I get more noise than signal on my grandparent’s Philco 38-5 (code 121), where do I look to resolve that?
I recently replaced the AC power cord and fired the radio up for the first time in a few years. I live in a poor reception area, hills all around, though I can pull in a couple of AM stations and SW band broadcasts. But I get more noise than signal. I’m using an ~15 foot wire as an antenna, the radio is louder with the wire connected, but the ratio of signal to noise seems to be the same with or without the antenna.
I’m moderately experienced repairing & restoring vintage guitar and bass amplifiers, this is my first try on a radio. I thought maybe I need to replace the main filter caps, though I don’t know if the signal to noise is merely my reception, or in the amplification, or…? The radio is quiet at idle with volume turned down, NOT like the 1939 Gibson EH 185 amplifier I’m working on that needs new electrolytic caps - it has a loud nasty buzz even with volume at zero, though I can faintly hear the signal come through the buzz when I turn the volume way up.
I’d greatly appreciate suggestions and troubleshooting methodology on resolving this issue. My grandfather held this radio on his lap riding home on the streetcar from Dayton’s department store in downtown Minneapolis. My mother grew up with this radio, I’d like to play it for her again with a reasonably clean signal while I still can.
Thank YOU!
Root
Hi Root, welcome to the Phorum
Unless you have strong local stations, you will probably need more than 15 feet of antenna. Also, check the antenna transformers for continuity. You may need to clean the band switch too.
Steve
Sounds like RFI coming from your house appliances. Try unplugging florescent or LED lights first.
Then the computer, etc. until you find the offender.
The radio is reproducing what it is fed, in this case, RFI ( Radio Frequency Interference ).
I have a problem here that when my neighbor turns on their Kitchen light, all I get is buzz. Took me a while to find the source.
Happy hunting.
Generally, if you hear the buzz with the volume down it's from the power supply. If you control the buzz with the volume control it's picked up from the antenna.
Root
The red flag for me is your having replaced the power cord.
If the radio was properly restored, even 20 years ago, cords last way longer than that, so this tells me the radio might be unrestored or maybe repaired some time in 40s or 50s but not fully recapped.
If this is the case and you are trying to play a very old set with no recap ever having been done, all kinds of things migh be wrong with it, that could affect the reception, sig/nouse etc.
If so, it is a good news it works and receives, but then you might want to properly recap it and check the resistors' values.
If this is not the case and all caps are reasonably new, the we can concentrate on the reception.
In which case you have gotten some good advice from other folks here.
Mike
Thank you all for the info and ideas in your replies, I welcome any further comments and observations on what I ask or state below:
Steve, thanks for leading me to deeper antenna research. I have a (little) better understanding of loop antennas now, how/why they work. I don’t really have a convenient spot/room in close proximity to the radio to set up a DIY loop antenna, so maybe I try another idea I found on the web: a grounded ~50 foot length of wire with six 6” turns near the end in close proximity to the radio? It’s ok to just lay (anchor if/as necessary) the wire out across my roof if I don’t have good a way to string it up?
New to this, I don’t yet understand why these antenna ideas are just in close proximity to the radio rather than connected to the antenna terminal of the radio??
Ed, I have done some searching for RFI sources, no luck yet, will keep trying. Hmmm… although wifi is at a MUCH higher frequency, I wonder if the base station/access point hardware in the home might generate other electronic noise within “x” proximity? AC/DC power supplies?
Rod, thanks for that A/B, reinforcing what I hoped would be a simple troubleshooting tree for that.
Mike, it is unrestored, yet in immaculate condition. So far I believe the only components ever replaced are the 18uf cap can & the 6A8G tube, and now the AC cord. All other parts are Philco, though I haven’t pulled all the tube covers yet, didn’t want to add any variables to my first operation on her. The cap and tube replacement were probably done before the early ‘60s, maybe even a decade or more earlier. Soooo… even though the radio behaves well, no nasty buzz like the 1939 Gibson EH 185 amp, I better start with the three electrolytic cap cans, 8+10uf dual, 16uf & 18uf.
I don’t think I can get those values in cosmetically correct cans, so what do radio restorers do, replace with modern cans, or abandon the existing cans cosmetically in place and try to find room for physically smaller caps in the underside of the chassis?
Just sharing, any of my vintage gear that hasn’t been played in more than 6 months to a year or so, I bring up slowly with a variac using a cap reforming “recipe” I learned from the recently late Bob Rissi of Risson Amplifiers: 25Vac for 5 minutes, 10Vac increase every 2 minutes up to operating voltage. I don’t know that i’ve ever saved or truly reformed any old caps, but I do it just in case it helps. If it is a repair job, I add an amp meter in front of the variac to help avoid surprises.
I’m going to investigate that procedure deeper on the EH 185 next time by measuring the B+ off the rectifier while the AC is ramped up. When I fired up the EH 185 the first time, it didn’t draw any current or make a hum until was up to 85Vac for about 90 seconds - then it just all of a sudden came alive with a loud nasty buzz. So I think at low voltages the 5U4 cathode doesn't get hot enough to generate the electron field used for the tube to operate --- therefore, no rectification and no high voltage. So I suspect the “Slow Cap Reforming" process up to that point really wasn’t useful, as the caps weren't getting any voltage! New procedure would be to bring up the AC until the rectifier produces DC and start the 5 minutes there, figure out the 2 minute increments from that point.
Thanks again, sorry, didn’t mean to go on so long!