working on zenith 12-s-266, the four section candohm
power resistor is out, cant find a replacement. Would
a series of 10 watt wirewound resisters work in its place? what would cause this resistor to burn out?
Thanks for ypur help. Nick

:working on zenith 12-s-266, the four section candohm
:power resistor is out, cant find a replacement. Would
:a series of 10 watt wirewound resisters work in its place? what would cause this resistor to burn out?
: Thanks for ypur help. Nick
:
:
:
These Candohm ("canned ohm") resistors have a history of burning out, most likely due to poor design of same. A set of power resistors will work fine. 10 watts is overkill but will work OK. (You can also bridge an open section with a single resistor.) This resistor stack is fed by the HV center tap of the power transformer and is used to generate the negative voltages needed for the grid biases. (Self-biasing of tubes wasn't in vogue back then.) Current through the stack is whatever total the B+ sees but is probably on the order of 80-100 mA, so choose your resistor power ratings accordingly (don't forget to derate by 70%). I replaced the Candohm in my 12-S-265 Zenith (same chassis as yours) with discrete wirewound power resistors about 36 years ago and it still plays great. Also did another 12-S-265 about a year ago with the same results. You have to look hard for the resistors but they are still being manufactured.

The Candohm was an attempt by Zenith to reduce its recurring cost by replacing four parts with one. It probably achieved its beancounter purpose; however, it's also doubtful that anyone at Zenith expected their schlock sets to still be playing in the 21st century.

Don't get me wrong: the Robot Dial Zeniths are iconic radios- but Zenith was in business to make money, and that sometimes meant cutting corners where it seemed at the time like no one would notice.

::working on zenith 12-s-266, the four section candohm
::power resistor is out, cant find a replacement. Would
::a series of 10 watt wirewound resisters work in its place? what would cause this resistor to burn out?
:: Thanks for ypur help. Nick
::
::
::
:These Candohm ("canned ohm") resistors have a history of burning out, most likely due to poor design of same. A set of power resistors will work fine. 10 watts is overkill but will work OK. (You can also bridge an open section with a single resistor.) This resistor stack is fed by the HV center tap of the power transformer and is used to generate the negative voltages needed for the grid biases. (Self-biasing of tubes wasn't in vogue back then.) Current through the stack is whatever total the B+ sees but is probably on the order of 80-100 mA, so choose your resistor power ratings accordingly (don't forget to derate by 70%). I replaced the Candohm in my 12-S-265 Zenith (same chassis as yours) with discrete wirewound power resistors about 36 years ago and it still plays great. Also did another 12-S-265 about a year ago with the same results. You have to look hard for the resistors but they are still being manufactured.
:
:The Candohm was an attempt by Zenith to reduce its recurring cost by replacing four parts with one. It probably achieved its beancounter purpose; however, it's also doubtful that anyone at Zenith expected their schlock sets to still be playing in the 21st century.
:
:Don't get me wrong: the Robot Dial Zeniths are iconic radios- but Zenith was in business to make money, and that sometimes meant cutting corners where it seemed at the time like no one would notice.
:

:::working on zenith 12-s-266, the four section candohm
:::power resistor is out, cant find a replacement. Would
:::a series of 10 watt wirewound resisters work in its place? what would cause this resistor to burn out?
::: Thanks for ypur help. Nick
:::
:::
:::
::These Candohm ("canned ohm") resistors have a history of burning out, most likely due to poor design of same. A set of power resistors will work fine. 10 watts is overkill but will work OK. (You can also bridge an open section with a single resistor.) This resistor stack is fed by the HV center tap of the power transformer and is used to generate the negative voltages needed for the grid biases. (Self-biasing of tubes wasn't in vogue back then.) Current through the stack is whatever total the B+ sees but is probably on the order of 80-100 mA, so choose your resistor power ratings accordingly (don't forget to derate by 70%). I replaced the Candohm in my 12-S-265 Zenith (same chassis as yours) with discrete wirewound power resistors about 36 years ago and it still plays great. Also did another 12-S-265 about a year ago with the same results. You have to look hard for the resistors but they are still being manufactured.
::
::The Candohm was an attempt by Zenith to reduce its recurring cost by replacing four parts with one. It probably achieved its beancounter purpose; however, it's also doubtful that anyone at Zenith expected their schlock sets to still be playing in the 21st century.
::
::Don't get me wrong: the Robot Dial Zeniths are iconic radios- but Zenith was in business to make money, and that sometimes meant cutting corners where it seemed at the time like no one would notice.
::
:Thanks, I have the resistors on order as soon as they arrive I will install them, and let you know
the outcome.
:

::working on zenith 12-s-266, the four section candohm
::power resistor is out, cant find a replacement. Would
::a series of 10 watt wirewound resisters work in its place? what would cause this resistor to burn out?
:: Thanks for ypur help. Nick
::
::
::
:These Candohm ("canned ohm") resistors have a history of burning out, most likely due to poor design of same. A set of power resistors will work fine. 10 watts is overkill but will work OK. (You can also bridge an open section with a single resistor.) This resistor stack is fed by the HV center tap of the power transformer and is used to generate the negative voltages needed for the grid biases. (Self-biasing of tubes wasn't in vogue back then.) Current through the stack is whatever total the B+ sees but is probably on the order of 80-100 mA, so choose your resistor power ratings accordingly (don't forget to derate by 70%). I replaced the Candohm in my 12-S-265 Zenith (same chassis as yours) with discrete wirewound power resistors about 36 years ago and it still plays great. Also did another 12-S-265 about a year ago with the same results. You have to look hard for the resistors but they are still being manufactured.
:
:The Candohm was an attempt by Zenith to reduce its recurring cost by replacing four parts with one. It probably achieved its beancounter purpose; however, it's also doubtful that anyone at Zenith expected their schlock sets to still be playing in the 21st century.
:
:Don't get me wrong: the Robot Dial Zeniths are iconic radios- but Zenith was in business to make money, and that sometimes meant cutting corners where it seemed at the time like no one would notice.
:Some people called those dials scalloped dials & some people called them robot dials. They were a very neat looking & attractive feature BUT they had a lot of problems with them so they stopped doing them because of the WILD linkage set-up. When they were new they worked fine. Sometimes the customers got to wild with the band sw. There was too much linkage & each one had to interact with each other. Sometimes they got dirty & the customers were real rough on those parts because they got real sticky. They rotated the band sw. too hard & too fast! So ZENITH discontinued them. They couldn't keep up with parts replacements. This came from ZENITH history & I had one of those. They were a BITCH to work on & even worse to get lined up. Sometimes one half would show shortwave & other half would show BC at the same time, linkage problems.