I am working with an Emerson CV301 (no schematic available) that is wired like a CV280 (per tip I found in search results) with the 12SA7 and 12K7 tubes. I have replaced all caps and resistors according to the CV280 lower schematic on this site and am getting distortion at all volume levels. Plate voltages are normal except for 50L6GT, which is reading 55 instead of 85. Voltage across field coil is supposed to be 27 but is reading 47. Resistance across field coil is supposed to be 450ohms and mine is measuring 477 ohms. I have swapped out all the tubes except the 12K7. It tests good and voltages appear normal, but I do not have a spare. Any ideas as to what the problem may be?

Hi Stan

Since plate voltage is low on the 50L6 it's probably drawing too much current. This tube draws the most current in a radio.

Have you replaced the cap connected to pin #5 of the 50L6? Is the resistor on pin #5 high in value. It should be no more than 500K.

Measure voltage between pin #5 and pin #8 on the 50L6. Pin #5 should be around 5 volts negative. If not there will be distortion and excessive current drawn by this tube.

12K7 most likely wouldn't draw enough current to efrect voltage readings.

Norm

:I am working with an Emerson CV301 (no schematic available) that is wired like a CV280 (per tip I found in search results) with the 12SA7 and 12K7 tubes. I have replaced all caps and resistors according to the CV280 lower schematic on this site and am getting distortion at all volume levels. Plate voltages are normal except for 50L6GT, which is reading 55 instead of 85. Voltage across field coil is supposed to be 27 but is reading 47. Resistance across field coil is supposed to be 450ohms and mine is measuring 477 ohms. I have swapped out all the tubes except the 12K7. It tests good and voltages appear normal, but I do not have a spare. Any ideas as to what the problem may be?

Pin 5 should be -5 volts with respect to the cathode, not B-....just to clarify.

T.

:Voltage of pin 5 with respect to pin 8 (Thanks Thomas for the clarification) was slightly positive with 510 Ohms between pin 5 and pin 2. I subbed a 390K resistor and plate voltage is now 53.2, pin 5 with respect to pin 8 is now -.28v and distortion is a little better. The cap from pin 5 to pin 6 of 12SQ7 is a new .022. Volts across field coil is now 42.

Is it possible that the resistor on 50L6 fin 5 to pin 2 should be 50K and not 500K for this unit?

Stan
:Hi Stan
:
: Since plate voltage is low on the 50L6 it's probably drawing too much current. This tube draws the most current in a radio.
:
: Have you replaced the cap connected to pin #5 of the 50L6? Is the resistor on pin #5 high in value. It should be no more than 500K.
:
: Measure voltage between pin #5 and pin #8 on the 50L6. Pin #5 should be around 5 volts negative. If not there will be distortion and excessive current drawn by this tube.
:
: 12K7 most likely wouldn't draw enough current to efrect voltage readings.
:
:Norm
:
::I am working with an Emerson CV301 (no schematic available) that is wired like a CV280 (per tip I found in search results) with the 12SA7 and 12K7 tubes. I have replaced all caps and resistors according to the CV280 lower schematic on this site and am getting distortion at all volume levels. Plate voltages are normal except for 50L6GT, which is reading 55 instead of 85. Voltage across field coil is supposed to be 27 but is reading 47. Resistance across field coil is supposed to be 450ohms and mine is measuring 477 ohms. I have swapped out all the tubes except the 12K7. It tests good and voltages appear normal, but I do not have a spare. Any ideas as to what the problem may be?

Hi Stan

Voltage must be more negative than that on pin #5 when measured from pin #8. The grid resistor should have a value no higher than 500K but not as low as 50K. Using 390K would be ok.

Three things can cause positive voltage on the grid, coupling cap, high value grid resistor or leaky tube. You replaced the cap and resistor. Now you should replace the tube. It can test good on a tube tester and still fail in a radio after some time.

