All things LA2a related

[rubric]

Success!!! HAHAHAHHAHAHHAHHHAHAHH!

I was about to give up ever fixing this thing, but I decided to have one last look at the wiring diagram.

I made an embarrassing discovery. I had the wire from the peak reduction pot going to the wrong place! I had it going to the wrong turret...the one by the T4B that provides the juice for the ELP via V4, not the one next to the input tranny! Now my Bloo LA2A compresses like a champ and sounds awesome!

Thanks so much for your help, CJ! Thanks as well to Scenaria for making it possible! To anyone who's ever contributed to this thread who happens to be reading this, thanks to you too!

I love this forum!!

:thumb: :thumb:

 

[cannikin]

I'm having the same Problem....

I turn the INPUT past 12 o'clock and it starts sounding like I'm tuning a station on an old radio eventually ending in a low flutter/farting/motorboat ....

funny thing is... I stick a 1K signal through it and with the t4B in it compresses pretty hard

my voltages are ballpark.....

Replaced the 12AX7 a few times --- no luck

Tried moving the output cap around made some difference but not much..

Checking the wiring of R1 & R2 seems fine.

Things sounds great when powering up and power down... theres a gremlin in there somewhere .... just have to find it... :roll:

Going to Dremel some of the paint in hopes its a bad ground connection

 

[Kid Squid]

Hiya Chaps,

Just wondering, could you have a check over my turret voltages for me?
I have checked through Scenaria's bloo manual, and i'm getting a few discrepancies (most look o.k., but i dont want to fry my t4b )

B21 - 360V ( 347V), B20 - 275V (277V), A1 - 60V (56.5)
A20 - 131V (211V ???), A14 - 216V ( 231V), A17 - 90V (91V), A19 - 105V (100V)

I'm using ECC83 - V1, 12BH7a - V2, ECC83 - V3, 6AQ5/6005 for V4

Used 10K for R34, 470 for R36.

and used Metal Flim resistors, (1%), instead of carbon comp (5%), only beacause i had them lying around.
All ground points are O.K.


Here's all my turret Volts,

A1 - 56.5 B1 - 278
A2 - 278.5 B2 - 216
A3 - 117 B3 - 216
A4 - 125 B4 - 216
A5 - 1.04 B5 - 19
A6 - 0 B6 - 19
A7 - 103.9 B7 - 95
A8 - 103.9 B8 - 80
A9 - 0 B9 - 80
A10 - 126 B10 - 80
A11 - 227 B11 - 0
A12 - 0 B12 - 0
A13 - 0 B13 - 0
A14 - 231 B14 - 277
A15 - 0 B15 - 0
A16 - 3.41 B16 - 0
A17 - 91 B17 - 277
A18 - 0.85 B18 - 0
A19 - 100 B19 - 277
A20 - 211 B20 - 277
A21 - 277 B21 - 347
B22- 347
B23 - 347

I'm thinking, the higher 6AQ5 volts are due to the different r34,r36's.

Also, I've left out the stereo adjust pot but included the 510pf cap from pin 6 (6AQ5) and put it to earth. is this o.k.?

Best Regards,
Steve :thumb:

 

[Bluzzi]

I'm having the same Problem....

I turn the INPUT past 12 o'clock and it starts sounding like I'm tuning a station on an old radio eventually ending in a low flutter/farting/motorboat ....
quote]

This is about the same thing I had. I followed CJ's advise and fiddled around with a chopstick (those Sushi take outs are useful). I found one wire that if tucked under a cap on the turret board stopped all the motorboating!

I don't know if that will help but its worth a try if you haven't already.

jim

 

[SSLtech]

Just wanted to say....

 

[SSLtech]

Happy 100 pages!!!

 

[Kid Squid]

bump.........
:thumb:

 

[dripelectronics]

i wanted to try a couple of different powertransformers
for the la-2a and test them out.
is the hammond that every one uses the 269jx (250-0-250 / 60mA /6.3v @ 2.5 amp) ?

(is using larger current better or worse , or are dropping resistors needed)

it doesnt say center tapped , so i guess you gotta do the 100 ohm
resistors on each leg of the heater wires to gNd.

or is it the 240-0-240 version.

noticed that adl uses a torridial x-former any one try this ?
(if so whered ya get it )

thanks .

g.

 

[Bluzzi]

I used the Allied p/n 227-0113.

PRI:110-120V, 50/60HZ,
500VCT @40DCMA,
6.3V @ 2.0A, LEADS
I believe Hammond makes them for Allied as they say "made in Canada" Mfr's part#: 6K88VG

at under $20.00 U.S. funds its hard to beat! I have one LA2A made and it sounds great! No problems. All the other transformers were more expensive. Why use them if they are all same specs (maybe more current but LA2A is well fed by the Allied one).

jim

 

[dripelectronics]

ah , the 6K88VG is the one i normally use ,

so i thought i would do a bit of exploration

and test out other makes and models.

iv never tried a torridal type xformer and wanted to
see if there are advantages .

along with the hammond wich i just ordered and will test out
on friday.

any other recomendations out there would be appreciated ,

ill have a power x former shoot out

g.

 

[jho-audio]

What about the edcor XPWR106? I am ordering one for my dual-drip-2a

 

[dripelectronics]

ah , holy shiznate , those folk are here in new mexico.
i should stop by and talk to them , although they are at the bottom
of the state and me here in the north

that looks like a great x former for the dual pcb project.

ill have to pick one up and give it a shot.

im looking for single unit power xformers , they dont show a 250-0-250
ct 40 ma 6.3 v @ 2a

or in the ball park , i think the one thats close is the 275-0275 @ 125 ma
(wow that would be perfect for the la/twin...good job! you found it!)

g.

