|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
71.70.154.214
Well folks, I took all the info everyone posted and came up with a solutuion for the 845 amp. The old amp was set up with dual switches for the filament supplies and plate, so I disconneted the tranny from the plate switch and hooked it to the variac and the amp psu to ac mains so I could use the filament switch and get all the filaments up to full voltage on all the tubes before turning on any plate voltage. I clip lead the 6au4 filament tranny off that circuit two. After about 30 seconds of warm up I brought the variac up and it came up just as smooth as could be with the max amp reading on the variac meter topping out at 2 amps. No blown fuses this time. I put a 5amp slo blow in the amp but I may drop that back down to see if 4 will work ok. My B+ is a little below target value at 930vdc, but that's not bad for first try and I would guess that some tweaking will get it to 1000. Still have one problem though; the first choke in the LCLC filter is humming like crazy. I tried a different choke and it did it too. Would appreciate any hints on what is happening there and why only the first one. Thanks for all the help so far, this has really been a learning experience for me.
Follow Ups:
Try a 2.5 amp fuse.Both problems, low voltage and choke humming, can be helped with a small cap in front of first choke...cLCLC. Use high a voltage part.
I think you gave me some values to start experimenting with, can you remember what they were?
Thanks
I would try a .5Uf to start with.Bring it up slow and see what happens.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
The hard part will be finding one with a high enough voltage rating.
Thanks
Buy 4X Xicon 0.47 muF./630 WVDC MPP caps. and a pair of voltage equalizing resistors. I know you can figure it out. Mouser stocks the parts.Be sure to stay under 1 muF. net capacitance in the "cheater" position.
Eli D.
Thanks Eli, I will give that a try.
Eli, what happens after 1Uf? Would it be higher PIV on the diodes?Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Somewhere in the vicinity of 1 muF. behavior changes from primarily choke I/P to primarily cap. I/P."Cheater" caps. that push the DC rail voltage up to the AC RMS voltage are certainly OK. Regulation degrades beyond that point. How much degradation is too much is a case by case thing.
Also, think about the available B+ current. A "pure" choke I/P filter can deliver slightly more "juice" than the AC RMS value. Adding capacitance in front of the 1st inductor lowers the amount of B+ current that can be drawn. As the conduction angle in the rectifier winding get smaller (larger cap. = smaller angle) the DC draw that can be supported declines. It's a matter of I^2R heating in the winding. The heating is inversely proportional to the amount of time conduction occurs and varies directly as the SQUARE of the current drawn. The I^2 term is dominant. That's why approx. only 0.5X of the AC RMS current is available as DC when cap. I/P filtration is used. A choke I/P filter allows access to the full VA capability of a rectifier winding.
A choke I/P filter is current rich and voltage poor. A cap. I/P filter is voltage rich and current poor.
Eli D.
Thanks for the explanation. That's just what I am seeing running sims on the Duncan PSUD 2.Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
That sounds familiar, I think Eli told me the same thing awhile back.
Thanks
| ||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: