JS trafo instead of S217D in Pultec EQP1R

[mg73]

I´m trying to use a JS trafo as a output transformer in a Pultec EQP1R design
it has similar data like a S217D 15KΩ Pri , 500Ω SEC
but the FB has 150Ω instead of 100Ω
and I´m getting high frequency self-oscillation at the output
I´ve manage to tame it a bit by connecting the 6072 cathodes direct to ground instead
of the 750Ω resistor but don´t know if this is the proper way to go.
And it´s probably many other aspects i missed.

 

[CJ]

try swapping the FB leads, they may be 180 degrees out,

do you have the 620-.003 uf zobel on the sec leads?

there might be too much phase shift with that transformer at hi freqs, getting a FB wind to be stable is kind of tricky,

you do not have to use the FB wind, stuff a 750 ohm lead into pins 3 and 8, ground the other end and fire it up, might be a tad bit more distortion but who cares?

 

[emrr]

Have you looked at JS prices on ebay?  I'd sell that sucker ASAP and get what you want.  Or maybe that is what you want.....

 

[mg73]

Ridiculous  prices!

Already tried phase-reverse, got worse.
Zobel is there, but even if I connect grid (pin 2,7) to ground it oscillates.
I try to connecting 3-8 and lead that to ground with a 750Ω resistor,thanks CJ




Maybe it will be a better suite for the  meq5,EH2  gain up amp?
and I could skip the interstage.
Or just sell it and buy the cinemag copy.

 

[mg73]

Borrowed an Cinemag S217D from a friend,
installed it and now it´s golden!!

As you said CJ the FB winding was the problem.

Thanks