UTC A-39

up for auction today is a UTC A-39 transformer rated at  600:2K @ +10 DBM,

response is 20-20K, with taps for 150 ohms pri and 500 ohms sec,

a great choice if building an active DI box like the Country Hick,

ok, who wants to start the bidding?



































nobody?

going once...going twice......


OK then. looks like this poor transformer has been sanctioned off to the care bears for breakfast,

 

you can use a drill to take the ridge off the mounting pipes,

but you can dmage the header plate as it is old and brittle most of the time and it cracks easy, but if you do it by hand you can rebuild it with a good plate,

jus like old times, eh?

Grandpa, tell me about the good ol days, 

got er off,  and a better pic of the silkscreen>

open the windows and pour on the heat, spin the can so you do not burn the paint,

stay away from the silkscreen, wait for the potting compound to tranfer heat to the xfmr inside, otherwise it will not come out, it is like a big heat-sink in there, but as soon as it reaches the curie point,

pops out like the thermometer on a butterball turkey,

looks cute, don't it? 

hey, never seen that style can before, always something new inside,

10 bucks says that there are 31 UI lams in there, but that is a no brainer,

see that blurr on the xfmr?

took me a while to figure that out,

these digi cameras are sensitive to infrared, so that is heat you are seeing,

what is really spooky is that they have camera jammers at trade shows so you can not bootleg designs,

I'm feeling all warm and fuzzy again .

oh yeah! break it down brother

were gonna break it on down further,  but first, i have to go down to the bank because it looks like i just lost a 10 dollar hubba rock,  ;D

check this action bro, another can!

you like the way i crank up the satutration on the image editor to make it look all psychedelic and shit?  8)

how many cans is that? i lost track, they are soldered together because people gave a crap about their audio back then,

dang if that don't look like the Jensen core, only when you buy a ProCo DI, you do not get this  kind of protection, it's like Linda, i always wore 2 just in case,  ;D

i'm a Lindaholic, and there ain't no miracle cure, because once you been loved by Linda, you gonna be sore all year, wtf, over?  jus sayin

is this fun or what? my heart is soaring like an eagle,

for shizzle my bizzle,

now here is the UTC, right? a nice close up just in case i break a lead..

and here is the UTC next to a ProCo/Jensen that i tore out of the box so i could put it in the same rack box as the country hick,

you don't think Deane Jensen would have....let's see, how can i put this nicely?

all i'm sayin is, somebody got worked, you get me?

hey, the first guy does not have a chance, right?

now i get to map the leads before the unwind, oh what a joy that is,

probably make me late for my Lindaholic meeting, oh well, there are so many of us that they won't miss one, right?  ;D

ok, if somebody else wants to get a thread in, nows your chance, 

Fasccinating CJ

Amazing that mess of goo can have utc audio 'mojo'.

you can smoke that black tar if you mix it with a little  isopropyl ,

got too burned out to unwind it so i crashed out for a while,

you do not want to document a coil when your hafl asleep, but we are ready to go now,

finally ready for the fun part, unwinding!

you can view a transformer 12 different ways, so it is easy to get screwed up when rebuilding if you do not have enough info, worst moment was when i screwed up a group order for poor Joel down in Tejas who did a Neve production run on some bad data i gave him, pretty embarassing, so i take no chances now days, you can never have too much info as far as lead orientation and winding direction,

color coding the core and coil really helps,

here is the A-39 lead sheet>

and having closeup pics can help,

they had the black tar on the outside of the transformer shield cans and wax on the transformer itself, so another reheat to get the lams apart>

here is the Lam info, this xfmr was done on a square stack,

these small wires require patience when blueprinting, they use real sticky cloth tape on the gray/green vintage of UTC transformers, so you have to heat up the bobbin and peel it apart very slowly, those thin wires will snap like a dry twig in a stiff desert wind if you torque them too much,

ink will not stick to nylon very well, so if you mark a bobbin with ink, by the time you are halfway through unwinding, the ink will be gone, so you can use electrical tape to establish a reference point on the bobbin.

the heat gun erased the white strip  on the red wire, so we had to deduce logically which lead was red, all the striped wires are on one side, all solid on the other, this is why you do the leads diagram before you take the coil apart,

notice that the blu and blu/wht wires and the grn and grn wht wires are directly opposite each other, but the grn and grn/wht  and the blk and blk/wht wires are not, this probably means  that the sec.coils are wound different as far where their Start and Finish locations are  located on the bobbin, we will find out shortly,

now the really really fun part after all the tedious lead blueprinting, getting the important data: the turns and the winding structure.

we have it mapped out good enuff now so that if a wire breaks away from the lead, we still know what terminal it was>

ok this thing is done, pretty simple really, wound Pri>Sec, both are bi-fi which is why i thought it was a split coil job as DCR was pretty well matched, 545 *2 =1090T Pri and 1000 *2 = 2000T Sec, both wound clockwise, #38 and #40-42 wire size for pri and sec, 1 turn of cloth tape between pri and sec,

10 extra turns on sec for insertion loss makeup, keeps the Z ratio honest,

i will put all the info on a blueprint with calculated inductance and post,

here is the coil being unwound, taped up the leads so they don't break>

ok here is a print, nuthin fancy but you should be able to wind from it,

if you need any more info, let me know,

transformer diagram looks funny but it is just a way to draw a bifi structure,

clipboard included at no extra cost,