Any advice on where to go next?
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:Any advice on where to go next?
Check your pilot lights. They are in series with the 1J6G output tube filament. If the wrong bulbs are in it, the tube may barely light. It originally had 291 bulbs in there. They are difficult to find today. You can order 1490 bulbs which are close. They are 3.2 volts compared to the 291 which was 2.9 volts. If you find 44 or 47 lamps in there, that is the problem. Also, change the bulbs in pairs. Diffiences in lamps or different kinds will cause unbalance and the set will hum on AC use.
Fred
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::Any advice on where to go next?
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:Check your pilot lights. They are in series with the 1J6G output tube filament. If the wrong bulbs are in it, the tube may barely light. It originally had 291 bulbs in there. They are difficult to find today. You can order 1490 bulbs which are close. They are 3.2 volts compared to the 291 which was 2.9 volts. If you find 44 or 47 lamps in there, that is the problem. Also, change the bulbs in pairs. Diffiences in lamps or different kinds will cause unbalance and the set will hum on AC use.
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:Fred
I tend to agree with Fred. The old Radio Troubleshooter's Handbook by Ghirardi, also mentions that if one bulb burns out, it can cause distortion on that model.
Steve
Could it be a partial short, bad trimmer or mica cap?
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:Could it be a partial short, bad trimmer or mica cap?
Could be carbon buildup on your volume control pot. If there is a problem there it can be taken apart and cleand up. Deoxit works great for that. If it is that it usually is accompanied with intermittent no sound at all spots.
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::Could it be a partial short, bad trimmer or mica cap?
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:Could be carbon buildup on your volume control pot. If there is a problem there it can be taken apart and cleand up. Deoxit works great for that. If it is that it usually is accompanied with intermittent no sound at all spots.
Neal
Could be your power transformer. Check your pin voltages where you should have HV both ac and dc. I had low volume on a Zenith 7S657R just last evening right before the power transformer fried.
Neal
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:::Could it be a partial short, bad trimmer or mica cap?
::
::Could be carbon buildup on your volume control pot. If there is a problem there it can be taken apart and cleand up. Deoxit works great for that. If it is that it usually is accompanied with intermittent no sound at all spots.
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:Neal
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:Could be your power transformer. Check your pin voltages where you should have HV both ac and dc. I had low volume on a Zenith 7S657R just last evening right before the power transformer fried.
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:Neal
Have you tried battery operation? Is it any different? I see on your schematic that you have 2 on off volume control switches.
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::::Could it be a partial short, bad trimmer or mica cap?
I don't think it would be a partial short if it's consistant. You've said that you aligned it so if there was no problem with that you can eliminate trimmers. I don't know about the mica caps. Measure there capacitance if you have a LCR meter.
Another thought. Could be impedence matching problem with your output transformer. See if there's a problem there. Measure your field coil and voice coil resistance and see the ohms are right. Twist the field coil gently and see if it opens up.
Neal
:::
:::Could be carbon buildup on your volume control pot. If there is a problem there it can be taken apart and cleand up. Deoxit works great for that. If it is that it usually is accompanied with intermittent no sound at all spots.
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::Neal
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::Could be your power transformer. Check your pin voltages where you should have HV both ac and dc. I had low volume on a Zenith 7S657R just last evening right before the power transformer fried.
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::Neal
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:Have you tried battery operation? Is it any different? I see on your schematic that you have 2 on off volume control switches.
There is no speaker field coil. Original PM speaker. Magnet seems fine. I tried a new speaker with same weak volume result. I don't know the ohms for the various coils but all seem resonable. Transformer is spec so impedance match should be fine. Based on this, speaker problem is eliminated.
I installed a NOS volume control and it matches spec. Volume change is smooth 0 to max.
Voltages are all within spec.
Battery operation gives same weak volume.
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:::::Already replaced the bulbs with the correct NOS bulbs. Also all voltages are correct.
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:::::Could it be a partial short, bad trimmer or mica cap?
:
:I don't think it would be a partial short if it's consistant. You've said that you aligned it so if there was no problem with that you can eliminate trimmers. I don't know about the mica caps. Measure there capacitance if you have a LCR meter.
:
:Another thought. Could be impedence matching problem with your output transformer. See if there's a problem there. Measure your field coil and voice coil resistance and see the ohms are right. Twist the field coil gently and see if it opens up.
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:Neal
::::
::::Could be carbon buildup on your volume control pot. If there is a problem there it can be taken apart and cleand up. Deoxit works great for that. If it is that it usually is accompanied with intermittent no sound at all spots.
:::
:::Neal
:::
:::Could be your power transformer. Check your pin voltages where you should have HV both ac and dc. I had low volume on a Zenith 7S657R just last evening right before the power transformer fried.
:::
:::Neal
::
::Have you tried battery operation? Is it any different? I see on your schematic that you have 2 on off volume control switches.
:
:There is no speaker field coil. Original PM speaker. Magnet seems fine. I tried a new speaker with same weak volume result. I don't know the ohms for the various coils but all seem resonable. Transformer is spec so impedance match should be fine. Based on this, speaker problem is eliminated.
:
:I installed a NOS volume control and it matches spec. Volume change is smooth 0 to max.
:
:Voltages are all within spec.
:
:Battery operation gives same weak volume.
:
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::::::Already replaced the bulbs with the correct NOS bulbs. Also all voltages are correct.
::::::
::::::Could it be a partial short, bad trimmer or mica cap?
::
::I don't think it would be a partial short if it's consistant. You've said that you aligned it so if there was no problem with that you can eliminate trimmers. I don't know about the mica caps. Measure there capacitance if you have a LCR meter.