Norm

::Voltage of pin 5 with respect to pin 8 (Thanks Thomas for the clarification) was slightly positive with 510 Ohms between pin 5 and pin 2. I subbed a 390K resistor and plate voltage is now 53.2, pin 5 with respect to pin 8 is now -.28v and distortion is a little better. The cap from pin 5 to pin 6 of 12SQ7 is a new .022. Volts across field coil is now 42.
:
:Is it possible that the resistor on 50L6 fin 5 to pin 2 should be 50K and not 500K for this unit?
:
:Stan
::Hi Stan
::
:: Since plate voltage is low on the 50L6 it's probably drawing too much current. This tube draws the most current in a radio.
::
:: Have you replaced the cap connected to pin #5 of the 50L6? Is the resistor on pin #5 high in value. It should be no more than 500K.
::
:: Measure voltage between pin #5 and pin #8 on the 50L6. Pin #5 should be around 5 volts negative. If not there will be distortion and excessive current drawn by this tube.
::
:: 12K7 most likely wouldn't draw enough current to efrect voltage readings.
::
::Norm
::
:::I am working with an Emerson CV301 (no schematic available) that is wired like a CV280 (per tip I found in search results) with the 12SA7 and 12K7 tubes. I have replaced all caps and resistors according to the CV280 lower schematic on this site and am getting distortion at all volume levels. Plate voltages are normal except for 50L6GT, which is reading 55 instead of 85. Voltage across field coil is supposed to be 27 but is reading 47. Resistance across field coil is supposed to be 450ohms and mine is measuring 477 ohms. I have swapped out all the tubes except the 12K7. It tests good and voltages appear normal, but I do not have a spare. Any ideas as to what the problem may be?

:OK...swapped to a NOS 50L6, which also tested good. Now pin 5 is -1.0v compared to 8, plate voltage is 60v and field coil voltage is 40v. Distortion is a lot better - just a bit 'fuzzy' but not bad. Speaker cone is intact and tight. Should I back the 390k resistor down to 330k and so on until voltages come into line?
:Hi Stan
:
: Voltage must be more negative than that on pin #5 when measured from pin #8. The grid resistor should have a value no higher than 500K but not as low as 50K. Using 390K would be ok.
:
: Three things can cause positive voltage on the grid, coupling cap, high value grid resistor or leaky tube. You replaced the cap and resistor. Now you should replace the tube. It can test good on a tube tester and still fail in a radio after some time.
:
:
:Norm
:
:
:::Voltage of pin 5 with respect to pin 8 (Thanks Thomas for the clarification) was slightly positive with 510 Ohms between pin 5 and pin 2. I subbed a 390K resistor and plate voltage is now 53.2, pin 5 with respect to pin 8 is now -.28v and distortion is a little better. The cap from pin 5 to pin 6 of 12SQ7 is a new .022. Volts across field coil is now 42.
::
::Is it possible that the resistor on 50L6 fin 5 to pin 2 should be 50K and not 500K for this unit?
::
::Stan
:::Hi Stan
:::
::: Since plate voltage is low on the 50L6 it's probably drawing too much current. This tube draws the most current in a radio.
:::
::: Have you replaced the cap connected to pin #5 of the 50L6? Is the resistor on pin #5 high in value. It should be no more than 500K.
:::
::: Measure voltage between pin #5 and pin #8 on the 50L6. Pin #5 should be around 5 volts negative. If not there will be distortion and excessive current drawn by this tube.
:::
::: 12K7 most likely wouldn't draw enough current to efrect voltage readings.
:::
:::Norm
:::
::::I am working with an Emerson CV301 (no schematic available) that is wired like a CV280 (per tip I found in search results) with the 12SA7 and 12K7 tubes. I have replaced all caps and resistors according to the CV280 lower schematic on this site and am getting distortion at all volume levels. Plate voltages are normal except for 50L6GT, which is reading 55 instead of 85. Voltage across field coil is supposed to be 27 but is reading 47. Resistance across field coil is supposed to be 450ohms and mine is measuring 477 ohms. I have swapped out all the tubes except the 12K7. It tests good and voltages appear normal, but I do not have a spare. Any ideas as to what the problem may be?

I am curious about the wiring you describe. Typically the 50L6 is much 'higher' up in the string, and neither of its pins connect directly to B- (pins 2 and 7). Because of this, I'm curious as to why the grid biasing resistor (going to pin 5) is connected to pin 2 (one of the filament pins). Take a look: http://www.nostalgiaair.org/PagesByModel/979/M0004979.pdf

If the grid biasing resistor is connecting to pin 2 of the 50L6, grid biasing will certainly be messed up. The audio will distort, the tube will draw excess current, and you may even hear hum in the speaker. Connect the grid biasing resistor to wherever the cathode biasing resistor connects from pin 8, which would be B- (don't connect the grid biasing resistor to pin 8, but rather wherever the other side of the resistor on pin 8 connects to...which is B-.....). Follow the above schematic well. Even if your radio is somewhat different, the above schematic will give you clues as to how things should be.

