Old one Lafayette -new SuperReverb amp

[stoya]

Hi,
Since I was in high school,  have an old Univox- Lafayette U-50 bass Head (2x 6L6 output- 50W RMS) . I was think to make Fender super revrb Ab763 from that crap. OT has blown up 15 years ago, so i rewind it then. But PT is on 110v, and before 25 years ago i wind second autotransformer with only one wind - now i realise it was stupid I confess. Can enyone help me with exact number of turns and all stuff to make a Fender-like Output and Power transformer for 2x 6L6 output, please. I have an SF `71 twin reverb and I ike that sound.
thanks

 

[Pip]

Hi,
Since I was in high school,  have an old Univox- Lafayette U-50 bass Head (2x 6L6 output- 50W RMS) . I was think to make Fender super revrb Ab763 from that crap. OT has blown up 15 years ago, so i rewind it then. But PT is on 110v, and before 25 years ago i wind second autotransformer with only one wind - now i realise it was stupid I confess. Can enyone help me with exact number of turns and all stuff to make a Fender-like Output and Power transformer for 2x 6L6 output, please. I have an SF `71 twin reverb and I ike that sound.
thanks

Try this:

http://behindthetone.com/johnfisher/ot1/ot.htm

 

[CJ]

Fender 018343 Concert OPT had 1600 turns for the pri,

so 800 T for each half,

plate to plate Z for 6L6 should be about 5000 ohms,

if you want a 16 ohm sec you would need 5000/16 = 312 , so take the root to get the turns ratio,

root 312 = about 18,

so 1600/18 = about 90 turns,

you want to tap it for 8 ohms, divide by root 2,

so 90/1,41= 64 turns,

so

1600T pri,
64T-90T sec,

#28 wire for pri should be good,

sec wire should be the heaviest stuff you can fit,

most power  OPT's  combine the inner and outer sec winds in  parallel, and bifi wind the center section,

 

[stoya]

Thank`s for reply. Original Univox OT has 2x 995 turns for pri, and  on top 70 turns for sec. (pri-sec  combination)
CJ  you gave me a hard homework. :  I want to tap it for 4 ohms, divide by root 2,so 64/1,41= 45 turns,

so 1600T pri,45T-64T-90T sec,

I find your older post for Fender Bassman 100 Bass amp OT specs and I change few things ,  so correct me if this is wrong
And your (modified) magic (please correct me if I wrong):

put down about 200 turns of #28 pri, wind it tight!
sec wire #17 at once, wind 1 layer, 32 turns per layer,
lay down about 400 turns of #28 pri,
sec wire #17 at once, wind 1 layer, 13 turns per layer, out wire for 4 ohm terminal
then about 400 turns of #28 pri,
sec wire #17 at once, wind 1 layer, 13 turns per layer,
lay down about 400 turns of #28 pri,
sec wire #17 at once, wind 1 layer, 32 turns per layer , after 4 turns out wire for 8 ohm terminal
now about 200 turns and we are done.
I must confess that i don't know " how to combine iner and outer sec winds in parallel, and bifi wind in center position for that OPT."

 

[CJ]

your calculation for 4 ohms is correct,

you do not need that much coil interleraving for a guitar amp,

in fact, a bandwidth limited transformer may even sound better than a 20-20k xfmr,

so you could just wind sec-pri-sec-pri sec with no bifi winding or parallel sec hookup,

or even sec-pri-sec with a CT for the pri,

i have even seen sec-pri used for 6V6 single ended,

or pri sec pri, will also work ok, DCR does not have to be balanced for guitar,


be careful when pulling heavy sec wire over pri wire, this can upset the lay of the pri wires,