The radio seemed to perform quite well... the audio was clear and all voltages seemed to be correct... though none are listed on the print.
The Eye tube was the real surprise... bright clear and closing almost completely on the strongest stations.
So all was good... at that time...lol
Well the chassis was in a terrible rusted state. There wasn't a clear shiny metal part showing anywhere it seemed.
Now I'm quite used to that ...and have de-rusted many a chassis. So I just took out my Emory cloth and wire brushes and started scrapping that ugly rust off.
Afterward I removed the tuner and the power transformer and took the entire chassis to the kitchen sink for a wash.... again as usual.
After washing and rinsing everything ( I used BAM spray cleaner and dish soap as usual) I noticed a weird form of rusty brown film coating everything very quickly.
As soon as I saw this.. I was puzzled and tried scrubbing it off with some dish washing liquid on a brush.. and it was sort-of working.. but I had a hard time keeping up with this creeping all over my metal chassis that I just sanded down
I have use this BAM on masny metal chassis but never got instant rust before.
I thought maybe this was some strange early steel chassis that might react badly to this BAM stuff.
so I took a guess that maybe somehow that BAM cleaner might be the culprit and quickly wiped everything dry with paper towells.
I thought.. mybe I'm getting some kind of accelerated rust going on here. So I figure that I might need to seal the metal quickly.I usuallu spray on lacquer but this was to soon to do that as it was still damp everywhere.
So I tried to clean it off with some flux cleaner.. that seemed to help a bit.
I tried WD40 thinking it would displace water and maybe put a thin film of oil on the metal.
Not working.
So I tried some Brasso... and got mild results.
Then I wiped it all down after all that with a rag... feeling a bit in a panic.
Then I though... maybe some silicone spray like Glayzit would help.
So I rubbed everything down with that.
Well that seemed to keep it shiny and no more "instant rust".
So I let it dry over night in a shut off oven.
Next day I reassembled everything and fired it up.
Well... it came up alright but all noisy..hissy... tweetering squealing and what not.
What happened to that nice sounding radio from the day before??
I noticed that I had forgotten an RF bypass cap at the plate of the 75... and that helped a lot.
But things were still all screwy.
Then I found the metal shield (goat thingie) on the 6D6 was not grounding as it was all rusty and not contacting the ground clamps against it.
I cleaned that and got better results. But then the Radio stared to play!
So I flipped it over to work on the other side... and it stopped!!
Flipped it back and no help.
Eventually found that was caused by 2 things.
1.) The 6A7 was slightly cocked in its socket and when juggled a bit it started to work. Cleaned the socket and pins.. but still there seems to be a bad spot that it won't play. I've cleaned it with contact cleaner.. and still only works when pressed in a little crooked.
2.) The 6D6 was micro-phonic intermittent.
I solved that by re-soldering the pins... Then it was playing solidly.
Well ok ...now the radio was playing steady.. but I couldn't get the good volume I had and the audio was a little garbled sometimes.
That audio bothered me because it had been so nice.
I checked the B+ and found it to be sort of low I thought.
It was at 210 .. but I thought I remembed it being near 250v the day before.
This irritated me but I had nothing to PROVE it was low.
Just that the input to the rectifier is 325vac... why do I loose 115v after the rectifier?
Well I moved along to the other headache of weak signal now.
I knew something was WRONG because the eye tube was not closing at all like it was... so I KNEW the AVC was low meaning the RF signal must be low too.
I was beginning to think that maybe there was some kind of high resistance leakage from signal to ground somehow in the RF section. I thought that maybe that silicone stuff was shorting the signal between wires or between socket pins or something.
So I pulled all the tubes and thoroughly sprayed everything with brake cleaner spray... Whew what a stink.. Heptane I think.
I dried everything and then used a hairdryer on the whole area and each socket and then let it cool and went to dinner.
After dinner I reassemble and no help!...lol
So... I examined the antenna coil and re-soldered the the primary coil lead to the ground lug to make sure it was good.
Each winding had continuity.
The primary measured 32 ohms.
The 2 secondaries were 1.5 ohms and 2.7 ohms.
While poking around there I noticed that if I clip the external antenna wire lead directly to the secondary side where it goes into the grid of the Rf amplifier... the signal was booming in!!!
