All things LA2a related

[Sredna]

Thing is, the CT on the primary of the input, has to be grounded in order for me to get signal at R5.R6 test point...The CT shows in the schematic, that it floats... not grounded...

Ok, let´s disconnect the 1009 and test it!

Connect the COM lead (black) of your DMM (OHM setting) to one of the leads of the 1009, measure the other leads and write the results down.
If you just get readings on one lead and the other three show no connection, you´ve found the secondary winding.
If two leads gets readings, you´ve found the primary.
The secondary should have a much higher resistance (Ohm) than the primary.
To find the CT, find the leads (from the three) who have the highest resistance when connected to the DMM. The lead left over from the three is the CT.

 

[college101]

OK..the results are in

RED on red wire+ BLACK on white wire=9.0 Ohms

BLACK on Blue wire+RED on White CT wire=11 Ohms

RED on Red wire+Black on Blue wire=20 Ohms

Then

RED on green wire+ BLACK on Grey wire=1.487 KOhms

This was what I found,..

 

[Sredna]

Perfect, the transformer seems to be in order!

Just for fun you could connect your CD player to the primary (red/blue of your earbud cable to red on the transformer, the shield on earbud cable to blue on the transformer) and the croc clip of the probe to grey.
When you now touch the green lead with the probe, you should hear music.

 

[kazper]

Also if you measure the AC coming in via a set tone and volume it should be exactly 9.1 times larger on the secondaries of the input.... as the ratio is 1:9.1

 

[college101]

ok...why would I not hear any music then, if I had the Green going to 7 on Recproaudio's set up, and then the Grey going to the ground connected to R5 and the Neon, why would I only hear music if I ground the CT?

Yes it seems the transformer is working, but NO audio seems to go past the first set of points?

Basically with R5 having wires on either side...I should be getting audio at the R5/R6 audio test point, but I dont, inless I ground the CT...but the CT is supposed to float per the schematic!

 

[Sredna]

Forget the CT!

Do the check that I described in my last post, it's important to be shure that the transformer and the test equipment work.

 

[college101]

OK sredna...I did your test...The ear bud wires are too small to make proper connection...after a few attempts, I gave up!

SO I re wired the blue and red wires up to the TB#1 and plugged the guitar cable/CD tester up...
Connected grey to ground of test tracer, and then connected the test tracer node to the green wire...NO audio! None will go threw,,,But when I connect to the blue or red wires...BINGO, music comes threw...

SO for giggles,I went to the White CT wire, and BINGO...AUDIO goes threw it...This makes me think that the green and white wires are mislabeled...Am I right or wrong?

 

[Sredna]

Just to be shure, measure with you DMM (set to OHM) between Red<->Green, Red<->Grey, Blue<->Green and Blue<->Grey on the transformer.(The transformer must of course be disconnected from everything else)
If you get any other result than NC (no connection) then there's a problem in the transformer.


To do the test described in my second last post study this picture below. NO other connections, no TB#1, no CT. Otherwise you cant be shure what you tested, if it was the transformer or faulty connections...

Sorry to nag about this but ramdomly connect things together and measure here and there won't help you.

 

[college101]

SREDNA!! You were right(Good thing I listen to you)...I must have set the first test up wrong...The correct test I just ran...worked..and the Green wire signal is stepped up! The Audio signal level was increased from the CT signal(which was much lower)

Problem is...when I have this in the circuit, why am I not getting any audio at R5/6 test point then?

 

[lassoharp]

This makes me think that the green and white wires are mislabeled...Am I right or wrong?

The DCR measurements you took says: NO

You can prove this by measuring the DCR from Green to Red or Blue.  It should read no continuity.

To check for a connection problem on the barrier strip (TB1).  Do the same DCR readings with the transformer wired in circuit.  They should read the same.

 

[Sredna]

Ok good!

Now connect Red and Blue on the transformer to the correct points on TB#1, use the probe on Green/Grey as in the picture, do not connect to R5/R6. Check with the probe. Get audio?

If yes, connect the ground (with the neon) to the Grey lead,
then solder R5 between Green and Grey. No other connections!
Check with probe, if no sound R5 is faulty.

Next step: Connect R6 to the junction of Green and R5, check with probe.

 

[college101]

Thanks Sredna    Little by little, Im starting to have faith in this compressor!

Re-wire will be taking place soon...As I am disgusted with how it looks..neat and tidy will be the next "look"...

 

[college101]

So today..I got some new 12AX7A tubes...hoping this will set my voltages correctly to spec,

Anybody got a good source for the 12bh7 and 6aq tubes?  Ebay did not work well with me on the other tubes I bought...

Starting the re-wire job tonight...after some homework!

 

[college101]

I just de-solder'd my entire La-2a.. all new wires

 

[college101]

Im gonna order a 12bh7 and 6aq5 from tubedepot... Cleaned out the entire insdie of the compressor...Getting ready to wire it up...

Pondering if I should get a hot air gun, and shrink some tubing over connection..I think its a good idea

I re-checked all my capacitors and resistors...everything seems to be tip top!

 

[Sredna]

Pondering if I should get a hot air gun, and shrink some tubing over connection..I think its a good idea

How do you going to check the connections whith shrink tubing all over the place?  

That you could always do later when you're shure that everything work...

 

[college101]

I know...and I thought about that.. I am going to put two small pieces of tubing on each wire, where needed, like around pots and near other wire junction points...BUT I wont shrink them  until after I have taken all the readings and verified everything is working...

Im hoping these brand new tubes( 2 mesa 12AX7a's and Electro Harmonix 12bh7 and 6aq5a, and new wiring will do the trick...Im not going to do all Red wires either...I need to keep track of what Im connecting...Im not going to use cayacosta's layout diagram either...Im going to go all by the '68 schematic, and get it RIGHT this time...I have faith, and the petience to do this!

While Im at it, Im going to rotate the power tranny to match everyone else's set up's...as well as trim the additional wires from the PT that are not needed... Im hoping this is it!

 

[Sredna]

When rewireing, maybe you could save yourself some headace and omit TB#1.
Just wire XLR IN pin #2 to the blue lead on the transformer and XLR IN pin#3 to the red lead....
On the CT (White lead) you can put some heat shrink tubing! 

Also be shure to insulate the not used leads from the power transformer.

 

[college101]

Good call..I will add heat shrink to the CT for sure...I'm going to be improving the look of my wiring...

 

[college101]

Hey whats up guys...Ive been checkin my stuff...re-wiring twice...the wires are beautiful..

BUT..

  What is R8's function in the circuit? 2.2M Resis Grounded on one side...