I have a Zenith 7s530 with noise comming through the speaker but no signal. I replaced the caps and checked the coils. The 7B8 converter tube is weak. I tried subing a good 7A8 but still nothing. Can a 7A8 sub in this application as a converter? I also am trying to learn how to operate a signal tracer. I was able to pick up a radio signal from the antenna coil through the Converter grid but lost it at the plate of the converter. At that point it turned into a loud buzz. What should I be listening for after the signal is passed to the plate of the converter? Thanks for any suggestions or advice. Al

Hi Al

In this radio a 7A8 should work as 7B8.

Does the oscillator operate? The osc circuit is pins #3, #4 and #7. Pin #4 will be several volts negative when the osc operates. Check voltage and coil continuity around this tube.

http://www.nostalgiaair.org/PagesByModel/333/M0025333.pdf

Norm

:I have a Zenith 7s530 with noise comming through the speaker but no signal. I replaced the caps and checked the coils. The 7B8 converter tube is weak. I tried subing a good 7A8 but still nothing. Can a 7A8 sub in this application as a converter? I also am trying to learn how to operate a signal tracer. I was able to pick up a radio signal from the antenna coil through the Converter grid but lost it at the plate of the converter. At that point it turned into a loud buzz. What should I be listening for after the signal is passed to the plate of the converter? Thanks for any suggestions or advice. Al
:

Not sure how accurate my pin location and readings are on these loctals but from the plate clockwise I show a negative on pins 4 and 6 and no voltage reading on pin 7. Plate shows 256. Pin 4 is barely negative as opposed to several volts. My guess is the osc. is not working. All the coils appear to have continuity. This one may be beyond my skill set. Any thoughts? As always thanks for your help. Al

:Hi Al
:
: In this radio a 7A8 should work as 7B8.
:
: Does the oscillator operate? The osc circuit is pins #3, #4 and #7. Pin #4 will be several volts negative when the osc operates. Check voltage and coil continuity around this tube.
:
:http://www.nostalgiaair.org/PagesByModel/333/M0025333.pdf
:
:Norm
:
:
::I have a Zenith 7s530 with noise comming through the speaker but no signal. I replaced the caps and checked the coils. The 7B8 converter tube is weak. I tried subing a good 7A8 but still nothing. Can a 7A8 sub in this application as a converter? I also am trying to learn how to operate a signal tracer. I was able to pick up a radio signal from the antenna coil through the Converter grid but lost it at the plate of the converter. At that point it turned into a loud buzz. What should I be listening for after the signal is passed to the plate of the converter? Thanks for any suggestions or advice. Al
::
:

When looking at the bottom of the tube socket, from the key-way the next pin clock wise is #1. One thing to look for is the tuner itself. If any of the gangs of the rotating part touch the stationary section, this kills the oscillator. The shorter gangs are the oscillator, the taller ones antenna.

Al

The oscillator isn't operating. Pin #4 will be a fraction of a volt negative even without oscillation. When right it will be more like negative 5 volts.

Was pin #3 positive? That is 2nd grid in the tube. It's used as plate for the osc circuit.

Norm

:Not sure how accurate my pin location and readings are on these loctals but from the plate clockwise I show a negative on pins 4 and 6 and no voltage reading on pin 7. Plate shows 256. Pin 4 is barely negative as opposed to several volts. My guess is the osc. is not working. All the coils appear to have continuity. This one may be beyond my skill set. Any thoughts? As always thanks for your help. Al
:
::Hi Al
::
:: In this radio a 7A8 should work as 7B8.
::
:: Does the oscillator operate? The osc circuit is pins #3, #4 and #7. Pin #4 will be several volts negative when the osc operates. Check voltage and coil continuity around this tube.
::
::http://www.nostalgiaair.org/PagesByModel/333/M0025333.pdf
::
::Norm
::
::
:::I have a Zenith 7s530 with noise comming through the speaker but no signal. I replaced the caps and checked the coils. The 7B8 converter tube is weak. I tried subing a good 7A8 but still nothing. Can a 7A8 sub in this application as a converter? I also am trying to learn how to operate a signal tracer. I was able to pick up a radio signal from the antenna coil through the Converter grid but lost it at the plate of the converter. At that point it turned into a loud buzz. What should I be listening for after the signal is passed to the plate of the converter? Thanks for any suggestions or advice. Al
:::
::
:

Pin #3 is supplied through R5 and although didn't find voltage called out on the schematic would expect around 100 volts.