That was strange.... at least 4 or 5 times stronger.
I removed and inspected the antenna coil and found nothing unusual.
So I tried a .01uf cap from the primary to the 2ndary.. and that works beautifully.
The question is. WHY did I have to do this now???
And can I leave it?... or what?
Well now I was feeling a lot better and I went back to the alignment procedure and everything tuned nicely.
There were only two or 3 little nagging problems now.
1.) The audio kinda seemed a little less than perfect.
2.) B+ still seemed oddly low at 210v.
3.) A tad of hum in the audio.. which went away.. but only if I replaced the second 4uf filter cap with a 22uf cap.. (now this was real weird because it had been working nicely with 4uf the day before)
I poked around everywhere... re-soldering connections and measuring resistors and taking voltage readings.
I found a REALLY strange problem now... lol
The field coil connects between the CT and a 450 ohm bias resistor to ground.
... and the bias should be around -22v as I remembered it.... BUT... there was no bias voltage!!! .. just some little mili-volts trickle of measurable voltage.
WHAT??
WHY?
I pulled the field coil off and measured that at 1200 ohms. That seemed fine.
I measured the bias resistor and it was right at 450 ohms as it should be.
Now that is a real odd thing because I was measuring NO voltage across THAT resistor!!
How could that be?
I DO measure 100 v dropped across the field coil but NOTHING across that 450 ohm resistor...lol
That cannot be... but it is TRUE.
Now here's a clue.
The old 8uf electrolytic can mounted on the chassis was left in place for looks only.
That cap's ground was floating from the chassis by the use of two flat fiber insulating washers.. and the neg side connection was made with a large lug between the fiber washer and the retaining lug nut.
The old wire leads coming out of that can we snipped off.
The only part still being used was the insulated lug to solder that 450 ohm resistor and the field coil together.
Since yesterday I removed and returned that cap however.
So NOW ..I removed all wires from it and measured the resistance to ground.
Well there was my gremlin!!!
I measured 1 ohm.
What a crazy low resistance leak!!
That was my problem... a one ohm leak in parallel with the 450 ohm bias resistor... so what should have been -22 volts was below 1/2 volt!!
I guess I somehow miss-positioned that fiber washer thingie causing the short.
I scrapped the entire thing and put a new free-standing wire-lug terminal in its place.
Now ALL was well voltage-wise... AND audio-wise...lol
The b+ came right up to 270v and the bias on the grid of the 42 tube was right at -22v where it ought to be.
Wow... now I can go to bed feeling like I can conquer the world again....lol
So the only remaining question to anyone out there with an answer is:
Why did I have to put a .01uf cap from primary to 2ndary on the antenna/RF coil to get the signal strength I had before?
If I understand the problem: the radio had very good RF gain before the intense cleaning. After the cleaning the RF gain was horrible. Adding a capacitor between the pri and sec on the antenna coil improved the RF gain?
Here's my two cents:
I believe antique radio components are not impervious to harsh cleaning agents. I have found that these chemicals can damage coil wire coatings, but most importantly, the chemicals wick between coil windings and into trimmer capacitors. This changes the characteristics of the components enough to affect the alignment.
I had one radio that I cleaned in a similar manner, then dried it, or so I thought. After alignment it worked great. The next day it didn’t. Another alignment brought it back, and so on and so on. Strange? After many hours of head scratching I removed the mica dielectric from the trimmers and found the culprit, moisture!
Maybe this is the problem with your radio?
My suggestion would be to remove the capacitor installed on the antennal coil, dry the mica dielectric on all trimmers then re-align the radio.
Then we can postulate how the added capacitor appeared to fix the problem.
Gary
:The other day I recapped and tested this Packard Bell 46A... ( it has the tone control of the model "B" but otherwise seems to follow the "A" print.)
:http://www.nostalgiaair.org/PagesByModel/874/M0012874.pdf
:
:The radio seemed to perform quite well... the audio was clear and all voltages seemed to be correct... though none are listed on the print.
:
:The Eye tube was the real surprise... bright clear and closing almost completely on the strongest stations.
