need opinion on xfrmr continuity test please - Printable Version
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need opinion on xfrmr continuity test please - davebyoung - 11-21-2012
Hi guys, I need your opinion on a continuity test. Philco 84B Power transformer: HV winding reads 419 ohms plate to plate. Plate 1 to CT is 203 ohms and plate 2 to CT is 218 ohms. Is this normal? Could they have missed the CT that far or do you think there may be a shorted winding layer on one side? Checked with two different Ohm meters, both gave same results.
It looks like that is going to introduce a pretty good ripple on the B+.
Just want to get an expert opinion before I repaint this thing.
Any help would be appreciated,
Dave
RE: need opinion on xfrmr continuity test please - rghines1 - 11-21-2012
Resistance is not the best method for verification of the HV winding.
Measure the AC voltage and should be equal on both sides from the center tap.
RE: need opinion on xfrmr continuity test please - Radioroslyn - 11-21-2012
Seems like your CT isn't exactly center? Actually it is electronically. Think a bout it as the first half is being wound and then the second half over it the first half tends to be a bit small than the second. Winding the second half over the first makes it a bit bigger than the first. Bigger = more turns = higher resistance but same inductance.
GL
Terry
RE: need opinion on xfrmr continuity test please - davebyoung - 11-21-2012
Thanks Terry, that makes sense!! This is my first restore and I haven't touched a vacuum tube since the late 60's. So rghines1 made a good point that resistance can't always be the assuring factor. Anyway, looks like I may have a functional xformer.
Thanks guys, I will feel a lot better when I finally power her up,
Dave
RE: need opinion on xfrmr continuity test please - morzh - 11-21-2012
Terry wrote what I just wanted to write.
Your second half is longer, so the resistance is more. But what matter is the number of turns, and those two are equal.
RE: need opinion on xfrmr continuity test please - codefox1 - 11-21-2012
Every week or so. So long as secondary voltage is about equal and transformer is not overheating, all is probably well. On to rectifier, filters, and voltage divider.
RE: need opinion on xfrmr continuity test please - Radioroslyn - 11-21-2012
PS
Usually the windings that are bad on the 84's and the ant and osc coils. The primary and the the feedback. Did I mention all of the resistors too. After that you should be in good shape.... The IF alignment is fairly critical too. Will make big difference in the performance if it's not on the nose.
All in all I think it does a great job for a four tube set!!!
GL
Terry