41-250 Restoration - Printable Version
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RE: 41-250 resistor size - bridkarl - 08-05-2023
This has the original 84 tube. As I’m reading the schematic the positive side of the 12mfd capacitor
goes to pin 5. The schematic symbol in the Philco schematic doesn’t match the tube data sheet I have. More to think about
RE: 41-250 resistor size - RodB - 08-05-2023
The cathode of an 84 is pin 4. Pins 1 and 5 are the heater pins. Connect the positive of the 12 mfd cap to pin 4 and the field coil lead. One of the first things I do to the schematic is number all tube pins (in pencil).
RE: 41-250 resistor size - bridkarl - 08-05-2023
Thanks. I was having a time figuring out the tube diagram.
For some reason this person connected a cap to the 41 tube. Plus two 20 mfd caps - one connected directly up to the bakelight block. I’m not sure how this even was working. And two 20 mfd caps in series.
I’ve got an 8, 12, and 16 mfd cap on order so I can make this all correct. Parts 27 - an 8-16 dual cap and 62 on the parts list - 12 mfd
Probably too much detail but for the benefit of others -
The lesson here is that working doesn’t mean right. The second lesson is put in a fuse.
I did that when I got this. Third lesson - don’t trust other people’s work
Clearly the radio was powering up so it’s fundamentally sound. My thought is that some of that crumbling wiring just shorted out.
RE: 41-250 resistor size - bridkarl - 08-06-2023
My 41-250 works - and I recapped it according to what was there. It appears to be wrong. I started looking at this and see it’s all miswired.
I plan to recap this with the correct values. I still need to figure out where the 8mfd goes to ground. The chassis I think judging from the schematic.
I plan to assume going forward that every radio I touch has been wired incorrectly.
I’m sort of wondering how this even worked wired like this. I plan to take a week while I wait for my parts and consider this further. There is a 5Y3 substitution for the 84 but I don’t understand yet what difference that would be making in the circuit.
RE: 41-250 resistor size - Ron Ramirez - 08-06-2023
Did you know you can find the 41-250 service information, along with all other prewar Philcos (and many postwar Philco models as well), right here on this website?
And they are high resolution scans, also, not low-res like you get on that other site you obtained your schematic from.
Just click the Philco Library link at the top or bottom of any page in the Philco Phorum.
Then, hover your mouse over Service Info on the top banner, and pick the year range you need.
From there, pick the schematic you need.
Simple as that
RE: 41-250 resistor size - MrFixr55 - 08-06-2023
That may be a typo somewhere. The 12 uF cap + lead and the input to the field coil (also serves as a choke) should be going to the cathode of the 84, Pin 4 per the RCA Receiving Tube Manual RC12 (1934). Pins 1 and 5 are the filament (heater), which is insulated from the cathode. Pin 5 will either be chassis ground or 6VAC above chassis ground, as this tube is heated by the same winding as the rest of the tubes are heated. So, if the input to the filter is actually connected to Pin 5 instead of Pin 4 of the 84, then the radio will not work.
The "other guy" put 20uF caps in series, likely to lower the capacitance to somewhere near the spec. Back in the day, electrolytics were rated - 20% / + 100%, so a 12 uF cap could be anywhere between 10 and 24 uF. I don't think that using 20uF caps in the power supply would be too much of an issue. It would raise the voltages a little. The only issue here is that both RCA and Sylvania indicate the cap value for a cap input filter is 4uF.
RE: 41-250 resistor size - bridkarl - 08-06-2023
I know. I just included it by habit since I’m used to getting yelled at on Facebook when I forget to include a schematic. I’ll grab that schematic you suggest. Thanks.
RE: 41-250 resistor size - Ron Ramirez - 08-06-2023
Ouch. Sorry you were getting yelled at, that is never good.
I just thought this would help, since it is the factory Philco data - and scanned at high resolution.
RE: 41-250 resistor size - MrFixr55 - 08-06-2023
A 5Y3 or an 80 is NOT a direct substitute for an 84. The 80 and 5Y3 are directly heated cathodes and their power must come from a transformer secondary winding that is isolated from ground. The 84 has an indirectly heated cathode that is insulated from the heater, therefore the heater and the heaters of the other tubes can be grounded at either side or by a center tap. The 84, 6X4 and 6X5 were commonly used in Automotive radios of this vintage.
