Thanks Spec,
I am sure it will, Though it still has the heat issue
That is true about the heat, but I would think the single supply bridge circuit of post #147 is a practical proposition as long as a good physical design to allow sufficient heat dissipation is realized.
The very absolute minimum heat dissipation using a switch mode PSU to generate a stabilized supply rail with no ripple and without any control would be 70V (tube operating V) * 12mA * 100= 84W.
With control, allowing 10V across the transistors, would give an additional 10V * 12mA * 100= 12W, making a total of 84 + 12W = 96W.
Assume that the switch mode PSU is 75% efficient would add 96W * 0.25 = 24W.
This gives a grand total heat dissipation of 120W.
So the message is that the tube display unit (TDU) is quite power hungry by definition.
I have spent the day learning a little eagle cad and have fleshed out the Les Buck Bucker Circuit (made it pretty).
Very impressive. It is not easy to get started wit EAGLE, although once you get past the initial stage it is quite easy (you should be running beta version 7.5.2)
This circuit (if it works) could be the answer to all the problems ?
The way I see it .. limited amps for striking through the fat resistor he has put in. Eliminating heat problem.
Diode protection so we don't go back to the 78v side.
And .. it's so sweet that even the main sustaining voltage is above spec and will have plenty of current.
Waiting on some caps before I test build. Have no idea what I need so am just going to try a few smaller HV types.
This is my first eagle file .. so ignore all the values for now.
Will put the popper ones in if I can get it to spark up.
Wotchathink ?
I don't like being a killjoy, but afraid the circuit will not meet your specification.
The 55V transformer secondary windings have a tolerance of 57.25 +- 9% when all the variables are taken into account.
(1) 57.25 RMS - 9% = 52.095 RMS
(2) 52.095 RMS * 1.414= 73.67V peak - 1V for both rectifier diode forward drops (500mV each) gives, 72.67V peak.
(3) 72.67 peak - 5V ripple voltage = 67.67V trough.
This does not meet the tube running forward voltage of 70V. Neither does it give any voltage across the control transistor. If you allow 10V minimum across the transistor you need 85V minimum, taking ripple voltage, to run and modulate the tubes (I would put a tolerance of +-5% on the tube running voltage too).
Of course, the extra voltage required can be provided by an extra winding on the transformer core.
Because of the variation of the supply lines and the ripple voltage the circuit will not be as efficient as you might at first think. That was why I went for the simpler circuit in post #147
Incidentally, the Les boost strike supply can be reduced to one capacitor and one diode as a DC supply is not required to strike the tubes.
Al in all though, nice work
spec