Marshall Mk. II Fifty Watt Output Transformer

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CJ

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been waitin to get the saw out on one of these for eons, dream came tru today,

why not tear this up and blog it out, makes me happy, howabout you?

 

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CJ

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Pri Inductance max at about 160 Henries,

low level excitation, Henries will go up at higher voltage inputs,

 

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CJ

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very flat and stable freq response,meter did not jump around at all>

 

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CJ

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open the can, layered paper old school coil,

rewind with nylon bobbin,
 

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CJ

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hi-fi coil, interleaved, looks like P-S-P-S-P, 

 

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CJ

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good question!  probably the same if the secondaries are not loaded,
we can hook some resistors to the 3 taps and check the high end again,

 

CJ

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toast that transformer at 250, different varnish smell, almost like a pine tree smell, maybe organic compound,  Langevin used something similar,

split the lams before they get cold so they do not bend,

might be cold rolled (barn roof, can't see grain)


 

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CJ

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was gonna take this apart last night, but got to thinkin that a complex coil needs a full head of sleep,

can use winder counter to keep track of turns,

guessing we see a bi-fi sec in the middle,
 

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CJ

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we got a 4 page jacked up jimmy, but there ain't no shimy,  ;D

why not call it 1600T:112/78/56 and be done with it?

looks like 1/2 pri - sec- pri - sec - 1/2 pri  with partial layers and tweaked margins, engineered, fo sho,

will build a print from this tomorrow>
 

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CJ

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what makes this xfmr tick -  we need to take a look under the hood to figure that out,

a winder's most dreaded task, and a common source of failure, leads>
 

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CJ

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every transformer we take apart has something new and exciting inside to discover,

this one is no exception, check the weird lead plate  in the second pic,

looks like trouble waiting to happen, but not if you lay down some KP underneath,

saves winding over lumps of wire, especially large sec spk gauges,
 

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CJ

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they use these strips for all the splices and lead hookups, what about extra capacitance? well, the strip is small compared to the area of a full layer of copper,
 

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CJ

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no two margins were the same on this coil, layers all started and finished at different locations on the coil, so there was some tweaking involved, maybe Drake copied Radio Spares, who might have copied Partridge,

sec wind hookup, gray is the last finish, this transformer runs 180 out of phase, Fender runs in phase, so if you use a Fender next to a Marshall, be sure to reverse the spk polarity on either one, unless you want to cancel bass,
 

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CJ

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there is a pretty heavy wrapper between winds, this leeps the capacitance between layers down.

and it also provides a flat winding surface as partial layers will leave a void were there is no wire,

and there is also high voltage protection as one end of the speaker wind is usually referanced to ground via the output jack,

just noticed from the pic that the org lead starts at the right end of the coil so we will change the print,
good to have photo backup,

 

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CJ

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yes, we did a lam count and divided that number into the stk ht to get the thickness,

.018 is only listed in the Mag Metals catalog as Non Grain Oriented Silicon 

as opposed to GOSS - grain orient silicon steel

here is an alternate diagram of this coil,

note how pri  DCR is balanced due to different turn lengths depending on their coil location


 

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