thanks for all your replies.

I think that i will give up on the dc feeding heaters on the 813 for
the meantime. The current demands are too high for passive managment
and the heat output excessive for active.

The amp I am looking at is a Stereo SE 813 device.

Soooo, I have found a supplier who can provide me with a 160 VA
toroid, with two 12v, 80VA windings.

The 813's, need 10v at 5A, So i am going to 'burn off' some of the
volts over some dropper resistors. I will put one in each leg. so to
drop the one volt per leg i will get some 0.2ohm resistors. The same
supplier has 0.2 and 0.47 ohm resistors in 5 watt packages, i will
parallel up two 0.47 beasties per leg, giving a drop of 2.35v, net
result on the heater, 9.65. Heat dissipation is in the order of 5w,
with two 5 watt resistors in parallel, I have 100% coverage, so that
is ok.

I will then use an old fashioned heater pot to null out any hum.

Also using fixed bias so i don't have to elevate the cathode/heater.

Interestingly, I have done a search on 813 amps, and, Pete Millet,
www.pmillett.addr.com\default.html uses a switched mode psu device
from teleco service to create the dc required. can't get them here in
NZ, so I am back to my dropping resistors.

I will post some pictures in the next couple of weeks on progress. I
am also putting together a web page, I have some old and interesting
articles on transformer design, how hanna curves are actually made,
interestting ultra low impedance drivers etc. I have been promising
myself some time to do this, now that it is coming into winter here,
maybe the time is ripe.

kind regards

bill