Just replaced 4 section candohm power resistor, with
4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
I'M thinking this is what caused the original to
burn out.Any Need your input. Thanks, Nick

:Just replaced 4 section candohm power resistor, with
:4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
: I'M thinking this is what caused the original to
:burn out.Any Need your input. Thanks, Nick
:

::Just replaced 4 section candohm power resistor, with
::4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
:: I'M thinking this is what caused the original to
::burn out.Any Need your input. Thanks, Nick
::
:Ment to say that i could use your input.
:

:::Just replaced 4 section candohm power resistor, with
:::4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
::: I'M thinking this is what caused the original to
:::burn out.Any Need your input. Thanks, Nick
:::
::Ment to say that i could use your input.
::
:
:
Hello Nick,

I restored one of these some time ago and used 5 watt resistors. They were warm to the touch but not hot.

When your radio came to life does it mean normal operation, receiving stations with a volume control?

Did you change all of the old capacitors? Can you post the wattage the radio is drawing before we think about looking for a short (leaky capacitor to ground)?

Mitch

::::Just replaced 4 section candohm power resistor, with
::::4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
:::: I'M thinking this is what caused the original to
::::burn out.Any Need your input. Thanks, Nick
::::
:::Ment to say that i could use your input.
:::
::
::
:Hello Nick,
:
:I restored one of these some time ago and used 5 watt resistors. They were warm to the touch but not hot.
:
:When your radio came to life does it mean normal operation, receiving stations with a volume control?
:
:Did you change all of the old capacitors? Can you post the wattage the radio is drawing before we think about looking for a short (leaky capacitor to ground)?
:
:Mitch
:
:I dont know what wattage draw, but I did replace all
the old caps. Iget several stations, with volume control. the 11k resistor gets too hot to touch.
:
:

:::::Just replaced 4 section candohm power resistor, with
:::::4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
::::: I'M thinking this is what caused the original to
:::::burn out.Any Need your input. Thanks, Nick
:::::
::::Ment to say that i could use your input.
::::
:::
:::
::Hello Nick,
::
::I restored one of these some time ago and used 5 watt resistors. They were warm to the touch but not hot.
::
::When your radio came to life does it mean normal operation, receiving stations with a volume control?
::
::Did you change all of the old capacitors? Can you post the wattage the radio is drawing before we think about looking for a short (leaky capacitor to ground)?
::
::Mitch
::
::I dont know what wattage draw, but I did replace all
:the old caps. Iget several stations, with volume control. the 11k resistor gets too hot to touch.
::
::
:
:
Nick,

If you could amp clamp the input wire (AC) you could measure the current draw and multiply that by the voltage to get the wattage. If the wattage draw is correct you may just need a larger wattage resistor, but 10 watts is alot.

How close to 670 ohms is the speaker field coil?

Does the 5Y3 glow very bright, very?

Seems this B+ supplies several circuits that that can be isolated in looking for a short.

What do you guess the original wattage of this 11K resistor was by looking at it?

Mitch

:::::Just replaced 4 section candohm power resistor, with
:::::4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
::::: I'M thinking this is what caused the original to
:::::burn out.Any Need your input. Thanks, Nick
:::::
::::Ment to say that i could use your input.
::::
:::
:::
::Hello Nick,
::
::I restored one of these some time ago and used 5 watt resistors. They were warm to the touch but not hot.
::
::When your radio came to life does it mean normal operation, receiving stations with a volume control?
::
::Did you change all of the old capacitors? Can you post the wattage the radio is drawing before we think about looking for a short (leaky capacitor to ground)?
::
::Mitch
::
::I dont know what wattage draw, but I did replace all
:the old caps. Iget several stations, with volume control. the 11k resistor gets too hot to touch.
::
::
:
:

Hi Nick,
Measure the voltage (V) across the 11K resistor then do the calculation, Watts = V*V/11K. This will give the wattage being dissipated by the resistor. If it is less than the rating you are OK. Some resistors are designed to run at a temperature that is too hot to touch.

