[jrblasde]

Good evening, folks! It's been a couple of months since I completed the restoration of the cabinet on my 46-480. I've been working intermittently on creating a more readable schematic than the scan available on the Philco Radio Library. Not only are a few of the values too blurry to read, but I've noticed a handful of discrepancies.

1) In Section 3, the overall schematic on page 113 of the document shows resistor R300 to have a resistance of 4700 (in other words, 4.7kΩ), whereas the parts list on page 114 indicates that R300 has a resistivity of 47,000 (in other words, 47 kΩ). Furthermore, the given part number is 66-3473340, which is the part number for a 47 kΩ +/-10%, 1/2 watt carbon resistor.
           

2) In Section 4, the overall schematic on page 113 of the document does not show a grid resistor on pin 8 of the 7F8 tube, whereas the partial schematic on page 109 of the document does.
           

3) In Section 4, the overall schematic on page 113 of the document is missing an instance of the S401A switch, whereas it may be seen on the partial schematic shown on page 109.
           

Anyway, I have combed through all of the available paperwork and here's the resultant schematic (also see attached PDF). I now intend to comb through the chassis in its current state to verify that the schematic matches the as-built condition of the radio. Some of the capacitor values in the IF cans were not readable, so I'd like to confirm those by seeing what is physically installed. I also had to make my best guess on a few of the wires crossing over each other on the schematic--do they intersect or not? And, finally, I'd like to verify the pins on the wafer switch. Many of the pin numbers on the schematic were not readable.
   

I'll note that not everything is laid out exactly as you'll find it on the Philco schematic. I rearranged Section 2, for instance, to flow from left to right. I've also replaced older notations (for example MF and MMF) with modern-day equivalents (µF and pF, respectively). I've also moved the filaments of the tubes to the power supply section of the schematic (many other Philco schematics, for instance the 49-906, do it this way). You will also notice that tubes with multiple diodes and/or triodes within the same envelope (the 6H6GT/G and the 7F8) are shown as split. This is just how I've always drawn them.

I will follow up with a revised schematic after I parse my way through the chassis. I also plan to create a new revision depicting the replacement equipment. I'd like to add a 1A fuse to the power section for instance. I already have this depicted in revision 1 of my file. I also have the safety capacitors for the AC line depicted in revision 1.

[radiorich]

Hello Joseph,
Wow that is great news that schematics looks very well done !

Sincerely Richard

[jrblasde]

Thank you, Richard! The biggest effort is to create all of the symbols which don’t exist in much of the newer circuit software. It was a labor of love, but I’m happy to share what I find. I plan to get this schematic updated with all of my findings after going through the chassis. I’m always afraid to start disassembly until I am absolutely confident that I have the documentation to put it back together correctly.

[morzh]

I work mostly in DxDesigner (recently had to switch to Altium, which I don't like), and in it (as well as in OrCAD, which I have not used for a long while, but know fairly well) a symbol creation is a snap.
I did this about 1-1/2 years ago. In DxDesigner. The tube symbol took....5 minutes?

   

[jrblasde]

Thank you for sharing! I’ll have to investigate my options. I’ve long been an avid supporter of the Linux operating system and the free software paradigm supported by the GNU GPL. Consequently, I’ve taken to using KiCAD for schematic and PCB design. The software’s primary focus is on PCB development, and so the schematic is more of a means to an end. I do find that I have to fuss with the software sometimes to get a clean and well-styled schematic.

[morzh]

I used KiCad briefly; I never created parts in it; just had to quickly fix a problem in an old board done before me.
I know that PADS Logic, unlike DxDesigner, was a free tool, that CAD software, then Mentor and now Siemens supplied for free.
As I remember (I have not used it for quite a while) symbol creation was not complicated in it either.
Especially, considering that we do not have to create a parameter database that would always accompany a real part used in real schematics: P/N, internal P/N, price, PCB footprint name, manufacturer, etc etc.
Pretty much graphics with pins.

[jrblasde]

I'm still combing through the chassis, but I just found something which doesn't match the prints. R305 connects to pins 5 and 7 of the second IF 7H7 tube. Every mention of this resistor in the manual indicates that it is a 150 Ω resistor. Even the listed part number would hint that it's a 150 Ω resistor. However, I see a resistor marked brown-grey-black-silver (15 Ω with a tolerance of +/-10%).

