A came across a non-working 37-62 a couple weeks ago. I replaced all the caps, most of the resistors, the way out of tolerance volume pot, a bad 6A8, and a pile of dry rotted wire....and lo and behold the thing works.
The thing is, when I reached to turn on the light over my work bench....with my hand on the chassis, I touched the metal switch box and got lightly zapped. The switch is on the same run with the receptacle that it was plugged in to. When I measure from the chassis to the conduit and I get 60v.
I know this is a dumb question but, is this normal? Thanks in advance.
reverse the plug in wall,,,maybe ???? need one of the polarity plugs???
Or remove the screw from #30. Methinks what you are experiencing is ac leakage from the line bypass caps which is normal. Since this set has a cap on each side of the ac line I don't think flipping the plug around will matter. Back in the old days the chassis would have a ground wire connect to the chassis so it would be an issue.
No matter what you do you should never complete the circuit with two hands. Transformer or no transformer.
I agree with Terry, you are experiencing the leakage through the #30 cap. And these caps have the value which is about 6 times what they allow today for home equipment for Y-caps.
This one won't kill you but one day you might encounter a transformer with a breakdown and the outcome might be different.
One hand behind your back, always.
Thanks guys, I'll take the screw out of the Bakelite this evening and see what happens.
And lesson learned, one hand from now on.
I removed the screw from #30 last night, it's still hot. I'm going to trace everything part by part and see if I can find some mistake I've made. Thanks for the help.
Just for grins measure the ac voltage from wall socket, neutral to earth ground and measure from the ground on the socket to earth ground. Maybe some leakage before it get to your set.
The most probable causes:
1. The C30.
2. The power transformer leakage.
3. Possibly the Power switch on the Volume control potentiometer.
4. Just measure for shorts between MAINS plug and the chassis, see if the resistance is very low or even in a few kOhms range, still bad.
With good transformer and no C30 whatever short is after the transformer it should not matter, it is decoupled.
The two capacitors in item 30 a connected from each side of the line cord to chassis ground. This creates a voltage divider, putting one half of the line voltage on the chassis. The current is very low so, it is not a safety issue. The main reason for these capacitors is to provide an RF ground path for the antenna circuit. Think of it this way, if you look at the schematic, imagine a wire connected from the ground symbol on the antenna transformer (item 2) to the ground symbol the item 30 capacitors. As terry said remove the screw from item 30, then check to see if the voltage is gone from the chassis. If the voltage is gone, put the screw back in and don't worry about it anymore.
Steve
Thanks all for the advice, I'll dig into it and update/beg for more help.