Testing a T4B before building an LA-2a

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kiira

Well-known member
Joined
Aug 2, 2004
Messages
536
Location
Baltimore - Blobsville USA
I am going to build an LA-2 clone (when I finish my V672 project). I have the Jahnson book but er um... seems like there's a lot of errors. I have the original HA-100x input transformer and the A24 output and an additional A10. Love those hamfest grabbags! ha ha.

I have a used T4B and was wondering how I could make sure it works before I start building just in case I have to buy another one or repair this one. Any ideas?

I am used to building guitar amps on turret boards and love this layout...
http://www.vacuumbrain.com/The_Lab/TA/LA2/la2a_layout2.jpg

If I use this and the schematic in the JBL manual on page 14 will I run into any gotchas? It seems like this is a better approach than the Jahnsson book...

Tra!

Kiira
 
not much that can go wrong with a T4. other than the EL being weak/dead from age or one of the photocells being bad.

is it in a long can or short can?
 
[quote author="Scenaria"]not much that can go wrong with a T4. other than the EL being weak/dead from age or one of the photocells being bad.

is it in a long can or short can?[/quote]

gee I don't know if it's long or short. I could measure it when I get home. It's just an aluminum can that says T4B on it from what I remember. I was just hoping to test it somehow in case I mess something up building... there's always some little thing I do.

thanks,

Kiira
 
just drop an ohm meter accross the LDR's to make sure they are working... if the EL lights up then you have something to work with...

odds are it'll probably work just fine.

before you power up the la2 I would leave the tubes and T4 out of circuit. check your readings first then drop in the tubes make sure everything looks good before putting in the T4...
 
[quote author="Scenaria"]just drop an ohm meter accross the LDR's to make sure they are working... if the EL lights up then you have something to work with...

odds are it'll probably work just fine.

before you power up the la2 I would leave the tubes and T4 out of circuit. check your readings first then drop in the tubes make sure everything looks good before putting in the T4...[/quote]

cool cool... but what's a LDR, the light emitters?

yeah I usually bring my efforts up on the variac and check out voltages just to make sure.

yow just looked at your LA-2 kits! Sweet!
 
LDR= Light dependant resistor

theres two of them in the module... silver looking disks with two leads comeing off of each.. on the other side is a glass lense. Its sensitive to the light that the EL panel gives off :)

its what makes the LA2 what it is :)
 
[quote author="Scenaria"]LDR= Light dependant resistor

theres two of them in the module... silver looking disks with two leads comeing off of each.. on the other side is a glass lense. Its sensitive to the light that the EL panel gives off :)

its what makes the LA2 what it is :)[/quote]

'K I'm hip. I'll just put my Beckman across each of them them and see if I get some action.

I know I'll sound exactly like Patsy Kline when I use an LA-2a, my tube pre and my ribbon mic. ha ha :wink:

thanks!

Kiira
 
tru tru

but.... I dont recommend it...

ive killed a few EL panels during cell matching...

it would suck to smoke the EL just to see if it worked :shock:
 
so that's where my panels went!
Use green led's fool!
and test around 1.5 to 2 seconds for delay time, not 50-100ms!
:guinness:
how was Austin, fool?
 
austin was good :)

im going back sept 15th for a few weeks

now im just trying to play catch up

By the way

LSI sucks ass

I could hardly get em to cut a break on 100+ EL's


I sold the DDA console.. soo im pretty happy at the moment

Bon Jovi lives on :D
 
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