Best Regards,

Bill Grimm
:::::Just replaced 4 section candohm power resistor, with
:::::4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
::::: I'M thinking this is what caused the original to
:::::burn out.Any Need your input. Thanks, Nick
:::::
::::Ment to say that i could use your input.
::::
:::
:::
::Hello Nick,
::
::I restored one of these some time ago and used 5 watt resistors. They were warm to the touch but not hot.
::
::When your radio came to life does it mean normal operation, receiving stations with a volume control?
::
::Did you change all of the old capacitors? Can you post the wattage the radio is drawing before we think about looking for a short (leaky capacitor to ground)?
::
::Mitch
::
::I dont know what wattage draw, but I did replace all
:the old caps. Iget several stations, with volume control. the 11k resistor gets too hot to touch.
::
::
:
:

:Hi Nick,
: Measure the voltage (V) across the 11K resistor then do the calculation, Watts = V*V/11K. This will give the wattage being dissipated by the resistor. If it is less than the rating you are OK. Some resistors are designed to run at a temperature that is too hot to touch.
:
:Best Regards,
:
:Bill Grimm
::::::Just replaced 4 section candohm power resistor, with
::::::4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
:::::: I'M thinking this is what caused the original to
::::::burn out.Any Need your input. Thanks, Nick
::::::
:::::Ment to say that i could use your input.
:::::
::::
::::
:::Hello Nick,
:::
:::I restored one of these some time ago and used 5 watt resistors. They were warm to the touch but not hot.
:::
:::When your radio came to life does it mean normal operation, receiving stations with a volume control?
:::
:::Did you change all of the old capacitors? Can you post the wattage the radio is drawing before we think about looking for a short (leaky capacitor to ground)?
:::
:::Mitch
:::
:::I dont know what wattage draw, but I did replace all
::the old caps. Iget several stations, with volume control. the 11k resistor gets too hot to touch.
:::
:::
::Bill, the voltage across the 11k resistor is 225 volts the resistor is 10 watts
::
:
:

::Hi Nick,
:: Measure the voltage (V) across the 11K resistor then do the calculation, Watts = V*V/11K. This will give the wattage being dissipated by the resistor. If it is less than the rating you are OK. Some resistors are designed to run at a temperature that is too hot to touch.
::
::Best Regards,
::
::Bill Grimm
:::::::Just replaced 4 section candohm power resistor, with
:::::::4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
::::::: I'M thinking this is what caused the original to
:::::::burn out.Any Need your input. Thanks, Nick
:::::::
::::::Ment to say that i could use your input.
::::::
:::::
:::::
::::Hello Nick,
::::
::::I restored one of these some time ago and used 5 watt resistors. They were warm to the touch but not hot.
::::
::::When your radio came to life does it mean normal operation, receiving stations with a volume control?
::::
::::Did you change all of the old capacitors? Can you post the wattage the radio is drawing before we think about looking for a short (leaky capacitor to ground)?
::::
::::Mitch
::::
::::I dont know what wattage draw, but I did replace all
:::the old caps. Iget several stations, with volume control. the 11k resistor gets too hot to touch.
::::
::::
:::Bill, the voltage across the 11k resistor is 225 volts the resistor is 10 watts
:::
::
::
:
:
-----------------------

Nick,

If the voltage drop across the 11K resistor is 225 volts? then: Watts = 225X225 / 11,000 = 4.6 Watts.

Too Much.

What is the voltage drop across the other 11K resistor?

Reread Tom's post, follow his instructions and it will lead you to your problem.

Mitch

Hi Nick,
The resistor is 10 watts it is dissipating 4.6 watts. The hot resistor is OK. Don't worry about it.

Best regards,

Bill Grimm

Bill, the voltage across the 11k resistor is 225 volts the resistor is 10 watts

:-----------------------

Nick,

If the voltage drop across the 11K resistor is 225 volts? then: Watts = 225X225 / 11,000 = 4.6 Watts.

Too Much.

What is the voltage drop across the other 11K resistor?

Reread Tom's post, follow his instructions and it will lead you to your problem.

