[Art Hoch]

You lost me. My variac has no meter.

[morzh]

You do not need a meter in the Variac.

Just increase the votage until you have 300mA through or or 6.3V across a filament that is 6.3V while with the lamps in place. Measure the otal voltage then across the whole string (all filaments etc). Then you know exactly what you need to drop which is your MAINs minus what you have measured.

[Art Hoch]

schematic says 133 ohms in the line resistor cord.

[Radioroslyn]

Hey Art it's a very nice looking set!!!
Good job
Terry

[morzh]

Art,

roughly speaking, if you know your resistance, it is that 133 Ohms times 0.3A squared, so it is 12W or so.
Given the length of the cord it is not too bad. And this is the power you have to dissipate.
A compact resistor however is a sizeable thing, especially considering the fact that it should be sized to 2-3 times the dissipated power.

This is a 30W 115 Ohms resistor. (just to give you an idea, you should probably be closer to that 133 Ohm).

http://www.mouser.com/ProductDetail/Vish...s6Dg%3d%3d

[Art Hoch]

7 weeks to get one???  And chassis mount?  No room to mount it except on far opposite side of the chassis.  Maybe I'd better get a diode.  But what size/#?  I know nothing about diodes. I have a few in a box but I think they are way too small--1N34A and 1N914. Help!!!

[Mondial]

Art, didn't you mention that there is a candohm already on the chassis? Perhaps this particular radio used the candohm as the filament dropping resistor instead of the line cord.

Did you measure the resistance of the existing candohm?

If the original cord was resistive, it would have 3 conductors, two normal and a separate resistance wire. If there is only a 2 conductor cord then it was not.

[Art Hoch]

Yes, it had a resistive cord ahead of the 50 ohm candohm.  Candohm checked out at 52 ohms so it's okay.  The power cord is bad; is was supposed to have 135 (not 133 as I said earlier) ohms but only measured about 22 ohms.  So I have to replace it with a non-resisitve cord and knock down the voltage. Now I'm thinking a diode on the power cord leg going into the 25Z5 tube.  That's what I'm needing a size or a # on---the diode.  I figure with the correct diode, I can add a 17ohm 2 or 3 watt power resistor and have little heat involved. 

[Mondial]

These rectifier diodes would work fine. They are rated at 1 Amp and 1000 Volts reverse, which is more than adequate and they can be used for other uses as well:

http://www.ebay.com/itm/10pcs-1N4007-1A-...7580&rt=nc

You want the diode in series with only the filaments, not the plates of the 25Z5. Actually it will work that way, but if the diode polarity is reversed you will get no DC out of the rectifier tube.

[Arran]

 If you go the diode dropper route I would use a larger amperage diode, and use a pair of them, the difference in cost between a 1 amp and a 3 amp diode is pennies. Now the reason that i suggest using a pair in series is in case one of the diodes decides to short out, it will only drop an extra .7 volts but will prevent the full line voltage from ending up across your tube filament string.
Regards
Arran

[Art Hoch]

Well, this little curtain burner is playing!  I wound up using one diode between the tie point on the 25Z5 tube and the candohm.  New power cord is installed and new caps and some resistors were replaced.  4 out of the 5 tubes were good.  I had the replacement.  It's not exactly "hi-fi" but it's better than I thought it would be.  One more knob coming and it will be completed.

Not sure I want another one with the line resistance cord, but at least I have an experience I hadn't had before

[Radioroslyn]

Glad to hear you got it going. Thought the diode would do the trick and it's cheap.
Terry

[Arran]

Well, this little curtain burner is playing!  I wound up using one diode between the tie point on the 25Z5 tube and the candohm.  New power cord is installed and new caps and some resistors were replaced.  4 out of the 5 tubes were good.  I had the replacement.  It's not exactly "hi-fi" but it's better than I thought it would be.  One more knob coming and it will be completed.

Not sure I want another one with the line resistance cord, but at least I have an experience I hadn't had before

I would still add another diode ahead of the first as a safety measure, that way if one diode shorts out your tube filaments won't go bye bye. It's not exactly a Hi Fi set but compared to some early AC/DC sets it looks pretty good, many were four tube cheapies with a two stage TRF circuit, not very selective with strong stations and not very sensitive for distant ones either, I have one of those, and it's basically a mini space heater with audio. This one has more in common with one of the International Kadette Radio models from the same period, though the Kadettes usually used a ballast tube rather then a curtain burner.
Regards
Arran

[Art Hoch]

The paper label on the back of the chassis is 80% gone. Believe the chassis was made by Echophone. New felt feet and this baby is done.

[Art Hoch]

All done with 3 correct knobs!