:
:So all was good... at that time...lol
:
:Well the chassis was in a terrible rusted state. There wasn't a clear shiny metal part showing anywhere it seemed.
:
:Now I'm quite used to that ...and have de-rusted many a chassis. So I just took out my Emory cloth and wire brushes and started scrapping that ugly rust off.
:
:Afterward I removed the tuner and the power transformer and took the entire chassis to the kitchen sink for a wash.... again as usual.
:
:After washing and rinsing everything ( I used BAM spray cleaner and dish soap as usual) I noticed a weird form of rusty brown film coating everything very quickly.
:As soon as I saw this.. I was puzzled and tried scrubbing it off with some dish washing liquid on a brush.. and it was sort-of working.. but I had a hard time keeping up with this creeping all over my metal chassis that I just sanded down
:
:I have use this BAM on masny metal chassis but never got instant rust before.
:I thought maybe this was some strange early steel chassis that might react badly to this BAM stuff.
:so I took a guess that maybe somehow that BAM cleaner might be the culprit and quickly wiped everything dry with paper towells.
:I thought.. mybe I'm getting some kind of accelerated rust going on here. So I figure that I might need to seal the metal quickly.I usuallu spray on lacquer but this was to soon to do that as it was still damp everywhere.
:So I tried to clean it off with some flux cleaner.. that seemed to help a bit.
:I tried WD40 thinking it would displace water and maybe put a thin film of oil on the metal.
:Not working.
:So I tried some Brasso... and got mild results.
:
:Then I wiped it all down after all that with a rag... feeling a bit in a panic.
:Then I though... maybe some silicone spray like Glayzit would help.
:So I rubbed everything down with that.
:Well that seemed to keep it shiny and no more "instant rust".
:
:So I let it dry over night in a shut off oven.
:Next day I reassembled everything and fired it up.
:
:Well... it came up alright but all noisy..hissy... tweetering squealing and what not.
:What happened to that nice sounding radio from the day before??
:
:I noticed that I had forgotten an RF bypass cap at the plate of the 75... and that helped a lot.
:But things were still all screwy.
:Then I found the metal shield (goat thingie) on the 6D6 was not grounding as it was all rusty and not contacting the ground clamps against it.
:I cleaned that and got better results. But then the Radio stared to play!
:So I flipped it over to work on the other side... and it stopped!!
:Flipped it back and no help.
:
:Eventually found that was caused by 2 things.
:1.) The 6A7 was slightly cocked in its socket and when juggled a bit it started to work. Cleaned the socket and pins.. but still there seems to be a bad spot that it won't play. I've cleaned it with contact cleaner.. and still only works when pressed in a little crooked.
:2.) The 6D6 was micro-phonic intermittent.
:
:I solved that by re-soldering the pins... Then it was playing solidly.
:
:Well ok ...now the radio was playing steady.. but I couldn't get the good volume I had and the audio was a little garbled sometimes.
:
:That audio bothered me because it had been so nice.
:
:I checked the B+ and found it to be sort of low I thought.
:It was at 210 .. but I thought I remembed it being near 250v the day before.
:This irritated me but I had nothing to PROVE it was low.
:Just that the input to the rectifier is 325vac... why do I loose 115v after the rectifier?
:
:Well I moved along to the other headache of weak signal now.
:I knew something was WRONG because the eye tube was not closing at all like it was... so I KNEW the AVC was low meaning the RF signal must be low too.
:
:I was beginning to think that maybe there was some kind of high resistance leakage from signal to ground somehow in the RF section. I thought that maybe that silicone stuff was shorting the signal between wires or between socket pins or something.
:So I pulled all the tubes and thoroughly sprayed everything with brake cleaner spray... Whew what a stink.. Heptane I think.
:I dried everything and then used a hairdryer on the whole area and each socket and then let it cool and went to dinner.
:
:After dinner I reassemble and no help!...lol
:
:So... I examined the antenna coil and re-soldered the the primary coil lead to the ground lug to make sure it was good.
:Each winding had continuity.
:
:The primary measured 32 ohms.
:
:The 2 secondaries were 1.5 ohms and 2.7 ohms.
:
:While poking around there I noticed that if I clip the external antenna wire lead directly to the secondary side where it goes into the grid of the Rf amplifier... the signal was booming in!!!
