I was aligning my E trimmer to weaken the signal there when zap, blew a fuse. I have learned from Doug that you don't need the E trimmer because it was used during wartime to keep interference out of certain frequencies. So I took it out.
That left me with a motorboating problem on SW. I have found that if I ground that point through a cap It eleminates that problem. Just ground the circuitry from the point it hooked to the E trimmer through a cap.
My question is, what does varying (up and down) the capacitance do to your signal?
Norm and Steve: I got through my weak volume problem, and separately, I have the voltage on 7B7 pin 3 down to 130vdc...Neal
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:I was aligning my E trimmer to weaken the signal there when zap, blew a fuse. I have learned from Doug that you don't need the E trimmer because it was used during wartime to keep interference out of certain frequencies. So I took it out.
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:That left me with a motorboating problem on SW. I have found that if I ground that point through a cap It eleminates that problem. Just ground the circuitry from the point it hooked to the E trimmer through a cap.
:
:My question is, what does varying (up and down) the capacitance do to your signal?
:
:Norm and Steve: I got through my weak volume problem, and separately, I have the voltage on 7B7 pin 3 down to 130vdc...Neal
Neal: glad to hear you solved your low volume problem and got the converter pin 3 voltage down. The purpose of the wave trap was to null out offending signals at or near the IF frequency. As Doug pointed out, there really aren't any strong signals down there anymore to cause problems as when the radio was in production. The E trimmer works in combination with coil 6 (part of the wave trap assembly). Combinations of coils and caps make a resonant circuit, the frequency depending on the values of the cap and coil. By adjusting the trimmer cap you could adjust the null point of the frequency range to ground out the offending signal if any. I would guess the actual tuning range of the wave trap would be something on the order of plus or minus 100 Hz of the IF, maybe a bit more.
Steve
"I got through my weak volume problem, and separately, I have the voltage on 7B7 pin 3 down to 130vdc."
This had fallen so far down the threads that I had almost forgotten the situation of the high B+ on the converter stage.
I do remember pointing out of the particular series in line resistors of concern on its derivation loop from the main B+ .
And actually, that might have really been the problem , since, if you look at the initial source of that particular supply. . . it is right at THE MAIN B+ origin point at the cathode of the 6X5 and is mainly dependent on that initial R16 ..8200ohm / 2 watt for the initial setting of the level of that supply line that then feeds
the screen grids of the IF and mixer stage as well as the grid of the mixer stage that functions as its “plate” in its oscillator function.
One usually sees that supply line having its derivation from the sub B+ line that is on past the filter choke and you see feeding the plate supplies of those
tubes.
The real point of interest here, I do believe, is the possibility / fact ? that this set was one in which you had replaced the power transformer in, and that you
had opted for the use of a replacement unit with a bit higher voltage output on the HV secondary than the original one was probably supplying.
Ergo, you likewise got an overall increased B+ output voltage and seems like afterwards was worrying about the higher voltage on downstream, past the
inductive filtering.
Well, it’s for sure that this mentioned 7B7 supply source line is going to be high, by virtue of it being derived from the point of the very highest source of B+ in the WHOLE supply.
Therefore, if you now have that screen supply line down to a normal value, apparently you have increased that 8.2 value upward to a greater value such that
the mentioned supply line falls into accordance with the original voltage norm that was originally on that line.
Am I correct that the above was the manner of your getting your supply volatage down, and now , what was the additional corrective action that produced the mentioned :
" I got through my weak volume problem"
And then now:
I was aligning my E trimmer to weaken the signal there when zap, blew a fuse.
Looking at that units connections, seems like the only way to do that would be to have been touched the grounded side of the trimmer and let the blade of
the screwdriver get to B+, as the other side of the trimmer is void of high level B+.
As for the "touchiness" on the SW band, one aspect of that was just touched on by Sir Steve, whereupon there is a very low Z path to ground via that LC
series trap at its tuned frequency.
That path, being the lower B+ side of the of that RF choke coil feeding the plate circuitry of the 7H7, it then has an
RF bypassing route being coupled down through C7 and finally ending up down at the series tuned trap with its inductive element of item #6 and your
mentioned variable trimmer capacitor of "E" .
Now here is the real kicker on your shortwave-us-ceses-us-es situation, when you opened the "E" element link to ground, you impaired bypassing action to
ground.
Look at the B+ path ver at the right and you will see the flow up to the cold side of the plate side of the plate connected primary of the first IF transformer,
it being appropriately bypassed with cap C8. Follow the flow to the left where there is a voltage drop and some isolation provided by R6 and then the feed to
the cold side of your RF coil primary, now what bypassing action at the SW frequencies, ( and less is needed at SW frequencies than was afforded at the BCB)
is now unable to complete its loop on thru to ground . Without adequate bypassing at that point you are subject to possible onset of
feedback and oscillation. The only other RF bypassing route available is over thru R6 and sharing C8 for bypassing but R6's high isolative value precludes that.
Sooooooo...if that was my situation, I would put the trimmer back in and tune it for a null as was done previously, or otherwise, you might try lifting and grounding
the low side of C7 coupling capacitor in order to get that RF stage bypassed at that point.
Tech Referencing:
73's de Edd
Doug
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: "I got through my weak volume problem, and separately, I have the voltage on 7B7 pin 3 down to 130vdc."
:
:
:
:This had fallen so far down the threads that I had almost forgotten the situation of the high B+ on the converter stage.
:I do remember pointing out of the particular series in line resistors of concern on its derivation loop from the main B+ .
:
:And actually, that might have really been the problem , since, if you look at the initial source of that particular supply. . . it is right at THE MAIN B+ origin point at the cathode of the 6X5 and is mainly dependent on that initial R16 ..8200ohm / 2 watt for the initial setting of the level of that supply line that then feeds
:the screen grids of the IF and mixer stage as well as the grid of the mixer stage that functions as its “plate” in its oscillator function.
:
:
:One usually sees that supply line having its derivation from the sub B+ line that is on past the filter choke and you see feeding the plate supplies of those
:tubes.
:The real point of interest here, I do believe, is the possibility / fact ? that this set was one in which you had replaced the power transformer in, and that you
:had opted for the use of a replacement unit with a bit higher voltage output on the HV secondary than the original one was probably supplying.
:
:Ergo, you likewise got an overall increased B+ output voltage and seems like afterwards was worrying about the higher voltage on downstream, past the
:inductive filtering.
:Well, it’s for sure that this mentioned 7B7 supply source line is going to be high, by virtue of it being derived from the point of the very highest source of B+ in the WHOLE supply.
:
:Therefore, if you now have that screen supply line down to a normal value, apparently you have increased that 8.2 value upward to a greater value such that
:the mentioned supply line falls into accordance with the original voltage norm that was originally on that line.
:
:
:Am I correct that the above was the manner of your getting your supply volatage down, and now , what was the additional corrective action that produced the mentioned :
:
:
:" I got through my weak volume problem"
:
:
:And then now:
:
:
:I was aligning my E trimmer to weaken the signal there when zap, blew a fuse.
:
:
:Looking at that units connections, seems like the only way to do that would be to have been touched the grounded side of the trimmer and let the blade of
:the screwdriver get to B+, as the other side of the trimmer is void of high level B+.
:
:As for the "touchiness" on the SW band, one aspect of that was just touched on by Sir Steve, whereupon there is a very low Z path to ground via that LC
:series trap at its tuned frequency.
: That path, being the lower B+ side of the of that RF choke coil feeding the plate circuitry of the 7H7, it then has an
:RF bypassing route being coupled down through C7 and finally ending up down at the series tuned trap with its inductive element of item #6 and your
:mentioned variable trimmer capacitor of "E" .
:
:
:Now here is the real kicker on your shortwave-us-ceses-us-es situation, when you opened the "E" element link to ground, you impaired bypassing action to
:ground.
:Look at the B+ path ver at the right and you will see the flow up to the cold side of the plate side of the plate connected primary of the first IF transformer,
:it being appropriately bypassed with cap C8. Follow the flow to the left where there is a voltage drop and some isolation provided by R6 and then the feed to
:the cold side of your RF coil primary, now what bypassing action at the SW frequencies, ( and less is needed at SW frequencies than was afforded at the BCB)
: is now unable to complete its loop on thru to ground . Without adequate bypassing at that point you are subject to possible onset of
:feedback and oscillation. The only other RF bypassing route available is over thru R6 and sharing C8 for bypassing but R6's high isolative value precludes that.
:
:Sooooooo...if that was my situation, I would put the trimmer back in and tune it for a null as was done previously, or otherwise, you might try lifting and grounding
:the low side of C7 coupling capacitor in order to get that RF stage bypassed at that point.
:
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:Tech Referencing:
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:73's de Edd
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I think you are a little young to know about Kilroy, c. WW2.
Doug
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: "I got through my weak volume problem, and separately, I have the voltage on 7B7 pin 3 down to 130vdc."
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:Hello Edd, Steve, and Doug,
Edd...I've had so many power transformer problems that I think I have you confused with another set. On the Zenith 10S589 I did settle for a little higher voltage on the secondary. But that set is working well and I'm through the electronic repairs and working on refinishing the console.
