Maxson Compressor OPT

[CJ]

oh boy, fresh meat on the table,  this time a rare treat that luckily came this way,  full props going out to Mr Rippe for taking away the only stumbling block to building the simple but often sought after Maxson device that is supposed to have a unique sound, a limiter with limited response, can i say that?

the weirdness lies in the  440K  secondary wind for feeding the 6AL5 tube rectifier which generates the control voltage.

 

[CJ]

gonna be a job getting that header off without damage,  this is a rewind job so we have o put away the hack saw for a while,  :-[

 

[CJ]

ok so here is how you take the lid off. first, you heat the while enchilada with a heat gun to get it nice and warm, which also builds internal pressure and preheats the header for the soldering iron.

then you go around the lid a few times with the soldering iron to briefly melt the old solder for better conductivity  and heat up the header. once the lid is hot enuff, you pry the can away with a Swiss army knife short blade,  then you put an old transformer lam I bar in there. the medicated goo will seep in between the can and the header plate which forms a heat insulator thus slowly thermally isolating the lid from the can so we can heat it even better.

 

[CJ]

we got a plethora of lams in their now, the preheat driving that expanded  goo up into the fissure,

 

[CJ]

success! Leggo my eggo, those are the secret words which must be uttered to facilitate the can popping  open like a tin o sardines,

 

[CJ]

we turn the after burners on for a brief spell to get the black tar loosened up a bit more so we can pop that bad boy out of there,  COPD starting to kick in, constricted bronchial tubes recoil in horror as the toxic fumes peniterate the passage ways and proceed to the cerebral cortex.

 

[CJ]

extraction complete, like pulling the hook out of a large mouth bass,

 

[CJ]

when the goo cools down a bit, you can pull it off the transformer like pulled pork,  if it is still molten, you have to scrape it off with a butter knife and the ol lady ain't gonna like that,

Stouffers mac cheese dish comes in handy as it is heat proof, and the goo smells about the same is the secret sauce from the meat loaf and taters dish,

 

[CJ]

side plates are unique, the have cut outs to go over the coil and bolt to the lid,

steel core laced 2 x 2,  with maybe one 3 x 3 by a sleepy stacker,  nobody gonna see it when it is buried in that can with the goop,

 

[CJ]

unbolt the plates from the lid and scrape out the clay so we can document the leads before snipping,

losing track of starts and finishes is a real drag so you have to be careful during this part,

 

[CJ]

we use glass cloth tape to mark leads as there have been cases where we used yellow poly tape and it either melted or blew off when heating the coil during the unwind, 

 

[CJ]

side plates

 

[CJ]

delam, a very square coil, must have been wound slow, red  sleaving over the smaller breakout leads,

super glue on finger tips from last acoustic jam, 

 

[CJ]

75 EI core sq stk so a 3/4 x 3/4 inch mandrel,  winding machines are good for unwinding also, that counter and all,

 

[CJ]

leading,  tape flaps protrude from the side of the coil and are used to protect the fine wire as it wraps around to the top of the coil for splicing, we cut the heavy leads off so they do not fly around and rip out he wire and relabel them, got a piece of tape trying to make it's escape on the right, so we press that pressure binding adhesive together again.  we will be heating the coil frequently to loosen up the impregnate medium which smells like pine tree wax, typical of the Langevin plant.

 

[CJ]

looks like the 600 ohm wind is the first to come off. the wire is big enough to easily wind it onto a spool so we can measure the length easier than having to untangle it from the floor,  why measure the length? so we know how much wire to order and also to figure out the DCR per 1000 ft as to cross check it against the wire chart.  it is interesting how the DCR per wire gauge changes over the years, a #29 might 82 ohms per 1000 ft in the old days and now be  65 ohms these days due to better insulation which allows more copper for the same width wire.

 

[CJ]

next up is the primary, looks like a 3/4" wind length and 1/8 margins on each side, we can use this data to calculate leakage inductance,  the less copper in the window, the more leakage as the magnetic flux will be cutting through insulation instead of copper, which means the linkage between the primary and secondary will fall off a bit.

also note that less leakage is obtained by having the layers right on top of each other, this becomes important in power outputs where you might have partial layers on the speaker wind with that big wire. good engineers will design the coil to have equal turns per layer on those speaker winds, although sometimes partial layers are used on purpose to balance capacitance as in the Jensen 4:1 output transformer.

 

[CJ]

and the inner wind is 440K sec #2, thinner wire, as it does no have to carry the plate current of the 12AU7a push pull tube, this wind feeds the 6AL5 tube. 

no interleaving on the sections, just sec #2 - pri - sec #1

 

[CJ]

here is the print,

low Henries due to the steel core, most transformer companies would use 50/50 Ni for this application, so the steel core is going to roll off the lows quicker, and the lack of interleaving is going to roll off the highs, so you might have a 200 Hz to 10 K hz response, which is fine for broadcast speech limiters.

 

[CJ]

and here is the schematic so we can really load up the upload folder again!  ;D