:
:That was strange.... at least 4 or 5 times stronger.
:
:I removed and inspected the antenna coil and found nothing unusual.
:
:So I tried a .01uf cap from the primary to the 2ndary.. and that works beautifully.
:
:The question is. WHY did I have to do this now???
:
:And can I leave it?... or what?
:
:
:Well now I was feeling a lot better and I went back to the alignment procedure and everything tuned nicely.
:
:There were only two or 3 little nagging problems now.
:
:1.) The audio kinda seemed a little less than perfect.
:2.) B+ still seemed oddly low at 210v.
:3.) A tad of hum in the audio.. which went away.. but only if I replaced the second 4uf filter cap with a 22uf cap.. (now this was real weird because it had been working nicely with 4uf the day before)
:
:
:I poked around everywhere... re-soldering connections and measuring resistors and taking voltage readings.
:
:I found a REALLY strange problem now... lol
:
:The field coil connects between the CT and a 450 ohm bias resistor to ground.
:... and the bias should be around -22v as I remembered it.... BUT... there was no bias voltage!!! .. just some little mili-volts trickle of measurable voltage.
:WHAT??
:WHY?
:
:I pulled the field coil off and measured that at 1200 ohms. That seemed fine.
:
:I measured the bias resistor and it was right at 450 ohms as it should be.
:
:Now that is a real odd thing because I was measuring NO voltage across THAT resistor!!
:
:How could that be?
:
:I DO measure 100 v dropped across the field coil but NOTHING across that 450 ohm resistor...lol
:That cannot be... but it is TRUE.
:
:Now here's a clue.
:
:The old 8uf electrolytic can mounted on the chassis was left in place for looks only.
:
:That cap's ground was floating from the chassis by the use of two flat fiber insulating washers.. and the neg side connection was made with a large lug between the fiber washer and the retaining lug nut.
:
:The old wire leads coming out of that can we snipped off.
:
:The only part still being used was the insulated lug to solder that 450 ohm resistor and the field coil together.
:
:Since yesterday I removed and returned that cap however.
:
:So NOW ..I removed all wires from it and measured the resistance to ground.
:Well there was my gremlin!!!
:I measured 1 ohm.
:What a crazy low resistance leak!!
:
:That was my problem... a one ohm leak in parallel with the 450 ohm bias resistor... so what should have been -22 volts was below 1/2 volt!!
:
:I guess I somehow miss-positioned that fiber washer thingie causing the short.
:
:I scrapped the entire thing and put a new free-standing wire-lug terminal in its place.
:
:Now ALL was well voltage-wise... AND audio-wise...lol
:
:The b+ came right up to 270v and the bias on the grid of the 42 tube was right at -22v where it ought to be.
:
:Wow... now I can go to bed feeling like I can conquer the world again....lol
:
:So the only remaining question to anyone out there with an answer is:
:Why did I have to put a .01uf cap from primary to 2ndary on the antenna/RF coil to get the signal strength I had before?
:
marv
:
:Hi Peter,
:
:If I understand the problem: the radio had very good RF gain before the intense cleaning. After the cleaning the RF gain was horrible. Adding a capacitor between the pri and sec on the antenna coil improved the RF gain?
:
:Here's my two cents:
:I believe antique radio components are not impervious to harsh cleaning agents. I have found that these chemicals can damage coil wire coatings, but most importantly, the chemicals wick between coil windings and into trimmer capacitors. This changes the characteristics of the components enough to affect the alignment.
:
:I had one radio that I cleaned in a similar manner, then dried it, or so I thought. After alignment it worked great. The next day it didn’t. Another alignment brought it back, and so on and so on. Strange? After many hours of head scratching I removed the mica dielectric from the trimmers and found the culprit, moisture!
:
:Maybe this is the problem with your radio?
:My suggestion would be to remove the capacitor installed on the antennal coil, dry the mica dielectric on all trimmers then re-align the radio.
:
:Then we can postulate how the added capacitor appeared to fix the problem.
:
:Gary
:
:
:
:
:
::The other day I recapped and tested this Packard Bell 46A... ( it has the tone control of the model "B" but otherwise seems to follow the "A" print.)
::http://www.nostalgiaair.org/PagesByModel/874/M0012874.pdf
::
::The radio seemed to perform quite well... the audio was clear and all voltages seemed to be correct... though none are listed on the print.
::
::The Eye tube was the real surprise... bright clear and closing almost completely on the strongest stations.
::
::So all was good... at that time...lol
::
::Well the chassis was in a terrible rusted state. There wasn't a clear shiny metal part showing anywhere it seemed.
::
::Now I'm quite used to that ...and have de-rusted many a chassis. So I just took out my Emory cloth and wire brushes and started scrapping that ugly rust off.
::
::Afterward I removed the tuner and the power transformer and took the entire chassis to the kitchen sink for a wash.... again as usual.
::
::After washing and rinsing everything ( I used BAM spray cleaner and dish soap as usual) I noticed a weird form of rusty brown film coating everything very quickly.
::As soon as I saw this.. I was puzzled and tried scrubbing it off with some dish washing liquid on a brush.. and it was sort-of working.. but I had a hard time keeping up with this creeping all over my metal chassis that I just sanded down
::
::I have use this BAM on masny metal chassis but never got instant rust before.
::I thought maybe this was some strange early steel chassis that might react badly to this BAM stuff.
::so I took a guess that maybe somehow that BAM cleaner might be the culprit and quickly wiped everything dry with paper towells.
::I thought.. mybe I'm getting some kind of accelerated rust going on here. So I figure that I might need to seal the metal quickly.I usuallu spray on lacquer but this was to soon to do that as it was still damp everywhere.
::So I tried to clean it off with some flux cleaner.. that seemed to help a bit.
::I tried WD40 thinking it would displace water and maybe put a thin film of oil on the metal.
::Not working.
::So I tried some Brasso... and got mild results.
::
::Then I wiped it all down after all that with a rag... feeling a bit in a panic.
::Then I though... maybe some silicone spray like Glayzit would help.
::So I rubbed everything down with that.
::Well that seemed to keep it shiny and no more "instant rust".
::
::So I let it dry over night in a shut off oven.
::Next day I reassembled everything and fired it up.
::
::Well... it came up alright but all noisy..hissy... tweetering squealing and what not.
::What happened to that nice sounding radio from the day before??
::
::I noticed that I had forgotten an RF bypass cap at the plate of the 75... and that helped a lot.
::But things were still all screwy.
::Then I found the metal shield (goat thingie) on the 6D6 was not grounding as it was all rusty and not contacting the ground clamps against it.
::I cleaned that and got better results. But then the Radio stared to play!
::So I flipped it over to work on the other side... and it stopped!!
::Flipped it back and no help.
::
::Eventually found that was caused by 2 things.
::1.) The 6A7 was slightly cocked in its socket and when juggled a bit it started to work. Cleaned the socket and pins.. but still there seems to be a bad spot that it won't play. I've cleaned it with contact cleaner.. and still only works when pressed in a little crooked.
::2.) The 6D6 was micro-phonic intermittent.
::
::I solved that by re-soldering the pins... Then it was playing solidly.
::
::Well ok ...now the radio was playing steady.. but I couldn't get the good volume I had and the audio was a little garbled sometimes.
::
::That audio bothered me because it had been so nice.
::
::I checked the B+ and found it to be sort of low I thought.
::It was at 210 .. but I thought I remembed it being near 250v the day before.
::This irritated me but I had nothing to PROVE it was low.
::Just that the input to the rectifier is 325vac... why do I loose 115v after the rectifier?
::
::Well I moved along to the other headache of weak signal now.
::I knew something was WRONG because the eye tube was not closing at all like it was... so I KNEW the AVC was low meaning the RF signal must be low too.
::
::I was beginning to think that maybe there was some kind of high resistance leakage from signal to ground somehow in the RF section. I thought that maybe that silicone stuff was shorting the signal between wires or between socket pins or something.
::So I pulled all the tubes and thoroughly sprayed everything with brake cleaner spray... Whew what a stink.. Heptane I think.
::I dried everything and then used a hairdryer on the whole area and each socket and then let it cool and went to dinner.
