Coil audio transformers?

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

rackmonkey

Well-known member
GDIY Supporter
Joined
Sep 20, 2016
Messages
969
Location
Texas
Anyone seen these or, better yet, used them for something? Scroll to the bottom of the link below.

I just ran across them by accident and have never even heard of them. The description says they're modeled after "popular 1950s/1960s" designs, but doesn't specify which ones. They aren't Edcor cheap, but they're not obscenely pricey either at about $110.  Right in Cinemag price range.

BT

https://ozarkproaudiovideo.com/brand/coil-audio/

Coil-Audio-CT-41.jpg

 
The description on the CT-41 (15k-600 Output)  is a little funny.

CT-41’s smooth saturation imparts a rich, wooly, and hi-fi sound to anything that runs through it.

I think of "wooly" and "hi-fi" as mutually exclusive.  Prolly no official definitions in the AES Engineer's Handbook though.  :)
 
Hmmm wooly , maybe not the best metaphor for what seems to be nice bit of kit .
I wonder what the sheilding material is , looks like brushed aluminium, steel or Mu metal might be a more effective shield for emi.
Does the guy publish any specs aside from impedences
max levels ,bandwidth , gapped/ungapped , be interesting to see how it compares with other transformers of similar spec .
Probably a guy in a log cabin in the middle of nowhere ,just winding away .
 
Coil Audio make 2 different preamp products that are clones of late 1940's to mid 1960's Gates Radio products, and those are used in those products.  They also refurbish a number of tube consoles from that era, so that would be the overall provenance.  It's as easy as 'Google'. 
 
Never seen a Gates this side of the Atlantic pond , I did however hear an interesting story from a buddy of mine who worked on  a construction contract in the UN buildings in New York ,they were clearing out some part of the building and hidden inside a stud wall they found big bad tube compressor ,probably  a Gates from how he described it to me , 
Even walls have ears,  ;) :-X
 
There was a large Langevin install at the UN when it was built, in fact at least one Langevin catalog piece was designed specifically for that install. 
 
More similar than most things.  An SA-70 has much wider bandwidth transformers than a BA-2. 
 
Coil has been around for a few years. I saw them at AES LA last year also. Super friendly, out-going small company... Plus willing to send out their preamps for sampling too! I still haven't taken them up on that offer, but certainly will over the next year!

As for their transformers, I'm still considering buying a couple to try... Haven't pulled the trigger yet, but certainly no reason not to give them a try... I'm sure they're great, it's just a matter of if they truly have enough unique-characteristics to justify bothering to use them rather than the usual suspects.
 
Cool stuff they have. I'm intrigued. I keep threatening to dust off a project I never finished to build two Langevin 5116/Collins 356A/GE BA-1-F  knock-offs, and am vacillating between vintage and new iron. Came across these looking around for something besides the usual options.  The Coil output trans is pretty close to the nominal specs at least on the TF-321-B on the 5116. Tempted to just get it and try it out. If it doesn't work in that project, surely could use it in something else. You can't have enough 4:1 tube outputs. That's how i'd justify the purchase, anyway.

BT
 
Shoot. Won't work for that project. I thought there were two windings on both primary and secondary. On second look it's a single primary.

Have to find another excuse.
 
rackmonkey said:
Cool stuff they have. I'm intrigued. I keep threatening to dust off a project I never finished to build two Langevin 5116/Collins 356A/GE BA-1-F  knock-offs, and am vacillating between vintage and new iron. Came across these looking around for something besides the usual options.  The Coil output trans is pretty close to the nominal specs at least on the TF-321-B on the 5116. Tempted to just get it and try it out. If it doesn't work in that project, surely could use it in something else. You can't have enough 4:1 tube outputs. That's how i'd justify the purchase, anyway.

BT

You can't build any of those amps without the tertiary feedback winding.  No one makes that transformer. 
 
Yep, walked right into that one, Doug. Forgot about the feedback winding.

I do remember that this was a question I had when I put the idea aside. Probably better in a separate thread, but here goes. I'd read here on some old thread about the problems with the OPT availability when i was first looking into this and the two options I was thinking about were 1) ignore the fact that the best results for a global NFB loop are when the fb is taken from the secondary of the transformer and taking it from the second 5879 instead or 2) ignore the center tap on the primary of the Cinemag  CM-9600-T, which is a 4:1 with tertiary winding. What am I likely to run into with these options?

Last resort would be to ask Brian Sowter to build a couple, I guess.