The only way that you can substitute a 5Y3 for an 84 is by also replacing the power transformer with one that has a separate 5V heater winding that is well isolated from ground, as that winding will be at B+ potential. Most sets of this vintage other than Philco used an 80 or a 5Y3 (the modern (?) octal base replacement for the 80), as the 5Y3 had a much higher available output current. Philco possibly used the 84 in these vintage radios, as their output power was likely similar to a car radio, Philco was a major manufacturer of car radios and used the 84 for them, therefore they could get a volume discount for the tube, and since there was one less winding on the transformer, it was cheaper to manufacture, all a win-win for Philco.
The "Now" drawing of the 5Y3 circuit is incorrect and will not work. A cap can't couple DC.
The "correct" version may be slightly incorrect, though much better. The junction of the - terminal of the 12uF cap and the 146 Ohm resistor goes to the center tap of the HV secondary of the power transformer. this connection is NOT grounded. The - terminal of the 16uF cap and the 15 Ohm resistor is at chassis ground. This series of resistors between chassis ground and the B secondary center tap was a common method to get the bias required for the audio output tube and some others.
The filter circuit as drawn in the actual schematic 41-250 works with either the 84 or the 5Y3.
RE: 41-250 resistor size - bridkarl - 08-06-2023
Thanks. This doesn’t have the stock transformer in it. I assume this was done at the same time as the 5Y3 was installed.
Once I get my new parts in I’ll go carefully through this according to the schematic. I haven’t gone through the candleohm resistor to check that out. As I said the radio was working when I got it - most of the caps had been replaced- I’ll have to check the voltages later and see what’s what. It was sort of a lazy rebuild as they didn’t replace any wiring, left some cracked resistors in place, etc.
I appreciate people putting up with my questions. I’m really trying to do this correctly. I’ve done many repairs but this time I’m really digging into this above and beyond.
RE: 41-250 resistor size - MrFixr55 - 08-06-2023
Ron,R, I am bad that way too, because I have been using and keeping N/A schematics for about 14 years now. For Philcos, I have to get in the habit of grabbing them from the Phorum library asn they are very clear factory schematics.
Your work has helped preserve this hobby and Philco history. I hope that you are staying as healthy as you can. Prayers continue!
RE: 41-250 resistor size - Ron Ramirez - 08-06-2023
> I appreciate people putting up with my questions.
We're here to help.
> I hope that you are staying as healthy as you can.
As much as I can, yes, thank you.
> Prayers continue!
Thank you, that means a lot to me.
RE: 41-250 resistor size - bridkarl - 08-06-2023
Thanks Ron. My grandfather was originally from Ferdinand - 10th generation Hoosier here. Appreciate your advice. Stay healthy.
The more I look this over the easier it’s getting to visualize from the schematic to how the radio is actually laid out.
RE: 41-250 resistor size - MrFixr55 - 08-06-2023
@Bridkarl, you will get this to go. In terms of the "correctness" of having modified the circuit, this may have occurred during WWII when new radios and even replacement tubes were not available (although this radio should have been rather new). For the lack of being able to get an 84, replacing the transformer, so the tech could use a 5Y3 may have been a bit extreme but, hey, you do what you can do. Bottom line here, if you look at the 41-250 schematic, duplicate that exactly, except hook up what ordinarily went to Pin 4 of the 84 to pin 8 of the 5Y3, you should be good.
RE: 41-250 resistor size - bridkarl - 08-06-2023
Thanks for the encouragement. As it sits I have a 12 mfd and a 16 mfd connected negative to each end of the candleohm resistor.
I have the positives connected to lugs 2 and 4 of the terminal strip - counting from the top with the chassis lying on its back.
I connected the positive of 20 mfd cap to pin 8 of the 5Y3 with the negative just alligator clipped to the chassis.
All I’m getting is a buzzing noise. I’m just going to think about this for the work week and try again. There’s something I’m missing about the 5Y3 setup.