Mitch

:::Hi Nick,
::: Measure the voltage (V) across the 11K resistor then do the calculation, Watts = V*V/11K. This will give the wattage being dissipated by the resistor. If it is less than the rating you are OK. Some resistors are designed to run at a temperature that is too hot to touch.
:::
:::Best Regards,
:::
:::Bill Grimm
::::::::Just replaced 4 section candohm power resistor, with
::::::::4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
:::::::: I'M thinking this is what caused the original to
::::::::burn out.Any Need your input. Thanks, Nick
::::::::
:::::::Ment to say that i could use your input.
:::::::
::::::
::::::
:::::Hello Nick,
:::::
:::::I restored one of these some time ago and used 5 watt resistors. They were warm to the touch but not hot.
:::::
:::::When your radio came to life does it mean normal operation, receiving stations with a volume control?
:::::
:::::Did you change all of the old capacitors? Can you post the wattage the radio is drawing before we think about looking for a short (leaky capacitor to ground)?
:::::
:::::Mitch
:::::
:::::I dont know what wattage draw, but I did replace all
::::the old caps. Iget several stations, with volume control. the 11k resistor gets too hot to touch.
:::::
:::::
::::Bill, the voltage across the 11k resistor is 225 volts the resistor is 10 watts
::::
:::
:::
::
::
:-----------------------
:
:Nick,
:
:If the voltage drop across the 11K resistor is 225 volts? then: Watts = 225X225 / 11,000 = 4.6 Watts.
:
:Too Much.
:
:What is the voltage drop across the other 11K resistor?
:
:Reread Tom's post, follow his instructions and it will lead you to your problem.
:
:Mitch
:
I'm back at it,looking back, some of the information
that I pocted is not correct.When I replaced the candohm resistor, with 4 10 watt units, I used 2 10K
in place of the 2 11K units, and I used a 82 ohm in place of the 78 0hm, and a 200 ohm in place of the 180
ohm. my question is will this cause the problem I'm
having,also am getting a 60 cycle hum at any volume.
The scehmatic calls for a 12 mfd for C26 and 20 mfd
for C27 filter caps. I used 20 mfd for both caps.Would this cause the hum? Could use input.

Thanks, Nick

:I'm back at it,looking back, some of the information
:that I pocted is not correct.When I replaced the candohm resistor, with 4 10 watt units, I used 2 10K
:in place of the 2 11K units, and I used a 82 ohm in place of the 78 0hm, and a 200 ohm in place of the 180
:ohm. my question is will this cause the problem I'm
:having,also am getting a 60 cycle hum at any volume.
: The scehmatic calls for a 12 mfd for C26 and 20 mfd
:for C27 filter caps. I used 20 mfd for both caps.Would this cause the hum? Could use input.
:
: Thanks, Nick
:
:
= = = = = =

Replacing the two 11K resistors with two 10K resistors will raise the current draw by 10%, which is not enough to cause any trouble. The other two subs should not be problematic either- they will just screw up the tube bias a little, probably not enough to ever be noticeable. The bigger cap on the rectifier is more of a load to the rectifier tube but it shouldn't much care, either.

Your hum problem is symptomatic of an incorrectly wired electrolytic capacitor. Note that this set has a negative-DC-voltage "bias bus" created by the CT of the B+ winding and the 78 ohm section of the Candohm. If you garf up the polarity of the replacement electrolytics in this area, you will have hum. This is a little counterintuitive since for at least one electrolytic cap (C21) in this set, the "positive" side of the cap has to connect to ground (because the "hot" side of the circuit is actually negative with respect to ground). Hope that's not too confusing. The schematic doesn't have polarity markings for the electrolytics, which is a big hindrance- you have to figure out which side of the cap is at the higher DC potential.

The "trick", if there is one, is understanding that the B+ CT creates a negative voltage with respect to chassis ground- and the electrolytic caps on that negative bus have to be correctly oriented.

:
::I'm back at it,looking back, some of the information
::that I pocted is not correct.When I replaced the candohm resistor, with 4 10 watt units, I used 2 10K
::in place of the 2 11K units, and I used a 82 ohm in place of the 78 0hm, and a 200 ohm in place of the 180
::ohm. my question is will this cause the problem I'm
::having,also am getting a 60 cycle hum at any volume.
:: The scehmatic calls for a 12 mfd for C26 and 20 mfd
::for C27 filter caps. I used 20 mfd for both caps.Would this cause the hum? Could use input.
::
:: Thanks, Nick
::
::
:= = = = = =
:
:Replacing the two 11K resistors with two 10K resistors will raise the current draw by 10%, which is not enough to cause any trouble. The other two subs should not be problematic either- they will just screw up the tube bias a little, probably not enough to ever be noticeable. The bigger cap on the rectifier is more of a load to the rectifier tube but it shouldn't much care, either.
:
:Your hum problem is symptomatic of an incorrectly wired electrolytic capacitor. Note that this set has a negative-DC-voltage "bias bus" created by the CT of the B+ winding and the 78 ohm section of the Candohm. If you garf up the polarity of the replacement electrolytics in this area, you will have hum. This is a little counterintuitive since for at least one electrolytic cap (C21) in this set, the "positive" side of the cap has to connect to ground (because the "hot" side of the circuit is actually negative with respect to ground). Hope that's not too confusing. The schematic doesn't have polarity markings for the electrolytics, which is a big hindrance- you have to figure out which side of the cap is at the higher DC potential.
:
:The "trick", if there is one, is understanding that the B+ CT creates a negative voltage with respect to chassis ground- and the electrolytic caps on that negative bus have to be correctly oriented.
:

