All things LA2a related

[rove]

What I've seen is to get a 6VAC lamp (or close to that) and just hook it up straight up to the 6.3VAC coming from the secondary of the power trafo. This is what I'm planning to do, but haven't found the lamp yet. Or the lamp holder as well if I can find one. Gonna have to search around.

That is what I thought, basically wire it up like the heater wires for the tubes... If you find a proper lamp/holder please post about it. My guess is the lamp is pretty easy to source, but what about the holder?
thanks.

 

[CJ]

Radio Shack has lamps and holders...

 

[AnalogPackrat]

Rafita,

What did you use for R36? With R34 of 22k, R36 should be 1k. In case anyone else is wondering where A20 is, its the plate of the 6AQ5.

A P

p.s. I think it would be more useful for folks asking for help if they'd post voltages relative to nodes on the circuit diagram (e.g. plate of 6AQ5, between R6 and R7, etc.) rather than the Bloo manual labels since most people don't have the Bloo manual.

 

[bradb]

Hi everyone,

I'm working on a build of a dual/stereo la2a based on the pcb (found here on the forum).

EDIT: Just to clairfy, I'm building this dual LA2A into a single Rack case.

I'm designing the face plate and I have some operational questions. I'd like to bring the maximum functions to the front but leave things that are used only once to the back.

On the front of the unit, I plan on putting the Lim Response (R37), gain and peak reduction, +4/GR, Lim/Compress controls.

On the back, I plan on having the Zero adjust pots mounted...

The question is what to do with the stereo adjust pots (R3), every time I use the units in stereo, do I need to Re-adjust them? can I just do the stereo adjust procedure once, set it, forget it and then put a DPST switch on the front that connects the stereo parallel and grounds (terms 6 and 7)? I would just flip the switch when i wanted to move between dual and stereo.


also.....

I will wire R37 such that turning it clockwise will increase resistance and label the Lim Response on the face place "HF Sensitivity"... .does this make sense?


Thank you everyone!

 

[Rafita]

thank's analog

R34 22k
R35 220 k
R36 1k

so my readings are diferent on V4

my B+ 281 V

R34 92 V
R35 122 V
R36 9.07

also it doesn't change the readings after setting R3 and R37 full clock wise or ccw

thanks :roll:

 

[CJ]

set it and forget it. it won't move.

 

[bradb]

Thanks CJ,

Ok, Zero Pots will be mounted on the back (or sides) as will the stereo adjust pots. everything else will be on the face.

thar she blows:

 

[AnalogPackrat]

Rafita,

Looking back through some of the older posts in this thread may help. I believe others have had the exact situation that you have, but their units worked fine. If all your other voltages check out you should be OK. Have you tried to pass audio through it without the T4b in? Does the gain control work? If that all seems OK, you should be able to power down, plug in the T4b, and go for the final test.

Good luck,
A P

 

[Rafita]

Thank's A P

And Yes i found someone that have the same situation on page 73 , i've just send it a message.

Same Readings on V4

i did pass audio and it's working , just had some hum , i haven't put the grid stopers.

i have on Pin 5 (t4b) 8.5 V
so i thnk from what i read that it's safe to put the t4 module

Thank's :roll:

 

[AnalogPackrat]

Rafita,

You only need the grid stoppers if you used a Sowter output transformer. Hum is from somewhere else. Did you keep your heater wiring twisted tight and laid flat against the back of the chassis? Do you have dimmers on the lights in your lab? Did you get hum with the gain around 3 or 4 (which is where you'll end up setting it most of the time)? Was the chassis closed up? You're getting close!

A P

 

[dissonantstring]

hi rafael,
i saw your pm, but i guess i should have looked at the posts first to see where you were at. if your Bloo is passing audio and compressing o.k. then you are doing fine. :thumb:
AP is correct, you only need the grid stoppers for the sowter tx to prevent oscillation IIRC/ i could be wrong, but your hum is from somewhere else. i still have slight hum in mine, but i believe it's due to bad wiring layout which i have yet to correct.

hey AP, gotta find time to get together and get some grub in mt. view. i've been swamped at work. did you hook up cj's op tx on your api yet?

 

[CJ]

yeah, he was here. and I'm missing a a 1 k resistor.
son of a....

 

[mnats]

...get some grub in mt. view.

Go to La Costeña for me and have a lengua taco. Very hard to find them here...
dissonantstring - sorry I had no time to try hooking up this time around sj but sounds like you've been busy too. My poor wife was meeting either a relative or friend of mine for the first time at the rate of 2.6 per day.

I haven't forgotten about posting pics of my homemade LA2 chassis either - just got to find some time...

 

[AnalogPackrat]

[quote author="CJ"]yeah, he was here. and I'm missing a a 1 k resistor.
son of a....[/quote]

Excellent! He didn't notice me pocketing the Langevin iron... :shock:

Mr. String: We'll get it together sometime. Life's hectic. No, I haven't used my trifilar bastard son of Profile hand-wound job yet. Still working on the rest of the API. Stuffed a couple of 1731s and one works fine, the other not. This weekend is not looking too good for DIY, either. Oh well...carry on!

A P

 

[dissonantstring]

CJ - somehow my mind freaked when reading your post and lemmy became angry...i need coffee.

mnats - no problem. hopefully next time, i know how that can be, not always fun for either of you i'm sure when you're in a rush (2.6 persons/day? did you really calculate that?)
oh, did you get peets limited sulawesi stock? i'll try to get some for you, but i think it ends january, so hopefully i'll have time to get you some to try.
wait...dual 1176 completed, webpage on 1176 rotary switch and an LA-2A?
you are a monster!

AP wrote:

Oh well...carry on!

i don't think we have a choice? do we? :? i gotta work this weekend too - keep reminding myself it's for the kids.

my trifilar bastard son of Profile hand-wound job

:shock:
sounds a bit "steamy" :grin: -grant

 

[idylldon]

I've finished up building the PCB version of the LA2A and have encountered a weird problem with the VU meter. The meter only works correctly when I hook it up backwards; that is, I reverse the + and - leads. When I do this, I can set the meter to zero and it tracks correctly during compression; however, then I use it in VU mode when the leads are hooked up either correctly or reversed, the meter bounces around and then slams back to rest.

When I hook up the meter correctly, I can't get it to set on 0--it only goes to -7.

I'm using Jensen transformers and have checked and double-checked that they are hooked up correctly. I have verified the meter switch wiring, the values of the resistors on the board, the caps, etc., and I can't find anything that would explain this weird meter behavior. I know I have to be overlooking something, but at this point I'm stumped and need some other perspectives and ideas.

Any ideas would be greatly appreciated.

Cheers,
--
Don

 

[idylldon]

Well, it seems as though the compressor is working fine and the meter tracks the gain reduction IF I have the leads reversed to the meter. In VU mode, it's all wonky and sure isn't tracking what's going in correctly.

There's also a post by dripelectronics on the LA2A PCB thread where he experienced the same problem with different VU meters. I'm assuming that all VU meters aren't quite up to working in the LA2A, so what meters have folks found to work correctly in VU and GR mode?

Thanks,
--
Don

 

[bradb]

and more so, why are they different?

could it be a rectification issue?

 

[idylldon]

I figured out my meter needs a germanium bridge rectifier. Once I hooked one up, the meter seems to work perfectly.

Cheers,
--
Don

 

[Greg]

I just finished wiring up my Bloo LA-2A...

Fired her up no smoke with no tubes :thumb:

Measured some voltages:

Heaters: 7.21VAC
B21: 388VDC
B20: 383VDC

I think this looks ok... time for the tubes !!!