::
::Another thought. Could be impedence matching problem with your output transformer. See if there's a problem there. Measure your field coil and voice coil resistance and see the ohms are right. Twist the field coil gently and see if it opens up.
::
::Neal
:::::
:::::Could be carbon buildup on your volume control pot. If there is a problem there it can be taken apart and cleand up. Deoxit works great for that. If it is that it usually is accompanied with intermittent no sound at all spots.
::::
::::Neal
::::
::::Could be your power transformer. Check your pin voltages where you should have HV both ac and dc. I had low volume on a Zenith 7S657R just last evening right before the power transformer fried.
::::
::::Neal
:::
:::Have you tried battery operation? Is it any different? I see on your schematic that you have 2 on off volume control switches.
Have you done any work on your antenna connections inside your set? If there are more connections than 2 maybe they got switched around. I know it seems obvious...but it's a possibility.
Neal
Steve
Has anyone suggested peaking up IF Transformers? That can make a big difference in volume.
Norm
:Tim: If you've replaced all the caps it's unlikely that you have a leaky cap, although it's not impossible. Use your signal generator to inject an audio test signal (no RF) on the hot end of the volume control (R8). If volume is still weak, the trouble is in the audio section. If volume is good, then you'll know the problem is in the RF sections. Let us know what you find.
:Steve
:Hi
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: Has anyone suggested peaking up IF Transformers? That can make a big difference in volume.
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:Norm
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::Tim: If you've replaced all the caps it's unlikely that you have a leaky cap, although it's not impossible. Use your signal generator to inject an audio test signal (no RF) on the hot end of the volume control (R8). If volume is still weak, the trouble is in the audio section. If volume is good, then you'll know the problem is in the RF sections. Let us know what you find.
::Steve
Each IF Transformer (items 3 and 4 in the schematic) have two adjustments. Sometimes all it takes is adjusting these trimmer screws to bring up volume.
http://www.nostalgiaair.org/PagesByModel/137/M0025137.pdf
Norm
:I can inject the signal tonight. Can you explain "peaking up"?
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::Hi
::
:: Has anyone suggested peaking up IF Transformers? That can make a big difference in volume.
::
::Norm
::
:::Tim: If you've replaced all the caps it's unlikely that you have a leaky cap, although it's not impossible. Use your signal generator to inject an audio test signal (no RF) on the hot end of the volume control (R8). If volume is still weak, the trouble is in the audio section. If volume is good, then you'll know the problem is in the RF sections. Let us know what you find.
:::Steve
I re-checked voltages and found pin 3 (plate) voltage of the 6T7 tube was high at 70v vs. 15v spec. I changed out that tube with a NOS 6Q7. Voltage on that pin dropped to 50v with marked improvment in volume.
I further "peaked" the IFs and increased the volume level further to a point that is respectable and I coild live with. I would say it is still not blowing me out out of the water.
Could this be a AVC problem?
As per the query, of the gain possibly being pulled back by AVC action, merely go past the R6 resistor of AVC fed voltage and ground out the referenced green buss and see if your volume surges up and that would answer your question about AVC affectation.
Schema thumbnail reference:
73's de Edd
....Check IF transformer windings, too. Sometimes one can be open, and the set will still work (not often) somewhat from capacitive coupling.
T.
:As per the query, of the gain possibly being pulled back by AVC action, merely go past the R6 resistor of AVC fed voltage and ground out the referenced green buss and see if your volume surges up and that would answer your question about AVC affectation.
....Check IF transformer windings, too. Sometimes one can be open, and the set will still work (not often) somewhat from capacitive coupling.
T.
I checked the 6d8...-1.8v so good.
Did not find any open windings.
Rechecked cap sizes and even some of the resisters and it looks good. I did find tone control connects reversed from schematic but don't think that should matter. Think that is the way it was from the factory.
Maybe I'm being too picky. It's pretty loud. Just seems like usually the sound is deafening at 100%. Now it's loud enough to get some distortion...
:.....Also.....how many stations are you getting? Are you getting many, or just a few? Do the stations seem to repeat themselves? If so, you should be checking the oscillator section. Check grid 1 of the 6D8G. It should have a negative voltage. If not, then your oscillator isn't functioning. It is good practice, when all else fails, to check continuity of all coils, etc. Check resistors, and check to be absolutely sure that replacement capacitor values are correct, since modern capacitors are often coded, instead of having actual values being printed upon them. Eg: .01 MFD would be represented with 103 on a modern cap. That is 10, plus 3 0s, being read in picofarads....10000pF, which equates to .01uF.
:....Check IF transformer windings, too. Sometimes one can be open, and the set will still work (not often) somewhat from capacitive coupling.
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:T.
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How is the tone control backwards? If the resistor and capacitor are swapped, they will still be electrically the same (as you were guessing).
Do you have a nice long antenna hooked up? Are you in or out of the basement? Do you have a jumper between the Z and G terminals? If you are using a single long wire, be sure that the jumper is in place. If not, use a V-doublet. I have found that it significantly increases reception and reduces interference. Split your long wire in half (idealy at least 25 feet long). Put an insulator in the middle. Join two 3 foot sections of wire 3 feet on either side of the insulator to form a triangle. Connect the two wires to 100 feet of twin-lead flat television antenna cable, or use a twisted pair of your own make. Be sure to use wire with nice thick insulation so that there is good distance between the wires to limit capacitance.
.....Or just use a long single wire.....reception will be good. Your radio has the doublet option, and I like doublets better. They give me exceptional results.
As always, do not turn corners with the antenna. Don't fold it back on itself (or wrap it around the room). Doing either of these sets up opposing waves on the antenna, which cancel out and make for an inefficient antenna.
T.
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:Any advice on where to go next?