T.

:Rats, I lied; the 50L6 grid biasing resistor is connected from pin 5 to pin ONE, which is connected to the chassis. Pin 8 runs straight to pin 8 of the 12SQ7, which is jumped to pin 1, which is also connected to the chassis.
What is missing (and apparently never present in this unit) is C22 and R3. They are not present at all, and chassis uses 12SA7GT, per note 1b on schematic. Boy am I confused...this schematic of the tube components is causing me to have to cross reference 'real' tube diagrams to even make sense of it. Thomas, do you have the patience to continue helping me with this?
Would installing these components bring the field and 50L6 plate and bias voltages into line? (The radio had a cut cord when I got it, but is did not appear to have been hacked. Is the condition I'm experiencing the reason they made the production change and this unit fell between the cracks??)
Arrggg! I really do appreciate the help. It sure would be nice to get a 'normal' radio to restore one day...

:I am curious about the wiring you describe. Typically the 50L6 is much 'higher' up in the string, and neither of its pins connect directly to B- (pins 2 and 7). Because of this, I'm curious as to why the grid biasing resistor (going to pin 5) is connected to pin 2 (one of the filament pins). Take a look: http://www.nostalgiaair.org/PagesByModel/979/M0004979.pdf
:
:If the grid biasing resistor is connecting to pin 2 of the 50L6, grid biasing will certainly be messed up. The audio will distort, the tube will draw excess current, and you may even hear hum in the speaker. Connect the grid biasing resistor to wherever the cathode biasing resistor connects from pin 8, which would be B- (don't connect the grid biasing resistor to pin 8, but rather wherever the other side of the resistor on pin 8 connects to...which is B-.....). Follow the above schematic well. Even if your radio is somewhat different, the above schematic will give you clues as to how things should be.
:
:T.

:I'm going to report current state and, unless someone has some ideas, I'm going to have to move on and revisit this one later.
Using CV280 lower schematic on page 11-7 and the data sheet from 11-8:
12SQ7 plate is 50v (should be 40) and 50L6GT plate is 59 (should be 82), screen is 77 (should be 88) and pin 5 is -1.0 compared to pin 8 (should be -5). All caps and resistors have been replaced and checked against the schematic to be sure they match up. I have swapped tubes around in almost endless combinations and have settled on 'best possible performace' set. I have a bit of distortion, but not too bad...same at all volume levels. Improves if I touch the tuner knob stem. Distortion is much worse with plug polarity one way versus the other.

Any final thoughts before I set it aside?

Thanks much!!!
Stan
:Rats, I lied; the 50L6 grid biasing resistor is connected from pin 5 to pin ONE, which is connected to the chassis. Pin 8 runs straight to pin 8 of the 12SQ7, which is jumped to pin 1, which is also connected to the chassis.
:What is missing (and apparently never present in this unit) is C22 and R3. They are not present at all, and chassis uses 12SA7GT, per note 1b on schematic. Boy am I confused...this schematic of the tube components is causing me to have to cross reference 'real' tube diagrams to even make sense of it. Thomas, do you have the patience to continue helping me with this?
:Would installing these components bring the field and 50L6 plate and bias voltages into line? (The radio had a cut cord when I got it, but is did not appear to have been hacked. Is the condition I'm experiencing the reason they made the production change and this unit fell between the cracks??)
:Arrggg! I really do appreciate the help. It sure would be nice to get a 'normal' radio to restore one day...
:
::I am curious about the wiring you describe. Typically the 50L6 is much 'higher' up in the string, and neither of its pins connect directly to B- (pins 2 and 7). Because of this, I'm curious as to why the grid biasing resistor (going to pin 5) is connected to pin 2 (one of the filament pins). Take a look: http://www.nostalgiaair.org/PagesByModel/979/M0004979.pdf
::
::If the grid biasing resistor is connecting to pin 2 of the 50L6, grid biasing will certainly be messed up. The audio will distort, the tube will draw excess current, and you may even hear hum in the speaker. Connect the grid biasing resistor to wherever the cathode biasing resistor connects from pin 8, which would be B- (don't connect the grid biasing resistor to pin 8, but rather wherever the other side of the resistor on pin 8 connects to...which is B-.....). Follow the above schematic well. Even if your radio is somewhat different, the above schematic will give you clues as to how things should be.
::
::T.