::
:::I'm back at it,looking back, some of the information
:::that I pocted is not correct.When I replaced the candohm resistor, with 4 10 watt units, I used 2 10K
:::in place of the 2 11K units, and I used a 82 ohm in place of the 78 0hm, and a 200 ohm in place of the 180
:::ohm. my question is will this cause the problem I'm
:::having,also am getting a 60 cycle hum at any volume.
::: The scehmatic calls for a 12 mfd for C26 and 20 mfd
:::for C27 filter caps. I used 20 mfd for both caps.Would this cause the hum? Could use input.
:::
::: Thanks, Nick
:::
:::
::= = = = = =
::
::Replacing the two 11K resistors with two 10K resistors will raise the current draw by 10%, which is not enough to cause any trouble. The other two subs should not be problematic either- they will just screw up the tube bias a little, probably not enough to ever be noticeable. The bigger cap on the rectifier is more of a load to the rectifier tube but it shouldn't much care, either.
::
::Your hum problem is symptomatic of an incorrectly wired electrolytic capacitor. Note that this set has a negative-DC-voltage "bias bus" created by the CT of the B+ winding and the 78 ohm section of the Candohm. If you garf up the polarity of the replacement electrolytics in this area, you will have hum. This is a little counterintuitive since for at least one electrolytic cap (C21) in this set, the "positive" side of the cap has to connect to ground (because the "hot" side of the circuit is actually negative with respect to ground). Hope that's not too confusing. The schematic doesn't have polarity markings for the electrolytics, which is a big hindrance- you have to figure out which side of the cap is at the higher DC potential.
::
::The "trick", if there is one, is understanding that the B+ CT creates a negative voltage with respect to chassis ground- and the electrolytic caps on that negative bus have to be correctly oriented.
::
:I did have C21 backwards, so I replaced it with a new one. Can you tell me the polarity of C26, and C27?
I still have a hum. Thanks again.
:

::I did have C21 backwards, so I replaced it with a new one. Can you tell me the polarity of C26, and C27?
: I still have a hum. Thanks again.
::
:
= = = = = =

The positive side of C26 goes to one side of the speaker field, and the positive side of C27 goes to the other side of the speaker field. Both negative sides of the caps go to the B+ transformer center tap node, NOT CHASSIS GROUND.

In the original set, C24-C27 were part of a combo electrolytic. The black (common) lead of this part went to the B+ transformer center tap, so all four discrete replacement caps must have ther negative leads connected to the CT node... which, again, is NOT CHASSIS GROUND. If you have the negative sides of any of these four caps connected to chassis ground, you have a miswire.

:
:::I did have C21 backwards, so I replaced it with a new one. Can you tell me the polarity of C26, and C27?
:: I still have a hum. Thanks again.
:::
::
:= = = = = =
:
:The positive side of C26 goes to one side of the speaker field, and the positive side of C27 goes to the other side of the speaker field. Both negative sides of the caps go to the B+ transformer center tap node, NOT CHASSIS GROUND.
:
:In the original set, C24-C27 were part of a combo electrolytic. The black (common) lead of this part went to the B+ transformer center tap, so all four discrete replacement caps must have ther negative leads connected to the CT node... which, again, is NOT CHASSIS GROUND. If you have the negative sides of any of these four caps connected to chassis ground, you have a miswire.
:
Thanks Tom I'll check C24-C27 Nick

