I've had a Philco 49-901 "Secretary" around here for a couple years or so, sitting in a corner, gathering dust.
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attachment=26800]
I should mention that, for some strange reason, this radio has acquired the notoriety of supposedly being a "Secretary's Radio" which was operated with the foot. This is false; it is fake news; and how this false rumor started, I have no idea. It was never intended to be operated with a foot. The large roller was always intended to be used with one's hand, not foot. But I digress.
Recently, I decided I would try to rebuild this little five tube AC/DC radio and get it going.
The recapping went fairly smoothly. When I made it to my final step, which was rebuilding the three-section electrolytic, I found that I had no 22 uF electrolytics but had several 33 uF, 200 volt Panasonics on hand. So, I used three 33 uF electrolytics instead of one 33 uF and two 22 uF units.
After doing a quick and dirty IF alignment and getting the six preset channels aligned to stations (660, 710, 740, 810, 990 and 1280 kc) with the help of my signal generator, I tried it out with my home AM transmitter (SSTRAN).
Unfortunately, it is not doing well.
The signal is weak, and the sound is horrible.
All tubes have been tested and two which were weak were replaced. And, again, all paper and electrolytic capacitors were replaced.
Here is a sample of its horrible, garbled sound:
If you want to follow along in an actual service manual, you can find that information
HERE (in the
Philco Library).
Thanks in advance for any help.
It shouldn't take too much to connect a known good speaker to it. But you have to stop tuning in the garbled music stations.
hello Ron ,
have you checked out the speaker as Rob says?
Sincerely Richard
Ron
You have hum superimposed on sound. Find out where the hum is coming from.
+1 on the speaker. It could be the cone itself
On these loctal sets, I take a safety knife and scrape each pin on each tube until they're nice and shiny. Then follow up with some Deoxit in the sockets, taking the tube in and out a few times. I'm sure scraping the pins on loctal tubes is SOP for you already though, Ron.
You also might want to double check and re-solder if necessary, the antenna connections. Those flimsy wire antennas Philco was using at the time are very finicky if not making a solid connection. I've had that cause garbled sound on several radios over the years. If the antenna was disconnected, I always scrape those wires too before resoldering to make sure all the enamel coating is off of the wire.
I feel kind of silly offering what are probably obvious things to check to you Ron, as you've been doing this far longer and know far more about Philco's than I ever will! And I mean that with the greatest respect and admiration.
Why would anyone think this radio was intended to sit on a floor is beyond me, that would assume it would sit under a desk with the sound projecting at about ankle level. With loctal tube I must be luck, I've seldom had contact problems, but then again I have a habit of buffing the pins with 600 grit sandpaper, or 0000 steel wool, if I think they look off. The only problem I had related to loctals was with some wide wafer sockets in an early 40s Transitone model, most of the others are molded.
Poor performance could be faulty mica caps in the IF cans, or a gassy tube, particularly the audio output tube. Could also be a drifted resistor, but I think you would have found that with the recapping job, the plate load resistor on the 1st audio tube could cause this.
Regards
Arran
Thanks, guys. For those of you who are wondering Why doesn't Uncle Ron automatically know the answer and why is he asking for help?, I must tell you that chemotherapy alters one's brain permanently. While I have been off chemo for a year now, save for the three days last month that I took chemo pills until they started making me sick, the effects remain.
Greg, I especially appreciate your very kind comments - thank you so much. And I think perhaps you may have hit the nail on the head with the antenna terminal suggestion. After reading your post I remembered that a disconnected or poorly connected loop antenna will cause such garbled reception with hum modulation. I'll look into that first.
The comments about the speaker are also worthy of checking into. This was the first thing I had thought of, especially since the output transformer is not original - it is a Stancor universal replacement. I have a spare 4 inch speaker with proper output transformer, and I will try it later.
It's funny (strange) - I had set one of the presets to the local Jasper station at 990 and it was coming in at first, but when I made the video, it would not. Ditto a talk station in Evansville at 1280 which I had set another preset to. All it would receive in the video was my home SSTRAN at 660 kc, and that was very weak and poor. And, yes, I do play music on my SSTRAN, and will continue to do so.
Forgot to mention: I did scrape all the tube pins with a knife, and also sprayed the contacts of each tube socket with DeoxIT. The volume control was also given a shot of FaderLube.
