LA2a 'almost' alive, need help.. (IT's ALIVE!)

[fallout]

My La2a is almost working. I used Kent's layout w/ Jensen transformers. The gain stage seems to be working fine. Amplifies signal, no hum whatsoever.. However, I can't seem to get it to compress. I'm using a T4B kit that CJ sent me a few years back, perhaps i messed it up when i built it years ago but i have no way to test it. Maybe that's the problem right there. The zero adjust pot also doesnt work. My voltages on the tubes seem ok:

V1: pin1 = 120V, pin2 = .2mV, pin3 = 1V, pin6 = 127V, pin7 = .1mV, pin8 = 1.2V

V2: pin1 = 100V, pin2 = 0-20mV, pin3 = 2.2V, pin6 = 282V, pin7 = 83V, pin8 = 106V

V3: pin1 = 102V, pin2 = 0V, pin3 = .85V, pin6 = 102V, pin7 = .2mV, pin8 = .9V

V4: pin1 = 0-.3mV, pin2 = 6.2V, pin5 = 124V, pin6 = 114V, pin7 = 0-3mV

Besides getting a known working T4B any idea what else i can look for? Thanks!

-jay

 

[PRR]

> a known working T4B

??? Open it. Feed a STRONG signal, turn OFF the lights.

Does the glow-panel blink with the music? If not, it could be a glo-pad thing, but I'd look at the 3-stage sidechain first.... more to go wrong (and the module WAS good when CJ sent it to you).

Turn on the lights. Does the signal get VERY weak? It should, as the photo-R goes low-resistance and sags the input.

 

[fallout]

Hey PRR thanks for the tip.. The T4B was indeed working! I thought maybe I put it together wrong but turns out everything was ok. After double checking my work looks like i connected pin7 of the T4B socket to the wrong side of the limit/compress switch, oops! I also found the problem with the zero adjust pot. I forgot to connect the 23k resistor from the pot to ground. I guess I was so excited to finally get it finished, I got a bit sloppy.

But now I have another problem with the meter not working in gain reduction mode but i think i know where the problem is.. Almost there! Thanks again for your help..

-jay

 

[fallout]

Just as I suspected, forgot to connect another wire in my rush to finish the LA2A. Now the unit appears to be working 100%. I must also add the it sounds pretty damn good too! Very fun and rewarding project..

-jay