audiog wrote:Hello Shannon,
Yes I will use PSUDII for simulation.
It will be of some help to know the Rprimary and Rsecondary (HV) of P782 power transformer and the Vout without load. If someone know this figures, please replay the post.
The P782 has a 117 Vac primary and a 400-0-400 Vac secondary. This is used with full wave rectifier tube to achieve B+ voltages at around 490Vdc, loaded.
Examinating the datasheet of KT88, I think that for a "Class AB PP UL fixed bias KT88" with Va=490V and I(a+g2)=70mA for each tube in idle state, it will be necessary consider about Imax=150mA for each tube at max power, for first stage Ik=1.1mA costant because it work in class A, for phase divider Io=6.2mA fixed by corrent source. So for one channel I need 308mAdc, the rated rms current in the secondary could be 218mAac with FWCT rectification and 435mA with graetz bridge rectification at max power.
My idea is to design a new power supply for PP kt88 and investigate about various configurations: FWCT rectification with GZ34 and SS diode,
hybrid graetz bridge rectification, ss graetz bridge rectification.
Another possibility is to use a HV stabilized power supply for first and second stage.
I for the time being am waiting for to receive the ST70 board from Shannon, where I will mount the components for a stereo MKIII.
A stereo MKIII will need a substantial power supply. One P782 will not provide adequate amperage.
Meantime I design a first power supply with a 400Vac secondary, with a tap at 360Vac, since the st70 board have only one supply line for both channel. I suppose for best performance a rated secondary current of 700mAac would be enough.
Ciao.
700ma should do it.
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This transformer has (2) 360Vac coils at 500ma each. You could parallel these HV coils. With a capacitor input, full wave bridge rectifier, you should get 507Vdc with about 620ma current capacity.