Norm

:Al
:
: The oscillator isn't operating. Pin #4 will be a fraction of a volt negative even without oscillation. When right it will be more like negative 5 volts.
:
: Was pin #3 positive? That is 2nd grid in the tube. It's used as plate for the osc circuit.
:
:Norm
:
::Not sure how accurate my pin location and readings are on these loctals but from the plate clockwise I show a negative on pins 4 and 6 and no voltage reading on pin 7. Plate shows 256. Pin 4 is barely negative as opposed to several volts. My guess is the osc. is not working. All the coils appear to have continuity. This one may be beyond my skill set. Any thoughts? As always thanks for your help. Al
::
:::Hi Al
:::
::: In this radio a 7A8 should work as 7B8.
:::
::: Does the oscillator operate? The osc circuit is pins #3, #4 and #7. Pin #4 will be several volts negative when the osc operates. Check voltage and coil continuity around this tube.
:::
:::http://www.nostalgiaair.org/PagesByModel/333/M0025333.pdf
:::
:::Norm
:::
:::
::::I have a Zenith 7s530 with noise comming through the speaker but no signal. I replaced the caps and checked the coils. The 7B8 converter tube is weak. I tried subing a good 7A8 but still nothing. Can a 7A8 sub in this application as a converter? I also am trying to learn how to operate a signal tracer. I was able to pick up a radio signal from the antenna coil through the Converter grid but lost it at the plate of the converter. At that point it turned into a loud buzz. What should I be listening for after the signal is passed to the plate of the converter? Thanks for any suggestions or advice. Al
::::
:::
::
:

:the converter. At that point it turned into a loud buzz. What should I be listening for after the signal is passed to the plate of the converter? Thanks for any suggestions or advice. Al
:

Thanks Richard - very helpful advice on the tracer. Al

::the converter. At that point it turned into a loud buzz. What should I be listening for after the signal is passed to the plate of the converter? Thanks for any suggestions or advice. Al
::
:
:Should hear the radio station with more gain. Signal tracers are basically an untuned demodulator with a audio amp to drive a loudspeaker. Does take some practice to get confident using it. They tend to de-tune the circuit in question making interpretation dicey. Practice using it on a working radio. Richard
:

:I have a Zenith 7s530 with noise comming through the speaker but no signal. I replaced the caps and checked the coils. The 7B8 converter tube is weak. I tried subing a good 7A8 but still nothing. Can a 7A8 sub in this application as a converter? I also am trying to learn how to operate a signal tracer. I was able to pick up a radio signal from the antenna coil through the Converter grid but lost it at the plate of the converter. At that point it turned into a loud buzz. What should I be listening for after the signal is passed to the plate of the converter? Thanks for any suggestions or advice. Al

I have serviced 3 of these recently and just finished one. Be sure to check the 27K and 10K R's in the B+ line . . .Also, the little 50 pf mica connected to the control grid of the 7B8 is notorious for being partially open. It is located down at the bottom of the wafer band switch and tedious to change but do it.
:

I checked the suggestions out and did find an open resistor in the B+. I replaced it and now hear a faint station from the speaker. The osc. however is still not working since it will not tune other stations. I still do not get the negative volatage reading on pin 4 that it should have. Pin 3 is 99. Readings from the conv./osc. tube are: pin 2(250); 3(99); 4(-1); 5(99); 6(-1); 7 and 8(0) dc. The schematic I have is poor and it is difficult to make out the values of both resistors and caps. Thanks for the help and suggestions so far. Al

::I have a Zenith 7s530 with noise comming through the speaker but no signal. I replaced the caps and checked the coils. The 7B8 converter tube is weak. I tried subing a good 7A8 but still nothing. Can a 7A8 sub in this application as a converter? I also am trying to learn how to operate a signal tracer. I was able to pick up a radio signal from the antenna coil through the Converter grid but lost it at the plate of the converter. At that point it turned into a loud buzz. What should I be listening for after the signal is passed to the plate of the converter? Thanks for any suggestions or advice. Al
:
:I have serviced 3 of these recently and just finished one. Be sure to check the 27K and 10K R's in the B+ line . . .Also, the little 50 pf mica connected to the control grid of the 7B8 is notorious for being partially open. It is located down at the bottom of the wafer band switch and tedious to change but do it.
::
:

Just a brief note and followup on the zenith project. I did finally get it working very well. After replacing a couple of resistors in the circut and realigning the osc. and IF it came to life. What a huge difference allignment makes. Thanks for the help. Al

::I have a Zenith 7s530 with noise comming through the speaker but no signal. I replaced the caps and checked the coils. The 7B8 converter tube is weak. I tried subing a good 7A8 but still nothing. Can a 7A8 sub in this application as a converter? I also am trying to learn how to operate a signal tracer. I was able to pick up a radio signal from the antenna coil through the Converter grid but lost it at the plate of the converter. At that point it turned into a loud buzz. What should I be listening for after the signal is passed to the plate of the converter? Thanks for any suggestions or advice. Al
:
:I have serviced 3 of these recently and just finished one. Be sure to check the 27K and 10K R's in the B+ line . . .Also, the little 50 pf mica connected to the control grid of the 7B8 is notorious for being partially open. It is located down at the bottom of the wafer band switch and tedious to change but do it.
::
: