DuKane 3A25 and 3A55 transformers

Found these in my junk box; they're octal plugins. Anyone have the pinouts or other specs?

I've got a couple original DuKane pages - I'll scan them in tomorrow.

In a nutshell, 3A25 is a 50 ohm input, 3A55 is 150-250 ohms. +-1dB 20-20k.

The heavy one will take quite astonishing levels. I think I used about 4dB gain behind a couple of these fed from AKG 414 over the 3rd row, and potted down to -10dBV. So they must have been swinging several Volts on the secondaries.

A modern good/not-great transformerless input was noticably smoother. (ART TubeChannel, with tube and everything but the mike-amp bypassed.)

For-sure worth playing with.

Thanks guys, that's good information. Once I have the pinouts (and I assume those are in Sco's datasheets), I'll try them out. I'm building a simple tube mic preamp right now and I've been looking through my stock of input transformers.

I've been sitting on a few of these transformers since I gave away a whole DuKane institutional PA years ago - never quite got around to using them. I'd be curious how they work out, though.

Thanks for the info!

Good info, thanks guys. I have about 30 assorted Dukane trannys to play with.

:thumb:

I summon this thread back from the land of the dead...  ;D

I recently dug out my old high-school DI box based around one of these transformers.  Slapped it on my work table (dining room table most of the time) and hit it with SMAART, since I've been doing that lately when I run across new isolation / mic split transformers at work.  It measures extremely well, needing line level or hotter signals to start distorting.  Flat 20-20 in both magnitude and phase, though I found that I'd wired the thing pin-3 hot.

Got curious about the whole transformer impedance question, though.  Hadn't really thought about that before, but obviously DuKane based the input impedance on what happens when this (and others out of the product line) transformer is plugged into one of their standard mic preamps.  So presumably the input impedance is very tightly related to the design output impedance, right?  So what should I be thinking about when I see the high-impedance end of this transformer going through a 68K resistor and then into a tube grid?  There's also a 47K resistor between the high-impedance output and the center tap of the low-impedance side, which I guess might count as a virtual ground of some sort.

On one hand I'm amused at the crudeness of this old stuff, on the other I'm amazed at how sophisticated it probably is once I start trying to comprehend the impedance stuff.

they have math for all that, the main thing to remember is to divide the load by the ratio squared thing to get the reflection.

BTW, the 2A55 is a good poor m,ans MC cartidge input trans, not as good as the peer;ess or tamura, but 400 bucks compared to 1.99 at auction,

OK, so I think I understand that enough to get the turns ratio from the load and input impedance, and the number that popped out was around 30.

Near as I can figure from there is that in a DI box application into a 1Kohm modern mic input, the instrument would be seeing a load around 900K, which is a pretty decent place to be for a passive pickup.

Hey Scodiddly or CJ: (or anybody, really)

I have a 3A55A, which fortunately has the pin-out on the label, but is the "A" an upgrade or something?

But I also have a 3A65 and would like to know the specs.  Seems you need to know the guy that made 'em to get any info on 'em. 

Thanks!

Hi everyone.

I have a dukane ia485 on the slab here and was wondering if anyone could point me in the direction of what number dukane transformers to pop in?

Anybody have a schem?

Thanks in advance for any help offered

sameal said:

Hi everyone.

I have a dukane ia485 on the slab here and was wondering if anyone could point me in the direction of what number dukane transformers to pop in?

Anybody have a schem?

Thanks in advance for any help offered

Click to expand...

Just posted the 1A485C manual/schematic in Technical Docs section here: http://groupdiy.com/index.php?topic=60762.0

Thank you so much for posting the manual mjrippe!

bad news is we obtained a few transformers
1) We learned from the docs that the 3A75 rolls off below 600 hz (we have one of these)
2) Now we wonder if this will prove to also the case with the 50:600 model 3A80, which we bought two of?.

Thanks again!
Danny

3A80 are full range, but not good for tube input stages.

Anyone still have this transformer data? Would be nice to have it in the technical documents section!