::
::After dinner I reassemble and no help!...lol
::
::So... I examined the antenna coil and re-soldered the the primary coil lead to the ground lug to make sure it was good.
::Each winding had continuity.
::
::The primary measured 32 ohms.
::
::The 2 secondaries were 1.5 ohms and 2.7 ohms.
::
::While poking around there I noticed that if I clip the external antenna wire lead directly to the secondary side where it goes into the grid of the Rf amplifier... the signal was booming in!!!
::
::That was strange.... at least 4 or 5 times stronger.
::
::I removed and inspected the antenna coil and found nothing unusual.
::
::So I tried a .01uf cap from the primary to the 2ndary.. and that works beautifully.
::
::The question is. WHY did I have to do this now???
::
::And can I leave it?... or what?
::
::
::Well now I was feeling a lot better and I went back to the alignment procedure and everything tuned nicely.
::
::There were only two or 3 little nagging problems now.
::
::1.) The audio kinda seemed a little less than perfect.
::2.) B+ still seemed oddly low at 210v.
::3.) A tad of hum in the audio.. which went away.. but only if I replaced the second 4uf filter cap with a 22uf cap.. (now this was real weird because it had been working nicely with 4uf the day before)
::
::
::I poked around everywhere... re-soldering connections and measuring resistors and taking voltage readings.
::
::I found a REALLY strange problem now... lol
::
::The field coil connects between the CT and a 450 ohm bias resistor to ground.
::... and the bias should be around -22v as I remembered it.... BUT... there was no bias voltage!!! .. just some little mili-volts trickle of measurable voltage.
::WHAT??
::WHY?
::
::I pulled the field coil off and measured that at 1200 ohms. That seemed fine.
::
::I measured the bias resistor and it was right at 450 ohms as it should be.
::
::Now that is a real odd thing because I was measuring NO voltage across THAT resistor!!
::
::How could that be?
::
::I DO measure 100 v dropped across the field coil but NOTHING across that 450 ohm resistor...lol
::That cannot be... but it is TRUE.
::
::Now here's a clue.
::
::The old 8uf electrolytic can mounted on the chassis was left in place for looks only.
::
::That cap's ground was floating from the chassis by the use of two flat fiber insulating washers.. and the neg side connection was made with a large lug between the fiber washer and the retaining lug nut.
::
::The old wire leads coming out of that can we snipped off.
::
::The only part still being used was the insulated lug to solder that 450 ohm resistor and the field coil together.
::
::Since yesterday I removed and returned that cap however.
::
::So NOW ..I removed all wires from it and measured the resistance to ground.
::Well there was my gremlin!!!
::I measured 1 ohm.
::What a crazy low resistance leak!!
::
::That was my problem... a one ohm leak in parallel with the 450 ohm bias resistor... so what should have been -22 volts was below 1/2 volt!!
::
::I guess I somehow miss-positioned that fiber washer thingie causing the short.
::
::I scrapped the entire thing and put a new free-standing wire-lug terminal in its place.
::
::Now ALL was well voltage-wise... AND audio-wise...lol
::
::The b+ came right up to 270v and the bias on the grid of the 42 tube was right at -22v where it ought to be.
::
::Wow... now I can go to bed feeling like I can conquer the world again....lol
::
::So the only remaining question to anyone out there with an answer is:
::Why did I have to put a .01uf cap from primary to 2ndary on the antenna/RF coil to get the signal strength I had before?
::
Also, on the intermittant note, my Crosley 148 was intermittant whenever it was flipped upside down. Turns out that the 42 had a faulty cathode weld inside of the tube (unfortunate). ....And all these years someone used it that way!
T.
You're all on the right track... in fact RIGHT-ON.... at least as far the coupling at the antenna and how it might effect response at various points of the BC band.
The whole radio has had more time to "dry out" as I've been playing it for many hours each day lately.
Each day I've had to re-touch the alignment again... so that was the MOST obvious clue that it was moisture.
But I was initialing discounting that as the cause since the mica trimmer on the tuning condenser was really dry and clean... BUT.. I had forgotten about the low end padder cap .. which is ceramic and really holds moisture.... lol
Also ... now that the whole thing is dry.. The chassis was re-buffed w/wire brush the other day and wiped down and fully protected from rusting-up again now by a couple of good coats of clear lacquer.
