Lionmouth wrote:

I'm planning to build an SE tube amplifier with a pair of KT88 each channel
connected in Parallel as "g2 to B+ Triodes"
Is the impedance of the transformer=1k ohms?
I have Z11 laminated silcon iorn with tongue width 38mm and
bobbins stack height = 60mm.
Is it suitable to use 0.22 wire for the primary while the DC resistance
will be arround 250 ohms and current 260 mA, heating
rate (260mA^2)*250ohms=16.9watts?

I'd use a taller stack of iron, about 75mm,
and reduce the turns, and increase the wire size to about 0.4mm Cu dia.
0.22 mm wire sounds too thin to me.

The Ra of the trioded pair of KT88 will be about 500 ohms.

The load R will be about 2.5k, with Ea = about 450v.

The dcr of the primary should be less than 5% of the RL, so
no more than 125 ohms.

Then if Pda = 66 watts total, Ea = 450v, Ia will be 146 mA,
so the power dissipated in the primary will be 125 x 0.146 x 0.146 = 2.7 watts
only.

0.22 mm wire has a copper area of 0.038 sq.mm,
and this is good for 0.038 x 3 amps per sq.mm = 114 mA only.

You need to have some reserve current capacity in case of some problem
with over currenting.
0.4 mm is good for 377 mA at 3 amps per sq.mm.

There is some useful OPT design info at
http://www.turneraudio.com.au/htmlwe...utputtrans.htm

I'd say about 2,000 primary turns would be about right.

Maybe you can configure the secondaries similarly to my OPT No1 design,
which uses tongue width of 44 mm, so careful thought has to be given to
turns per layer, insulation etc, but if you have 5 primary sections
and 4 secondaries you should achieve 20Hz to 80 kHz of bandwidth
at no more than 12% total primary and secondary losses.
If the P loss is 5%, the secondary can be maybe up to 7%.

Patrick Turner.