On a Zenith H723, which is closest to Riders 23-7, model H723Z2: What is resistor R21, in the filament string between the 1st & 2nd IF's. They call it a "special resistor" with no value listed. The only thing I found special about it is that it gets real hot and smokes a lot, and keeps the filaments from lighting up (2.5K ohms, cold). Similar models have a 39 ohm power resistor at that point. What do you suggest? Thanks.....

:On a Zenith H723, which is closest to Riders 23-7, model H723Z2: What is resistor R21, in the filament string between the 1st & 2nd IF's. They call it a "special resistor" with no value listed. The only thing I found special about it is that it gets real hot and smokes a lot, and keeps the filaments from lighting up (2.5K ohms, cold). Similar models have a 39 ohm power resistor at that point. What do you suggest? Thanks.....

That resostor has a "negative TC", which means that if the temperature goes up, the resistance goes down. The filaments have a positive temperature coefficient, so that when the set is first turned on, the resistor will allow the filaments to warm up more slowly and keep one from hogging all the Voltage and becoming white hot while the others warm up.

Lewis

::On a Zenith H723, which is closest to Riders 23-7, model H723Z2: What is resistor R21, in the filament string between the 1st & 2nd IF's. They call it a "special resistor" with no value listed. The only thing I found special about it is that it gets real hot and smokes a lot, and keeps the filaments from lighting up (2.5K ohms, cold). Similar models have a 39 ohm power resistor at that point. What do you suggest? Thanks.....
:
:
:That resostor has a "negative TC", which means that if the temperature goes up, the resistance goes down. The filaments have a positive temperature coefficient, so that when the set is first turned on, the resistor will allow the filaments to warm up more slowly and keep one from hogging all the Voltage and becoming white hot while the others warm up.
:
:Lewis

Neal,
What is the chassis number for your radio?
When I looked at the schematic for an H723, that resistor was not in the filament string.
Carl T

:::On a Zenith H723, which is closest to Riders 23-7, model H723Z2: What is resistor R21, in the filament string between the 1st & 2nd IF's. They call it a "special resistor" with no value listed. The only thing I found special about it is that it gets real hot and smokes a lot, and keeps the filaments from lighting up (2.5K ohms, cold). Similar models have a 39 ohm power resistor at that point. What do you suggest? Thanks.....
::
::
::That resostor has a "negative TC", which means that if the temperature goes up, the resistance goes down. The filaments have a positive temperature coefficient, so that when the set is first turned on, the resistor will allow the filaments to warm up more slowly and keep one from hogging all the Voltage and becoming white hot while the others warm up.
::
::Lewis
:
:Neal,
:What is the chassis number for your radio?
:When I looked at the schematic for an H723, that resistor was not in the filament string.
:Carl T

It looks like it only goes with the Z2 model.
Lewis
:

::::On a Zenith H723, which is closest to Riders 23-7, model H723Z2: What is resistor R21, in the filament string between the 1st & 2nd IF's. They call it a "special resistor" with no value listed. The only thing I found special about it is that it gets real hot and smokes a lot, and keeps the filaments from lighting up (2.5K ohms, cold). Similar models have a 39 ohm power resistor at that point. What do you suggest? Thanks.....
:::
:::
:::That resostor has a "negative TC", which means that if the temperature goes up, the resistance goes down. The filaments have a positive temperature coefficient, so that when the set is first turned on, the resistor will allow the filaments to warm up more slowly and keep one from hogging all the Voltage and becoming white hot while the others warm up.
:::
:::Lewis
::
::Neal,
::What is the chassis number for your radio?
::When I looked at the schematic for an H723, that resistor was not in the filament string.
::Carl T
:
:
:It looks like it only goes with the Z2 model.
:Lewis

Oh, the value is 100w nominal. I guess that means room tmperature.
Lewis
::

:::::On a Zenith H723, which is closest to Riders 23-7, model H723Z2: What is resistor R21, in the filament string between the 1st & 2nd IF's. They call it a "special resistor" with no value listed. The only thing I found special about it is that it gets real hot and smokes a lot, and keeps the filaments from lighting up (2.5K ohms, cold). Similar models have a 39 ohm power resistor at that point. What do you suggest? Thanks.....
::::
::::
::::That resostor has a "negative TC", which means that if the temperature goes up, the resistance goes down. The filaments have a positive temperature coefficient, so that when the set is first turned on, the resistor will allow the filaments to warm up more slowly and keep one from hogging all the Voltage and becoming white hot while the others warm up.
::::
::::Lewis
:::
:::Neal,
:::What is the chassis number for your radio?
:::When I looked at the schematic for an H723, that resistor was not in the filament string.
:::Carl T
::
::
::It looks like it only goes with the Z2 model.
::Lewis
:
:
:Oh, the value is 100w nominal. I guess that means room tmperature.
:Lewis
:::

Thats 100 ohms, not 100W, and most likely at room temp as you indicate.

::::::On a Zenith H723, which is closest to Riders 23-7, model H723Z2: What is resistor R21, in the filament string between the 1st & 2nd IF's. They call it a "special resistor" with no value listed. The only thing I found special about it is that it gets real hot and smokes a lot, and keeps the filaments from lighting up (2.5K ohms, cold). Similar models have a 39 ohm power resistor at that point. What do you suggest? Thanks.....
:::::
:::::
:::::That resostor has a "negative TC", which means that if the temperature goes up, the resistance goes down. The filaments have a positive temperature coefficient, so that when the set is first turned on, the resistor will allow the filaments to warm up more slowly and keep one from hogging all the Voltage and becoming white hot while the others warm up.
:::::
:::::Lewis
::::
::::Neal,
::::What is the chassis number for your radio?
::::When I looked at the schematic for an H723, that resistor was not in the filament string.
::::Carl T
:::
:::
:::It looks like it only goes with the Z2 model.
:::Lewis
::
::
::Oh, the value is 100w nominal. I guess that means room tmperature.
::Lewis
::::
:
:Thats 100 ohms, not 100W, and most likely at room temp as you indicate.