::
::::I did have C21 backwards, so I replaced it with a new one. Can you tell me the polarity of C26, and C27?
::: I still have a hum. Thanks again.
::::
:::
::= = = = = =
::
::The positive side of C26 goes to one side of the speaker field, and the positive side of C27 goes to the other side of the speaker field. Both negative sides of the caps go to the B+ transformer center tap node, NOT CHASSIS GROUND.
::
::In the original set, C24-C27 were part of a combo electrolytic. The black (common) lead of this part went to the B+ transformer center tap, so all four discrete replacement caps must have ther negative leads connected to the CT node... which, again, is NOT CHASSIS GROUND. If you have the negative sides of any of these four caps connected to chassis ground, you have a miswire.
::
:Thanks Tom I'll check C24-C27 Nick
:
C24-27 ARE HOOKED UP IN THE PROPER DIRECTION.Question
on the ON-OF switch. The only way the radio will come
on with full volume, is if the switch is turned fully
clockwise on the last 2 clicks. Is this normal?
On alignment, it calls for a 200mmfd cap to be connected to signal gen. to radio.can any other cap be used? Thanks, Nick

:C24-27 ARE HOOKED UP IN THE PROPER DIRECTION.Question
:on the ON-OF switch. The only way the radio will come
:on with full volume, is if the switch is turned fully
:clockwise on the last 2 clicks. Is this normal?
: On alignment, it calls for a 200mmfd cap to be connected to signal gen. to radio.can any other cap be used? Thanks, Nick
:
= = = = = = = = =

Well, it's sort of normal. The on-off switch also has a "local-distance" switch on it. First click "on" gives Local, second click past that gives "Distant". Basically all the switch in "Distant" mode does is to short out the cathode resistor of the tracking RF stage, making the stage run wide open for max gain. So, stations will be louder. Since the set already has AVC, it's kind of a pointless feature, but Zenith probably thought that it was a cheap, cool marketing gimmick since it only required the addition of another switch and a length of wire.

I don't know that the 200 pf cap value is supercritical, but they aren't that hard to come by, either. A .001 microfarad cap would probably work fine.

Did you fix the hum problem? These sets are somewhat sensitive to lead routing in the area of the audio stages; if the hum goes away when you turn down the volume, you probably have a hum pickup problem. If the hum is still there at minumum volume control setting, you have a miswire in your B+ filter or the tube bias network.

::C24-27 ARE HOOKED UP IN THE PROPER DIRECTION.Question
::on the ON-OF switch. The only way the radio will come
::on with full volume, is if the switch is turned fully
::clockwise on the last 2 clicks. Is this normal?
:: On alignment, it calls for a 200mmfd cap to be connected to signal gen. to radio.can any other cap be used? Thanks, Nick
::
:= = = = = = = = =
:
:Well, it's sort of normal. The on-off switch also has a "local-distance" switch on it. First click "on" gives Local, second click past that gives "Distant". Basically all the switch in "Distant" mode does is to short out the cathode resistor of the tracking RF stage, making the stage run wide open for max gain. So, stations will be louder. Since the set already has AVC, it's kind of a pointless feature, but Zenith probably thought that it was a cheap, cool marketing gimmick since it only required the addition of another switch and a length of wire.
:
:I don't know that the 200 pf cap value is supercritical, but they aren't that hard to come by, either. A .001 microfarad cap would probably work fine.
:
:Did you fix the hum problem? These sets are somewhat sensitive to lead routing in the area of the audio stages; if the hum goes away when you turn down the volume, you probably have a hum pickup problem. If the hum is still there at minumum volume control setting, you have a miswire in your B+ filter or the tube bias network.
:
The hum is there at low volume.The voltage going to the grids off 10 K resistor is 30 volts.It should be
about 83 volts.The b+ is about 275 volts.Do I have the
polarity of C25 right,with the negative giong to the grids?

:The hum is there at low volume.The voltage going to the grids off 10 K resistor is 30 volts.It should be
:about 83 volts.The b+ is about 275 volts.Do I have the
:polarity of C25 right,with the negative giong to the grids?
:
= = = = =

C25 negative side goes to the B+ center tap node, same as C24, C26, and C27, as previously discussed. The positive side of C25 connects to the 11K/11K voltage divider junction, which in turn goes to the aux screens of the RF amp, detector, and IF tubes- and nowhere else. You should see 50% of B+, or 137 VDC at this node, not 30V.