 

[Kid Squid]

Hiya Chaps,

spent all day checking through my la2a, and still i'm getting a high reading on turret A20 ( 6aq5 pin5 - c11 - t4b) .
I'm getting close on 200VDC instead of the 155V on the drawing. Also, I'm not getting any AC after C11 ( mV, nowhere near the 100VAC I should be getting)
I've spent all day , checking thru all of these posts, comparing with my la2a, and I can't for the life of me, track down where I've gone wrong.

I copied the layout from cayacostas site.R34 IS 10K.
the only things I've got different are :-
I'm using a 6AQ5W /6005 ( got 2, and tried both) instead of a 6AQ5A,This is what i got sent .
and I've omitted the stereo adjust - I've connected pin 1 of R37 limiter response (top pin on drawing) to a 1M resistor, then to earth.
the 510pF cap, comes off pin 6 (6aq5), connected to earth,
pin 1 & 7 (6aq5) coneected together, and connected to earth.

Is this correct ?

I've checked all front panel wiring a few times, and it all seems correct. :?
I've checked all earths o.k.,

with no T4b plugged in, and a 1K sine wave (0.7V), meter set to out+4, I can alter needle position with zero adjust pot,but nothing on meter in GR or out+10,
Is This Correct?

with T4b plugged in, meter set to GR, when a light is shone on the cell, meter deflects to the left o.k.

Valve Voltages.

V1 12 AX7 #1 (ECC83)

1- 119
2- 0
3- 1.05
4- ac
5- ac
6- 122.6
7- 0
8- 1.1
9- ac

V2 12BH7

1- 92
2- 0
3- 3.8
4- ac
5- ac
6- 222.5
7- 78
8- 107.6
9- ac

V3 12AX7 #2 (ECC83)

1- 91.6
2- 0
3- 0.82
4- ac
5- ac
6- 91.5
7- 0
8- 0.82
9- ac

V4 6AQ5W /6005

1- 0
2- 3.78
3- ac
4- ac
5- 197 :shock:
6- 108.7
7- 0

6AQ5W and 12BH7 are running quite hot. hotter than the ECC83's.

I hope someone can give me a bit of guidance with this one

I got to go to bed soon, I've been up since yesterday 12.30pm, I stayed up after my 12hr nightshift , to try and sort this out !, and its getting on for 12 midnight tonight.
my head is in the shed !!

Best Regards,
Steve :thumb:

 

[AnalogPackrat]

Steve,

You've tied the control grid of the sidechain output amp (6aq5) to ground! You need to tie pins 1 & 7 to the other end of the 1M fixed resistor you used to replace R3. You should then see a healthy signal at the T4b.

:guinness:
A P

 

[Kid Squid]

Hiya Analog,

checked and done the alteration, but i'm still getting high volts on A20 /V4 - 6AQ5- pin 5 - 210VDC,
I'll try my other 6AQ5 this afternoon, I'm thinking, I've fried them maybe ?

got my daughter for this afternoon,
I'll get back this evening, and let u know how it's going.
Steve :thumb:

 

[AnalogPackrat]

Is C7D also connected to pin 6 of your 6AQ5? If you pop the cover off of your T4B, dim the lights, feed a signal in, crank up the GR pot, do you see the EL panel glowing/blinking?

As for the bh7 and aq5 running hotter--they should. No problem there.

A P

<edit> After more coffee...I wouldn't worry too much about the high voltage on the 6AQ5 screen grid. Others have had similar readings and everything still works. If you do the math for screen grid current you'll see that according to the schemo voltages, it should be 600-700mA or so. You're getting more like 300mA. I don't think it's a problem. Try passing audio through it and compressing now that you've got the conrol grid issue sorted. I think you'll find that its working.

 

[dripelectronics]

switch r34 to a 22k 2watt

and r31 to a 1 k , that will put all the voltages right ,

every time i built an la-2a if i did not do this , all the voltages were way to
high.

one of the original la2's used this 22k/1k config.

as far as the 110 ac voltage on c11 , i never have had
my meter actually register anything AC .

so dont worry ,

ill double check , but im sure it doesnt actually register 110 ac.

g.

 

[Kid Squid]

Analog,

Sorted it mate !, inbetween my daughter getting some sleep, checked it thru, with a t4b in place, put input sine to 1.2v, glowing like a good one :grin:

Does what it sez on the tin :thumb:

I'll set the final value of R25 tomorrow, and do the R7 calibration, put some sounds thru it, and post some pics.

dripelectronics,

AC on the t4b, goes up to about 65 -70 VAC, depending on the gain reduction setting. LA2a no.2 , i will try the different R34, R31.
Thanks for the input guys :grin:

the earlier problem I had with the switch in +4 reading gain reduction,
is that , on the switch's mechanical stops, I had removed the wrong stop !
so, in position 1 ( out+10), the switch poles, were not connected to anything. Only pos2 was showing out+10, pos3 was showing GR.
removed other stop - got the switch sorted !!

Cheers Lads,

Best Regards,
Steve :guinness: :guinness:

 

[AnalogPackrat]

Good job, Mr. Squid! Now go forth and squish...

Iechyd da!
A P

 

[raysolinski]

I built Drip's unit with edcor's on the input and output....just for giggles I put a UTC A25 on the output last night...REALLY different...the UTC was way more thick and vintage sounding..I prefer the Edcors hands down ..I could see a place for the UTC but the Edcor is much cleaner..I was suprised how different the two tranny's sounded..I was expecting subtle differences...

Cheers,
Ray