Fender Tremolux 1959 Tweed OPT

well the boss walked in to work this morning with a shipping envelope containing an original Triad #108 output transformer from a 1959 Tremolux and asked me if i would be interested in rewinding it, 

that is like throwing a steak to a hungry linebacker,
i tried not to drool on it on the way to the bench,

Fender used a bunch of different OPT's, quote from the web:
"The early amps had the Triad #108 OT, and then in 1959 they started using the
Schumacher 125A1A OT. The same OT that was used in all the Brown, BF and SF Deluxe Reverb amps"

so we will blog this thing out,

guts

chassis pic off the web, we only have the xfmr on the bench,

should probably ask the guy for the choke also, probably could use fresh wire after 56 years,

notice ground lead of sec soldered to the xfmr frame, so frame must be well grounded, which means scraping varnish off the mounting hole area,

will post some pics tomorrow, (today)

rev 1 print attached,

this is the first time i have seen a push-pull OPT laced as a butt stack,
this is usually done on SE amps to handle the DC,

so what does this do? since the core is not that big, 87 EI, it means the perm is very low do to the 10 mil gap, this means pri inductance will be low, so we expect a sharp roll off on the low end,

this will protect the old speaker from blowing up and also shape the tone of that amp a bit differently,

it will also be far less sensitive to tube mismatch, or even removing one of the tubes for decreased wattage, not much DC flux, only a few Gauss due to the gapped core,

with the gap we need a lot of turns which means small wire getting pushed hard and lots of DCR which means heat, and voltage drop at the plates and phase shift at the bottom end (arctan DCR/XL)

normally we see about 1000 to 2000 turns on a P-P OPT, this one has 4200,
inductance is quadratic in turns so we still get just enuff Henries with the low perm core,

this is kind of a cheap transformer, no end bells, pri was scatter (random) wound on a nylon bobbin with no inter-layer insulation and a very thin layer between pri and sec (10 mils of kraft paper)

we will sweep it and check real inductance after completion so the print might change, inductance at this point was derived mathematically,

enjoy...

pics

more pics

Loving these blogs CJ. 

glad you like this stuff, got a Decca guitar amp in the house,

this Triad 108 might be gapped so that you can use it for an SE amp or push pull, either tape off the CT or use half the winding depending on the tube,

UTC HA-133 is built like this,

edit: we count 4000 turns instead of 4200 derived from electrical ratio test,

print has been revised, cj

rewind complete on this OPT,
inductance graph shows flat line which is typical of a gapped core as perm is watered down by air gap,
25-30 Henries which is low for this application but works anyway, bass response will take a hit but this is a guitar amp so no big,
rise in graph at low end is really DCR, 884 ohms worth,