The way these radios were conventionally wired, with the switch as shown in your schematic, meant that the chassis would be live either when switched on, or else when switched off (through the heater string), depending on which way it was plugged in. As has been said, in principle this didn't matter, as long as the whole chassis, and things attached to it, was electrically isolated from anything touchable by the user.
Whenever I restore these radios I always rewire so that the on/off switch is switching the upper lead in your schematic, with the lower lead going direct to chassis. I use a polarised power plug, and ensure that neutral is the one connected directly to the chassis, and so the live lead is switched. (And I make sure that any power sockets it may be plugged into are correctly wired!)
And finally, I in any case treat it at all times as if the chassis *might* be live (even though it shouldn't be because of the other measures); in other words, make sure all the original isolation safeguards (rubber washers, if the cabinet is metal, whatever) are all refurbished and safe.
Half wave rectification places "standing" DC on the power trafo. Toroidal power transformers intensely "dislike" being subjected to "standing" DC.
Touching on Eli's comment that results in loud unpleasant sounding buzzing and the potential for overheating due to core saturation.
The cabinet and chassis mount insulators are all in good shape. Too much modding to put a transformer into the case, but I like the idea of moving the switch to the load lead, polarizing the plug, and I have a Toroid isolation transformer to run the unit through and to power when working on the unit.
Still wondering about that power lead through C43 to the FM antenna. Can someone address the purpose of that? It is currently on the load lead. Should I leave it there when I rewire the switch which would then be the neutral to the antenna or should I swap the lead back to load for the antenna? Is there another alternative?
As always, thanks for the help.
Jeff
Still wondering about that power lead through C43 to the FM antenna. Can someone address the purpose of that? It is currently on the load lead. Should I leave it there when I rewire the switch which would then be the neutral to the antenna or should I swap the lead back to load for the antenna? Is there another alternative?
As always, thanks for the help.
Jeff
When does a polarized plug not do any good.
Whenever . . .
Some 2-wire house outlets are wired wrong, and some 3-wire house outlets are wired wrong.
Use one of those testers to check your outlets.
Then take your radio, amplifier, etc. it to a friend. check his outlets.
Then plug it in.
Safety First!
Whenever . . .
Some 2-wire house outlets are wired wrong, and some 3-wire house outlets are wired wrong.
Use one of those testers to check your outlets.
Then take your radio, amplifier, etc. it to a friend. check his outlets.
Then plug it in.
Safety First!
If you're bound and determined to use a toroid despite advice, you might be able to convert to a full wave bridge rectifier, but it seems an uphill battle.
YOS,
Chris
YOS,
Chris
This radio, and millions like it, worked fine for decades.
Why do you think it suddenly needs "fixing"?
Why do you think it suddenly needs "fixing"?
"...worked fine for decades..." And electrocuted untold thousands in the process. That's why we have the newer protocols.
---------------------------------------------------------------------Rick..........
---------------------------------------------------------------------Rick..........
PRR, not clear if your comment is for me, but my (only) defense is along the lines of "Extremism in the defense of Safety is no Vice", to butcher a phrase from America's last real conservative politician.
But, yeah, if it were mine, I'd make double sure everything's safe and keep it unmolested. Definitely don't always practice what I preach. Vanity goeth before the fall, as always.
YOS,
Chris
But, yeah, if it were mine, I'd make double sure everything's safe and keep it unmolested. Definitely don't always practice what I preach. Vanity goeth before the fall, as always.
YOS,
Chris
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Rick, your caution is really the only course that a general readership forum like this can responsibly adopt. There are a variety of ways to get to modern safety levels, isolation transformers with safety ground (PE), GFI, or double insulation layers.
The old single insulation layer designs are fine if everything is fresh and maintained and have the advantage of *not depending* on a transformer - the weakest link in the chain.
There's good reason for DIYaudio's usual ban of these discussions - if an OP *has* to ask, it's too dangerous. Fortunately Kevin is checking in (hopefully), so maybe some good discussion can happen safely. It's an important topic to get right.
YOS,
Chris
The old single insulation layer designs are fine if everything is fresh and maintained and have the advantage of *not depending* on a transformer - the weakest link in the chain.
There's good reason for DIYaudio's usual ban of these discussions - if an OP *has* to ask, it's too dangerous. Fortunately Kevin is checking in (hopefully), so maybe some good discussion can happen safely. It's an important topic to get right.
