All things LA2a related

[Scenaria]

not that this has anything to do with the work you have put into it.. but I can say the the biggest problem I have been seeing with the la2 lately is not taking the time to be neat with the point to point wiring... being sure to twist the heater wires tightly and pay attention to the way they are routed in the box along with using shielded cable at the appropriate places...if you are not passing audio... then send some signal in the box and start with the scope at the front end (tranny) make sure you have signal at that point then work forwards from there..I'd checl the "gain pot" to see if any signal is present at that point... check to see if the signal goes up and down with that pot.. so on and so on

 

[Zee1usa]

:sad: I have 5 volts at R33 again.

Last night when I was trying to do a audio test I noticed the connection at R2 pin 2 was broken. It was probably broken when I *thought* I fixed it.

So it is 114vdc with R2 pin 2 disconnected and 5vdc when connected.
When I adjust R2 ithe voltage varies between 85vdc and 5vdc.

This is probably the reason why I am not passing audio etc.

Cayocosta:

"Also, what voltage do you read from pin 3 or 8 to chassis ground? Should be less than 1 volt DC."

I have 2.7vdc measured here.

My wiring looks good. I'll let you know if I make any progress.
Z

 

[Zee1usa]

Ok, I found the moronic error I made fer christ sakes.

Let me give you a hint.... I had a left over insulated-turret in my bag.

:shock:

I was wondering why I had that extra turret. Now I know what it is for.
I accidently skipped that sentance in my instructions because I got the input transformer plate for a HA-100X and I had a A10 instead. So I skipped that part of the build until scenaria sent me my new pate for my A10. Well I missed that part of the paragraph. I installed my A10 plate and forgot to mount the input trafo corner turret. And when ever the instruction said to go to the insulated turret, I just tied it to the 1 and only insulated turret that was mounted by the T4B.

I have no excuse. It is obvious on the diagram. I wasnt even loaded
or enhanced while wiring, I was sober. That may be why?

Hope my T4B is ok. :?:

I am off to fix it, I'll let you know.

Humble,

Z

 

[Scenaria]

no need to feel bad...

its how we all learn

im sure your t4 is ok..


thos el's can handle some serious voltage..

lesson learned though... never rush to put the t4 in until you have verrified that everything checks out ok..

 

[Zee1usa]

Update :


Ok, passing audio.. No hum..

I do hear a very faint ringing oscillation, which I am sure moving a few wires will cure. The gain works fine. I gotta check to make sure its compressing/Limiting properly. I'll check it out more tomorrow evening and let ya know.

Thank You, Cayocosta, CJ and Scenaria! Help Appreciated very much.

Here is a pic of the wiring:

http://img.photobucket.com/albums/v359/zee1usa/bloowiring.jpg

Z

 

[Zee1usa]

More Pics:

Face:

http://img.photobucket.com/albums/v359/zee1usa/Blooface.jpg

http://img.photobucket.com/albums/v359/zee1usa/blooface1.jpg

Back:

http://img.photobucket.com/albums/v359/zee1usa/blooback.jpg

Good Company:

http://img.photobucket.com/albums/v359/zee1usa/Bloowithcompany.jpg



Turret board:

http://img.photobucket.com/albums/v359/zee1usa/turretbloo.jpg

Z

 

[Scenaria]

looks good..

check to see that the coupling cap isnt hitting the back pf the vu meter..

if it is then you might need to lenghten the leads and tuck it up top.. thats what I had to do to mine

 

[wilebee]

ok heres what I've got on v4 the bias voltage is 8.78vdc and 90v on the plate and 57 on the grid Wil

Wilebee

 

[wilebee]

bump cj scenaria help ? Wil

 

[Scenaria]

dbl check your voltage divider...

R34 is it a 10k2w or 22k2w?

what value do you have for R36?

 

[wilebee]

r29 is 4.7k 2w
r34 is 22k 2w
r35 is 1k

 

[wilebee]

I mean r36

 

[cayocosta]

Wilebee,

The only voltages I have are on the 1968 schematic, so that's all I can reference.

For the 6AQ5, the 68 schematic calls for a 10k plate resistor and a 470R cathode resistor.

In this configuration with 275V B+:

The plate volts should be around 135V.
The cathode around 7V.
The screens around 100V.

Wilebee, in one of your posts I think you said that you had this configuration originally - but with a 1k cathode resistor. If that's so, try going back and using a 470 ohm cathode resistor with the 10k plate resistor.

Ron

 

[Scenaria]

[quote author="wilebee"]ok heres what I've got on v4 the bias voltage is 8.78vdc and 90v on the plate and 57 on the grid Wil

Wilebee[/quote]

I just checked one of mine that has a 22k/2w

9.05v

89.6v

and

127v on the grid

seems that your seeing about half that value..

first thought would be R35.

 

[Scenaria]

Wil,

have you made any progress yet?

 

[Scenaria]

[quote author="wilebee"]Steve Thats what I had to begin with minus the 1k for R36 so 4.7 then 22k then 1k for r36 will do Wil[/quote]

I was going back over your posts...

make sure that R29 is a 47k/2w not 4.7

 

[wilebee]

you sent me 4.7 k 2 w and the layout on vaccuumtubebrain says 4.7k so which is it 47k or 4.7 k because my first voltage drop is right on the far side of r29 I have 275vdc Wil

 

[cayocosta]

Wilibee, the '68 schematic also shows 4.7k, and all the schematics show 275V B+, therefore it's reasonable to assume the older schematics are simply missing a period with regard to R29. Furthermore, increasing R29 to 47k would knock the B+ down considerably from the universal schematic figure of 275V - that you already have with 4.7k installed.

4.7k is correct.

 

[Scenaria]

there is two versions of the schematic...

oops my bad...

the newer schem is missing the period :\

the newer rev used a 22k, 4.7k and 1k config...

the older version used a 10k, 4.7k and 470 config..


I believe the newer one was to salvage some life out of the EL panel..

 

[wilebee]

ok so what voltages should I have on my grid , screen and cathode on v4 ? Wil