Oops, that from my days at AT&T, where a lower case "w" meant Ohms, and a upper case meant Watts.
Lewis

:::::::On a Zenith H723, which is closest to Riders 23-7, model H723Z2: What is resistor R21, in the filament string between the 1st & 2nd IF's. They call it a "special resistor" with no value listed. The only thing I found special about it is that it gets real hot and smokes a lot, and keeps the filaments from lighting up (2.5K ohms, cold). Similar models have a 39 ohm power resistor at that point. What do you suggest? Thanks.....
::::::
::::::
::::::That resostor has a "negative TC", which means that if the temperature goes up, the resistance goes down. The filaments have a positive temperature coefficient, so that when the set is first turned on, the resistor will allow the filaments to warm up more slowly and keep one from hogging all the Voltage and becoming white hot while the others warm up.
::::::
::::::Lewis
:::::
:::::Neal,
:::::What is the chassis number for your radio?
:::::When I looked at the schematic for an H723, that resistor was not in the filament string.
:::::Carl T
::::
::::
::::It looks like it only goes with the Z2 model.
::::Lewis
:::
:::
:::Oh, the value is 100w nominal. I guess that means room tmperature.
:::Lewis
:::::
::
::Thats 100 ohms, not 100W, and most likely at room temp as you indicate.
:
:
:Oops, that from my days at AT&T, where a lower case "w" meant Ohms, and a upper case meant Watts.
:Lewis

::::::::On a Zenith H723, which is closest to Riders 23-7, model H723Z2: What is resistor R21, in the filament string between the 1st & 2nd IF's. They call it a "special resistor" with no value listed. The only thing I found special about it is that it gets real hot and smokes a lot, and keeps the filaments from lighting up (2.5K ohms, cold). Similar models have a 39 ohm power resistor at that point. What do you suggest? Thanks.....
:::::::
:::::::
:::::::That resostor has a "negative TC", which means that if the temperature goes up, the resistance goes down. The filaments have a positive temperature coefficient, so that when the set is first turned on, the resistor will allow the filaments to warm up more slowly and keep one from hogging all the Voltage and becoming white hot while the others warm up.
:::::::
:::::::Lewis
::::::
::::::Neal,
::::::What is the chassis number for your radio?
::::::When I looked at the schematic for an H723, that resistor was not in the filament string.
::::::Carl T
:::::
:::::
:::::It looks like it only goes with the Z2 model.
:::::Lewis
::::
::::
::::Oh, the value is 100w nominal. I guess that means room tmperature.
::::Lewis
::::::
:::
:::Thats 100 ohms, not 100W, and most likely at room temp as you indicate.
::
::
::Oops, that from my days at AT&T, where a lower case "w" meant Ohms, and a upper case meant Watts.
::Lewis
::If I bypass that surge resistor completely, and say, change the 36C5 tube to a 50C5,l so that the string adds up to 117 volts, would I be doing anything risky?

Looking at the four models of the Zenith H723, 723Z, 723Z1, and 723Z2, it would appear that Zenith fooled around with the filaments quite a bit, finally using that NPO resistor you have. That resistor might be replaced with a thermistor, which is the same thing, only you would have to see what kind of temmperature/resistance curve you are working with, e. g. 100 Ohms cold and ??? hot. (50 Ohms? 75? I am sailing thru uncharted waters here). But, it does appear that Zenith had a bit of a problem getting that filament string working to their satisfaction.
Lewis

:::::::::On a Zenith H723, which is closest to Riders 23-7, model H723Z2: What is resistor R21, in the filament string between the 1st & 2nd IF's. They call it a "special resistor" with no value listed. The only thing I found special about it is that it gets real hot and smokes a lot, and keeps the filaments from lighting up (2.5K ohms, cold). Similar models have a 39 ohm power resistor at that point. What do you suggest? Thanks.....
::::::::
::::::::
::::::::That resostor has a "negative TC", which means that if the temperature goes up, the resistance goes down. The filaments have a positive temperature coefficient, so that when the set is first turned on, the resistor will allow the filaments to warm up more slowly and keep one from hogging all the Voltage and becoming white hot while the others warm up.
::::::::
::::::::Lewis
:::::::
:::::::Neal,
:::::::What is the chassis number for your radio?
:::::::When I looked at the schematic for an H723, that resistor was not in the filament string.
:::::::Carl T
::::::
::::::
::::::It looks like it only goes with the Z2 model.
::::::Lewis
:::::
:::::
:::::Oh, the value is 100w nominal. I guess that means room tmperature.
:::::Lewis
:::::::
::::
::::Thats 100 ohms, not 100W, and most likely at room temp as you indicate.
:::
:::
:::Oops, that from my days at AT&T, where a lower case "w" meant Ohms, and a upper case meant Watts.
:::Lewis
:::If I bypass that surge resistor completely, and say, change the 36C5 tube to a 50C5,l so that the string adds up to 117 volts, would I be doing anything risky?