I've replaced the power transformer on this 7S657R also, but my secondary voltage is right on the money (275vac) and the DC output of the 6X5 is also correct {305vdc).
I have since this post reconnected the E Trimmer. I had outstanding SW but the BC was all messed up. So I gave up on grounding that point with the E trimmer out. It still makes me wonder why that fuse blew and I bottomed out the adjustment screw.
:
The tone control swithes were destroyed on this set when I got it. I've have been trying to reproduce that circuitry of 5 switches with 2 3 swith units. As I have been working on this the volume has improved, but it doesn't blast you out like it should with a 12" speaker. I also had to replace the 'automatic' pushbutton assembly, so that could factor in also.
As to the voltage on the converter. I meticuously replaced all the resistors involved with the proper resistance and wattage rating. I was encouraged with the voltage when I made this post. But since then it has gone back up to 165vdc. I'm wondering if I could possibly have 2 bad tubes that I have been trading back and forth having the same problem. Today I ordered a couple of 7b8's from antique electronic supply, along with others that set uses.
I had pretty much dead ended with the only hope in getting the tone and pushbutton assemblies wired right, so I set it aside and started working on a Philco 46-1203 for my sister in law. But I will return to the 7S657R and try what you've instructed my to do to help my motorboating problem on SW. I hope I've covered all your questions. You've given me new hope.
This had fallen so far down the threads that I had almost forgotten the situation of the high B+ on the converter stage.
:I do remember pointing out of the particular series in line resistors of concern on its derivation loop from the main B+ .
:
:And actually, that might have really been the problem , since, if you look at the initial source of that particular supply. . . it is right at THE MAIN B+ origin point at the cathode of the 6X5 and is mainly dependent on that initial R16 ..8200ohm / 2 watt for the initial setting of the level of that supply line that then feeds
:the screen grids of the IF and mixer stage as well as the grid of the mixer stage that functions as its “plate” in its oscillator function.
:
:
:One usually sees that supply line having its derivation from the sub B+ line that is on past the filter choke and you see feeding the plate supplies of those
:tubes.
:The real point of interest here, I do believe, is the possibility / fact ? that this set was one in which you had replaced the power transformer in, and that you
:had opted for the use of a replacement unit with a bit higher voltage output on the HV secondary than the original one was probably supplying.
:
:Ergo, you likewise got an overall increased B+ output voltage and seems like afterwards was worrying about the higher voltage on downstream, past the
:inductive filtering.
:Well, it’s for sure that this mentioned 7B7 supply source line is going to be high, by virtue of it being derived from the point of the very highest source of B+ in the WHOLE supply.
:
:Therefore, if you now have that screen supply line down to a normal value, apparently you have increased that 8.2 value upward to a greater value such that
:the mentioned supply line falls into accordance with the original voltage norm that was originally on that line.
:
:
:Am I correct that the above was the manner of your getting your supply volatage down, and now , what was the additional corrective action that produced the mentioned :
:
:
:" I got through my weak volume problem"
:
:
:And then now:
:
:
:I was aligning my E trimmer to weaken the signal there when zap, blew a fuse.
:
:
:Looking at that units connections, seems like the only way to do that would be to have been touched the grounded side of the trimmer and let the blade of
:the screwdriver get to B+, as the other side of the trimmer is void of high level B+.
:
:As for the "touchiness" on the SW band, one aspect of that was just touched on by Sir Steve, whereupon there is a very low Z path to ground via that LC
:series trap at its tuned frequency.
: That path, being the lower B+ side of the of that RF choke coil feeding the plate circuitry of the 7H7, it then has an
:RF bypassing route being coupled down through C7 and finally ending up down at the series tuned trap with its inductive element of item #6 and your
:mentioned variable trimmer capacitor of "E" .
:
:
:Now here is the real kicker on your shortwave-us-ceses-us-es situation, when you opened the "E" element link to ground, you impaired bypassing action to
:ground.
:Look at the B+ path ver at the right and you will see the flow up to the cold side of the plate side of the plate connected primary of the first IF transformer,
:it being appropriately bypassed with cap C8. Follow the flow to the left where there is a voltage drop and some isolation provided by R6 and then the feed to
:the cold side of your RF coil primary, now what bypassing action at the SW frequencies, ( and less is needed at SW frequencies than was afforded at the BCB)
: is now unable to complete its loop on thru to ground . Without adequate bypassing at that point you are subject to possible onset of
:feedback and oscillation. The only other RF bypassing route available is over thru R6 and sharing C8 for bypassing but R6's high isolative value precludes that.
:
:Sooooooo...if that was my situation, I would put the trimmer back in and tune it for a null as was done previously, or otherwise, you might try lifting and grounding
:the low side of C7 coupling capacitor in order to get that RF stage bypassed at that point.
