All things LA2a related

[Bluzzi]

Thanks CJ. For now I'll keep it and try it after finishing the project.

Jim

 

[Bluzzi]

Moving on, I finally got some time to do some more wiring. My turret boards are done and I am onto the back part (tubes & transformers). I'll reserve the front panel and turret hookup for last.

My wiring is starting to get the spaghetti look and so I am worrying about hum problems because of my wire routing. I am trying to keep as close to Cayocosta's layout. (some unmarked components there by the way).

Does anyone have any hints/tips as to what wires to keep from each other (ie: ac power from input or output wires).

Also I am missing C13. Its a 510pf cap. Can I use a 470pf or 560pf in its place?
I am not sure if its part of the stereo part of the circuit (which I would do without if I was certain of which components to exclude)

jim

 

[punk]

Bluzzi,

check the resistor and you will probably find that it's 33k. You should use it if it is different but CJ's advice is right on.

C13 wasn't used in earlier LA2's so I can't imagine it making a big difference between those values.

You have the right idea about the wiring, seperate signal and power wires. I'm not familiar with Cayocosta's layout but think it out and plan your routes before firing up the iron.

good luck,

byron

 

[Bluzzi]

Thanks Byron. I'll put in a 470pf for the time being. Even for the variable capacitors I am using a fixed value.

I know to keep away from AC power but I am afraid of the tube heater feed wires. I am trying to keep them along the bottom corner and everything else higher up.

I guess you would have to be a super neat freak to avoid any kind of proximity. Also I believe crossing wires at 90 degrees diminishes hum.

I'll just have to finish one and take it from there. I may be a bit too timid as its my firs DIY since I built Dynaco and other kits. My first kit was a shortwave radio and was way beyond my abilities, plus it came with the worst instructions. I f...ed it so bad I couldn't even tune in a local station!

After that all my projects worked. Its just been so long I've lost some of my feel for wiring point to point. But my soldering skills are much better though.

I am almost there and the anticipation is killing me! I hope I don't muck this one up!

scared but excited.

jim

 

[sysexguy]

Please forgive me if this had been discussed before (search only gave a partial mention).

Why does one have to ground the centre pins of the tube sockets? I have assured my sockets are properly secured and that the tube shields, once complete will be at chassis ground.

btw, side note, I found a great source for hardware: www.rtlfasteners.com
great value, great service...and ships to Canada!!!!!!!

TIA

Andy

 

[CJ]

More mechanical than anything else.
In RF or high voltage work, you sometimes need to ground what they call "floating metal".

This is anything made of metal that is not grounded.

 

[Bluzzi]

OK, I'm almost there on my first unit. Just have to wire up front panel and double check my connections.

Past threads advise on leaving the T4B out until all checks out.

So now the question is should I turn it on with the tubes in or out ?



jim

 

[Bluzzi]

OK, I am re-reading this entire thread and the tubes can be in from the beginning.

I'll be turning it on as soon as I verify my wiring. So if you hear the entire East coast has had a power failure you'll know when I flipped the switch.

jim

 

[synthi]

Good luck!!!

Synthi

 

[drpat]

...

 

[drpat]

...

 

[Pierrelegere]

Hi, I was reading this forum for some months, and I really like the attitude here, so I decidet to join! I did some modification on old German broadcast units (V276, V372...), and now I will start my first DIY project, either the La2a or the ssl clone... I wonder if anybody here is located in Germany / Europe, and has some experience with using Haufe or Pikatron (often used in German modules) transformers. They are availible here for cheap money, so maybe someone has already made some experiments???

 

[The Kid]

Pierrelegere, Welcome to the forum!

And, yes, there's lots of folks in your neighborhood here; they'll probably be along momentarily! :grin: :thumb: :sam:

 

[fum]

allright, need some troubleshooting wisdom.

One of my la2a's is doing this thing that I need to track down.

At random time intervals, it will make a pop, and then go back to merrily workin fine.

It could be 5 minutes, 10 minutes, etc., between pops. Sometimes two pops within 15 seconds, and then some time gap before it comes up again.

thoughts?

regards

ju

 

[fum]

And the answer lies in the chopsticks, young grasshopper.....

thanks CJ :thumb:

 

[CJ]

Kung Pao!
:thumb:

 

[khstudio]

[quote author="fum"]allright, need some troubleshooting wisdom.

One of my la2a's is doing this thing that I need to track down.

At random time intervals, it will make a pop, and then go back to merrily workin fine.

It could be 5 minutes, 10 minutes, etc., between pops. Sometimes two pops within 15 seconds, and then some time gap before it comes up again.

thoughts?

regards

ju[/quote]

Fum,
Try the easy stuff first:

- Change 1 tube at a time.

- I think the LA-2A will work without the T4B installed so you can try that to eliminate it being the cause.

- Take it out of the rack & open it up, turn on, pass signal & listen while "Carfully" poking around & wiggling tubes to see if you can find it.

I find over %50 of my problems with guitar amps this way... give it a little beating to make sure it's tight with good connections.

You probably knew all this... just trying to help.

Kevin (The guy you helped last year with my LA2A... it's been kickin ass ever since, Thanks again for the tips)

 

[fum]

guess my post was kinda cryptic (but CJ reads minds). I fixed it, with chopsticks.

Left it open while I was workin, whenever I'd hear a pop, I'd take the chopsticks, and move some of the wires that were close to each other, re-arranging, cleaning etc.

Leave it for some time, if I hear the pops again, repeat.

After the fourth iteration, no more pops. Have no idea which wires were causing the problem, but have been contemplating the phrase "silent as the grave" for the last several hours , so am feeling pretty good about it =)

Regards

ju

 

[Bluzzi]

Wiring now checked & I caught 1 wire on the meter switch that was on pole 1 instead of 3 but I believe it owuld not have been a problem (only the switch would have worked backwards).
Corrected anyway. Also I had the Neutral wired into the fuse and switch! That I corrected right away and now my Hot is on fuse "& switch. All now as per Cayocosta's layout.

Only one thing is bothering me. On my VU meter there is no marking for the positive or negative. Its an old Weston meter. Is there a way to know which one is which? If its reversed can I blow the meter?

I'll be turning it on in tonight. Fingers crossed and chicken sacrificed to the God of DIY.

Thanks.

Jim

 

[Bluzzi]

OK, turned it on without tubes and nothing blew up! Fuse still good (.5A SloBlo)!

Then tried with tubes and all seems OK, no explosions or parts burning up! I left it on for 5 minutes with same results.

Only thing is the VU meter needle is at -2 and wobbles back and forth, almost like a 60HZ AC is getting in there?!

I'd like to start measuring voltages soon before I plug in the T4B but this VU thing has me baffled. Could it be that it needs a diode like some meters?

By the way the meter adjust pot does nothing to change the location of the meter needle.

I'm so close now I want to get going but I don't want to make mistakes because of my excitement.

Any ideas about the meter? HELP!

Thanks

jim