Audio trafo winding help

[lassoharp]

@Lassoharp:  I'm not sure I follow what you're saying (I'm thick)  so I'll await your further analysis! 

I had in my notes 40-50K pri impedance for at least one of those outputs.  In that case you'd have a 12K or higher triode rp working into about 4X load vs 2x load of 25K, which would be more typical of triode output stages.  At the higher loading the triode has a little more gain but is fighting against the huge step down loss.  In other words, why design/load for more gain and then lose it all through step down loss? And, is there a point where gain overcomes step down loss, or just about equal and better for keeping distortion low?  In the 76 console there's just one tube, having to be part voltage amp and part output driver.

25K:600 looks like just where you'd want to be for a low mu triode working at 3-4ma.  The apparent mistaking of a 40-50K pri Z is where all the questions came from.

 

[emrr]

It's the preamp output in the 76 series consoles.  It feeds a 250 ohm ladder attenuator.    It's also in the 85-X pentode isolation amp, and I just recently found catalog info on 85-X referring to 600 ohm output.  Maybe they are loading it past spec in the 76 console to force a broader response with low and high resonance bumps; EQ in other words.  If so, it'd be the only example of that I can point to.

Whatever thread we started the unwind thing in (BA-2? BC-2B?), it was changed there.  Now the 1st version has spread everywhere.

It may be the red herring of the lot.  We have the BA-11A output rated at 600 ohms which is 440 DCR, and numerous WE and Langevin inputs with published pri and sec ratings which have very high DCR ratios.

In the case of the tube preamp inputs, maybe it's about the freq/Z plot, giving up some loading loss noise in the trade off.  In the case of the outputs, maybe they are using high DCR like buildout R, to compensate for lower internal Z due to NFB. 

 

[mitsos]

Thanks both for the info.  LAssoharp, note the RCA is 25K:250, not 25K:600.

 

[CJ]

i have all that hard copy transformer stuff,

let me know which transformer you need,

 

[lassoharp]

note the RCA is 25K:250, not 25K:600.

There are two variants - one with 500/600r sec, one with 250r.

 

[mitsos]

hey lasso, I didn't know that. thanks. Is the info around for the model with the 500 ohm sec?

i have all that hard copy transformer stuff,

let me know which transformer you need,

well, if you have info on (UTC?) PA5946 or PA6003 that'd be nice. Nothing to do with the 10K:10K but I'm (still) working on the UA preamp build .

If you have any other 30K:600 trafos that can handle a bit of DC, that too would be cool.

we can start a CJ thread in the tech docs section, and you can post away!

 

[lassoharp]

I think it's the same iron only different sec impedances.  Best to ask emrr.


Maybe CJ has torn apart WE 197a or 185a?  Or dug up the info somewhere?

 

[CJ]

here is the beta on the  Triad HS 56 600:600 pultec filter input transformer(see pic below)

core is EI with 3/8" tongue and a 3/4" stack

bobbin is 5/8" high

there are 2 layers for the small tap and 3 layers for the large tap.

again, a balanced transformer is #1 priority for input 600/600 or 10K/10K bridging.

why? because they get input cables with nasty stuff on them that needs to be cancelled out.

Triad  output is easy to wind,

Triad HS 52

255 Turns of #31 

1425 Turnsa of #39

1425 Turns #39

255 Turns #31

50/50 Core 21 EI LAms 1/2 x 7/8 inch stack..


