anyone in NY area have a p2p la2a build?

[sr1200]

With (ouch)

 

[jwhmca]

Is the neon bulb installed/working?

 

[sr1200]

yeah meter works too... (in gr mode, it goes to 0 and in + 4 or 8 mode it goes back down)  The neon only lights up if the 0 adjust is slightly on, if its totally OFF, the neon is off.

 

[jwhmca]

Are we talking DS1?

I thought that was for voltage regulation?

 

[sr1200]

Yeah DS1 lights up if i dont have the 0 adjust all the way off.  I did not put a lamp in the unit yet (still out of stock, no wires hooked up to the 6.3v leads for it)

 

[sr1200]

Again, dunno if this means anything but the input transformer i have the grey white and black leads going to ground the violet is going inbetween R5 and R6 blue to pin 3 of the XLR brown to pin 2 XLR yellow and orange are tied together green and red are on the barrier strip, (separate) doing nothing.
http://cinemag.biz/mic_input/CMQEE-3440A.php

My output transformer is:
http://cinemag.biz/output/PDF/CM-2810.pdf
I have yellow to pin 2 xlr orange to pin3 xlr Red to R20 (insulated post) and brown to the neg side of the 10uf 450v cap.

edit: do i have my output tranny in backwards?

 

[pucho812]

looking at the data sheets.  brown and red are primary connections, orange and yellow are secondary connections.    so you have the transformer facing in the right direction however according to the data sheets

orange should be hot side of the balanced  output so should be going to pin 2 on an xlr or tip on a 1/4"
yellow should connection to the negative side so should be going to pin 3 on an xlr or ring on a 1/4"

As for your voltages being off, Double check solder joints, turret board wiring and jumpers, and make sure you have the correct resistor values in place.

 

[sr1200]

Ok cool, so the only thing bad there is my phase would have been inverted. (thanks for the eyes pucho)

The more I look at the board and the wiring the more I'm thinking there is a bad part somewhere.  I'm almost thinking I have a bad tube (dunno which one or all).  When I rewired the entire case this weekend, I went through wire by wire marking it off on the diagram (and schematic) as I went. 

One thing that WASNT on the diagram that WAS on the schematic was on the 6AQ5.  The schematic seemed to have pin 1 and 7 tied together whereas the diagram had pin 1 with NOTHING connected to it.  Anyone have insight on this?

 

[jwhmca]

What are you using for R34 and R31? What values?

 

[sr1200]

1k for R31 and 10K 2W for R34

http://www.recproaudio.com/diy_pro_audio/diy_files/la2a/la2a_layout.jpg
These are all my values.  I built the BOM from this and wired the components according to this. (with the exception of the pin 1 - 7 thing on the 6AQ5)  If anyone knows there to be an error on this layout, that would probably be a place to start.  :-\
I can pull them out and test if anything opened up tonight.

 

[jwhmca]

Have you mined the Groupdiy "All things LA2A" thread? Some sources say that R34 is 22k

 

[sr1200]

Im only up to page 60 something on that thread lol. but i did come across this:

The laster version which added C13 and R38 also changed R34 from 22k to 10k and R36 from 1k to 470 ohms.  I doubt this will fix your main problem, but this is a common thing with the Bloo build.  IIRC, the instructions and schematic don't match up on this point.  It may not matter, but why wonder?  I used 10k and 470R on mine, which, BTW, you can take a gander at here:

Im using the "newer" schematic which has the 10K/470 combo.

 

[pucho812]

The phase issue will only be a problem if the input transformer is is not wired properly. As it has been noted before pin 2/pin 3 hot is not a problem if both in and out are wired the same. In a balanced connection if it is pin 3 hot device in a pin 2 hot studio, the phase flips going into the device but flips again to be back in phase on the output of the device.  so make sure those are the same.

we have a couple of la2a's at work, I can compare with and I have a couple myself outside of work I can compare with. If you need measurements.  On mine I swapped the pots for stepped attenuators, 24 steps.  I can't say it was worth it so much as I can say people really flip when they use it.

The 6aq5 pins 1 and pins 7 are both connections to grid #1 of 2 for the tube.

Do you have a link to the schematic your referencing? As far as bad tubes it's  possible you have a faulty one. I always make sure I have a couple of extra's before working a project just in case.

Having said that, our la2a's at work have been on 24/7 365 since they were installed. They have been in use several years now and have only had the 12bh7 die. When that happens it doesn't work at all other then turn on.

 

[sr1200]

Im ordering some new (cheap) tubes today.  The ones I originally ordered were all NOS (expensive) and hopefully i didn't fry them all. as far as schematic goes... thats attached. (standard 1968 schematic, no "mods" or super secret golden voltages/values)

 

[sr1200]

One other thing i noticed as a discrepency with the layout and the schematic is R8 the 2.2M resistor from pin 3 to ground on the t4"A" im using a t4B (dont know if that matters) but it was not included in the layout, but IS on the schematic.

 

[pucho812]

trust the schematic.

Now has the unit passed audio at all? if so how did it sound?

 

[sr1200]

If i max the gain knob i can "kinda" hear a nasty distorted version of the material cOming through. But i dont consider that passing audio. Passing gas maybe, but not audio. In regards to R8, i dont see that resistor in the photos of all the builds i see either. If you can confirm a resistor hanging off the side of the t4 please let me know.

 

[jwhmca]

I think you can/should remove your T4 module until everything else is working right... as I understand it, it should pass audio just fine without the T4 installed.

 

[pucho812]

o.k. distorted audio, is it low level or average level. I concur about removing the t4b for now. Then I would go over your power section since it is a turret board build it's easy to wire something in the wrong spot.

 

[sr1200]

turret board pic 1 
btw I REALLY appreciate you guys helping out.  I'm gonna have to send out some 6er's after this thing gets goin!