Starting to consider working on my Philco 38-5. Wires are very brittle. Chassis is very dusty. At least one electrolytic is leaking (junk at the bottom of it). What is the black shiny junk at end of the tuning cap stack? It is hard and shiny. Way to much crammed into this chassis for my liking.
>What is the black shiny junk at end of the tuning cap stack?
Looks to be what's left of the rubber mount for the cap.
You've tons of room in that chassis. Also looks like it's
a Canadian built model w/a 25cy power transformer.
So what gives it away as a 25 Hz model? I think that may affect my filter cap values on the B+ filter. You are probably right about the cap mounts. What do I do about that?
Thanks,
TerryMSU
(10-13-2016, 09:10 PM)Radioroslyn Wrote: [ -> ]>What is the black shiny junk at end of the tuning cap stack?
Looks to be what's left of the rubber mount for the cap.
You've tons of room in that chassis. Also looks like it's
a Canadian built model w/a 25cy power transformer.
Terry;
I'm not sure if they made a 38-5 equivalent in Canada, but all Canadian Philcos had a brass data plate riveted to the back of the chassis rather then the perishable paper ones the U.S models all got, if they did it would have been called a 38-35. Contrary to popular belief not all Canadian sets came with 25 cycle transformers, and Canadian Philco sets in particular could come with either. There were also areas in the U.S that had 25 cycle service, such as parts of New York state near Niagara Falls, places like that required radios with 25 cycle transformers which many manufacturers like Philco would supply. I can recall someone either on here or the alternative forum that had an Atwater Kent model 84 with a 25 cycle transformer, which was fortunate for him as the 60 cycle ones had an almost Brand Z propensity for going out in a puff of smoke.
Regards
Arran
(10-13-2016, 09:24 PM)TerryMSU Wrote: [ -> ]So what gives it away as a 25 Hz model? I think that may affect my filter cap values on the B+ filter. You are probably right about the cap mounts. What do I do about that?
Thanks,
TerryMSU
The thickness of the iron core, 25 cycle transformers have more laminations to prevent core saturation with the lower line frequency. The values of the original filter caps might be higher in microfarads then in a 60 cycle set to deal with the 25 cycle ripple, but having larger cap values won't hurt anything for 60 cps.
Regards
Arran
A larger cap value than it is on 60Hz models could possibly raise the Vb a bit, making tubes run hotter. Not dreadfully important but might happen.
I am working on a 38-5. The first thing I did was to measure the power transformer resistances. They all were about 50% high. The number on the transformer is not the ono of the options listed for a 38-5. The one I have is a part number 32-7598N with what appears to be a date code of 8-37. Is that an acceptable replacement? What should the impedance read?
Thanks,
TerryMSU
I enlarged the parts list and found the 32-7598 number. It is the 25Hz part number. Does anyone have any insight as to the winding resistances being higher?
Physically the transformer is larger than the 60cy unit. It takes more wire to wrap around the core as it is larger. More (longer) the wire the higher the resistance. Seems like I posted that it had a 25cy transformer.
Resistance reading don't tell the whole story. It's easier and quicker to remove the rectifier tube and measure the HV from plate to plate. Most of the time I don't bother to do that I look for signs of severe overheating, larger glob of wax under the transformer, and does it smell burnt?
If it passes the visual and smell test I let her rip. Bottom line is that if it is shorted it's going to self destruct. Generally it just takes out the transformer and not other components like the field coil or filter choke.
Audio transformers are a different story as the copper wire used in manufacture is a small gauge and can rot rather than overheating from passing large amounts of current.
Winding resistances are generally higher for 25 cycle transformers, double or more would make some sense given that the core is larger and the frequency it's designed for is less then half. You can check resistances but the best way to know is everything is right is to yank the tubes, and apply power to the transformer, assuming that there are no obvious dead shorts across one of the secondary windings from exposed wires or a shorted pilot lamp socket, etc. In my experience 25 CPS power transformers work fine on 60 cps, the secondary resistances may be higher but so is the primary, what matters is the ratio between the primary and the secondaries.
Regards
Arran
So, the next issue I have to deal with is how to remove the shadowmeter from this radio. Any suggestions?
TerryMSU
Got it! Two spring wire clips were not visible, but easy to remove. Plus the shadow meter works, although it may be a little low in sensitivity.
Next question... how to remove the escutcheon on this radio?
Thanks,
TerryMSU
We had two threads going on the same radio. I have merged them into one. Multiple threads on the same subject is not permitted per Phorum Rules:
http://www.philcoradio.com/phorum/showth...p?tid=4586
Quote:II. Multiple threads on the same subject not allowed.
When you start a thread, please keep the discussion within the same thread.
Example: "Philco 90 broken"
After you've started that thread, please do not start another thread on "Philco 90 bad resistor" if it is the same Philco 90 being discussed in the original thread. Give others a chance to respond to your questions rather than asking them again in a new thread - please be patient.
These sort of threads will be immediately deleted, to keep clutter to a minimum.
Please cooperate with me in keeping one thread in the same place rather than scattering it around.
TerryMSU
Using the palm of your hand, carefully press down on the circular part of the escutcheon (the outer edge, if you will). Now twist either left or right, whichever way it will turn, and it will come off.
Be very careful as you do this, however, as the glass will also fall out as soon as you loosen the outer edge!
Once you have the outer edge and glass out of the way, you will see four screws holding the rest of the escutcheon in place. Remove them and set everything aside.
Reassembly is the reverse of disassembly.