UTC  LS-140  beefy 600:600,

http://www.groupdiy.com/index.php?topic=35773.msg439639#msg439639

Ampex Bridging  10K:10K

http://www.groupdiy.com/index.php?topic=18875.msg221801#msg221801

Peerless K-241-D  no pics

http://www.groupdiy.com/index.php?topic=5402.msg66219#msg66219

Webster Electric Mic Input

http://www.groupdiy.com/index.php?topic=36499.msg448449#msg448449

UTC  LS 68  cool splitting transformer, 600:600/600

http://www.groupdiy.com/index.php?topic=35694.msg438595#msg438595

JBL Mic Input

http://www.groupdiy.com/index.php?topic=36425.msg447531#msg447531

UTC Ouncer O-8

http://www.groupdiy.com/index.php?topic=35975.msg458898#msg458898

Ouncer P-12 or something,

http://www.groupdiy.com/index.php?topic=6822.msg81155#msg81155

Stancor WF-21 Input

http://www.groupdiy.com/index.php?topic=36416.msg447432#msg447432

UTC CG-133 Inner-stage

http://www.groupdiy.com/index.php?topic=36464.msg448010#msg448010

Triad HS-35 Innerstage

http://www.groupdiy.com/index.php?topic=35991.msg442229#msg442229

UTC A-23  Output

http://www.groupdiy.com/index.php?topic=36294.msg445836#msg445836

UTC  A-24  Output  LA2a

http://www.groupdiy.com/index.php?topic=35712.msg438449#msg438449

UTC  A-26 Output Transformer

http://www.groupdiy.com/index.php?topic=35639.msg437637#msg437637


Western Electric  186

http://www.groupdiy.com/index.php?topic=36509.msg448500#msg448500

this one hurt, probably the last one on earth,

UTC    Y-6431 Fairchild 670

http://www.groupdiy.com/index.php?topic=35548.msg436479#msg436479

Western Electric  618-B

http://www.groupdiy.com/index.php?topic=35586.msg437445#msg437445

this was my favorite discovery,
Peerless 16402

http://www.groupdiy.com/index.php?topic=35658.msg437970#msg437970

ADM Output

http://www.groupdiy.com/index.php?topic=35939.msg441619#msg441619

Freed 6L6 Output

http://www.groupdiy.com/index.php?topic=36092.msg447022#msg447022

Trident A/B Range Output

http://www.groupdiy.com/index.php?topic=46052.msg577253#msg577253

Scully Output  wound by Freed Transformer

http://www.groupdiy.com/index.php?topic=35874.msg440688#msg440688

UTC H-70 Filter Choke

http://www.groupdiy.com/index.php?topic=36493.msg448358#msg448358

 

[emrr]

note the RCA is 25K:250, not 25K:600.

There are two variants - one with 500/600r sec, one with 250r.

XT-2747; only one version.  It's the preamp output in the 76 series consoles.  It feeds a 250 ohm ladder attenuator in that case.    It's also in the 85-X pentode isolation amp, and I just recently found catalog info on 85-X referring to 600 ohm output.  No published spec for the transformer itself. 

2747 is officially 2650:120 dcr
2875 in BA-2 is 2570:208 dcr for 500 sec rating, 150 dcr for 250 sec.

2747 in 85-X amp suggests 50-60k, that amp is pentode with FB.  So what does that mean?  Pentode wants high z load, FB is knocking down output Z of tube. If its really spec'd as 25k:250 as 76 console suggests, then running into 600 load with FB pentode drive current might make it balance correctly for both conditions: light pentode load , but one with FB enhanced drive current to excite pri L correctly.

Or is my 76 theory correct, and they're slugging an open loop triode hard?  And it's really 50-60K:500-600 on paper?

Lassoharp reports his meter gives 254H @ 120Hz, but thinks it might register lower than other meters.

 

[mitsos]

holy crap that's a lot of links CJ! Did you ever make backups of the files on your old site? 

BTW, I finally got a bit of DCR/L testing done on the 10K:10K... My LCR doesn't read well in the highest (<200H) setting, which kinda sucks...  DCR is about 1375 for each coil.  Since they're wound in sections, I think I can extrapolate the L of the coil, but I'm confident it's over 80, maybe over 100H.

So, it's wound Pri-Sec-Pri-Sec-Pri.  22 layers total for each coil, sec is divided 11-11, primary is 7-8-7.  Don't know how to plan the balance of the coil, not sure how important it is, I'm assuming CMRR degrades with unbalanced coils.  But then, maybe this is balanced enough. I'll stick it in a circuit sometime this week after I put real leads on it.

