[ccomer1955]

http://www.nostalgiaair.org/pagesbymodel...017623.pdf

I'm still figuring out the math involved in calculating wattage on power resistors, so please bear with me. The schematic shows the voltage going into R14 is 250v. The voltage going out is 210v, so that's a voltage drop of 40v. The resistance of R14 is 1500 ohms, so amperage is V/R=.02666?

P=R(I squared), so P=1.06? Wattage should be three times the calculated value, so I need at least a 1500 ohm 3 watt resistor? Closest I have to that is a 1200 ohm 5 watt, so I guess a visit to the electronics store is in order.

Am I even close to correct here? What is currently in the radio looks to be a 1000 ohm wire-wound (possibly 10 watt) resistor?

Somebody with some math tutoring patience want to straighten me out here?

Also, what is the wattage on flex-ohm resistors? Or is that a function of length?

[Mondial]

Yes, your calculation is correct. The power dissipated is 1.06 W. You can also use a simpler formula for power when you know the voltage drop and the resistance:

P= V (squared) / R or in your case (40 x 40) / 1500 = 1.06

Power rating of the flex resistors is pretty much a function of the length, as the longer it is, the more area of resistance winding is available to dissipate the heat generated.

[Arran]

http://www.nostalgiaair.org/pagesbymodel...017623.pdf

I'm still figuring out the math involved in calculating wattage on power resistors, so please bear with me. The schematic shows the voltage going into R14 is 250v. The voltage going out is 210v, so that's a voltage drop of 40v. The resistance of R14 is 1500 ohms, so amperage is V/R=.02666?

P=R(I squared), so P=1.06? Wattage should be three times the calculated value, so I need at least a 1500 ohm 3 watt resistor? Closest I have to that is a 1200 ohm 5 watt, so I guess a visit to the electronics store is in order.

Am I even close to correct here? What is currently in the radio looks to be a 1000 ohm wire-wound (possibly 10 watt) resistor?

Somebody with some math tutoring patience want to straighten me out here?

Also, what is the wattage on flex-ohm resistors? Or is that a function of length?

 Is the resistor in question a flexible resistor or are you asking about another you have found? I don't know what the maximum wattage is for flexable resistors but in my experience they are not usually more then 2 or 3 Watts, so maybe not more then 5 Watts at the most.
 I looked at the schematic you linked to, and I would say that it would be highly unlikely that they would use anything like a 10 watt resistor in there originally, though there is nothing stopping you from using one as a replacement other then physical limitations, so clearly this 1000 Ohm job is a replacement. You could use a 1200 Ohm 5W in there in a pinch, it's acting mostly as a choke resistor in a Pi filter circuit not as a voltage dropper, the difference would be negligible. I'm not sure about the Rider manual they lifted this from but most Silvertone schematics usually have a parts list, perhaps whomever scanned and uploaded this to Nostalgia Air omitted it.
Regards
Arran

[ccomer1955]

No, the flex ohm is the 400 ohm one next to it on the schematic. The flexohm still works, so I'm leaving it. I can't find the parts list in my high-res Rider's volumes, either.

At this point, I'd rather get there mathematically, so I can be sure I get it right on future rebuilds. This radio was never a great set to begin with, but whoever repaired it in the 40s or 50s took some liberties and was fairly sloppy at soldering. I'm just trying to put it back to the way the schematic says it should be. It has a replacement transformer that shows about what you'd expect for resistance on the primary and the secondaries, but I haven't put any power on it, yet.

It was a $5 radio for me, so I'm using it as a learning experience. It reminds me of a cheap Air King I worked on. It has a round cardboard tube on the side with the loop antenna glued to it. The cabinet is going to be fun, too. It's missing a piece of trim across the grille cloth, and part of the cabinet between the dial and the push buttons is broken off and gone, so I'm going to try to fabricate both parts. I'm sure it will cost me more than I would ever make on it, but I'm learning about some octal tubes and having fun.

[Arran]

No, the flex ohm is the 400 ohm one next to it on the schematic. The flexohm still works, so I'm leaving it. I can't find the parts list in my high-res Rider's volumes, either.

At this point, I'd rather get there mathematically, so I can be sure I get it right on future rebuilds. This radio was never a great set to begin with, but whoever repaired it in the 40s or 50s took some liberties and was fairly sloppy at soldering. I'm just trying to put it back to the way the schematic says it should be. It has a replacement transformer that shows about what you'd expect for resistance on the primary and the secondaries, but I haven't put any power on it, yet.

It was a $5 radio for me, so I'm using it as a learning experience. It reminds me of a cheap Air King I worked on. It has a round cardboard tube on the side with the loop antenna glued to it. The cabinet is going to be fun, too. It's missing a piece of trim across the grille cloth, and part of the cabinet between the dial and the push buttons is broken off and gone, so I'm going to try to fabricate both parts. I'm sure it will cost me more than I would ever make on it, but I'm learning about some octal tubes and having fun.

 That kind of fits in with my experience then, is the 1500 ohm resistor was calculated at just above 1 Watt then the 400 Ohm resistor ahead of it would have been just a little bit more, so more then likely the 400 Ohm flexable resistor was probably a 2 or 3 Watt job. I would go to maybe 2 or 3 Watts for the replacement 1500 Ohm job, or up to 5 if space will allow.
  I take it that this Silvertone has a Bakelite or a Plascon cabinet? If this is the case then it need not be too expensive to repair, plastic auto body filler or fiberglass resins are fairly economical and will do a decent repair job if you do not mind a painted cabinet afterward. You could probably go into making molds and using epoxy and dyes to replicate the original material, but it probably isn't worth it unless it's a rare or valuable set. Sometimes it the set is common enough you can find an empty cabinet as a replacement. If it's a wooden cabinet it can be even easier, if you know what you are doing, repair on those can be made almost invisible.
Regards
Arran

[ccomer1955]

It's wooden. I manufactured a piece to go in the gap. It's about 4" long and maybe 1/2" wide. The hard part was figuring out how to router a curve for the corners without a router. The ribbed crossmember has me stumped. I'll have to hit the craft stores and look for something close, or just leave it off, but I'm taking this thread into cabinet restoration, now, so I'd better let it go. Here is the cabinet the way I got it. I plan on putting a darker tone around the edge of the top and on the bottom, so I think I'll match the darker tone around the dial and push buttons. Finding knobs and push buttons is going to be difficult.