All things LA2a related

[daArry]

Hey,

I got some of these ye oldie Altec plug-in modules thingies that I rek could be ideal for T4 housing. Fully enclosed with octal type pinout on base and plenty of room inside (that pcb can be removed):

Whatcharek?

 

[thedug]

I am building an LA2A. actually from the BLOO kit.

Anyway, his manual give instructions based on 1 schematic and I also have another schematic.

Anybody have any explanations why one would be better than the other.

The differences are around the values for..

R34, R36, R38, C10, C11, & C13.

The are all around/connected to the 6AQ5.

This is on version http://www.vacuumbrain.com/The_Lab/TA/LA2/la2a_layout2.jpg

I don't have a web link to the other.

I can try to send a table of the diffs if folks are familar with these revisions.

I am just basically curious if there is a general assumption that 1 is better than the other and why.

 

[thedug]

This is another version of the vaccum brain layout.. but in schematic format..

http://www.buzz-audio.com/stuff/jpgs/ureila2schematic.jpg

Bascially the other schematic changes:

R34 to 22k2W
R36 to 1k

C10 to 50uF
C11 to .1

and loses C13 & R38

 

[wilebee]

I think,because of something that sceneria said, that the variances in that part of the circuit were there to either save or extend the life of the t4b's EL pannel Wil

wilebee

 

[CJ]

I have Jahnsen's book. He has all the different values used over the years in the appendix.
I can post it if you want.
If somebody else has that book, put that page up. My book is at home and it's friday.

 

[jdr]

HTH :guinness:

 

[CJ]

Thanks jdr-HTH!

 

[thedug]

Cool, thanks!

I need to decide which one to build. The Bloo manual is a mixture of 65 and 79. Any thoughts?

 

[cayocosta]

Changing the bias point of the 6AQ5 - in my estimation - would have no effect on the AC voltage range to the El panel, which is set by the gain reduction control. (No DC voltage is present at the El as the coupling cap (C11) blocks DC.)

So, regarding the effect of the plate (R34) and cathode resistor (R36) of the 6AQ5 in each revision, the only impact would be on the tube itself, and from what I gather looking at the voltages of the various revisions listed in Jahsen's book, the 6AQ5 current draw at idle is actually higher with 10k/470R, thereby eliminating longevity of the tube as the motive for the change. Thus, the move to 10k/470R was most probably made only to facilitate a more linear operating range for the 6AQ5 - at higher gain reduction settings.

Lastly, as the latest revisions (1968 forward) use 10k/470R, it would be reasonable to assume these values represent best practice.

 

[JerryPbury]

I'm finally finishing off the first of my two Bloo LA2A's. I noticed that in the BOM C6 & R30 were included. And that C4 & C14 were shipped with the units. Also instructions are given for the Stereo Adjust Pot hookup. However there is nothing in regards to installing the Stereo connect.
Is this just an oversight or was it intentional? Can I just drill a hole and put in a 1/4" TS connector and hook up C6, R30 & C14? If I decide not to use the stereo connect how far do I go back as far as removing components (R3 & C13)?

Also, in the instructions for the small turret board it states to "connect R4 (contact 3) to B2 on the mini-turret board"(page 23). Shouldn't this be to B1?

Thank you.

 

[Scenaria]

the extra trimmer cap was a mistake on my part when I shipped yours out.. initially I did not think there would be much desire for anyone to want to run this type of compressor in stereo..

so yea you can ommit the C14 if you like...

I would suggest putting in R3 and C13 anyhow.. this way if in the future you want to use a TRS jumper to link two together it wont be much hastle...

Contact 3 should be tied to either B2 or B3 of the mini turret.
you have the numbering backwards on R4... it should be 1,2 and 3 starting with 1 being closest to the hinge. contact 1 goes to B1

 

[JerryPbury]

Thanks Steve,

I have the connection correct on the R4 to the mini turret board. I just quoted the wrong line. The connection I meant was from B3 to 2a on SW3. From the schematic it's 6 of one, half a dozen of the other as to where this connects (B3 or R4 contact 3).

So do I still need to use R30 and C6 if I'm not using the Stereo link option?


Jerry

 

[Scenaria]

I couldnt give you a difinitive answer as ive never tried to build one without...

I would put em in


the reason as to the Br, R4 thing.. (and I know eactly what your talking about) is that it keeps the wiring neater

doesnt matter if contact 2 is picking off B3 or R4 just keeps things cleaner

IMHO theres already enough wire in the boxes :roll:

 

[JerryPbury]

Plenty of wire!

OK. So TS or TRS? I only see connection & ground on the schematic for the stereo connect.

Need to get a smaller 10uf/450v (Nichicon?). There is just to much stuff going on in the middle of the chassis. I am using the Sowter for the output.

Jerry

 

[thedug]

....ignore me.....

 

[Scenaria]

B2 and B3 are linked

 

[EmoRiot]

I'm starting to realize the trap of my perfectionism - needing to have UTC transformers. I envision a future where I'm digitally fishing... obsessively checking ebay for a bite.

So I'm starting to wonder about options. If I were to go one step below UTC but still very good, where would I go - Jensen transformers?

If you were to choose between ordering a Jensen input transformer or the HA-100X reissue part from UAudio, what would you go with?

Can I have a UTC A-24 output transformer and something else as my input transformer? - since finding an A-24 seems easier.

Also, has anyone found a great hidden resource for HA100, HA100X, or A-10s? Something nice and convenient, like www.abundantUTCtrannies.com or something?

 

[fum]

Ebay is your best bet. patience and esnipe are your tools of the trade.

I did manage to salvage an A-10 out of an old broadcast transmitter that wil turned me on to, but i've gotten an a-10 and a quad of A-24's in the last year, all from the bay.


ju

 

[Scenaria]

you can mix and match if you want..

the input doesnt know the output

I find the jensens to be quite expensive (they also require some mods) thats not to say they sound bad.. though I still think the sowters look pretty darn impressive for the $$$

we ran alot of various sweeps comparing a sowter based la2 verses UTC trannys... and found them to be near identical.. as a matter of fact the sowters showed a bit more HF response overall...

 

[Scenaria]

this thread being brought up just reminded me...

wil?

did you have any success yet?