All things LA2a related

[cannikin]

I still have some really odd values/readings, some are right on, all others are way off. I checked my connections and component values at least 8 or 10 times over the coarse of 2 - 3 weeks. Everything is correct.

I have using reference ground from various places over the unit and the readings are the same.

B21: 361v
B20: 360v :evil:
A1: 57.1v
A20: 288v :evil:
A14: 241v :evil:
A17: 100v
A19: 188v :evil:

How can some values be happening and others wacked?
Could a cold Solder joint cause this? I didn't see any - but I could have missed it - too much to look at.

 

[Scenaria]

just send it down... I will be happy to look at it...

you say you put the 1ks across the grids?

I hope you mean in series with each grid... across to me means bridging between the two

 

[JerryPbury]

[quote author="cannikin"]I still have some really odd values/readings, some are right on, all others are way off. I checked my connections and component values at least 8 or 10 times over the coarse of 2 - 3 weeks. Everything is correct.

I have using reference ground from various places over the unit and the readings are the same.

B21: 361v
B20: 360v :evil:
A1: 57.1v
A20: 288v :evil:
A14: 241v :evil:
A17: 100v
A19: 188v :evil:

How can some values be happening and others wacked?
Could a cold Solder joint cause this? I didn't see any - but I could have missed it - too much to look at.[/quote]

Welcome to my world. My voltages are still high. I have checked every component, ground, wire, heater connection and touched every solder joint over again, yet my voltages are way high. Cayacosta said it was probably my bias. I checked every related component, ground and heater connection and it didn't change. I even changed all related caps. The voltages still remain high. I'm just dyslexic. I hope I don't do the same thing to the second one.

 

[sleepingtiger]

OK,

Finished wiring the Bloo tonight, threw in a fuse, fired it up, and....

nothing... :?

No smoke, no fire, no blown fuse, no voltages anywhere that I checked but at the rear of the power connector and on both sides of the switch (124.6). Obviously, I'm still having a problem at the Allied transformer...

I've got the live connection at the power connector going to B24 which is wired to one side of the switch. Both primary leads are wired to B25 which goes to the other side of the switch. The grey wire (I think that this is the problem) is going to the neutral connection on the power connector. Should this be going to ground? If so, isn't there supposed to be a connection to neutral? I'm afraid to just start moving wires around without getting a better idea of what's wrong. The Bloo instructions just tell me to connect the neutral wire, but I don't know what that is... The Cayacosta diagram doesn't show the connection in detail (or at least I don't understand it if it does...)

I know, I'm an idiot...

Thanks for any help offered...

 

[sleepingtiger]

OK,

Sorted it out... (Thanks, Scenaria!) For anyone else who might have the same problem:

Shielded grey to ground. Either black primary can go to neutral while the other goes to one side of the switch at B25. The live wire from the power connector goes to B24 and the other side of the switch... (this info appears earlier in this thread - I had looked over it before)

Turned it on and everything looks promising. I'm going to re-read this thread now before I put the T4B in tomorrow....

Fingers crossed.

 

[drpat]

...

 

[Scenaria]

tried big ole film caps.. and atoms

10 and 20uf

didnt hear a difference

 

[sleepingtiger]

OK,

Here's some voltages:

Location: should be: my reading:
B21 360v 365v
B20 275v 290v
A1 60v 53.5v
A20 131v 107.5v
A14 216v 238v
A17 90v 94v
A19 105v 129v

The compressor is behaving normally, with peak reduction knob at 9'oclock I'm seeing meter dips of -2 or -3 db when in gain reduction mode. With gain at about the same or a little more it sounds good but the output into my DAW is very low (this is with the gain knob at about 9 or 10o'clock). As I turn the gain knob up the signal begins to distort but even at full CW position I can only get to about -35 db or so into Protools (this is with peak reduction at full CCW - off - position). When I switch the meter mode to +4 or +10 the meter reflects the low output by barely rising from the far left position.