Well, I didn't want to butt in on Norm. I was just catching a few things that noone else caught, but if he runs out of ideas, I'll step in. He's pretty smart, though.

T.

Stan,

I realize that the coupling cap has been replaced, BUT, sometimes even new caps are defective.

Just my 2 cents.

Gary

::OK...swapped to a NOS 50L6, which also tested good. Now pin 5 is -1.0v compared to 8, plate voltage is 60v and field coil voltage is 40v. Distortion is a lot better - just a bit 'fuzzy' but not bad. Speaker cone is intact and tight. Should I back the 390k resistor down to 330k and so on until voltages come into line?
::Hi Stan
::
:: Voltage must be more negative than that on pin #5 when measured from pin #8. The grid resistor should have a value no higher than 500K but not as low as 50K. Using 390K would be ok.
::
:: Three things can cause positive voltage on the grid, coupling cap, high value grid resistor or leaky tube. You replaced the cap and resistor. Now you should replace the tube. It can test good on a tube tester and still fail in a radio after some time.
::
::
::Norm
::
::
::::Voltage of pin 5 with respect to pin 8 (Thanks Thomas for the clarification) was slightly positive with 510 Ohms between pin 5 and pin 2. I subbed a 390K resistor and plate voltage is now 53.2, pin 5 with respect to pin 8 is now -.28v and distortion is a little better. The cap from pin 5 to pin 6 of 12SQ7 is a new .022. Volts across field coil is now 42.
:::
:::Is it possible that the resistor on 50L6 fin 5 to pin 2 should be 50K and not 500K for this unit?
:::
:::Stan
::::Hi Stan
::::
:::: Since plate voltage is low on the 50L6 it's probably drawing too much current. This tube draws the most current in a radio.
::::
:::: Have you replaced the cap connected to pin #5 of the 50L6? Is the resistor on pin #5 high in value. It should be no more than 500K.
::::
:::: Measure voltage between pin #5 and pin #8 on the 50L6. Pin #5 should be around 5 volts negative. If not there will be distortion and excessive current drawn by this tube.
::::
:::: 12K7 most likely wouldn't draw enough current to efrect voltage readings.
::::
::::Norm
::::
:::::I am working with an Emerson CV301 (no schematic available) that is wired like a CV280 (per tip I found in search results) with the 12SA7 and 12K7 tubes. I have replaced all caps and resistors according to the CV280 lower schematic on this site and am getting distortion at all volume levels. Plate voltages are normal except for 50L6GT, which is reading 55 instead of 85. Voltage across field coil is supposed to be 27 but is reading 47. Resistance across field coil is supposed to be 450ohms and mine is measuring 477 ohms. I have swapped out all the tubes except the 12K7. It tests good and voltages appear normal, but I do not have a spare. Any ideas as to what the problem may be?

:Thanks Gary. Never can assume anything, that's for sure.
I'm going to report current state and, unless someone has some ideas, I'm going to have to move on and revisit this one later.
Using CV280 lower schematic on page 11-7 and the data sheet from 11-8:
12SQ7 plate is 50v (should be 40) and 50L6GT plate is 59 (should be 82), screen is 77 (should be 88) and pin 5 is -1.0 compared to pin 8 (should be -5). All caps and resistors have been replaced and checked against the schematic to be sure they match up. I have swapped tubes around in almost endless combinations and have settled on 'best possible performace' set. I have a bit of distortion, but not too bad...same at all volume levels. Improves if I touch the tuner knob stem. Distortion is much worse with plug polarity one way versus the other.
Any final thoughts before I set it aside?

