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Hello, I am new to this site and have a question about replacing one of the electrolytics in this radio. The schematic shows part number 45 as a 25uf - voltage not listed. The radio has what appears to be the original Mallory can with
a value of 30uf @ 500 (peak) volts. A little internet research has shown that a 450 volt can be used to replace this? I've never gone backwards on voltage and am unsure how to proceed so I thought I'd better ask before wasting parts.
Do I need to use a 500 volt cap here or can I use a 450 volt (that I have plenty of) to replace without something going bang?
Second part of question. The tuning capacitor is very loose - it has three "slots" with rubber grommets that have dry rotted so now the entire assembly is loose. What are these even called and are replacements available ?
Thanks for your help!
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Welcome to the Phorum!
I'll let one of the others answer the 450 vs 500 v question.
I've not worked on a 38-9 so don't quite know what the gromments you are asking about look like but the best place for rubber replacement parts is RenovatedRadios. The Philco rubber parts are located at this
LINK.
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Hi and welcome,
I would go ahead and use the 450v guys. I think most are rated @ 475v peak. Tack it in and measure the dc voltage across it. What you'll see is the voltage will creep up and up till the power supply has some load across it. Then it will drift downward till it stabilizes around 300vdc.The real issue is that the rectifier filament ( directly heated) heats much quicker than all of the other tubes. Till the others heat there cathodes there is very little current being drawn from the HV. This causes the HV to surgre upwards till all the tubes are heated and drawing current.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 07-31-2017, 06:42 PM by
Radioroslyn.)
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Thank you all - I appreciate the help. I'd really like to get this radio going - it's minty clean and beautiful. Haven't messed with brand P too much - the tar baby things in the chassis (capacitors buried in a bunch of tar) of Philco radios have caused me much, much frustration - now twice shy about restoring them. Glad to have experts here to help!
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Welcome to Phorum. Don't let the tar caps worry you. They are not that bad to do. There are different ways to do them. Some people just unbolt and turn them over to get at the tar. I like to take the cap block out and then remove the tar and restuff with new caps. Just take pics and make a good drawing of where the wires that connect to the solder tabs on the blocks go and do one at a time.
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I think you'll be fine with 450V caps, as the voltage directly out of the rectifier heater is 315V which kinda implies that it will not reach into upper 400s.
When having installed the caps, hook up the voltmeter to the rect filament, across the 45 cap, and see were the voltage actually reaches.
Oh.... use a good capacitor with as high as possible ripple rating for #45.
The best I found is made by Panasonic with the value of 22uF 450V. The PN is EEU-EB220
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(This post was last modified: 07-31-2017, 08:24 PM by
morzh.)
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If the bakelite blocks are done according to this handy Guide written by Gary Maker, they should be easy. I've also paired it with a Philco Service bulletin with the specs for replacements.
https://www.dropbox.com/s/kys1dskfkg0r81...g.pdf?dl=0
Blessings,
Jeff W.
Jonesboro, Arkansas
http://jeffsradios.weebly.com
God loves you as you are, not as you should be, because none of us are as we should be. - Brennan Manning
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Ok - thanks to all the electrolytics have been changed and I brought the radio up to 75 volts on the variac and it plays surprisingly well - just with the three new caps - all the way across the band! The beam of light bulb in this radio is an ancient GE #55 bulb and will not light. I've verified that it's not open so I'll have to check whats up with it. There is a giant 10K resistor in this radio it's reading high and I'd like to replace it. I have a supply of 3 watt 10K resistors but I'm thinking that is not going to be enough given the size of whats in there now. Just curious as to why the parts list does not show the power rating of this resistor?
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(08-01-2017, 08:37 PM)gcerio Wrote: Ok - thanks to all the electrolytics have been changed and I brought the radio up to 75 volts on the variac and it plays surprisingly well - just with the three new caps - all the way across the band! The beam of light bulb in this radio is an ancient GE #55 bulb and will not light. I've verified that it's not open so I'll have to check whats up with it. There is a giant 10K resistor in this radio it's reading high and I'd like to replace it. I have a supply of 3 watt 10K resistors but I'm thinking that is not going to be enough given the size of whats in there now. Just curious as to why the parts list does not show the power rating of this resistor?
According to the old Philco Repair Bench Site, The largest 10K watt resistor Philco used was only 2 watts, so a 3 Watt replacement will be fine. I've worked on close to a dozen from the 1930s, and unless you're replacing the Voltage dropping resistor strip, The biggest you should run across is a 3W.
Blessings,
Jeff W.
Jonesboro, Arkansas
http://jeffsradios.weebly.com
God loves you as you are, not as you should be, because none of us are as we should be. - Brennan Manning
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Thanks to all that have helped, I appreciate it. After replacing all of the rest of the wax capacitors the radio now motorboats and whistles all across the dial. The tube shields are on and I've checked over my work and didn't find any errant blobs of solder or crossed wires. Not sure if it matters but this radio did not have any tube shields and I don't have any (can't find them...) of the square Philco one's that are supposed to be on this chassis. I had several round ones laying around so I bent them to fit - and they do shield the tubes, fitting nicely around the square bases of them. Any thoughts on how to proceed?