This radio uses the Philco loctal sockets which have a thin insulator on top of the socket. The 50A5 socket's insulator is bowed up and has obviously been cooked to death. The insulator on one of the small signal tubes is broken. I was hoping that would not be an issue, but we shall see...
Try some Pu-erh tea before you get into it, the neurons will kick in.
Yesterday, I sat down and took a good look at the chassis of this radio.
First, I checked the loop antenna connections - everything was ok there (it had not been disconnected).
I had not replaced some of the resistors. I remembered that this radio had the appearance of having lived a rough "life". Or, to be crude, it appeared to have been "rode hard and rode often".
Therefore I set out to replace many of the resistors I had not replaced initially.
When I was done, all the resistors save two (R204, which had been replaced in the past, and R403 which was mounted on the selector switch) had been replaced. In addition, I went ahead and replaced four of the mica capacitors in the tuning circuit (C401, C402, C404 & C405). I did not trust C405 as it looked like a "dogbone" resistor with thin, fragile leads.
After replacing those parts, I tried the radio out again yesterday evening.
Was it working correctly now?
You be the judge...
The first station you hear is WITZ in Jasper at 990 kc. The 1280 preset was silent, but then my home SSTRAN comes in loud and clear at 660 kc. No longer did the volume control need to be at maximum to hear my SSTRAN. Most importantly, the sound was no longer garbled with hum modulation!
Lesson remembered: In an old AC/DC radio such as this that has obviously seen heavy use, don't stop at replacing the paper and electrolytic capacitors. Replace the old resistors as well, and mica caps as needed.
Now I will touch up the set's alignment and make sure the presets are tuned correctly and working, after which I will return the chassis to its cabinet and this project will then be complete. I may, or may not, replace the speaker anyway since it has a couple small holes in the cone. Nevertheless, it sounds ok now.
Thanks for looking and commenting.
This morning, I redid the 49-901's IF alignment the right way, using a VTVM as an output indicator. Following this, I redid the preset station frequencies as follows:
1 - 660 kc - my home SSTRAN
2 - 840 kc - WHAS, Louisville, KY
3 - 860 kc - WSON, Henderson, KY
4 - 990 kc - WITZ, Jasper, IN
5 - 1280 kc - WGBF, Evansville, IN
6 - 1420 kc - WVJS, Owensboro, KY
I also replaced the speaker and output transformer with a speaker that has a nearly perfect cone, no holes, only one very minor visible tear which I can easily fix with fabric glue. Its attached output transformer was made for a 50C5 which will also match the loctal 50A5 used in the 49-901.
After making these changes, I put the chassis through its paces once again. Listen:
I think it sounds somewhat better with the replacement speaker.
In the video above, you will notice that six stations can be heard - three (WHAS, WSON, WVJS) are very weak. Two (my SSTRAN and WITZ) are fairly strong. One (WGBF) is sort of in the middle as far as signal strength is concerned. My basement is not a good place for AM reception.
And that is it for this 49-901 chassis restoration. Thanks again for reading and for commenting. I'll post an extended version of this on my blog in the near future, with additional photos.
Sounds fine. Interference is what everyboty has. One station has no interference and sounds without hum.
I think the radio is fine.
Oh yeah, there is a big difference between typical AM interference and garbled reception with hum modulation.
This 49-901 no longer has that issue. In fact it doesn't hum at all, thanks to (a) a small, 4 inch speaker with limited frequency response and (b) the oversized electrolytics (33, 33 and 33 uF in place of the original 30, 25 and 20 uF configuration).
Glad you got it sorted out, Ron. It sounds great! This is an important lesson, and one that bears repeating:
"Lesson remembered: In an old AC/DC radio such as this that has obviously seen heavy use, don't stop at replacing the paper and electrolytic capacitors. Replace the old resistors as well, and mica caps as needed."
It had to have been one or more of those resistors / micas that was causing the garbled sound. Possibly the speaker was causing some of the distortion as well, but the main culprit had to have been one of those components. I had a Silvertone once that was dead. Would not receive any hint of a station (the output section was working fine). Turns out it was a mica cap that went south. Once I replaced that, the set came to life.
Hello Ron,
Nice Job using the right tools for the right job really helps and Yes A good speaker really does make a difference and at least with the aftermarket speaker that I have been using when replacing PM speakers these
Visaton brand speakers have a full-range frequency response from 100 to 13,000 Hz.
Sincerely Richard