Thanks much!!!
Stan

:Stan,
:
:I realize that the coupling cap has been replaced, BUT, sometimes even new caps are defective.
:
:Just my 2 cents.
:
:Gary
:
:
:
:::OK...swapped to a NOS 50L6, which also tested good. Now pin 5 is -1.0v compared to 8, plate voltage is 60v and field coil voltage is 40v. Distortion is a lot better - just a bit 'fuzzy' but not bad. Speaker cone is intact and tight. Should I back the 390k resistor down to 330k and so on until voltages come into line?
:::Hi Stan
:::
::: Voltage must be more negative than that on pin #5 when measured from pin #8. The grid resistor should have a value no higher than 500K but not as low as 50K. Using 390K would be ok.
:::
::: Three things can cause positive voltage on the grid, coupling cap, high value grid resistor or leaky tube. You replaced the cap and resistor. Now you should replace the tube. It can test good on a tube tester and still fail in a radio after some time.
:::
:::
:::Norm
:::
:::
:::::Voltage of pin 5 with respect to pin 8 (Thanks Thomas for the clarification) was slightly positive with 510 Ohms between pin 5 and pin 2. I subbed a 390K resistor and plate voltage is now 53.2, pin 5 with respect to pin 8 is now -.28v and distortion is a little better. The cap from pin 5 to pin 6 of 12SQ7 is a new .022. Volts across field coil is now 42.
::::
::::Is it possible that the resistor on 50L6 fin 5 to pin 2 should be 50K and not 500K for this unit?
::::
::::Stan
:::::Hi Stan
:::::
::::: Since plate voltage is low on the 50L6 it's probably drawing too much current. This tube draws the most current in a radio.
:::::
::::: Have you replaced the cap connected to pin #5 of the 50L6? Is the resistor on pin #5 high in value. It should be no more than 500K.
:::::
::::: Measure voltage between pin #5 and pin #8 on the 50L6. Pin #5 should be around 5 volts negative. If not there will be distortion and excessive current drawn by this tube.
:::::
::::: 12K7 most likely wouldn't draw enough current to efrect voltage readings.
:::::
:::::Norm
:::::
::::::I am working with an Emerson CV301 (no schematic available) that is wired like a CV280 (per tip I found in search results) with the 12SA7 and 12K7 tubes. I have replaced all caps and resistors according to the CV280 lower schematic on this site and am getting distortion at all volume levels. Plate voltages are normal except for 50L6GT, which is reading 55 instead of 85. Voltage across field coil is supposed to be 27 but is reading 47. Resistance across field coil is supposed to be 450ohms and mine is measuring 477 ohms. I have swapped out all the tubes except the 12K7. It tests good and voltages appear normal, but I do not have a spare. Any ideas as to what the problem may be?

The output transformer is bad.
Bill

::Thanks Gary. Never can assume anything, that's for sure.
:I'm going to report current state and, unless someone has some ideas, I'm going to have to move on and revisit this one later.
:Using CV280 lower schematic on page 11-7 and the data sheet from 11-8:
:12SQ7 plate is 50v (should be 40) and 50L6GT plate is 59 (should be 82), screen is 77 (should be 88) and pin 5 is -1.0 compared to pin 8 (should be -5). All caps and resistors have been replaced and checked against the schematic to be sure they match up. I have swapped tubes around in almost endless combinations and have settled on 'best possible performace' set. I have a bit of distortion, but not too bad...same at all volume levels. Improves if I touch the tuner knob stem. Distortion is much worse with plug polarity one way versus the other.
:Any final thoughts before I set it aside?
:
:Thanks much!!!
:Stan
:
:
::Stan,
::
::I realize that the coupling cap has been replaced, BUT, sometimes even new caps are defective.
::
::Just my 2 cents.
::
::Gary
::
::
::
::::OK...swapped to a NOS 50L6, which also tested good. Now pin 5 is -1.0v compared to 8, plate voltage is 60v and field coil voltage is 40v. Distortion is a lot better - just a bit 'fuzzy' but not bad. Speaker cone is intact and tight. Should I back the 390k resistor down to 330k and so on until voltages come into line?
::::Hi Stan
::::
:::: Voltage must be more negative than that on pin #5 when measured from pin #8. The grid resistor should have a value no higher than 500K but not as low as 50K. Using 390K would be ok.
::::
:::: Three things can cause positive voltage on the grid, coupling cap, high value grid resistor or leaky tube. You replaced the cap and resistor. Now you should replace the tube. It can test good on a tube tester and still fail in a radio after some time.
::::
::::
::::Norm
::::
::::
::::::Voltage of pin 5 with respect to pin 8 (Thanks Thomas for the clarification) was slightly positive with 510 Ohms between pin 5 and pin 2. I subbed a 390K resistor and plate voltage is now 53.2, pin 5 with respect to pin 8 is now -.28v and distortion is a little better. The cap from pin 5 to pin 6 of 12SQ7 is a new .022. Volts across field coil is now 42.
:::::
:::::Is it possible that the resistor on 50L6 fin 5 to pin 2 should be 50K and not 500K for this unit?
:::::
:::::Stan
::::::Hi Stan
::::::
:::::: Since plate voltage is low on the 50L6 it's probably drawing too much current. This tube draws the most current in a radio.
::::::
:::::: Have you replaced the cap connected to pin #5 of the 50L6? Is the resistor on pin #5 high in value. It should be no more than 500K.
::::::
:::::: Measure voltage between pin #5 and pin #8 on the 50L6. Pin #5 should be around 5 volts negative. If not there will be distortion and excessive current drawn by this tube.
::::::
:::::: 12K7 most likely wouldn't draw enough current to efrect voltage readings.
::::::
::::::Norm
::::::
:::::::I am working with an Emerson CV301 (no schematic available) that is wired like a CV280 (per tip I found in search results) with the 12SA7 and 12K7 tubes. I have replaced all caps and resistors according to the CV280 lower schematic on this site and am getting distortion at all volume levels. Plate voltages are normal except for 50L6GT, which is reading 55 instead of 85. Voltage across field coil is supposed to be 27 but is reading 47. Resistance across field coil is supposed to be 450ohms and mine is measuring 477 ohms. I have swapped out all the tubes except the 12K7. It tests good and voltages appear normal, but I do not have a spare. Any ideas as to what the problem may be?

