First post! 48-200 Code 121 differences? - Printable Version
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First post! 48-200 Code 121 differences? - J Paul - 04-14-2011
I have a 48-200, code 121. The Philco Service Bulletin and the Riders schematic I found online both cover code 125, but the Riders does mention the tube differences (code 121 has 35Z5 and 50A5 instead of 35Y4 and 50L6). Are there any other differences I should be aware of?
Example: in my radio, the cap C302 (from 14B6 pin 5 plate to B-) is not original and was replaced with a .05 µf cap, but the code 125 schematic specifies a .1 cap. Is the .05 correct for a code 121 model, or did the repairman make a mistake?
I forgot to mention that this is my first post on the Phorums - I joined months ago, but never got around to saying anything until now!
Re: First post! 48-200 Code 121 differences? - Ron Ramirez - 04-20-2011
Well, we're glad you joined in on the fun!
Very interesting. I see production of the 48-200 and 48-214 began with Code 125 instead of the usual Code 121. In the prewar days, Philco radio production usually began with Code 121 and then went up. In this case, they began with Code 125 and then went back to Code 121 later.
Anyway, from what I found in a quick search, the only differences between codes 125 and 121 are the output and rectifier tubes. And then there was a Code 122 which used a different oscillator coil.
Long story short...C302 should be 0.1 uF. This is the AVC filter, and in many sets this cap is .05 uF so this may be why some repairman installed a .05 uF cap. Or maybe that's all he had in stock at the time, and it made the radio work again.
Re: First post! 48-200 Code 121 differences? - J Paul - 04-21-2011
Thanks for the info, Ron! I looked at a Sylvania tube guide; they're practically identical except for the bases, so I can see that no other changes would be needed. I'd be willing to bet that Philco got such a deal on the tubes that they switched to.
I'll probably be hanging around here quite a bit. I've accumulated 6 radios so far - 3 are Philcos. I already seem to have an odd attraction to them. (Maybe it's a family thing - my mom worked at a Sylvania tube plant, and I understand they made a lot of Philco-branded tubes.)
RE: First post! 48-200 Code 121 differences? - ntsc525 - 08-30-2020
I know this is an old thread, but I'm reviving it because I'm now working on my second 48-200 Code 121 radio, and both of them had .05 uF original Philco capacitors in them. The first one worked just fine with that arrangement. The jury's still out on the second one, because it's not done yet, and has some issues.
Trying to Google info on the Code 121 is what brought me here.
What I didn't know and learned from this thread is for this model, the Code 121 came AFTER Code 125, so if the 121's have .05, I'm going to assume Philco made that change later, and that is the correct value for that run.
If anyone else has been inside other 48-200 Code 121's and finds an original C302, please post what value it was.
Dan
RE: First post! 48-200 Code 121 differences? - morzh - 08-30-2020
NTSC,
You are better off starting your own thread.
RE: First post! 48-200 Code 121 differences? - ntsc525 - 09-24-2020
For future reference, in case someone else finds this thread and is confused, I came across yet another Philco 48-200 Code 121 and C302, the AVC capacitor, is indeed .05.
That's three Code 121's (plus the OP's) that have .05 for that value, while the schematic which covers the Code 125 shows .1uF there.
For the record, I put a scope on the AVC line with my .047 in place, then put another .047 in parallel (approximating .1uF) and didn't see a difference in voltage or operation of the AVC.
I think if the original Philco cap is in there, you can trust the value if it's .1 or .05, and if someone had already replaced it, chances are it was a .1 in a Code 125, and a .05 in the Code 121.
Somewhere out there, I believe, is a 48-200 with .147 uF for the AVC, and that works also. That's because after recapping and checking the schematic, I came up one .1uF cap short and soldered it in, not realizing that because of where Philco had placed the AVC cap, it wasn't obvious that the .05 I'd replaced was actually in. I'm pretty sure I stuck a .1 in parallel, and then sold the radio. Didn't seem to make a difference, and the buyer never complained.
Sorry about the "necro-post", but I wanted to close out the question about C302 for future Googlers out there. I didn't realize until after posting my question, that I had a junker in the garage of the exact same model and version that was ready to answer my question!
Dan
RE: First post! 48-200 Code 121 differences? - Radioroslyn - 09-24-2020
I think what you'll find is that C-302 does 2 things. It filters negative voltage on the avc line. But it also maybe acting as part of a timing circuit thru the 2.75M back to the volume control. In this capacity changing the value won't change the voltage but will change the lag time before the avc voltage shifts from high to low when going from a weak station to a strong one.
Personally I wouldn't give much thought to the minor differences between the values of the two cap.