I've been working, off and on, for a couple years on Grand Mom's old 41-280. Replaced all the paper caps; discovered that the speaker winding for the power front end was open and replaced the speaker with a matching one purchased from a forum member here; discovered that the audio output transformer was bad and replaced that, but still couldn't get sound.
A friend with more tube electronics experience than I (my EE schooling had moved on to transistor theory when I got there) recently checked all the tubes, and discovered that the radio can be manually tuned in the push button mode, but the oscillator doesn't output in the other three band selection positions.
So currently I have a few AM stations programmed to the push buttons and it's working fine for that. It's producing wonderfully rich sound for a single-speaker AM radio! But without dial-tuning I can't repeat the joy I experienced as a kid, scanning across the shortwave bands and picking up who-knows-what overseas stations.
It's frustrating to have the radio so close to restored (electronically... still some cabinetry work to do) and I am stuck for ideas. Any suggestions from the forum on what to test, or to probe for, or even what to shotgun replace, to remedy this problem?
Mark Lipford.
Welcome to the Phorum!!
Here's the
schematic link for those who may have thoughts on this problem.
I might add this link as well for the schematic as it covers the front end of the radio. Welcome as well.
First, if you have not well cleaned the band switch decks and the pushbutton switches I would start there.
Best, Jerry
http://www.nostalgiaair.org/pagesbymodel...013415.pdf
(07-05-2015, 03:11 PM)jerryhawthorne Wrote: [ -> ]I might add this link as well for the schematic as it covers the front end of the radio. Welcome as well.
First, if you have not well cleaned the band switch decks and the pushbutton switches I would start there.
Best, Jerry
http://www.nostalgiaair.org/pagesbymodel...013415.pdf
Thanks for the links, but I do have schematics which were useful when I was re-capping. I did clean the rotary band selector switch contacts as best I could without disassembling the switch itself.
Because I don't think I'm the first person who has worked on this radio (although my mother swears no one has), I ohmed out all the connections to the switch in all four positions. Other than finding one error in the schematic, everything checked out OK.
The schematic links are meant to help those who are trying to answer your questions as well as for you if you did not have them.
If you can use the pushbuttons for preset AM stations but cannot receive anything on any of the manual tuning bands, you probably have a bad oscillator coil, part (13). The pushbuttons have their own individual oscillator coils so if the pushbuttons are working and manual tuning isn't, this is where I would look first.
Thanks Ron. I was hoping to avoid having to pull that many-terminal'ed device out of the circuit for testing, but you're right that's the best place to start. Cosmetically, it looks fine, for what that's worth. Hopefully will get to it this weekend, and then maybe I'll be posting in a want ad for a replacement coil.
Well...on the bright side, Philco made a bazillion of those 41-280 sets, so you shouldn't have any problem finding a replacement coil. Other similar Philcos include the 41-250, 41-255, 41-285, 41-287, 41-290, 41-296.
Well... I've learned a lot reading this forum, and acquired a replacement speaker from one member, so I feel compelled to close out this thread with an accounting of "how it turned out". Perhaps others can learn from my experience. It wasn't a bad oscillator transformer and fortunately I figured that out before I removed it from the circuit.
While ohm'ing it out in-circuit, looking for anything other than a fractional ohm between terminals, I noticed that cap #31 was connected to the wrong terminal on the terminal block mounted to the chassis side wall. One pin off, resulting in connection to chassis ground instead of a leg of the 1st I. F. transformer.
Fixed that, and voila, manual dial tuning works.
Now, I replaced that cap back when I recapped the unit. So -- although I'm not the first person to be doing repairs in this unit and it didn't work when I got it -- I have to conclude that I misplaced that cap when I replaced it. A real head-shaker, since I triple checked every cap I swapped out.
I used to tell the scouts in my BSA troop that every mistake is a learning opportunity, so here I'm concluding that comparing before and after photos after *every* component replacement is the rule from now on.
I'm refinishing the cabinet next and have a question about speaker grill cloth, so I'll post that on the other forum.
Lipfordm don't feel bad, we all do that. Glad you have it working.
Jerry