.electronicsurplus.com/dictionary/cat1734.htm

and (for silonnex)

http://www.alliedelec.com/Search/ProductDetail.asp?SKU=699-0100&SEARCH=&ID=309764&DESC=NSL-5910



im not sure about the la4 opto ,

i was starting to look into building t4bs , and moving them out
of the lame octal plug,

first i gotta buy the el panels and all the other goodies ,
ill probably sell the raw materials or atleast make them available
once i order them.

theres also the thing with testing the LDRs for some consistancy.

something im not sure of yet how to do , but hopefully some folks

can pitchin the info , so there can be an endless supply of

of diy t4b's
:twisted:

www.vacuumbrain.com

Mac, I have some 5910's that read a little high if you want a free reject sample.
cj

Thanks guys

I'm a little puzzled on this. The LA-3 schematic shows a T4B. OK, this is pretty well known but the LA-4 schem shows two LEDs and 2 LDRs which certainly seems different than what's shown on the other circuits.

I'm thinking these are Vactrols.

There is no octal socket on the LA-4 either so a T4B cannot be plugged in (I wish it could).

Eddie Cilletti has some info about LA-4 upgrades on his website so I'm gonna check that out a little more. He's selling 'matched' optos for LA-4 for $30 a pair too which I would certainly like to avoid but I may have to just bite it. Maybe I should order a few Vactrols and just try 'em.

The LA-4 belongs to someone else and if I tell him the parts cost $30 I'm sure he won't think twice anyway.

Hi,

The LDR's are available from JBL Pro. They are supposed to be matched for attack and release characterisitcs (I believe that release varies the most from part to part) - I don't know for sure if JBL has matched parts or not, but they are not very expensive (less than $10 each?). The LA-4 has an LED on the PCB inside a small, round, black plastic shell. On top of the shell, looking down at the LED is the LDR - this makes a sort of custom "Vactrol". I've been told that the black plastic shell is actually a small inductor housing. A T4B would not work without extensive mods since it requires a much higher drive voltage than the LED circuit does. The LDR's are available elsewhere and they should be pretty much the same as the LA-2A or LA-3 - if the JBL part number is the same for each then that would answer our questions.

Tim

Thanks for the info. I'll try JBL Pro.

JBLPro lists Vactrol VTL5C4's on their parts list for $17.95 each so I ordered some of these and also some VTL5C9's which Eddie Ciletti shows as his choice for a replacement. I ordered them from Banzai Musical products in Germany since he has them for a reasonable price (around $7.00 each). I got extras and I'll try and see how they match up when I get them.
Thanks again. I'll post here when I get the parts installed.