I’m needing to replace 3900 ohm resistor on the output tubes of this 41-250. The resistor is cracked in two.
I have a 3900 ohm 1/2 watt metal oxide replacement unit. The schematic is silent about the required wattage. Will this work or is a higher wattage required? I’ve enclosed a pic of the existing resistor.
I’ve just been replacing lots of this rubber wire while I rewire to get the lights to work.Another week or so and I should have all this done. Using 20 gauge single wire which seems to fit properly as I’m trying to follow the original dressing of the wiring.
I’m seeing no issues with this restoration - aside from some snarky Facebook comments so I cancelled my account. On this model it seems common people simply rewire the lights to the nearest tube socket rather than tracing out the wiring and replacing it - which involves disassembly. Not sure why people get mad about doing things right. Easy enough to find that 1.8 watt resistor under the metal cover. People are lazy I guess.
The radio seems to be working well. I need to replace the last few bad caps and resistors plus the block cap plus the last pieces of bad wiring
Hi, I'm just getting ready to restore a 40-180 that has two 41s in push-pull with a 3900 ohm resistor between the screen grids and the parts list says it's a half watt. I have to replace mine too.
That 40-180 schematic looks like it’s identical to the 41-250 judging from the 1940 rms yearbook.
in that section with the 41 tubes. Sounds like a 1/2 watt is sufficient.
I don't know why people on Facebook, etc. have to act like jerks. A restorer tries to make the set as original as possible. There are several ways to do things. Don't let anyone criticize your good work!
Check all of the resistors involving the grid and screen circuits. Instead of using a phase invertor or a cathodyne phase invertor, Philco uses a novel method of obtaining the inverted phase for the 2nd 41 in the push pull output. It is pulled from that screen resistor. Check the 41s for shorts and matching. Check the output transformer also. If an output transformer is open or disconnected and the radio is fired up, the screen current goes off the charts. You can actually see the screen grid glow, almost white hot. Had this happen to me. Almost lost a cool Philco globe shaped 42 from an open output transformer.
Max screen current for a 42 is 6.5mA or 0.0065A. If the voltage drop across the resistor is low, then the dissipation is also low.
Good luck with the restoration. When you got the output stage right, this radio should sound great.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
That’s very gracious of you to say I do good work. I try to be humble and just consider it workmanlike.
I’m doing as you suggest in regards to the audio section. The 3900 ohm resistor is cracked in half. That and the rest of the resistors are being gone through.
Right now I have audio but it appears to my ear to be half of what it should be - probably that resistor.
The total current draw on the radio is around .41. I need to check within the set more specifically.
I don’t know why people act like jerks either. Lots of people seem lazy and get mad that people take the time to do it right as opposed to doing it right now.
In any event I’ve been going through this rewiring pilot lights, pulling and replacing rubber wiring, the usual stuff. There’s a certain amount of disassembly to get to things. You won’t be getting to some things without a nutdriver. I have the tools. I think lots of people don’t and subsequently get frustrated and take a lazy approach like wiring the pilot light to the nearest tube socket.
Yep. That resistor and the others are going as soon as my shipment from justradios arrives. There are several 470K resistors on this which are all testing out of spec.
I clipped that one to remind me not to forget to do that.
I’ve spent two hours on this. I’ve been rewiring the pilot lights - one is totally trashed inside so I need to find a new light or a new pigtail.
I thought that the lead from B10 on the band switch went to the 7C6 but there’s not a 1.8 ohm. From the 1941 RMS Yearbook it seems that this is part 67.
Looking under the tuning coils I found what seems to be the correct resistor. I’ve soldered the wire from B10 to the top of this resistor since I understand it works as a fuse.
Lights still don’t work but I think this is due to bad socket ? The good news is that the radio seems louder now since I replaced more questionable parts and wiring. Seems to be working fine except for the lights.
(This post was last modified: 08-02-2023, 10:35 PM by bridkarl.)
I merged your two 41-250 threads together. Please keep all of this 41-250 electrical restore posts within the same thread. Makes it easier for folks to follow, and easier for people in the future to find and learn from others. Thanks.
Yes, the radio should be a lot louder if the 3900 Ohm resistor that you replaced was open. If it was open, no audio signal was getting to the other 41 and the screen would be floating.
Are the sockets bayonet and spring loaded or are they screw-in? If they are the bayonet style, you may be able to get the internals out of a dashboard light socket from a 1960s car. There are many companies that sell parts for 1960s era Ford Mustangs, as there are likely 100,000 or more still on the road. The contact, spacer and even the spring from the dash light socket may fit the original shell on the Radio. If a screw-in, this may be a little more difficult to get a look-alike part.
Congrats on your good work.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
The issue is that the rivet is gone. I see that renovated radios sells a pigtail assembly so that may work as a replacement.
I looked at the 1.8 ohm resistor yesterday. Tested at 4 ohms - then it just crumbled from touching it a totally burned inside. So I’m replacing that. Basically just going through and replacing bad wiring. Tomorrow I plan to replace some more resistors.
This looks like a 2.2 megaohm resistor and 1 megaohm - parts 29 and 46. From the schematic it doesn’t appear that they both are on 7C6 first audio.
I’ll have to check this further. I’m reading the wire going from the 2.2 megaohm resistor as the blue wire to the IF noted in the schematic.
In any event the radio is working very well. As I replace more parts and wiring it appears the sensitivity is increasing. Waiting on a parts delivery to finish this up. I think I’ve gotten most of the ratty wiring out of this.
The last two photos are not Philco but I found this 1936 GE today as a display piece in a local shop. Not sure the guy wants to sell, but it’s interesting. Seems mostly complete. I offered the guy $50.
Here’s another fine mess. I got a 41-255 that was working. I got it repaired, checked it out briefly, set it aside. It came mostly repaired fairly recently and the repairs looked OK.
Checking today because I couldn’t trace a loose wire on my 41-250 I see the 41-255 blowing fuses. Pulled it and put it on the bench. The previous owner did some strange stuff I’m seeing.
Looks like I need to pull out all the electrolytics and put in the correct values. One was wired right to the bake light holder???? 20 mfd caps in series ?? Not really sure how this was working. I’d installed a fuse so that saved my bacon on this.
Since I have these two together on the bench I plan to just duplicate the repairs I made in the 41-250 - these are basically the same radios. If you read my WTB post I need to find the plugs for the speaker. These are both damaged one beyond repair. The power supply setup is the same so that should be ok.
The 41-250 is working great. Just a few more parts to install. This is fun.
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