Philco 39-6 Power Transformer Issues - Printable Version
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Philco 39-6 Power Transformer Issues - Jake Blake - 03-23-2019
I wondered how critical it is to preserve the original phase relationship of secondaries also. I wouldn't say one way or the other at the moment. I kept mine on the 39-6 as they were originally.
It is worth noting that, much to my dismay, I discovered the 2 halves of the high voltage secondary or NOT symetrical in many instances! , . . one half having slightly more resistance than the other. Weird, the things that were done decades ago.
Jake
RE: RCA 811K question - morzh - 03-23-2019
Not critical. Usually.
Philco 39-6 Power Transformer Issues - Radioroslyn - 03-24-2019
JB,
> I discovered the 2 halves of the high voltage secondary or NOT symmetrical in many instances!
This true IF you are looking at resistance only. Turns ratio and number of turns they are. At the beginning of the winding the coil is smaller than at the the far end. If you measure the resistance from the beginning to the ct it going to be lower than from the ct to the far end of the winding as the wire used is longer. On power transformers a better way the check is to measure the ac voltage from the ct to each end. Voltages should be pretty close +/- 5v much more than that would be suspect. You can also do a no load test and check for heat. Shorted pt will get warm or hot after a few minutes.
Audios (interstage/output) and rf-if coils resistance checks work well to determine it's condition. Audios or going to be less than 1K but general if bad they will read much higher. In push/pull circuits it's not too uncommon to find half of the winding to be open. Rf and if coils are general going to be less than 50 ohms but again bad ones will read much higher.
GL
RE: RCA 811K question - Jake Blake - 03-24-2019
Radioroslyn
Hi.
So what you're saying is, even if the resistances aren't equal, the voltages can be. I guess that's all that matters. I assume that if the resistances are different, than the half with the greater resistance will produce a higher voltage,
. . . and another assumption: the off-balance voltages would create additional noise to filter out in the d.c. component.
Another item about the phase relationship-thing is in my 39-6, I notice that for some reason, they ground one side of the filiament voltage winding. I thought this may add additional importance to preserving the original phase relationship of the secondaries.
This printed resistance on Philco schematics has already led me down an erroneous path with the IF transformer I botched. Maybe I should stop paying so much attention to those winding resistances.
RE: RCA 811K question - Radioroslyn - 03-24-2019
>I notice that for some reason, they ground one side of the filament voltage winding
Couple of fine points. In a vacuum tube w/o a cathode the thingy that lights up is called the filament. If the tube has a cathode the thingy that lights up is called a heater.
Old skool sets that use filament or directly heated tube you will rarely find one side the filament grounded. What you will find is the filament winding will have a ct and at this point the ct acts as the cathode connection. Sometimes the ct is grounded but more often than not the ct is connected to a bias source.
On tube w/a cathode aka indirectly heated tubes, the reason for the one side being grounded is simple. It saves time and wire when construction.
GL
RE: RCA 811K question - Jake Blake - 03-24-2019
Well, just for the sake of the discussion, I went on and plugged the chassis of the 39-6 in and measured the two halves of the power transformer high voltage secondary. One half is 257 volts, and the other half is, . . . is, . . . zero.
RE: RCA 811K question - Radioroslyn - 03-24-2019
So what do you have across the two yellow wires (ac voltage)?
RE: RCA 811K question - Jake Blake - 03-24-2019
No voltage.
The question I have now is, I wonder if half the secondary was open when I first bought the set and it was playing.
RE: RCA 811K question - Radioroslyn - 03-24-2019
I would unplug it and use your ohm meter to find 3 wires coming out of the power transformer that show resistance to each other. These will be your HV leads. Perhaps you've got one of the wires miss marked.
RE: RCA 811K question - Jake Blake - 03-24-2019
I'm positive I didn't do that bud.
I had made my own notes of their positions on the rectifier, as well as the others. then obtained the schematic for it , which gave me the proper color coding. The two wires I put the yellow shrink insulation on are the two that were connected to the rectifier. . . the high voltage leads.
RE: RCA 811K question - Radioroslyn - 03-24-2019
Ok so there are a few suitable replacements on epay. Not sure abt the dimensions but should be reasonably close. https://www.ebay.com/itm/TRANSFORMER-POWER-480VCT-40-mA-5V-2A-6-3V-2A-THORDARSON-13R19-HAM-RADIO/264222687572?hash=item3d84e64154:g:hFUAAOSwC~9cLBIG:sc:USPSPriorityFlatRateBox!19001!US!-1 or https://www.ebay.com/itm/1-QTY-Stancor-PC-8418-Power-Transformer-117V-230-0-230V-50MA-6-3V-2-5-A/273773737547?hash=item3fbe2fb64b:g:GB8AAOSw04ZclRjm&frcectupt=true
GL
RE: Philco 39-6 Power Transformer Issues - Jake Blake - 03-24-2019
Radioroslyn,
Thank you bud. For a second , I was thinking of throwing in the towel on this project.
That Stancor sounds like a fairly-close match . . . only need one HEATER voltage.
Jake
RE: Philco 39-6 Power Transformer Issues - Radioroslyn - 03-24-2019
My best recollection is that the original pt is sort of narrow, doesn't have a lot of laminations. Double check the replacement's size to be sure it will fit the chassis.
RE: Philco 39-6 Power Transformer Issues - rfeenstra - 03-24-2019
Just dig in and rewind that thing. It's soooo much fun.............................................NOT!. But it is doable if you have a very difficult time finding a transformer that will fit.
RE: Philco 39-6 Power Transformer Issues - morzh - 03-25-2019
Jake
In the beginning you said the halves were SLIGHTLY different. This would mean to me that they are OK. I am not sure how a winding that is not open would NOT produce any voltage whatsoever.