YOS,
Chris
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Citation, please?
In the Depression, yes, some radios were dangerous.
Although from what I read and conversations with my parents, the "big danger" was knocking the radio into the bathtub. Which was not all that common. And has almost nothing to do with transformerless construction.
I was intimate with radios of the 1947 to 1967+ period. By this time UL was enforcing adequate safety rules and testing. You had to be a devilishly clever little brat
to get shocked by these radios. (TVs and outboard UHF tuners still shocked.)What?
There's good reason for DIYaudio's usual ban of these discussions - if an OP *has* to ask, it's too dangerous. Fortunately Kevin is checking in (hopefully), so maybe some good discussion can happen safely. It's an important topic to get right.
YOS,
Chris[/QUOTE]
Wow! Use an IT. Don’t use an IT. If OP has to ask???
If this website is only for those “in the know”, and only for mutual admiration of the experts, I don’t belong. Sorry I asked.
Moderator, folks looking for ways to be safer around such devices are best served elsewhere. Please delete this thread.
There's good reason for DIYaudio's usual ban of these discussions - if an OP *has* to ask, it's too dangerous. Fortunately Kevin is checking in (hopefully), so maybe some good discussion can happen safely. It's an important topic to get right.
YOS,
Chris[/QUOTE]
Wow! Use an IT. Don’t use an IT. If OP has to ask???
If this website is only for those “in the know”, and only for mutual admiration of the experts, I don’t belong. Sorry I asked.
Moderator, folks looking for ways to be safer around such devices are best served elsewhere. Please delete this thread.
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I'm sorry to have ruffled your feathers, although that was certainly not intentional.
But, safety first.
YOS,
Chris
But, safety first.
YOS,
Chris
Why do you think there are so many tubes on the market made for high voltage heaters like the 50C5-25L6-35L6-50L6 and 35 volt heater rectifiers ?
Because they were fitted in mains non isolated --series connected -dropper resistor radios .
Its all very well being blaze about 110V AC/120 V AC but the UK and a lot of the EU/Europe range from 220 V AC to 240 V AC --that Kills !!
Even "pulsing DC" can cause defibrillation of the heart --aka- Cardiac Arrest.
Because they were fitted in mains non isolated --series connected -dropper resistor radios .
Its all very well being blaze about 110V AC/120 V AC but the UK and a lot of the EU/Europe range from 220 V AC to 240 V AC --that Kills !!
Even "pulsing DC" can cause defibrillation of the heart --aka- Cardiac Arrest.
Standard 105 to 125 VAC North American mains are deadly dangerous, but less so than 220 to 240.
Anything above 45 V. can kill, all too quickly. Electricity is a marvelous servant, but it must be accorded respect.
Anything above 45 V. can kill, all too quickly. Electricity is a marvelous servant, but it must be accorded respect.
Thousands were killed?
Yes, grabbing the radio, and pulling it to be able to get to the volume control or the tuning knob.
Ooops, I touched the chassis, and I am in the bathwater.
Yes, I am 'smart', so I modified the radio to connect a turntable and crystal cartridge to it, and connected external speakers.
Ooops, one hand is grounded, and I touched the turntable/cartridge connections, or the loudspeaker connections.
Yes, I was connecting an external antenna to the first RF coil, and happened to be grabbing something that was grounded (all at the same time).
I did not want to pay a qualified service technician, so I did it myself. . . .
Yes, grabbing the radio, and pulling it to be able to get to the volume control or the tuning knob.
Ooops, I touched the chassis, and I am in the bathwater.
Yes, I am 'smart', so I modified the radio to connect a turntable and crystal cartridge to it, and connected external speakers.
Ooops, one hand is grounded, and I touched the turntable/cartridge connections, or the loudspeaker connections.
Yes, I was connecting an external antenna to the first RF coil, and happened to be grabbing something that was grounded (all at the same time).
I did not want to pay a qualified service technician, so I did it myself. . . .
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This fear of death by touching a live wire , chassis is over rated because of some unfortunate stories ... of course real , but I can asure you that even 230V is not that quickly 😀
Way back when, many people were taught to respect electricity.
I am not so sure about what is taught to the average person today.
I am not so sure about what is taught to the average person today.
Very little, I'm afraid. They definitely don't learn that the responsibility for safety begins with oneself.