I'm feeding the compressor with a very adequate signal from an A12 pre (I tested it without the comp in the chain to be certain). I'm using the Sowter output tranny. Unfortunately, I don't have a scope. Does anyone have a suggestion for isolating the problem?

Thanks...

 

[cayocosta]

Are the pots on the back (R3, R37) full clockwise?

 

[Scenaria]

with the pots on the back turn them all the way down then turn them fully clockwise...

 

[sleepingtiger]

Yes,

I've done that. At this point I think that I've tried every possible switch / pot position combination and I very specifically turned the ones in the back all the way down then all the way up. I've re-read these posts and tried everything that seems to be applicable...

It seems like the main clue is that the meter shows the low output level in the +4 and +10 modes. Right now I feel like the Sowter output transformer is the most likely culprit but at this point I'm at a loss for what to do. To me, it looks like it's wired in correctly. This is probably something obvious that will bring one of those great forehead-slapping moments later...

Thanks for the responses (Cayacosta - the wiring diagram has been extra helpful). Please keep the ideas coming... :grin:

 

[Scenaria]

when you switch to GR on the mter... does it show propper GR?

meaning does the needle reflect reduction as you bring up the Peak reduction knob?

I think I would simply begin tracing the signal forward..

start by scoping the wiper of the input gain knob.. if signal is strong there then move forward...by checking your 12AX7.. if it all looks good then check your 12BH7A

becareful... theres high voltage on those tubes... be sure to set your scope probe to X10

 

[sleepingtiger]

Yes,

The meter shows gain reduction normally in GR mode. The further the knob is twisted clockwise the more the needle deflects. It's audible as well. In fact it sounds totally correct and great, just quiet....

I don't have a scope or access to one. Is there any way to figure out what's going on with a meter?

There's also one odd thing that might be a clue. When I unscrewed the left faceplate screw to drop the faceplate, the meter dropped about two db. When I re-tightened it, it went back to zero. There was a point in its travel where the thumbscrew was like a control for the meter. Does that tell you anything?

Thanks again...

 

[Scenaria]

your using sowters right?

this wont have anything to do with gain but you should put some grid stoppers on the 12BH7A...

just put em in series with the leads going to each of the grids on that tube

1K is fine

if your seeing the needle changing as the door is opening and closing I would double check my wiring for any loose connections.

 

[sleepingtiger]

Yeah, Sowters, and I've already got the grid stoppers in place. I'm going back to the studio in a while and I'm going to re-heat some solder joints in the pertinent areas. Hopefully I'll find the problem that way...

 

[sleepingtiger]

OK,

Good news:
The meter no longer moves when the face is loosened or tightened. The negative side was barely touching one of the rear pots. Fixed it.

Bad news:
I'm at a loss as far as the output issue. I've reheated every joint that I can think of and am pretty much just stabbing in the dark. Any help is appreciated, especially from anyone with experience with the Sowter transformers....

Thanks.

 

[Scenaria]

ok the good news

no smoke!

just relax... we'll get it working... bear in mind long distance trouble shooting over text can take some time.

I'll see if I can find some time this evening to give you some ideas... no scope really does make it more difficult though...

no worries.. if all else fails you can always send it down to me... though im betting we can get it going in the next few days

 

[cayocosta]

Check your voltages for the amp section - the 12ax7 and 12bh7 - against the schematic.

 

[sleepingtiger]

ok the good news

no smoke!

Amen, brother! No shocks or injury either. Definitely a positive perspective...

I'm not worried. It'll all come together. I can already tell that it's the real deal even if the level's low...

Cayocosta, Thanks... Will do. I'm not sure where to find those voltages. I looked earlier but maybe they weren't on the particular schematic that I looked at but I'll figure it out. I'm not at the studio at the moment. I'll get back to it tomorrow...

Thanks again!

 

[cayocosta]

http://home.earthlink.net/~cayocosta/diy_files/la2a/la2a_1968.jpg