01-12-2016, 07:15 PM
(This post was last modified: 01-12-2016, 07:26 PM by Murphyv310.)
Correct Ref.
The addition of a diode that clips the negative half cycles cures this problem. The only snag is if you use two silicon diodes the HT could rise to 450+V before its loaded by the rest of the valves when cold, if the set has an indirectly heated rectifier then there is no problem.
I have done many sets this way and the advantages are many.
1, A cap for the heaters on its own is not a compromise, it only supplies the heaters and the value can be accurately worked out.
2, A separate HT cap can be tailored accurately for the HT you need with of course the exception of class B push pull stage outputs when the HT could sag on loud volume as there is less regulation.
3, Big reduction of heat
4, More efficient and less costly on electricity.
David's set will need a 4.19uf cap for heaters, I always dispense with a surge limiter as it's unnecessary and a 0.65uf cap for HT assuming 45ma HT current.
Run capacitors can be used and there is plenty of choice out there with obscure values too. Under no circumstances use electrolytic caps. I find that "X" rated caps are fine for the HT dropper, any faults will blow the fuse and that is one other mod I suggest for safety and reliability, I normally rate the fuse at 50% above the normal HT current, fit it in series with the Cap dropper.
Have Fun
The addition of a diode that clips the negative half cycles cures this problem. The only snag is if you use two silicon diodes the HT could rise to 450+V before its loaded by the rest of the valves when cold, if the set has an indirectly heated rectifier then there is no problem.
I have done many sets this way and the advantages are many.
1, A cap for the heaters on its own is not a compromise, it only supplies the heaters and the value can be accurately worked out.
2, A separate HT cap can be tailored accurately for the HT you need with of course the exception of class B push pull stage outputs when the HT could sag on loud volume as there is less regulation.
3, Big reduction of heat
4, More efficient and less costly on electricity.
David's set will need a 4.19uf cap for heaters, I always dispense with a surge limiter as it's unnecessary and a 0.65uf cap for HT assuming 45ma HT current.
Run capacitors can be used and there is plenty of choice out there with obscure values too. Under no circumstances use electrolytic caps. I find that "X" rated caps are fine for the HT dropper, any faults will blow the fuse and that is one other mod I suggest for safety and reliability, I normally rate the fuse at 50% above the normal HT current, fit it in series with the Cap dropper.
Have Fun
