Bought a model 70 a couple years ago, supposedly restored.......... So after sitting a couple years, I finally got up the courage to plug in the original cloth cord and snap on the power switch. Immediately, we had that classic 60 cycle hum, and fairly loud. Left switch made in louder in one position, quiter in the other. Volume had no effect, nor did the tuning. I noticed that after several minutes, that only one tube lit up. I know that the electrolytics are toast on account of the hum, but what about those non glowing tubes? It was not entirely dark in the room, but one was clearly lit up, the rest, no. No more experimentations until I can have the unit checked out. ;)
Music, If you have a 60 cycle (probably 120 cycle) hum, there would have to be at least two tubes lighting, the rectifier (80) and the output (47). If most of the tubes don't light, my guess is, someone removed the good tubes and replaced them with duds. Though it is possible that there is a break in the heater circuit.
Steve
Steve? Does the heater circuit control all the tubes or are the heating elements controled individually? I have other tubes that I could plug in... I believe I have two extra of each. I need to try it out when it's dark out I guess. So they should at the very least, be visable then? It is as I said, that it was making the hum instantly when the switch was snapped on. We recently purchased a totally restored 1937 Zenith tombstone...........Yeah, I know.......$$$$$$............ and I all of the sudden want to get the cheap old Philco 70 going now!
Strongly recommend you replace electrolytics and other non-mica caps in your set. Also take a good look at your power cord and consider replacing it too. Agree with Steve, you probably have some bad tubes, but the transformer hum is telling you that something is out of kilter.
Thanks TA. I have no idea what I'm doing so it's gonna go back to just sitting for now.
All the tubes are connected in parallel (same circuit) except the type 80 The tubes should light bright enough that it shouldn't be too hard to see. If you have spares, try them. If the tubes are bad, before you pitch them, try re soldering the large pins.
Steve
If you don't know what you are doing, that makes two of us.....