::The hum is there at low volume.The voltage going to the grids off 10 K resistor is 30 volts.It should be
::about 83 volts.The b+ is about 275 volts.Do I have the
::polarity of C25 right,with the negative giong to the grids?
::
:= = = = =
:
:C25 negative side goes to the B+ center tap node, same as C24, C26, and C27, as previously discussed. The positive side of C25 connects to the 11K/11K voltage divider junction, which in turn goes to the aux screens of the RF amp, detector, and IF tubes- and nowhere else. You should see 50% of B+, or 137 VDC at this node, not 30V.
: Tom,you saved my bacon. The cap was hooked up wrong.
The volume went up, the voltage is up to 135v, and
the sensitivy is way up. More stations, and very little hum. You're the best, Thanks again, Nick
:
:

:: Tom,you saved my bacon. The cap was hooked up wrong.
: The volume went up, the voltage is up to 135v, and
:the sensitivy is way up. More stations, and very little hum. You're the best, Thanks again, Nick

= = = = = = =

Once you align the set, you will find that it is a great performer.

You might want to consider replacing C25. Now that it has sustained a reverse voltage across it for some time, it might be compromised. I don't know if there's a way to predict by how much (if any) of its life has been reduced, but if the cap fails shorted it will almost certainly smoke the top resistor in the divider- possibly what happened to the original Candohm.

:
::: Tom,you saved my bacon. The cap was hooked up wrong.
:: The volume went up, the voltage is up to 135v, and
::the sensitivy is way up. More stations, and very little hum. You're the best, Thanks again, Nick
:
:= = = = = = =
:
:Once you align the set, you will find that it is a great performer.
:
:You might want to consider replacing C25. Now that it has sustained a reverse voltage across it for some time, it might be compromised. I don't know if there's a way to predict by how much (if any) of its life has been reduced, but if the cap fails shorted it will almost certainly smoke the top resistor in the divider- possibly what happened to the original Candohm.
:
Tom, I did replace C25 for that reason. I made plenty of mistakes on this one, so to make sure, can you tell
me the orentation on C20, so I can align the set and button it up.The trimmers that can be adjusted from the top of the chassis,are those the ones listed as:
F-GH-J on the alignment instructions? Thanks, Nick

... can you tell
:me the orentation on C20, so I can align the set and button it up.The trimmers that can be adjusted from the top of the chassis,are those the ones listed as:
:F-GH-J on the alignment instructions? Thanks, Nick
:
= = = = =

C20 is the audio output tubes' AC bypass cap. Its positive side connects to the cathodes.

Look up Zenith 9-S-203 in Resources. This has the trimmer map for the 1204 chassis (your set) on the right side of the second page. DOn't know why this info isn't under the "Chassis 1204" entry, but that's just the way it is for now.

As I recall, all trimmers are on the top of the chassis. There are no "E" or "I" trimmers.

This thing is a PITA to align- it is easy to get the wrong trimmer when trying to make an adjustment, and you won't immediately discover the effect of a misadjustment, since you will be trying to set up a different band than the one you are actually tweaking. I ended up making little paper labels so I could more accurately find the correct trimmers.

:... can you tell
::me the orentation on C20, so I can align the set and button it up.The trimmers that can be adjusted from the top of the chassis,are those the ones listed as:
::F-GH-J on the alignment instructions? Thanks, Nick
::
:= = = = =
:
:C20 is the audio output tubes' AC bypass cap. Its positive side connects to the cathodes.
:
:Look up Zenith 9-S-203 in Resources. This has the trimmer map for the 1204 chassis (your set) on the right side of the second page. DOn't know why this info isn't under the "Chassis 1204" entry, but that's just the way it is for now.
:
: As I recall, all trimmers are on the top of the chassis. There are no "E" or "I" trimmers.
:
:This thing is a PITA to align- it is easy to get the wrong trimmer when trying to make an adjustment, and you won't immediately discover the effect of a misadjustment, since you will be trying to set up a different band than the one you are actually tweaking. I ended up making little paper labels so I could more accurately find the correct trimmers.
:
C20 was connected properly. Found the trimmer layout
in 9-s-203 like yuo said. Is the grid on the first det.,the cap on the 6L7, that the signal gen. connects
to? Nick

Is the grid on the first det.,the cap on the 6L7, that the signal gen. connects
:to? Nick
:
:

= = = = =

Yes.