You should check to see what's pulling down the B+

If you unsolder the B+ from the 50L6 plate does it go up?

If you disconnect the output transformer does the b+ line go up?

:Problem solved. I had mentioned previously that C22 and R3 were missing from this radio when I got it. Since the schematic is not specifically for this radio, I did not think TOO much about it, but it still bothered me just a bit. Adding the electrolytic and the 140ohm resistor DID NOT work, but simply adding the 140 to the circuit brings the voltages more into line (not perfect, but close) and eliminates the distortion. Thanks to all for all the help and advice.
Stan

:You should check to see what's pulling down the B+
:
:If you unsolder the B+ from the 50L6 plate does it go up?
:
:If you disconnect the output transformer does the b+ line go up?
:

If adding a 140 ohm cathode bias resistor worked... then adding a small (20uf@15vdc) cap across it WILL also work.

That "cathode by-pass capacitor" can only help improve the action of the cathode resistor.

If, as you say, you put a cap across THAT cathode resistor and it didn't work??.. then you have something much more serious going on here.

:At the time, when I was still grasping at straws, I installed the 140 along with a 22mf 160 electrolytic, which was all I had on hand to try. When I began bringing the variac up, the pilot light began to glow very brightly at only a few volts, so I stopped and made the (erroneous) decision that it was not the problem. I was afraid I was overloading something. Perhaps it is because the cap was too high a voltage?
I have a 10mf at 50 volts, but was afraid to try that too. I guess part of the whole problem is that I never had REAL confidence that I could trust the schematic since it was not actually for this radio. I takes so long to learn all the 'whys' of this. Thanks so much for the insight.
Stan
:If adding a 140 ohm cathode bias resistor worked... then adding a small (20uf@15vdc) cap across it WILL also work.
:
:That "cathode by-pass capacitor" can only help improve the action of the cathode resistor.
:
:If, as you say, you put a cap across THAT cathode resistor and it didn't work??.. then you have something much more serious going on here.

A capacitor's working voltage rating won't harm anything so long as it isn't below the recommended value for the ciruit in which it is being used. You can go as high as you want for the voltage. It affects nothing. Some say that using an electrolytic with a higher than necessary voltage rating will reduce the rating of the capacitor over time. I suppose that this is so, since the capacitor will only be kept formed at the voltage at which it is working at. However, if the capacitor is going to be a semi-permanent part of the circuit in which it is used, that should be no concern for you.

Regarding the pilot lamp, if it is glowing really brightly before the tubes are even warmed up, then you have issues in the pilot lamp circuit (such as a blown filament between pins 2 and 3 of the 35Z5). If it doesn't glow brightly until after the tubes warm up, then the trouble lies somewhere else in the radio, such as the problem that's causing excessive field coil voltage drop, and low output plate voltage.

Again I suggest you remove the B+ loads from the power supply then see if the power supply is putting out the right voltage.

Disconnect the input B+ to the audio output transformer for starters ans see what the B+ measures.

This may all see rather intimidating at first... but with a little logical troubleshooting you can easily solve this problem... and you'll feel exhilarated.

Just keep removing B+ loads until only the B+ after the field coil on the 2nd filter cap is being measured with no loads.
If it doesn't come up to normal there the rectifier or power supply is at fault.