Does anyone have a 46-480 who can double check this resistor?

   
   
   

[jrblasde]

I also settled the question about R300. The schematic indicates that it should be 4.7 kΩ whereas the parts list calls for a 47 kΩ resistor. I can see yellow for the 4. The violet band looks more brown to me, and the third stripe is not visible. I used an ohmmeter, and it measures about 4.9 kΩ. I’m betting that it’s a 4.7kΩ with a 10% tolerance.

[jrblasde]

Good afternoon, folks! I've gotten a lot covered since I last provided an update. First, I created a separate post to ask about replacing the power transformer. Per the advice of many others, I was encouraged to salvage the original unit. It worked perfectly after some cleanup, repainting, and sleeving the cables.
   

Next, I began combing through the chassis to verify the circuit. I was able to make MANY corrections to my schematic. I had noted in one of the earlier posts that I wasn't able to read some of the pin numbers on the wafer switches for band selection from the Philco schematic, so I have now gotten those corrected. I also corrected a few wire crossings on my schematic--sometimes I couldn't tell from the Philco schematic if two overlapping wires formed a node or not, so I had to give it my best guess. I corrected three of them that I had gotten wrong.

I have an answer to another discrepancy I noted earlier. I showed two screenshots, one from the overall schematic on page 113 of the documentation and another from a Section 4 schematic on page 109 of the documentation. The overall schematic did not depict a grid resistor connecting to pin 8 of the 7F8, whereas the other schematic did. I have confirmed that there is a 10-ohm resistor, per the section 4 schematic. Thus, I have added it into my schematic.

I have also determined the production run of this radio. There were eight listed production runs for the main chassis and nine production runs for the RF chassis in the Philco documentation. This particular chassis has the modifications indicated for production run 8 of the main chassis and production run 9 of the RF chassis, so it was among the last of the 46-480's to ever be manufactured. I've also determined that three capacitors have been replaced at some point or other, but the work was done very cleanly. The guy from whom I bought this radio mentioned that he "inherited" it when his father passed away. He said that his father was a collector of older radios, and he didn't want to throw them all away.

It took me a very long time to make my way through the RF chassis. The reason is that there is a complex assembly of four double-sided wafer switches for the band selection, and most of the components are woven around and in between the wafers. I have no good way to convey this in words, so here are a few photos.
   
   
   

I dread rewiring this portion, because it is VERY densely packed. This assembly is also obstructing the underside of the 7F8 socket and the underside of the C404A/B/C trimmer caps. But I know that I will have to rebuild it, because there is evidence of mice having chewed on a few of the cables which connect to this wafer switch assembly. There's also two paper capacitors embedded into the assembly that I need to replace, and a mica capacitor that I can see with a broken lead.

As I made my way through the circuit, I've created drawings to depict the physical wiring. I created four drawings--one for each section of the schematic. I know that I will have to do a fair amount of disassembly to get this chassis cleaned and all of the components repaired/replaced, so I needed to make sure that I exactly how everything is placed.
   

At this point I have confirmed the values of about half of the resistors and only a few of the capacitors. Many of them I need to get to as I remove them in order to see the color codes. I will update my schematic with corrections to the values if I find any during disassembly. I've attached the schematic as it currently stands, both here as an image and as a PDF attachment.
   

[MrFixr55]

Hi Joseph,

Fantastic job on the transformer. When working on the RF Subchassis, think of the factory worker who actually assembled it. Sometimes, it is more difficult to take something apart than it is to reassemble it.

[jrblasde]

You make a great point! I’ve needed to be very delicate in disassembling, so that I can reverse engineer the schematic from the circuit. Surely now that I’ve got the schematic sorted out and the wiring documented, it won’t be so bad to rebuild it.

[Arran]

One other thing to be careful with whilst you are rebuilding the RF section is not to accidently change the shape those large coils made out of the thick wire. You have probably realized this but those are for the FM section, and there is likely a procedure for adjusting them, but I think that they are very fussy and best left alone, unless there is some component you need to replace under them.
Happy Christmas
Happy New Year
Arran

[jrblasde]

Correct, yes. Those are part of the FM section. They control the width of the dial across which you tune. If memory serves correctly, I believe that more spacing between the coils equates to using more of the tuning dial and vice versa.