Magnetone Varsity Guitar Amp

Model # M-197-3-V

6SJ7 grid leak > 6V6  with a 5Y3 rect

blown OPT

probably about 1953, big bucks on the vintage market, sometimes,

schematic has a few values changed,

pwr trans putting out  too much voltage, 7 istead of 6.3,  annd 5.6 instead of 5,  112% of desired,

390 from plates to CTwill be about 450 on the ancient dry lytic, big trouble,

had a 6L6 installed, extra current and voltage to the OPT, 1K pwr sup R was bypassed,
excess pwr was not a welcome sight to the #37 pri wire,
so  the OPT surrendered,

rewind pwr and OPT, right?
otherwise we have a popcorn machine waiting to happen,

notice 1K in frot of first filter, might drop 40V and save cap but we want about 350 on that plate,
at least the screen runs lower than B+,

we will run 500 ohms instead of 1k in the pwr supply for less heat, this will drop 20 volts at 40 mils, so if we want 350 on the plate of the 6V6 we need 350+20=370, with a 5Y3 the RCA book says we want about 312 volts AC feeding 40ma to the 5Y3,

so we need 312/390=80 pecent of the turns already on the pwr xfmr, and about 90 percent of the heater turns,

3 ohm speaker, wtf? 

topside

bottom side,

will move the line cord cap to the coupling cap to replace non stock replacement and put anew poly cap in the shocker position,

pwr xfmr

these things seem to last longer tha the normal lytics, no chemicals leaking so we willkeep it since resale value ca change with the amount of parts you change,

did not see a gap in the SE OPT, what gives?

E-E, never seen this in a pwr OPT,

7/8" tongue, sq stack, no gap paper, about 70 turns of #25 for the voice coil,

unwind #37 tonight,

> 3 ohm speaker, wtf?

I bet the voice coil measures 3 Ohms on DC.

The 400 CPS impedance will be close to 4 Ohms.

CJ said:

did not see a gap in the SE OPT, what gives?

Click to expand...

May give interesting distortion, 2nd harmonic?

there is a natural air gap whose length depends on assembly and the flatness of the stack,

here is the output, we will get the DCR after the rewind,

there were about 4 breaks in the primary around layer 1, which is where all the heat is,

> did not see a gap in the SE OPT

EE makes a gap just like EI.

If the ideal gap is much less than about a scrap of paper, the natural mis-fit is good enough, at least for cheap rock-n-roll.

lead method on the OPT primary>

there were about 4 breaks in the primary wire in layer 2,

first layer, they wind right over the lead wire to hold it in place,

here is the pwr trans print which will be altered to drop the B+ and heater voltages which is needed because of the higher line voltages,

delam easy with .025 lams, coil ready for tear down,

outer layer is the 5 volt wind served with old school cloth.

6.3 wind

brass E shield

goes between first section (secondary) and second section, (primary)

sandwiched between 10 mil KP