Hello all, new to the forum. I have a Philco 80 Jr. that I'm repairing / restoring. The first question I have is just how "hot" is normal for the rectifier tube? I put a temperature probe up against the glass and base and it read around 140 degrees Fahrenheit. I know it is normal to get warm, just want to make sure its not too hot.
A little back story on this radio. This radio has been in the family since it was new. This was the first tube radio I ever repaired. Back then the 4mF cap failed and a resistor was burnt. That was 22 years ago and I kind of got out of the hobby (kids and wife, etc.) Now kids are grown and I have time to re-learn. This radio stopped working again when the rectifier tube failed. I replaced the tube and it works but gets very warm. I'm slowly replacing all the caps and out of tolerance resistors. So far both the electrolytic caps and one of the Bakelite block cap (the one with the wire wound resistor) have been rebuilt. One part at a time to make sure it is still working. Any information and advise would be appreciated. Thanks.
Hi Mike,
Have never measured the bulb temp of an 8o tube. 140 deg seem reasonable as it's very uncomfortable to touch. With that said a few things to check. Measure the DC voltage from the 80 filament to chassis ground. Should see about 250vdc. If it's below 200v or so something is a miss. If there is a short somewhere in the HV the plates in the 80 will start to glow RED, turn it off and find the problem. Be aware that #37 has the + side connected to the chassis and - the the WW resistor.
For other service notes search the site for model 80 and 84, both are similar and share the same issues.
Would go ahead and replace all of the wax/paper caps, electrolytics (there's 3) and check the values of all the carbon resistors. I've serviced a bunch of these sets and most of the resistor are way off in value. http://www.nostalgiaair.org/pagesbymodel...013843.pdf
Welcome to the Phorum!
Terry
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: 08-28-2016, 06:07 PM by Radioroslyn.)
(08-28-2016, 03:29 PM)Mike L Wrote: Hello all, new to the forum. I have a Philco 80 Jr. that I'm repairing / restoring. The first question I have is just how "hot" is normal for the rectifier tube? I put a temperature probe up against the glass and base and it read around 140 degrees Fahrenheit. I know it is normal to get warm, just want to make sure its not too hot.
A little back story on this radio. This radio has been in the family since it was new. This was the first tube radio I ever repaired. Back then the 4mF cap failed and a resistor was burnt. That was 22 years ago and I kind of got out of the hobby (kids and wife, etc.) Now kids are grown and I have time to re-learn. This radio stopped working again when the rectifier tube failed. I replaced the tube and it works but gets very warm. I'm slowly replacing all the caps and out of tolerance resistors. So far both the electrolytic caps and one of the Bakelite block cap (the one with the wire wound resistor) have been rebuilt. One part at a time to make sure it is still working. Any information and advise would be appreciated. Thanks.
Hi Mike,
If the tube is overheating good chance it’s shorted. The amount of current your radio is using will indicate if it’s shorted. To determine how much current the radio should be using calculate it by solving P=E*I where P is Watts, E is volts and I is amperes. You can get watts from the back of the radio or the wiring diagrams, the volts is from your power source which should be matched to Philco’s recommended operating power. With that operating current value in hand put an ammeter in series with the power supply and measure. If the current is normal then don't worry about the tube, it's likely operating normally. If the current is too high then this explains why your tube may be getting hot.
(This post was last modified: 08-28-2016, 10:43 PM by IowaPhilco.)
Thanks for all the info and suggestions. Hopefully this weekend I can get back to it and check a few thing out. I did notice a few "cold" solder joints from prior to me repairs, so I'll address those issues as well. Still trying to decipher the schematic out as my part locations are not quite the same. I know there were several different chassis runs. Some of the part reference numbers are not very clear. I do have one resistor that I cannot explain its location vs. the schematic. I know I have seen it on others photos of their chassis so It is most likely a run change. It is a 1meg. and runs from center terminal of cap block #10 to the 4mF electrolytic.
Looks to be #19, supplies the dc voltage to the screen grid for the 2nd detector. Some of the block capacitors may have an unused terminal used for a tie point. .09mfd is an odd value so .1mfd is the proper subtitute
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: 08-31-2016, 09:22 AM by Radioroslyn.)
Yes that would be resistor #19. Block cap #10 is a twin 0.09uF block with the leads between lugs 1&2 and 1&3 with 1 being ground. The two cap#10 caps show up in different places on the schematic even though they are physically located together. I know because I wired mine up incorrectly when I first stuffed the block but eventually tracked it down.
As long as the plates inside the #80 are not glowing red, then it's probably fine, though the filter caps and any bypass caps should be replaced at a minimum before operating the set for any length of time. But since a model 80 is a four tube set it doesn't take much more effort to replace them all.
Regards
Arran
Thanks for the tips. I was able to work on it last night for a little while.
Arran, the plates on the 80 never got to a glowing stage but I'll keep that in mind at the next power up.
Bob, thanks for the links to Ron's repair tips. I had seen the modification for the gimmick and the 2meg resistor change. I was going to wait on those until all other work was done. I missed the tip on resistors 9 and 11. That was timely advise. I'm currently in that section and was going to replace #11 the 16k and then noticed the wattage. Back when I first repaired this (22 years ago) I replaced that resistor with a 1 watt carbon composition, rookie mistake. Ron's recommendation was a three watt. I didn't have a three watt so I made a replica dogbone with 3 resistors in parallel. I have a 33k and two 56k 1 watt flameproof resistors inside a tube filled with epoxy. Is my theory correct that 3; 1 watt resistors can handle the same power as a single 3 watt? Actual resistance measurement was within 1% of rating called for. I still need to paint it though. I also missed there fact that cap block #10 was shown twice on the schematic, now it all makes sense. I don't know how many times I tried to trace this out and still missed that.
Should you ever burn your finger on an 80 tube you must turn off set and put it away, immediately place thumb against a bottle of an ice cold beverage of your choice. Repeat as needed.
Thanks Paul, I haven't burnt my thumb yet, but I was able to practice your first aid advice a few times.
Attached are a couple photos of my attempt at replicating the dogbone resistors. #11 the 16k I posted a photo of earlier is painted. A little glossy and not a perfect color match but...
The second photo is of my attempt at molding the #19 1meg resistor. The process is sound, I just had mold release issues. In the second photo on the left side is the original, on the right is the copy. Still need to clean it up and paint it.
Here is where I'm at now. Both electrolytic caps have been replaced. All of the Bakelite block caps have been rebuilt. resistor #9 has been replaced with a 13k as suggested in the link to Ron's website. Resistor #11 has been replaced as described in earlier posts. The radio has been on and playing for a couple hours now. The 80 tube is no hotter than before and seems normal. Resistors #9 and #11 do get quite warm, but not hot. Resistors #26 and #22 measured within limits so they were left. I did voltage checks on all tubes following the Riders data. Here are my results.
119vac line, radio turned up all the way and on a 55 kilohertz station
#80 5v at filament 328v at plates.
#42 output tube 6.28v at filament, 256v at plate, 267v at screen, 16.59v at control grid, 0v at cathode.
#36 2nd Det. tube 6.25v at filament, 86v at plate, 26.6v at screen. no control grid, 0v at cathode.
#36 Det-Osc, tube 6.27v at filament, 259v at plate, 108.8v at screen, no control grid, 9.37v at cathode.
The transformer is a little low but I think it is ok, right?
The other voltages in bold are quite a bit off from what was listed, I have taken into account the correction for the screen voltage misprint of 165v in the Riders supplement. Still quite high over the corrected 80 volts.
Any suggestions on where to go from here would be appreciated.
but eventually tracked it down.
