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In Reply to: RE: KT-600 with film cap power supply suggestions posted by rickl on December 18, 2014 at 08:08:50
First things 1st. Get the wretched 1/2 wave rectifier out of there! If a quad of Cree C3D02060F Schottkys will mechanically fit, look no further. If space is a problem, use 4X UF4007s. Either way, full wave bridge rectify the B+.Put a CL-130 inrush current limiter between the bridge and the PSU filter. Use a 100 muF./400 WVDC cap. as C1A. A top notch 'lytic is fine here. Film caps. after the choke will give you maximum bang for the buck. It looks like C2B does not directly feed any tube plates. So, another GOOD 'lytic will be fine. Where a PSU cap. feeds 1 or more plates, use a metalized polypropylene film part of adequate WVDC, such as Solen.
BTW, try for 105o C. rated parts, when buying capacitors.
edit: grammar
Eli D.
Edits: 12/18/14 12/18/14Follow Ups:
position if using only 1 (or 2). I have read that the film cap should be the first (input) cap, someone else the last cap in the filter, and you are saying somewhere in the middle?
Let me clarify
I stress the film cap in the first stage when you are coming off a rectifier tube. If you are coming off sand diodes,you want a low ESR high ripple current electrolytic such has a 105 degree Panasonic or Nichicon or CDE. You can use a film cap but keep in mind that you usually need a higher value capacitance and that can take up some real-estate in the amp or preamp. Anyway,you can use the film caps downstream even if you use an electrolytic.
"
thanks, Michael, so if I am using a tube rectifier, first cap should be film/foil, whereas if it is a sand rectifier, use a 'lytic cap, correct?
The generalization is flawed. Consider a choke I/P filter. A large value, low ESR, 'lytic after the I/P choke is fine, regardless of rectifier technology. Remember that per older additions of the ARRL Handbook, LCLC is the way to go. A cap. that feeds small signal tube plates is an excellent candidate for metalized polypropylene film. Save the film and foil parts for signal path duty.
Given the intolerance of vacuum rectifiers to large valued cap. I/P filters, a MKP part as the I/P cap., when vacuum rectification is employed, makes sense. Dielectric absorbtion and other losses have to be minimized. Whatever energy is stored needs to be available.
Eli D.
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