: Is the grid on the first det.,the cap on the 6L7, that the signal gen. connects
::to? Nick
::
::
:
:= = = = =
:
:Yes.
:
Thanks Tom

:: Is the grid on the first det.,the cap on the 6L7, that the signal gen. connects
:::to? Nick
:::
:::
::
::= = = = =
::
::Yes.
::
:Thanks Tom
:After all is said and done, I still have that 60 cycle hum. Ive double checked all the electrolitics, to make sure they are wired correctly. I know I must be missing somthing.Any thoughts ? Nick

::Thanks Tom
::After all is said and done, I still have that 60 cycle hum. Ive double checked all the electrolitics, to make sure they are wired correctly. I know I must be missing somthing.Any thoughts ? Nick
:
:
= = = = = =

Are you sure that the hum is 60 Hz and not 120 Hz? 60 Hz hum is symptomatic of AC pickup in the audio amp stages; 120 Hz hum indicates a power supply filter problem (the full wave rectifier produces pulsating DC at 2X the line current frequency).

Does the hum go away with the volume control set to minumum? If so, you have AC pickup hum. If not, your power supply filtering is still not right.

These sets won't have zero hum- but it shouldn't be noticeable by someone located a few feet from the speaker.

:::Thanks Tom
:::After all is said and done, I still have that 60 cycle hum. Ive double checked all the electrolitics, to make sure they are wired correctly. I know I must be missing somthing.Any thoughts ? Nick
::
::
:= = = = = =
:
:Are you sure that the hum is 60 Hz and not 120 Hz? 60 Hz hum is symptomatic of AC pickup in the audio amp stages; 120 Hz hum indicates a power supply filter problem (the full wave rectifier produces pulsating DC at 2X the line current frequency).
:
:Does the hum go away with the volume control set to minumum? If so, you have AC pickup hum. If not, your power supply filtering is still not right.
:
:These sets won't have zero hum- but it shouldn't be noticeable by someone located a few feet from the speaker.
:
The hum is there at 0 volume. I replaced C26 and C27
twice, stillno change. Negative side to trans. center
tap. Nick

About the only thing that I've got left to suggest is to try reversing the speaker field connections and see if that reduces the hum.

The speaker has a "hum-bucking" coil and if this is in phase with the pulsating current through the field coil, it will make hum worse, not reduce it as intended. Reversing the speaker field connection will reverse the current with respect to the hum-bucking coil.

If there is no improvement, or the hum gets worse, reconnect the field coil the way that it originally was. You can easily make these changes at the speaker plug socket on the rear wall of the chassis, by the 6V6 audio output tubes.

:About the only thing that I've got left to suggest is to try reversing the speaker field connections and see if that reduces the hum.
:
:The speaker has a "hum-bucking" coil and if this is in phase with the pulsating current through the field coil, it will make hum worse, not reduce it as intended. Reversing the speaker field connection will reverse the current with respect to the hum-bucking coil.
:
:If there is no improvement, or the hum gets worse, reconnect the field coil the way that it originally was. You can easily make these changes at the speaker plug socket on the rear wall of the chassis, by the 6V6 audio output tubes.
:
Tom,Didn't have to reverse leads speaker field.As usual in my case, I found a cold solder joint on one of the filter caps. Like you said:CHECK YOUR WORK!
The hum is now tolerable,not notcible from a few feet away. Thanks again for your great help. Nick

:::Just replaced 4 section candohm power resistor, with
:::4 10 watt wirewound resistors. The radio came to life, But the first 11k resistor runs very hot.Thats the one that connects to the speaker field coil.
::: I'M thinking this is what caused the original to
:::burn out.Any Need your input. Thanks, Nick
:::
::Ment to say that i could use your input.
::
= = = = =

Note that two of the Candohm sections are both 11K ohms and form a voltage divider between B+ and ground. There is nothing that would draw significant current at the junction of the two resistors, so the voltage there should be 50% of B+, or around 125 VDC. Also note that since the current is the same through both resistors and they evenly divide the voltage, they should both "heat up" to the same amount.

In normal operation, power dissipated by either of the 11K ohm resistors should be less than 1.5 watts.

My guess is that you have a shorted or leaky C25. If you remove the wire from the resistor junction and ohm the wire to ground, it should be >100K ohm. If not, the excess load is on that node somewhere. However, it's always good to "check your work" vis a vis possible incorrect parts or miswires. A short or low resistance path from the resistor junction point would cause the same problem.