Sovtek Mig 50 OPT

CJ · Jun 21, 2017

we had a problematic Mig 50 come into the shop, somebody snipped the leads to the stand by sw and main caps, cobbled in a 4007 rect bridge, all to no anvil, as the blu pri was shorted to sec blk, which is groundedm that ain't no good,

probably a tube went funny and now the amp won't make no money, took down the winding and cooked it like fried bacon,

looks like the Ruskies stole some German surplus somehow, check that core tube>

CJ · Jun 21, 2017

every transformer teardown has something that has never been seen before and we have no exception as you can see from this out of focus shot of some twine being used to anchor the leads,

CJ · Jun 21, 2017

this is the first Russian transformer we have done, looks like they at least have the layers put down nice and flat, #35 is a bit light for two 6L6GC tubes, but hey, reactors melt so why not an output transformer?

CJ · Jun 21, 2017

secondary finish uses twine also, pretty hefty wire, we have 4, 8 and 16 ohms tapped out,

CJ · Jun 21, 2017

how would you like the steak cooked, comrade? medium well...

CJ · Jun 21, 2017

or well done?

CJ · Jun 21, 2017

another secondary in there so two secondaries and three primaries, outer primaries must be split,

CJ · Jun 21, 2017

there was no varnish holding the lams so they fell right apart, metric, slightly over 3/4" with a 1 9/16" stack, very little varnish on the windings also,

we will wind on that cool bobbin to preserve the funk which will keep us from having to cut down a nylon bobbin to fit the metric lams which would be real PITA if you know what i'm sayin and i think you do.

don't know what that weird writing on the core tube is,
maybe the encryption code for an IP address on a US server, ;D

TheJames · Jun 21, 2017

CJ said:
#35 is a bit light for two 6L6GC tubes, but hey, reactors melt so why not an output transformer?

Ha ha!!!! I've wondered about these Mig amps. I guess we'll find out how it sounds after the transformer is rebuilt.

Matador · Jun 21, 2017

My Mig100B has been going strong for over 15 years.

One thing: despite the stupendously high B+ (490V on mine), Sovtek biases output stages SUPER cold from the factory (about 8W per tube). I always thought it was just to keep from early returns, but maybe this was on purpose to keep the current low through the OPT?

CJ · Jun 23, 2017

here is the print for this guy, turns out the primary wire is #35 not 35, so not as bad as we thought, calipers told the story better than the eyes, :

we have some #26 on the way so we can avoid the heavy 17 gauge mashing into the primary wire, so we pull 8 wires for the 4 ohm wind, and maybe 4 wires for the rest, might add some DCR but the tubes will be happy about that,

CJ · Jun 23, 2017

here is the Permali bobbin taken apart,

what is Permali? glad you asked>

"Laminated Beechwood Technical Information Permali® or Insulam® is an insulating material used in applications which require high tensile and compressive strength (see table below). In addition, due to its exceptional resistance to moisture, it serves as a suitable insulator where the support (flare lines & dummy legs) is exposed to harsh environment elements. Permali® or Insulam® is a phenolic laminated (densified, impregnated wood) product made from carefully selected thin beechwood veneers. These wood layers are impregnated under vacuum conditions with a special synthetic resin and then densified through the application of heat and pressure. The result is a homogenous material that combines the great strength and toughness of wood fibers with the excellent stability and dielectric properties of the most advanced thermosetting. The phenolic laminated block material is furnished with cross-directional fibers as shown in Figure 10 below."

Sovtek Mig 50 OPT

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