I have acquired a small Silvertone console 3 band radio(BC,Police, SW) Sears ID No.101407-don't know the model No. - it isn't indicated anywhere. However it did have the original envelope with all the paper supplied to the customer (now brown and brittle with age) including schematic and parts list with prices for replacements. It's all there except for the speaker. This radio Uses a type 84 rectifier, a 6A7 Osc./"Translator", a 78 IF, a 6H6G AVC/Det, a 6F5G Audio Amp, and a 6B5 output. All the cathodes in this set are grounded directly to chassis except for one section of the 6H6G and the 84 rectifiier. The schematic lists the field coil where its used in the power supply as being 1300 ohms. My question is: If I use a 300 ohm resistor in series with a speaker with a field coil resistance of 1000 ohms(which I have)would it work and if so, what wattage is required? Thanks in advance for any help.

:I have acquired a small Silvertone console 3 band radio(BC,Police, SW) Sears ID No.101407-don't know the model No. - it isn't indicated anywhere. However it did have the original envelope with all the paper supplied to the customer (now brown and brittle with age) including schematic and parts list with prices for replacements. It's all there except for the speaker. This radio Uses a type 84 rectifier, a 6A7 Osc./"Translator", a 78 IF, a 6H6G AVC/Det, a 6F5G Audio Amp, and a 6B5 output. All the cathodes in this set are grounded directly to chassis except for one section of the 6H6G and the 84 rectifiier. The schematic lists the field coil where its used in the power supply as being 1300 ohms. My question is: If I use a 300 ohm resistor in series with a speaker with a field coil resistance of 1000 ohms(which I have)would it work and if so, what wattage is required? Thanks in advance for any help.

welcome carl,i'm not the best for advise,there are alot of sharper guys here but the last time i did the same thing i used a 10watt. it worked but still got warm,good luck,phil

I think that you can probably use that 1000 ohm field coil speaker in place of the 1300 ohm field coil and probably not realy see much difference at all. And if it's a bit different probably the voltage vairation won't be a big deal.
I'm basing that on field coils that I have seen used that measured 20-25 % off from the print...and everything still measured close to the voltage values in the schematic.

Typical B+ currents are not usually over 60-ma so you could just measure the current too... or use the guess-timate and you can calculate a resistor if you feel after using the 1000 ohm coil that you really need to drop more volts.
But it's the inductive reactance here that's more responsible for helping the smoothing than just the pure resistance in the r-c time constant capacitor charging ripple smoothing.

As a consideration ...to ease your mind..... we typically have about 125 VAC nowadays in our homes as opposed to 105-110 back when your radio was made. ... and everything still runs nicely withthe old radios.

If you must use a resistor, a 10 watt will do well. It will get quite warm, so isolate it appropriately...prefferably under the chassis so that there isn't a shock hazard, and away from other parts that might be cooked by it. 300 ohms won't get too hot. I used a 1,800 ohm unit in an amplifier I built (80, 2A3, 57...Magnavox A-501), and it got REALLY hot. The amplifier worked quite well, though (regarding the absence of a field coil...though I always prefer to use original equipment when possible).

T.

:If you must use a resistor, a 10 watt will do well. It will get quite warm, so isolate it appropriately...prefferably under the chassis so that there isn't a shock hazard, and away from other parts that might be cooked by it. 300 ohms won't get too hot. I used a 1,800 ohm unit in an amplifier I built (80, 2A3, 57...Magnavox A-501), and it got REALLY hot. The amplifier worked quite well, though (regarding the absence of a field coil...though I always prefer to use original equipment when possible).
:
:T.

::If you must use a resistor, a 10 watt will do well. It will get quite warm, so isolate it appropriately...prefferably under the chassis so that there isn't a shock hazard, and away from other parts that might be cooked by it. 300 ohms won't get too hot. I used a 1,800 ohm unit in an amplifier I built (80, 2A3, 57...Magnavox A-501), and it got REALLY hot. The amplifier worked quite well, though (regarding the absence of a field coil...though I always prefer to use original equipment when possible).
::
::T.Thanks for your time and info - I will be using a field coil- I was just concerned about the difference in resistance. I was also curious about the direct grounding of the cathodes - was that a common practice? I don't recall seeing that before.

Not quite sure about what you mean by direct grounding of cathodes. I take it that there are resistors between the chassis and the center tap of the transformer. A voltage difference exists across these resistors (and the field coil, if it is in this circuit). Grid bias is tapped off of these resistors at appropriate points (center tap of transformer is more negative than chassis). You can either have all of the cathodes above the most negative point in the radio by varying amounts, with the grids at ground potential, or you can have all of the cathodes at one potential with all of the grids at various points below this potential. Either method creates appropriate grid bias.

Thomas

:Not quite sure about what you mean by direct grounding of cathodes. I take it that there are resistors between the chassis and the center tap of the transformer. A voltage difference exists across these resistors (and the field coil, if it is in this circuit). Grid bias is tapped off of these resistors at appropriate points (center tap of transformer is more negative than chassis). You can either have all of the cathodes above the most negative point in the radio by varying amounts, with the grids at ground potential, or you can have all of the cathodes at one potential with all of the grids at various points below this potential. Either method creates appropriate grid bias. Thanks.
After reading your explanation and further study of the schematic I have a better understanding of things. It's a big help to a beginner to be able to draw on the knowledge that the folks on this site possess. Again, Many thanks