To get where I'm coming from on this, like with most (all?) of these classics, I know I'm not gonna replicate the qualities of the original without the original iron or a close facsimile thereof, so I don't do these kinds of projects aiming for that necessarily. This one is motivated by the fact that I have a box full of NOS 5879s and the fact that I heard the Collins version in a session in Austin years ago and really dug em. If I can get within a mile and it sounds good I'll be pretty happy.

Thanks,
BT
 
rackmonkey said:
Last resort would be to ask Brian Sowter to build a couple
am fairly certain Sowter's model 1200 transformer could be made to work in the 5116 circuit.
configuring the feedback to be  optimum might take some patience.
 
Hmm.  7K:600 versus 16k5:600 for starters.    Maybe, could be a stretch. 



gridcurrent said:
am fairly certain Sowter's model 1200 transformer could be made to work in the 5116 circuit.
configuring the feedback to be  optimum might take some patience.
 
For anyone interested, I contacted Steve Squire  at Coil about getting hold of one their CT-41 output transformers to try out. Really nice guy. They don't make a habit of selling these for DIY or as replacements for non-Coil gear, but if they have enough stock they will try to accommodate DIY requests. When they do sell them a-la-carte, they just provide a standard channel frame - they don't come in the nice looking Coil Audio housing with the octal plug, which are just sold for Coil preamps.

They did have a couple of extras on hand and sold me one CT-41 for $80. Steve is also sending me one of their CT-41HN (hi nickel) transformers as a "sample" to try out/provide feedback on.  Pretty cool.

I asked them which "popular 1960s design" the CT-41 is based on, and here's what he said:


"You arent far off - its based on the red peerless 15095 made for Altec but
with a particular interleaving on the secondary similarly to a western
electric/utc LS build. This allowed us to extend the bandwidth which gave it
an even richer sound.

-Steve Squire
COIL AUDIO LLC
www.coilaudio.com"

i'll give my impressions and post some sound clips when I'm able.

BT


 
Tubetec said:
Hmmm wooly , maybe not the best metaphor for what seems to be nice bit of kit .
I wonder what the sheilding material is , looks like brushed aluminium, steel or Mu metal might be a more effective shield for emi.
Does the guy publish any specs aside from impedences
max levels ,bandwidth , gapped/ungapped , be interesting to see how it compares with other transformers of similar spec .
Probably a guy in a log cabin in the middle of nowhere ,just winding away .

We actually use a mil spec winding company here in the states, although Ron Swanson winding transformers in a log cabin would be way cooler.

The company we use utilizes very old school winding technics, and have older machines that allow them to use much thinner wire than most modern CNC winding machines, which break the thin enamel wire. Very important, especially for small signal transformers with high step up ratios, to keep DCR to a minimum,  and to keep phase shift and ringing to a minimum. Our transformers are designed to go straight to the tube, no weird networks to compensate for poor design and manufacturing.

We more or less send them a vintage transformer to sacrifice to the winding gods. They unwind it, count and study the windings, and do a metallurgical study to find the core material. They also note the lamination size, shape, and grain orientation. They cut their own core laminations as well, so we're not limited to off the shelf cores like most companies, and they allow us to request weird core materials. Plus they have all kinds of sweet old school tricks for improving bandwidth, tweeking freq response, saturation levels, etc. The brilliant gentleman that winds our prototypes is 70 years old.

The enclosures we use are plain aircraft aluminum, and are just considered a simple octal housing for us. Our output transformers are open frame, but our inputs our in a nested Mu metal can.

All our current transformers are ungapped, and cannot take DC on the primaries. As far as max levels, our CT41 begins to saturate at around 18DB, carefully chosen to work in modern situations, and allow you to get into the saturation point of the transformer, i.e., when the wooliness begins to happen ;) ... Freq response is +/- 1db from 20hz-30k, and down only a db or 2 at 60K.
 
abbey road d enfer said:
How can a 1:10 xfmr be described as 150:60k?  :eek:
This and the incoherent blurb act as a strong repellent for me.
Pro audio is a science...

wow... "incoherent blurb"... hmm...

1:10 is the ratio of windings from the primary side to the secondary side. 150:60k is the "nominal impedance" or "reflected impedance", has more to do with inductance, and is not necessarily relevant to the turns ratio, or DCR readings. This describes the two loads the transformer is meant to see on the primary and secondary windings to operate at proper bandwidth. That's why an old school 50ohm mic sounds so weird and mid rangey  when plugged into a modern mic pre meant to see 150ohms or higher.
 
Back
Top