OK, so on to L.  Primary I got a reading of 17.3H each on the first and last sections of the primary.  (the <20H setting normally reads well). The middle section is over 20H, and in the <200H setting it keeps bouncing around.  I'll look for a new battery to see if that changes anything.  Anyway, just those two sections alone should give 17.3 x 4 = 69.2H if wired in series, so I'm fairly certain we're over 100H on this coil, cuz the third section has an extra 194 turns. 

I also measured the Sec L, and got 28.7 on the first section, but the second I couldn't get a good reading. But if these coils are equal, then the same "2 squared" rule applies, and we should have 28.7 x 4 = 114.8H. 

Moral of the story, (besides that I need a new LCR, prefereably a nice bridge), is I overdid it on the henries, or rather, didn't account for the fact that you get more henries per turn as you get further from the center (at least that's how it is on inductors I've wound).  That said, I could probably cut the turns down by a bunch (and/or use larger wire) and still be over 80, with much less DCR to boot.

thanks for all the help guy, I'll keep working on this thing until I get the PCBs for the compressor.

 

[lassoharp]

Pentode wants high z load, FB is knocking down output Z of tube. If its really spec'd as 25k:250 as 76 console

Only thing I can think of is - would pentode not be considered essentially immune to loading over a wide range?

 

[mitsos]

Do you guys have a schematic to that RCA amp?

 

[emrr]

I had to draw one, as usual.  Note 22 dB loss through output transformer. 

http://farm8.staticflickr.com/7047/6790208726_15ea6f96a5_b.jpg

 

[mitsos]

you draw very neat!  Thank you for sharing. 

Interestingly simple looking amp...  do we have the input trafo specs as well?

There are some tubes on ebay right now.  would be an interesting future experiment?

 

[emrr]

Specs are in the drawing.  Infer the input sec to be 50K-80K by the step up gain. 

I don't see any experiment there, that amp is what it is.  Compare it to the 76 console preamp for same output in different environment, newyorkdave posted that one. 

In case you missed it:

http://www.groupdiy.com/index.php?topic=41032.0

 

[mitsos]

I don't see any experiment there, that amp is what it is. 

sure, but I don't know what it is!   Iso amp? Is this like some kind of buffer? 

Compare it to the 76 console preamp for same output in different environment, newyorkdave posted that one. 

found it! thanks!  you gotta be kidding me, that's too simple.

In case you missed it:

http://www.groupdiy.com/index.php?topic=41032.0

How did I miss that! That's beautiful stuff!

 

[emrr]

Yes, buffer amp with bridging taps on input. A rare example of a classic tube amp designed for unity gain.  What's not simple in either amp is the iron, though I'm sure you could build either with off the shelf Cinemag, Sowter, or Lundahl parts. 

 

[mitsos]

I need to buy me more lams!

 

[PRR]

emrr> 2747 in 85-X amp suggests 50-60k

BTW for others: 1620 is 6J7. 6SJ7 may be used if you move the grid. All the same tube with different quality/price/license issues.

The loading: if running 250V at 5mA then a first-dart approximation for a maximum-power load is 250V/5mA or 50K. Max "undistorted" power could approach 0.5 Watts (+24dBm) at 5%-15% before NFB. Around 20db NFB is applied. Rated output might be +18dBm (0.06W) at <1% (typ <0.5%)?

So yeah, 50K-60K to the plate.

Because of the NFB, the inductance does not have to be REAL high, as long as you do not ask for max power at min frequency. Probably does want to be well over 100H just to cover 50Hz at >+10dBm.

C3 has no direct function. I bet it is there only so the wire M can run all around the console to a central meter, without crap back-sneaking into the cathode and corrupting the signal.

 

[mitsos]

Thanks PRR.

emrr> 2747 in 85-X amp suggests 50-60k

BTW for others: 1620 is 6J7. 6SJ7 may be used if you move the grid. All the same tube with different quality/price/license issues.

6sj7 only difference is it doesn't have the grid tab on top? What are the quality/license issues you mention? I've seen the price differences on ebay, is it only cuz the 1620 is the Elvis tube or is better somehow?

thanks again!