Blunderof the Week

[init4fun]

Originally Posted by Winky Dink

I’ve rewired my transformerless sets to eliminate hot chassis. This is the last one I have, but I’m not sure what to do with it. This is an AC/battery portable in which we replaced the original voltage-dropping resistance with capacitance.

Link to schematic:

https://goo.gl/photos/EMuXaAP2JWrNPPWo6

As it is now, the chassis is at 45VAC with switch off and 27VAC with switch on (or vice-a-versa with a non-polarized plug). Do I need to address the hot-chassis issue? It’s a small “suitcase” portable, and a small child can easily unlatch and open the back to stick a hand inside.

The other sets were straightforward, but this one puzzles me. What can I do to fix this?

Hi Winky ,

Two solutions come to mind ;

# 1 , a small 1:1 transformer to isolate the set from the line .

# 2 , keep it the Hell OUT of small children's hands so no modifications to the radio are needed .


(only partially joking with suggestion # 2 , some things ya just can't "idiot proof" no matter how ya try)

[Winky Dink]

Thanks for the suggestions. I’m trying to follow the simple method of polarizing the plug and putting the hot line through the switch and the neutral to ground--best explained by Phil Nelson here:

http://antiqueradio.org/safety.htm

I’ve done this successfully on several AA5’s, but the layout of this set confuses me. Here’s what it looks like to me (after erasing the battery connections from the schematic):



You can see where I get lost from not knowing what to do with the capacitors.

This is the cheapest-looking “vintage” radio I’ve seen. It must have had little use to have survived in such good condition. But it’s cute, and it adds some variety to my very small collection.

- Henry

[init4fun]

Winky your drawing looks perfect to me , you have the neutral connected straight to the chassis and your hot going through the switch to the tube's heater (via the dropping capacitor) and it's plate . The across the line cap C4 .05 MF is electrically identical in both it's originally drawn position on the schematic and where you drew it in with a question mark . Drawn either way , it's got one lead on the hot side and one lead on the neutral side , just as the circuit needs it .