CJ

Ampeg SVT VR Power Transformer
« on: December 02, 2019, 05:07:35 AM »
here we go again, another transformer, another victim.

but this one deserved to die. heck, it was dead already.

so we are going to bring it back to life, but we must do an complete autopsy to do that.

this was not a well made power transformer.

and seeing that it powers one of the most powerful tube amp that ever lived, well, i guess that is what fuses are for.

this thing clocks in at about 18 lbs.



If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html


CJ

Re: Ampeg SVT VR Power Transformer
« Reply #1 on: December 02, 2019, 05:11:36 AM »
looks like this thing was dipped with the cans on, as you can see accumulated potting compound,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #2 on: December 02, 2019, 05:15:18 AM »
not much final insulation between the wind and the cans, just a few layers of 3 mil mylar, there is some paper inside the cans, but usually you see a heavy wrapper  on the outside, like 20 or 30 PB (press board)

If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #3 on: December 02, 2019, 05:18:19 AM »
the bobbin has some built in shims, provides a bit of cooling for the coil,

we chop the long leads before heating it up to de-lam.
« Last Edit: December 02, 2019, 05:22:11 AM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #4 on: December 02, 2019, 05:25:41 AM »
lams come out pretty easy since it is a new xfmr,

175 EI (1.75" blade)

20 mil thick,  some weird metal, non grain,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #5 on: December 02, 2019, 05:29:26 AM »
we need a mandrel for the winding machine, so we grab a 2 x 4 from the attic and hammer it in there,

shim it up with an old perry como album cover, drill an off-center hole, wrap the drill bit with cloth tap to get a tight fit and hammer it into the hole just like your grandmother,  ;D
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #6 on: December 02, 2019, 05:32:31 AM »
since we drilled off center, there is some scraping of the winding platform during one half of the rotation, so we had to file 1/16" off the platform to gain clearance,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #7 on: December 02, 2019, 05:34:58 AM »
secondary lead breakout
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #8 on: December 02, 2019, 05:43:14 AM »
primary leads, dual sections with two wires each, each section has a thermal fuse,

so you can wire for 120/220/240

If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #9 on: December 02, 2019, 05:46:48 AM »
this is something i saw throughout the coil, it appears that the transformer was hung up to dry in such a way so that the varnish or air dry epoxy was settling on one side of the coil and maybe etching away at the enamel,

here is a pic  of one side vs the other,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html


CJ

Re: Ampeg SVT VR Power Transformer
« Reply #10 on: December 02, 2019, 05:53:01 AM »
so the hard to believe thing about this coil is that even with the large diameter wire, they still decided to speed wind, that is, no even layers, but a random wound coil with crossovers on all windings, even the #22 AWG primary that sits on the lower line,  :o

no wonder that the secondary shorted out,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #11 on: December 02, 2019, 05:56:47 AM »
pri/sec insl was 2 layers of 10 mil KP (kraft paper)

If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #12 on: December 02, 2019, 05:59:11 AM »
primary wind, outside section,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #13 on: December 02, 2019, 06:03:38 AM »
now this is pretty bad, i mean you have a crossover wire sitting on top of the primary wind with nothing underneath it to prevent the force of the outer winds from smashing it into the wires and causing a short across one or more wires, a pro shop would put something over and under to protect.

not the winder's fault, but his manager boss who is calling the shots to save time.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #14 on: December 02, 2019, 06:06:08 AM »
2nd layer of first primary, crossover city,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #15 on: December 02, 2019, 06:14:43 AM »
they did get the fist layer down right, but after that this thing is a mess, and they get big money for this amp,

Fender does a great job on their Vintage Modified amps, but this thing is a rip,

i have seen replacement transformers go for up to 500 dollars, and down to 150, i am going to tell they guy that he should have the output done also just to be safe,

looks like 150 turns pri to 641 turns sec, so 512 VAC sec B+  volts, , and an aux wind that goes 146 - 146 - 146 - 146 in series,

the heater transformer is separate,  we will build a print tomorrow,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Re: Ampeg SVT VR Power Transformer
« Reply #16 on: December 02, 2019, 11:05:29 AM »
Shockingly poor quality , looks like it was designed to just about  pass Qc and they dont give a hoot what happened afterwards ,
Maybe the winder had a bad day ,or have you noticed a trend with modern SVT's quality ?



 

CJ

Re: Ampeg SVT VR Power Transformer
« Reply #17 on: December 03, 2019, 04:13:25 AM »
here is th print,

very big wire and few turns means low sag when you hit those current drawing open E notes,

If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html


 

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