Hi all,

I got this old Sylvania radio from a trade at a local pawn-shop yesterday (an antiques and collectables pawn shop!), which I am quite happy about. It's a small Sylvania radio, of unknown model. It looks identical to the one linked below, only it is brown (bakelite or plastic?).

The valve line-up on it is: 12AT6, 12BE6, 12BA6, 5OC5 & 35W4. It is American, and as such has a mains rating of 117V A.C at 25-60Hz or 117V D.C. Unfortunately, the labels with the model and serial number are torn off...

http://www.tuberadios.com/bakelite/sylvania510h.jpg.

Am I right in thinking that this is a 1950 Sylvania 510-H?

http://imageshack.us/photo/my-images/607/qx4o.jpg/.
http://imageshack.us/photo/my-images/209/dgs9.jpg/.
http://imageshack.us/photo/my-images/268/75y.JPG/.

Chris

That valve line-up matches Radiomuseum's listing for a 510:

http://www.radiomuseum.org/r/sylvania_1_215_510h.html.

You'll note that the prefix numbers of those valves, which indicates their filament voltages, add up to 121 volts, so it's a transformerless set -- in other words the valve filaments are wired in series across the mains potential (each such filament draws the same amount of current, in this case 150mA).

In most transformerless sets, one side of the mains is attached to the metal chassis. That means that if the plug is incorrectly wired such that active is on the chassis instead of neutral, you have a "live" chassis which is very dangerous so insulation of every metal part -- including set screws in knobs -- is critical to safety of these sets.

Some later model transformerless sets used a busbar insulated from the chassis rather than the chassis itself.

And the usual low price 240v/120v step down transformer does not provide isolation from the mains because these are autotransformers -- where there is no isolated secondary winding.

Likely what the Americans call a AA5 circuit the layout of which is a common as dishwater. You will likely find the circuit on Nostalgia air, or there may be a "SAM's" sheet for it.

Do as said be cautious with this type of set and equipment of Japanese & American origin, albeit the Europeans are not innocent of doing similar (often with printed circuit boards).

Apart from the "Hot" chassis and later, "Floating mains" This lot had a bad habit of using two wire cables (& I have a 110V Grid dip Meter on the bench, this way) and, with or, without transformer, used no earthing on metal cases and chassis, or alternatively put a capacitor of dubious integrity from what was supposed to be Neutral to the chassis, or case.

All fine until the cap fails, or the case becomes alive and some one who touches it becomes dead.

One of the reasons to the point of pedantic that I keep telling people to asses the thing, before even thinking about powering it. I have already spotted one death trap device this week.

Marc



Marc

Your radio's schematic is likely extremely similar to this:


You could modify it like this for 230V50Hz:


or


But it will still be a hot chassis.

More at my page here

Do note relative to my comment the .01Cap paralleled with the 0.22M resistor to chassis

That in my book bleeds AC onto the chassis & should be a mains type cap.

A family of sets that really need to be worked on via an isolation transformer (not an autotransformer and that includes "Variacs")

Not really sets, once the chassis is removed, that can be considered "intrinsically safe" so one has to be extremely careful. The fuse box RCD will not save you in this situation.

Marc