Hi Group:
I am working on a low power PP output transformer design for a pre amp.
16K primary 600 ohm secondary. I need to have a 20% BIFILAR wound
feedback winding in this transformer. My question is: Should I spec this
feedback
winding to be wound with the primary or the secondary? I have heard of it
being
done either way. It seems you would want it on the secondary to get a true
mirror
image of the output. And then again, winding it with the primary would help
flatten
out the load the PP tubes were seeing. I don't have the luxury or budget to
try it both ways.
Any thoughts or ideas on this subject.

Thanks
RonL

R Laury wrote:

Hi Group:
I am working on a low power PP output transformer design for a pre amp.
16K primary 600 ohm secondary. I need to have a 20% BIFILAR wound
feedback winding in this transformer. My question is: Should I spec this
feedback
winding to be wound with the primary or the secondary? I have heard of it
being
done either way. It seems you would want it on the secondary to get a true
mirror
image of the output. And then again, winding it with the primary would help
flatten
out the load the PP tubes were seeing. I don't have the luxury or budget to
try it both ways.
Any thoughts or ideas on this subject.

Thanks
RonL

Again we have no circuit description or schematic to refer to.

16k to 600 ohms is 26.6:1 ZR, which gives a 5.16:1 TR, say 5::1,
so you might have 5,000 turns of primary turns,
of which 1,000 are feedback which we might assume are in a cathode circuit,
and then 1,000 turns are the 600 ohm secondary, which might have no DC present.

Indeed the bifilar winding of feedback to sec would be best,
but is difficult, but if you had two 600 ohm sec layers with a FB layer between
them
of equal turns, then the coupling would be fine.
But to get the widest BW, the transformer should be interleaved,
so that you have at least S-FB-S--P--S-FB-S, presuming that the size of core
for the preamp
OPT is only say a 20mm stack of 25 mm tongue grain oriented steel.
The insulation between S and FB should be thin if the FB winding is at earthy
potential, but thicker between S and P, which might be at B+ potential.
The use of some other core with higher u might be appropriate.

Patrick Turner.