Tonight I noticed that the alignment was still a tad off... and that although I had pretty good RF sensitivity across the entire band... there was some noticeable fall off down at the low end of the BC band.
So realizing that a "damp" ceramic padder was probably what was screwing things up before... I decided to REMOVE the .01uf coupling cap across the antenna coil Primary to Secondary... and see how it aligns now that everything is really dry.
Well I'm very glad to report that... NOW it all aligns perfectly without that .01 cap and the low band sensitivity has vastly improved as well.
Everything is now back to original design... and .. DUH !
... it works well. .. lol... what a surprise huh?
Now I do KNOW that moisture can screw things up badly as I've experienced in the past... and I "thought" all the moisture was gone.... but I FORGOT about that ceramic padder...lol
Needless to say I WILL NEVER AGAIN WASH A POWER TRANSFORMER!
Gary
:OK Guys...Here's the answer:.. "time" ...lol.. time to fully dry out a ceramic padder that is... Smile)
:
:You're all on the right track... in fact RIGHT-ON.... at least as far the coupling at the antenna and how it might effect response at various points of the BC band.
:
:The whole radio has had more time to "dry out" as I've been playing it for many hours each day lately.
:
:Each day I've had to re-touch the alignment again... so that was the MOST obvious clue that it was moisture.
:
:But I was initialing discounting that as the cause since the mica trimmer on the tuning condenser was really dry and clean... BUT.. I had forgotten about the low end padder cap .. which is ceramic and really holds moisture.... lol
:
:Also ... now that the whole thing is dry.. The chassis was re-buffed w/wire brush the other day and wiped down and fully protected from rusting-up again now by a couple of good coats of clear lacquer.
:
:Tonight I noticed that the alignment was still a tad off... and that although I had pretty good RF sensitivity across the entire band... there was some noticeable fall off down at the low end of the BC band.
:
:So realizing that a "damp" ceramic padder was probably what was screwing things up before... I decided to REMOVE the .01uf coupling cap across the antenna coil Primary to Secondary... and see how it aligns now that everything is really dry.
:
:Well I'm very glad to report that... NOW it all aligns perfectly without that .01 cap and the low band sensitivity has vastly improved as well.
:
:Everything is now back to original design... and .. DUH !
:... it works well. .. lol... what a surprise huh?
:
:Now I do KNOW that moisture can screw things up badly as I've experienced in the past... and I "thought" all the moisture was gone.... but I FORGOT about that ceramic padder...lol
So how did you get the laminations out and back properly..to do the winding? When I try it all falls apart and they don't fit back .. easily if at all.
For only about $10-$12 you can always pretty easily find replacements from Gary at www.oldradioparts.com
Peter,
I could not find a replacement, and, of course, there was this element of pride that inspired me to do this.
I plan to document the restoration of this Model 20, pictures and all. But this is something I will be doing when I retire, which is still a few years off.
The construction of the transformer used in the Model 20 made it easy to remove the laminations, which were “E” type. For each “E” lamination there is a “bar” lamination. I took detailed notes to ensure the laminations were put back in the same order.
The coil form was almost square and the windings, starting from the innermost were: Primary, A Fil, Rect Fil, C Fil, HV.
The HV winding ended up being 2720 turns of #32 wire. I made a jig with a mechanical counter to count the windings. My initial calculations were 16 layers of 170 turns per layer, CT connected at turn 1360. I had to keep the winding tight by using a plastic tool to push the winding together. Not doing this, as I learned, resulted in less than 170 turns on a layer. At first I had trouble keeping the windings on the form. I solved this by applying a layer of Kapton tape over each layer. This also provided additional insulation between layers. Unfortunately, the addition of the tape made the completed winding too big for the laminations. I solved this by filing the laminations down a bit.
When it was done the HV secondary produced 735V (369 CT 366) and ran cool cucumber. This voltage is about 5% higher than the original but I thought not bad for my first ever power transformer.
On thing I discovered during this effort that contradicted the schematic is there was a connection from Pin 6 (CT of A Fil) to Pin 10 (Rect Fil). I could not find a reason for this connection so I removed it.
Gary