Hi:

Philco 80 Riders 3 Philco 3-25. Need to replace the wire wound 325 ohm resistor (35). Can not find one with the exact ohm rating of 325. Would replacing it with a wire wound 300 ohm 5 watt be OK? Thanks

Long story short, 300 ohms/ 5 watts should work. This resistor sets the grid bias voltage (several volts negative WRT chassis ground) for the #42 output tube. Assuming that your set draws about 100 mA in B+ current (which flows through this resistor), a 5 watt resistor should be adequate. Given the possibility that the set could draw more than 100 mA, you might want to meter the current through your (temporarily-installed) 300 ohm 5 watt resistor to see if that power rating will stand up over the long haul.

Using 300 ohms instead of 325 ohms will also tend to jack up the B+ voltage a bit. Combined with the higher line voltages we have these days, that might be a concern, although probably not one to lose sleep over.

Edd- OEM resistance was 325 ohms, not 350, making the error only approximately 10% as opposed to 20%.

Rgr RGr made an earlier misread and a memory cache error.

:Edd- OEM resistance was 325 ohms, not 350, making the error only approximately 10% as opposed to 20%.
:

:Rgr RGr made an earlier misread and a memory cache error.
:
::Edd- OEM resistance was 325 ohms, not 350, making the error only approximately 10% as opposed to 20%.
::
:
CV:
Considering today's higher line Voltages, I tend to agree with Edd's figures. 350 Ohms might get the B+ down closer to what it was supposed to be in the days of 110 Volt power.
Lewis

From the Rider data on this set, the allowable line voltage range on the Philco 80 transformer was 105-125 VAC, with an apparent "assumed nominal" of 115 VAC- not really that far off from what we have today (our present AC standard is 117 VAC). But, suppose that the line voltage is 120V- that's only 1.04X the set's nominal voltage of 115VAC, meaning that if B+ was 250VDC at nominal, at 120VAC it could be expected to rise to only about 260VDC. At most (if it were reduced to zero ohms) the resistor in question would only jack up B+ by several volts- so the difference between 325 and 300 ohms is niggling in terms of its effect on B+. It might have an effect on the set's sound quality if the grid bias is shifted significantly- but again, the proposed value change just isn't enough to do that.

My suggestion is "try it and see", then take voltage/current measurements to ensure that the radio hasn't been put into a corner condition of operation- which is very unlikely.

:From the Rider data on this set, the allowable line voltage range on the Philco 80 transformer was 105-125 VAC, with an apparent "assumed nominal" of 115 VAC- not really that far off from what we have today (our present AC standard is 117 VAC). But, suppose that the line voltage is 120V- that's only 1.04X the set's nominal voltage of 115VAC, meaning that if B+ was 250VDC at nominal, at 120VAC it could be expected to rise to only about 260VDC. At most (if it were reduced to zero ohms) the resistor in question would only jack up B+ by several volts- so the difference between 325 and 300 ohms is niggling in terms of its effect on B+. It might have an effect on the set's sound quality if the grid bias is shifted significantly- but again, the proposed value change just isn't enough to do that.
:
:My suggestion is "try it and see", then take voltage/current measurements to ensure that the radio hasn't been put into a corner condition of operation- which is very unlikely.

CV:
Yeah, I am nitpicking...Right now my Voltage is 118.5, but it is 90 degrees outside, and air conditioners are running all over the town. On mild days, I have seen it get up to 124.7.
Lewis
:

::From the Rider data on this set, the allowable line voltage range on the Philco 80 transformer was 105-125 VAC, with an apparent "assumed nominal" of 115 VAC- not really that far off from what we have today (our present AC standard is 117 VAC). But, suppose that the line voltage is 120V- that's only 1.04X the set's nominal voltage of 115VAC, meaning that if B+ was 250VDC at nominal, at 120VAC it could be expected to rise to only about 260VDC. At most (if it were reduced to zero ohms) the resistor in question would only jack up B+ by several volts- so the difference between 325 and 300 ohms is niggling in terms of its effect on B+. It might have an effect on the set's sound quality if the grid bias is shifted significantly- but again, the proposed value change just isn't enough to do that.
::
::My suggestion is "try it and see", then take voltage/current measurements to ensure that the radio hasn't been put into a corner condition of operation- which is very unlikely.
:
:
:CV:
:Yeah, I am nitpicking...Right now my Voltage is 118.5, but it is 90 degrees outside, and air conditioners are running all over the town. On mild days, I have seen it get up to 124.7.
:Lewis
:
John:
I'll give it a try with the 300 and check the voltage for any dangerous rise in voltage. My house AC current here where I LIVE IS 120 SOMTIMES 121 AC. Thanks again!
:
:

The power companies are pretty good about regulating the HT voltage that goes out for distribution... but from that point, it becomes a little less controlled. Reason being that each home has a step-down transformer associated with it, and several homes may share the same step-down transformer. So, the power demand of all homes on a given transformer gets aggregated at the transformer input, which is in parallel with many other transformers. In order to maintain a nominal HT distribution voltage, the power company will increase or reduce the line voltage to serve this aggregated load at any given instant. Since different transformers on the same line will have different loads on them at any given time, there will be some variability in the 220V being put out by each transformer. Plus, it's inevitable that some homes are closer to/further away from the transformer, causing unequal line loss among individual service drops. All in all, it's a marvel that home line voltage is able to be regulated as closely as it is.

:The power companies are pretty good about regulating the HT voltage that goes out for distribution... but from that point, it becomes a little less controlled. Reason being that each home has a step-down transformer associated with it, and several homes may share the same step-down transformer. So, the power demand of all homes on a given transformer gets aggregated at the transformer input, which is in parallel with many other transformers. In order to maintain a nominal HT distribution voltage, the power company will increase or reduce the line voltage to serve this aggregated load at any given instant. Since different transformers on the same line will have different loads on them at any given time, there will be some variability in the 220V being put out by each transformer. Plus, it's inevitable that some homes are closer to/further away from the transformer, causing unequal line loss among individual service drops. All in all, it's a marvel that home line voltage is able to be regulated as closely as it is.
:
In my broadcast engineering days, I firwt worked for a crappy little station that was run on a shoestring, and we didn't have line regulation on the incoming AC. We would sign on at six, and promptly at eight the transmitter power would drop about 10 %. We would retune, and promptly the power would go up about 10%. We didn't monitor line Voltage from the studio where we took the remote readings, so the chief went to the transmitter site and monitored the incoming AC. We complained to Georgia Power, and they found a stuck regulator in the substation that fed our transmitter site. Also on the same primary was a factory of some sort that used a LOT of power. They started at eight, took lunch from noon to one, and shut down at five. They repaired the regulator, and the mystery was solved.
Lewis