UTC A-26 Transformer Question (LA-2A)

[abby normal]

I was checking the LA2A META for possible transformers to use and saw the A-26 on that list and happen to have one laying around. My UTC catalog shows the A-26 primary as having 30k "split".

Two questions what does split mean (15k + 15k)? And how would I wire that up for the LA2A (use half at 15k)? I'm seeing they want you to tie together and center tap pins 8 and 9 for push pull.

Specs

http://www.bunkerofdoom.com/xfm/UTC_1970_WEB/020.jpg

Pinout and wiring

http://www.bunkerofdoom.com/xfm/UTC_TERMINALS_LS_9_57_50M/001.jpg

http://www.bunkerofdoom.com/xfm/UTC_TERMINALS_LS_9_57_50M/003.jpg

http://www.bunkerofdoom.com/xfm/UTC_TERMINALS_LS_9_57_50M/004.jpg

LA-2A

http://www.waltzingbear.com/Schematics/Urei/LA_2.htm

 

[PRR]

 

[CJ]

a look inside this xfmr if you are curious>

http://www.groupdiy.com/index.php?topic=35639.0

 

[emrr]

You could also try using half of the primary, but I suspect you'd need to experiment with loading on the unused half.  Like, a 15K resistor termination for instance.  Or a zobel. 

Or, you could treat the other unused half as a 1:1 output, for those times when you had a higher Z destination and wanted the extra gain of 1:1 versus a step-down.  More loading experiments to try.

Or, you could dump the A-26 and buy an A-24.  Not too long ago, they were selling at comparative prices, at least for a little while.  The A-24 may have taken off again.

 

[abby normal]

Guys thanks for helping me out.


PRR- Just one question is there an advantage to wiring it up at 7.5k? Just wondering, I see it calling for 15k.



CJ - I saw that one in my search   Every time  I see your dissections I don't know whether  to be happy or cry. Half of me loves the info and the other half (the poor half) wishes I had that for a project.  ;D

Or, you could treat the other unused half as a 1:1 output, for those times when you had a higher Z destination and wanted the extra gain of 1:1 versus a step-down.  More loading experiments to try.

emrr- That looks pretty cool. I like the high z switch idea. Do you think it would sound the same as a A-24 if I only used half the primary on the A-26?

Or, you could dump the A-26 and buy an A-24.   Not too long ago, they were selling at comparative prices, at least for a little while.  The A-24 may have taken off again.

I lost out on an A-24 I sold some months ago, I wish I had just hung on to it.  It looks like they are getting back up there. :'(

 

[bdubya]

I just got done with one using Stancor WF-36 on the input and output.  I just wired the same as you would an a-24 for the output and it sounds great . . . I'm no expert, though, maybe there's something not-so-desirable about wiring it in this manner . .does the 12BH7 mind over time?  Haven't given it much more than the ear test.  Sounds gorgeous, though, enough that I didn't experiment just yet with different wiring . . .

  I guess I'm wondering the same thing as you, abby normal, what's the advantage to wiring it up at 7.5k as opposed to the 15k of the a-24, or the 30k that I have it wired at?

 

[PRR]

bdubya 2010> what's the advantage to wiring it up at 7.5k

M today> The original A-24 has a 15k primary

The A-26 has a 30K Split primary. Your only simple choices are series 30K and parallel 7.5K.

Other choices possible by "mis-"loading the secondary. I am not able this month to sit-and-squint those fuzzy images and think what may be possible. If you really need to explore this, a test-rig (level, response, loading) and jumper wires may be faster than thinking.

Or just get a A-24. Or one of many 10K:600 transformers.

I don't think the WCF on the end of the LA2 is load-fussy. Actually I think 15K will be a rather high load for it once you correct the too-high upper plate resistor.

Also note that "nobody" drives 150/600 lines today. You probably have >10K on the "600" winding. So the primary impedance will be high over most of the audio band. If you truly drive a 23-mile wire from studio to transmitter today, get a better line-amp than the lightweight LA2.