Peerless S-217-D Pultec OPT

here is the latest "guess" at the prized and unobtainable EQP-1a OPT,

combined notes from Winston O Boogie along with catalog data,

no info on the web, Mike at Magnaquest is the only person i know of with the orig. prints,

so we will build this to make sure it does not oscillate while in circuit, like the last one did, 

pretty straightforward, pri-tertiary-sec, with the sec's reverse wound,

we have a stack of L-12 lams, from the 16402 take-a-part, probably not as high in the perm dept as original, but it should work fine since we have a stack that is 2.2 times the tongue width, (3/8")

we do have part of the print file with a parts list which was a big help,

here is the cat blurb>

(math from turns info dictates a 12K to 600 xfmr,  not 12.5K, variance is common, false advertising from the marketing dept.)

Did you hack one apart?
I dig those transformer autopsy threads you do...

So is the winding method Primary:tertiary:secondary ?    I've got some modern "L" lams that are probably the wrong size for this trafo but I've been saving them for exactly this…. I saw your last thread showing you winding one, but I couldn't quite grasp how you it was done…

Thanks for all the hard work with this trafo info throughout the years!!!

yes,  pri-tertiary- sec,  see structure on print under WIND,

someday i hope to get a hold of a real one to verify that print,

maybe we can get somebody to due an induction test on a real one inside a Pultec,

Also, on the cheatsheet, it shows the Pri and Ter going in the same direction, then the Secondary going back and forth, but marked "Reverse wind."  Just to make sure here, on the Primary, is it wound left to right, and at the end of each layer do you go back to the left side to wind the next one, or wind back and forth?   

Tertiary is just one layer so left to right. 

Then how do you do the Secondary?  Flip the mandrel?  Is there a misprint? Because, the first half of the secondary the numbers switch  (beginning,end wrt phase) so I guess that's flipped, but the other one (10,11,12) the way it's written, shouldn't 12 be the in-phase beginning of the winding?

thanks again!

let's break this thing down a little further to make sure i did not screw it up, 

first, the primary, which uses back and forth winding, as opposed to "foldback" winding where you wind a layer and bring the wire back to the beginning before starting the next layer (UTC A-10 and other high ratio cois are done like this to lower capacitance and preserve high end)

since this is a dual coil affair, we connect the coils a bit differently,

to preserve the correct polarity so the signal does not cancel out, we wire the two coils so that they are in phase with each other, so with two coils we do not connect it as start-finish-start-finish like single coil sections, we do the opposite>
start- finish-finish-start

when i have room, i show each layer on the print, so a four layer sec is not hard to fit on the paper, but seven layers and four layers is a bit much, so only the sec., is broken down layer by layer,

now if a coil has an even number of layers, the finish will end up on the same side of the start,

and for an odd number of layers, the finish will end up on the opposite side of the start,

if i were to break down the pri layer by layer, it would look like this>

so we verified the primary, lets look at the feedback winding,

they us S as the center tap terminal notation, which can be confused for a start if we are not careful,

i think it probably stands for splice as the center tap is created by joining two wires, one from coil A and one from coil B,

this feedback wind is only 1 layer per coil, so we can show that on the print without taking up a lot of space, since 1 is an odd number, the finish will be on the other side of the start,

there is no reverse winding going on yet, that is done on the secondary winds only,

so here is the FB diagram>

and finally the secondary,

both coils have the secondaries reverse wound,

you can do this two ways:

1) flip the coil around and keep the motor direction the same,
2) do not flip the coil, but reverse the direction of the motor,

note: you need a DC motor to reverse direction unless you are using a monster motor that runs on three phase,

you can also do a "cheater" reverse wind, do not flip the coil, do not reverse the motor direction, just connect the lead to the finish instead of the start,
however, notice that the finish will be on the outside of the layer, where as in the true reverse wind, when you connect the lead to the start, the start will be buried under the rest of the layers, this can have an effect on the capacitance, as your voltage gradients between layers will be different when a signal is applied,
this is where you need some confusing math to analyze the symmetry of the coil,

ok, here is the secondary, since both coils have the sec's  reverse wound, you use the same connection practices for keeping the signal from canceling, but instead of taking  our output signal off the starts, we take if off the finishes,

why? because due to the reverse winding, if we were to take the signal off the starts, the output would be 180 degrees out of phase with the input,

this is why you see those dots on some transformer diagrams, if you mix reverse winding with forward winding, you want the electrons of the primary sections to circle the core in the same direction, and you want the electrons of the secondary sections to circle the core in the same direction, so the dots usually signify where the electrons will enter the wire for say, a positive half cycle,

example: a single coil primary is wound with two sections, one section is a fwd wind, the other section is a reverse wind, to get the electrons to orbit the core in sync, you would have them enter the fwd wind coil at the start, and the rev wind at the finish,

so it looks like our blueprint  is correct, but the acid test is to wind the xfmr according to the print and see how good it works, we want good frequency response, and we want the feedback winds to have as little phase shift as possible at the upper end so that the amp does not oscillate,

here is the secondary aux drawing:

fwd-rev wind with polarity dots>

wow, thanks for that exhaustive explanation.  Really clears it up.  Dual coils, reverse winds, finish becomes the start... I got all mixed up.  I think I got it now!! 

here is a link to the Pultec EQP manual and a schematic>

http://www.advancedaudiorentals.com/docs/PultecEQP.pdf

here are the L-12 lamination dimensions,

never had a real S-217-D to check inductance which would give the alloy,

probably 80 Ni, or maybe 50/50,  made by AEM , whoever that is,

thanks for the explanation

Cinemag makes these now.