:
:
:
:Tech Referencing:
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:73's de Edd
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: "I got through my weak volume problem, and separately, I have the voltage on 7B7 pin 3 down to 130vdc."
:
:
:
:This had fallen so far down the threads that I had almost forgotten the situation of the high B+ on the converter stage.
:I do remember pointing out of the particular series in line resistors of concern on its derivation loop from the main B+ .
:
:And actually, that might have really been the problem , since, if you look at the initial source of that particular supply. . . it is right at THE MAIN B+ origin point at the cathode of the 6X5 and is mainly dependent on that initial R16 ..8200ohm / 2 watt for the initial setting of the level of that supply line that then feeds
:the screen grids of the IF and mixer stage as well as the grid of the mixer stage that functions as its “plate” in its oscillator function.
:
:
:One usually sees that supply line having its derivation from the sub B+ line that is on past the filter choke and you see feeding the plate supplies of those
:tubes.
:The real point of interest here, I do believe, is the possibility / fact ? that this set was one in which you had replaced the power transformer in, and that you
:had opted for the use of a replacement unit with a bit higher voltage output on the HV secondary than the original one was probably supplying.
:
:Ergo, you likewise got an overall increased B+ output voltage and seems like afterwards was worrying about the higher voltage on downstream, past the
:inductive filtering.
:Well, it’s for sure that this mentioned 7B7 supply source line is going to be high, by virtue of it being derived from the point of the very highest source of B+ in the WHOLE supply.
:
:Therefore, if you now have that screen supply line down to a normal value, apparently you have increased that 8.2 value upward to a greater value such that
:the mentioned supply line falls into accordance with the original voltage norm that was originally on that line.
:
:
:Am I correct that the above was the manner of your getting your supply volatage down, and now , what was the additional corrective action that produced the mentioned :
:
:
:" I got through my weak volume problem"
:
:
:And then now:
:
:
:I was aligning my E trimmer to weaken the signal there when zap, blew a fuse.
:
:
:Looking at that units connections, seems like the only way to do that would be to have been touched the grounded side of the trimmer and let the blade of
:the screwdriver get to B+, as the other side of the trimmer is void of high level B+.
:
:As for the "touchiness" on the SW band, one aspect of that was just touched on by Sir Steve, whereupon there is a very low Z path to ground via that LC
:series trap at its tuned frequency.
: That path, being the lower B+ side of the of that RF choke coil feeding the plate circuitry of the 7H7, it then has an
:RF bypassing route being coupled down through C7 and finally ending up down at the series tuned trap with its inductive element of item #6 and your
:mentioned variable trimmer capacitor of "E" .
:
:
:Now here is the real kicker on your shortwave-us-ceses-us-es situation, when you opened the "E" element link to ground, you impaired bypassing action to
:ground.
:Look at the B+ path ver at the right and you will see the flow up to the cold side of the plate side of the plate connected primary of the first IF transformer,
:it being appropriately bypassed with cap C8. Follow the flow to the left where there is a voltage drop and some isolation provided by R6 and then the feed to
:the cold side of your RF coil primary, now what bypassing action at the SW frequencies, ( and less is needed at SW frequencies than was afforded at the BCB)
: is now unable to complete its loop on thru to ground . Without adequate bypassing at that point you are subject to possible onset of
:feedback and oscillation. The only other RF bypassing route available is over thru R6 and sharing C8 for bypassing but R6's high isolative value precludes that.
:
:Sooooooo...if that was my situation, I would put the trimmer back in and tune it for a null as was done previously, or otherwise, you might try lifting and grounding
:the low side of C7 coupling capacitor in order to get that RF stage bypassed at that point.
:
:
:
:Tech Referencing:
:
:
:
:
:
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:73's de Edd
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:Hi Edd...I agree with Doug, your are a genius. I have to let you know what has happened this morning before I hit the sack. I had a substitute E trimmer installed (which had a broken base), so I decided to put the original one back in. As I was putting it back in I recalled all the oxidation that was around the mounting bolt. Having this new information from you about the importance of the ground, I put some Deoxit on the trimmer mount and found a clean bolt. As I screwed it in, the SW reception that was oscillating began to clear up. It almost was gone when I got it mounted, and tuning the trimmer took it away completely!!! The automatic pushbuttons were working once again also.
My SW is tons louder than BC. If I could get a little more volume on BC I would be done except for tone control assembly. Also, my strongest station on BC has a distortion to it.
I'll measure the converter point that has been too high right now. It's 140v. That's 25 volts lower than before this development.
Well, like Doug said, you're a genius...Neal