need help

[Reece]

Re: Isolation Transformers -- there is a dangerous shock potential existing between the hot side of the power line (the black wire, brass screw, shorter slot in a receptacle) and ground. If you're touching that line and some other part of your body is grounded, you complete a circuit and receive a shock, which could be fatal. With an isolation transformer, there is no direct connection between the secondary of the transformer and the primary, so the danger of a fatal shock between ground and a device plugged into this transformer is eliminated. Other precautions to be observed: rubber mat or dry wood floor (not bare concrete), rubber sole shoes, long pants (dropped solder burns!), and keep one hand in your back pocket when probing live chassis.

[radio nut]

oh okay. That makes sense now. I figured power up equals powered up the same either way. I guess I will need to go to Fair Radio and get one. My next project is a transformerless ac/dc Meck radio so I will need an isolation transformer quick.

[radio nut]

one last question. in the same room plugged into the same outlet is a zenith 10s ? that I repaired years ago. If my friend turns on his 6 or 8 foot fluorescent shop light the zenith sounds like the lytics are really bad. only picks up local and still hums very badly and very loudly. turn the light off and it is fine. The 1928 stromberg picks up more stations when the light is off but is not really affected otherwise. Any ideas?

[radio nut]

I guess my point is that certain things interfere with a radio's performance but I have never seen it so extreme before

[bob91343]

In the old days, manufacturers were not compelled to make their stuff immune to RFI and they were not regulated regarding generating it.

The serious susceptibility is testimony to the lackadaisical engineering, making it work at the lowest cost without regard for such things. It was expected that the user find a solution. They sold line filters to the consumer, similarly to surge protectors today. Waste of money, patching poor engineering.

[Reece]

Many of the sources of interference today didn't exist when antique radios were new. Switching power supplies in modern electronics come to mind as bad interference sources. On the other hand, if you read old manuals, they write about interference from brushes on motors of all sorts, electrical signs, streetcars, vacuum cleaners, and so on. Sometimes a line safety cap or two added to a set, or at the noise source, will help, if the noise is coming in over the power line.

http://www.justradios.com/safetytips.html

[DavGoodlin]

Originally Posted by radio nut

If my friend turns on his 6 or 8 foot fluorescent shop light the zenith sounds like the lytics are really bad. only picks up local and still hums very badly and very loudly. turn the light off and it is fine.

Sometimes the lamp radiates the harmonics that hum, buzz and/or hiss (like a weak signal) on AM and FM. A line filter cannot always fix that, only a well-grounded light fixture may help AND physical separation.

I repaired a friend's Philco 37-650 by adding a line filter I salvaged from a monitor. It had an M-filter, that is a cap across the line, two inductors with common core (like in an old Zenith TV) and a cap on the radio side across the line. It really cut down on interference from dimmer switches (buzz).

Ironically, old T12 lamps and magnetic ballasts seem to generate very little interference compared to electronic ballasts driving linear OR compact fluorescent lamps. The higher the wattage or number of lamps driven, the worse it gets.

[Electronic M]

I've had problems with large linear fluorescent lamps before too, but it was with 40's era sets. Not terrible, but there was enough hum with them on for me to wonder what was still wrong with recapped sets, that is until I turned the fixture off.

[radio nut]

So if I understand it correctly the 1928 stromberg isn't affected that much since it has line to ground caps and the zenith probably doesn't have any. Since line to ground caps are dangerous if they short I believe I took the originals out and never replaced them because 8 or nine years ago when I worked on it I did not know about safety caps. And I sure don't want to be liable for a house fire if a normal cap ran from line to ground went bad.

I will have to get safety's and put them in!