All things LA2a related

[sleepingtiger]

Now I get it! (I think...)

C3 isn't C5. It's C3. There's no mention of it (C3) that I can find in the Bloo instructions 'til the end of the audio transformer section. There the 10uf electrolytic is called C3 when in reality it's C5. C3 is the .1 that goes between pins 2 and 6. I never placed C3...

 

[Scenaria]

what voltage do you measure between ground and the otherside of R19?

what voltage is your B+ rail at?


and your sure your using a 10k for R17? not a 1k... and they are 1/2w right?

correct C5 is the 10uf coupling cap to the o/p tranny

C3 is the .1 uf off of pin 6

ah I see on page 13 it said

Mount C3 (10µF/450V) from V2 pin 1 [+] to the output transformer signal input (UTC pin 7)


the wrong designation is in there...

UGH

there is a C3 on page 15

Turret Board Components:

Component: Value: Turret Locations: Check
R28 470K A1, B1
R16 68k A2, B2
R9 220K A3, B3
R13 220K A4, B4
R11 68K A5, B5
R10 1.5K A5 A6 (left-right)
R22 33K B5, A6 (diagonal)
R21 100K B6, A7 (diagonal)
C4 50-380pF A6, B6
R18 1K A7, B7
R15 470K A8, B8
C2 0.1µ/400V A10, B10
C3 0.1µ/400V A11, B11

 

[sleepingtiger]

Hey, I really appreciate you guys hanging with me this afternoon. I had to leave (home now). I'll get back to it tonight or tomorrow evening. I've got a good feeling about doing some compressing real soon.... :grin:

 

[cayocosta]

"I never placed C3..."

That's your problem.

C3 blocks the DC from the grid - Pin 2 - you've got 120V on your grid.

Put that cap in there.

 

[JerryPbury]

Hey guys, I finally figured out what I did wrong on mine. R36 was a 470K instead of a 470 ohm. I don't know how many times I checked this area out but I decided to look at it one more time and it just jumped out at me.

Gain reduction works perfect. Output is great. I just tried it out with an SM57 into a Seventh Circle N72 into the LA2A. Wow!

Thanks guys! Now to finish up the 2nd one and put the 2 1176's into thier chassis and finish the SSL and the G9 and install the 2 finished J99's in the Seventh circle chassis, paint the Tele and finish ordering parts for the Harley. Oh yeah and do some recording! Did I mention that I "suffer" from OCD?
:grin:

 

[Scenaria]

thats awsome!

it usualy happens that way... :\

just takes one resitor

 

[AnalogPackrat]

Ok, it's a good thing I decided to do some house painting before working on my Bloo today. :wink: I had stopped at page 9. Steve, are the text (page 9) and table (on page 10) both swapping pin 7 and pin 8 on V4? Just want to make sure before I fire up the Weller tonight... Looking at the three schematics I have it looks that way.

Thanks,
Analog Packrat

 

[Scenaria]

yea

 

[sleepingtiger]

OK...

That whole thing about C3 was a snipe hunt. It was there the whole time. Sorry about that. I was looking a little too hard for a solution and I suddenly expected to see it jutting out from the tube socket when all along it was right there in the turret board where I soldered it the other night. My turn...

I replaced R17 and there's no smoke. All of the voltages on the schematic and that you guys have given me are close. Everything around V2 checks out now...

I've got signal coming through the compressor but something's definitely still not right. Now, in GR mode it distorts horribly. I also get the same distortion in the other two modes but not so easily. The gain knob is low. The distortion is a hard sudden clip instead of a linear thing. A slight rise in the volume of my voice makes the sound go from pleasant to awful in an instant....

That's it for tonight.

Thanks again :!:

 

[dukasound]

Hi
Does anyone used C5 10uF poly instead elco. I cant find elco good quality and I have two 4,7uF.
Duka

 

[SSLtech]

[quote author="sleepingtiger"]Now, in GR mode it distorts horribly. I also get the same distortion in the other two modes but not so easily.[/quote]
When I've seen this before, it was a bad secondary on the output transformer, which was confirmed by a DC resistance reading. You might want to check yours, just in case. Since the only thing that changes when you switch to "GR" is that the meter sits across the output (a very light load in the order of 7kΩ through some diodes) and if that can have an effect on the output, your output cannot hope to drive 600Ω as it should. It might be a transformer, it might be poor drive from the tube output (a high-resistance cap feeding the POT or similar) -Looks like it's definately in that area.

I assume also that you're feeding it into a very high impoedance destination, or it would balk at this as well.

Keith

 

[cannikin]

Hey Guys,

Today I was recording using my LA2a. After a couple of hours I started getting a major Buzz. I opened the unit while audio was passing through it and when I put my finger on one of the two C7 30uf 450V caps, the buzz disappears.

Now the same thing happens with no audio passing through it.

strange.. and you thought I wasn't going to bother you anymore

HAHAHA

 

[sleepingtiger]

Keith!

Spot on! You called it... The transformer seems to be fine but apparently I had a cold solder joint. Although I heated a few of them before plugging it in again I believe that it was on the low side of the primary which goes to ground. It's the only one that I hadn't checked before now. Regardless...

It works! :grin: I don't want to get too excited 'til there's been a little burn-in, especially in light of Cannikin's last post but it sounds and functions like an LA2a. It sounds beautiful!

Thanks again to all of you for your kind and generous help. :thumb:

All the best!

 

[Scenaria]

Hey David..

looking at your photos it looks like you tried to squeeze some giant caps in the box for your power supply... my first suggestion is to get some smaller sized ones (they are out there) and put them in on the tag boards...

the thing is that the location of those caps is not in a very good place...

try putting some leads on those caps and move them outside of the box to see if the hum goes away.. if it does then replace them with some that will actually fit on the tags..

 

[cannikin]

Thanks Steve; will do.....

 

[cannikin]

I'm having a heck of a time finding C7 caps. where are you guys buying them from? Every place I know of... has 33uf or 47uf or Sprague Atoms with the correct value.

 

[AnalogPackrat]

Cannikin,

I'm in the process of building my Bloo. I got my big 'lytics at DigiKey. Part numbers P5950-ND and P5951-ND for 33uf and 47uf 450V. Note that there are two sizes of the 33uF. One is taller and a little thinner, the other is shorter and stubby. I used the short and stubby ones and they fit on the tag strip next to V4 pretty well. I angled C7d down about 45 degrees to leave some room around V4.

Keep beating on that thing and you'll get it working. I can't wait to hear mine in action.

:guinness:

Analog Packrat

 

[SSLtech]

Cannikin,

33µF and 47µF work just fine... in fact a little better than 30 and 40. Within reason, the larger, the more ripple they will absorb, so the quieter things will be.

I use 33µ and 47µ in all of mine. I also use 105°C ratings, and everything is groovy.

Keith

 

[cannikin]

Thanks so much - AnalogPackrat and SSL tech.

I'm so close to this thing being completed. hopefully?
this is not the easiest DIY project for the beginner that has only been building gear for 5 months. I'm starting to feel very self-conscience about posting in this thread. Thanks for the support.

I just finished reading a little bit from Dave Jahnsen's "how to..." manual, he recommends 4 x 47uf. But I will order the parts you posted.

thanks

 

[AnalogPackrat]

No problem, David. The parts I listed are Panasonic EB series rated for 105C. Comparing to the other options at DigiKey they had reasonable leakage specs, too. The stubby 33uF will fit better than the 47uF, but using the "alternate" placement in the Bloo manual would work if you want all 47uF. Hang in there!

Analog Packrat