But along the way, things happen that can baffel the best of us.
I am very close to having this thing finished and trying to get it all put back together to put up on Ebay by Sunday.
So last night I attempted to do a few final stages. I had, the previous evening, removed the tuning condenser to wash it as usual. So after a day's drying I put it back in the circuit last night. Now to make sure of my steps I had even made a drawing of every connection in that area below the oscillator and antenna coils. I followed it to the letter during re-install.
However ....when I turned the radio on there was total silence!
I tested the center tap on the vol control and the audio was fine.
I fed modulated 455kc in the RF stage and that was fine too. A nice clean 400hz tone with sufficient volume... but no radio signals.
So I put the scope probe near the oscillator coil to see it it was running... nope!
Well why? Every re-connection was done perfectly.
So I spent several hours retracing every single wire in that area to see if it agreed with the schematic just in case my own hand drawing was wrong.
http://www.nostalgiaair.org/PagesByModel/101/M0025101.pdf
And YEP... all connections were fine. But the oscillator was still dead.
I tried removing a few things to check their connections and when I lifted one side of the AVC cap I noticed the oscillator was running.
.. but weirdly because there was still no real radio signals just squealing hetrodynes here and there.
So I measured the osc freq on my freq counter and it was way off...
At this point I thought that maybe while I was washing the tuning condenser ....perhaps I moved the trimmers enough to throw things off like this... so I tried tweaking them to bring the oscilator ack into range but no dice.
Well now what?, I thought to myself... here I am, almost finished, and this new puzzle happens and now I'm on sort of a deadline as well. ( glad I hadn't already put it up on Ebay expecting to finish it before the auction end... or I'd be dead.)
So I could only slowly begin to now suspect the oscillator coil itself.
.. but I couldn't determine which of the 5 pins on it are which windings ...so I was really stuck.
I was hoping I could find another similar Zenith in my stock pile of radios around here to compare with or at least to steal the oscillator coil from. (assuming the coil is the problem in the first place...lol)
... So luckily I have a file drawer with schematics for every single radio in the shop..... even all those many radios out in the garage still waiting to be worked on.
I always make a schematic print-out with a photo of every radio I buy the day I buy it and file it.
So as I was perusing my Zenith file, sure enough, I found a model 6d029 that has the identical circuit:
http://www.nostalgiaair.org/PagesByModel/062/M0025062.pdf
Well that meant I could pull that radio apart to compare ... but as I looked closer at this schematic I was greatly relieved to see that they show a nice clear drawing of the oscillator coil and each pin designation. Wow what luck!
So now I check it against my problem radio to be sure I have mine properly connected and it seems I sure do.
So now it's time to check for continuity of the each winding to be certain the coil itself is good.
But I had no reason otherwise to suspect it because although I was working all around it and moved it a bit a few times... there was no physical signs anywhere on the coil of broken leads or damage from my tools... it looked just fine. In fact each hair wire lead from the windings were all still complete in tact and still nicely covered under wax as they lead up to each terminal pin and still beautifully wrapped on each pin and nicely soldered.
But when I ohmed them out for continuity I found that one winding was open!!
Well this is good and bad. Good to find the problem but bad because what can I do to fix it?
I was hoping it was a bad solder contact but that was not the case.
Each lead on the bad winding led into a mass of black wax. So I used my solder iron to melt some away and sure enough out pops the bad broken disconnected lead end...only about an inch or two away from the solder lug... but I could not see the part it broke off of anywhere!!!
So I carefully worked with 3 pair of eye glasses and my eye loop using a tooth pick to dig at that wax for the longest time.
I never found the other half.
I finally had to take he bull by the horns. So I used my exacto blade and connected one lead from my ohm meter to it. The other lead to the other pin on the coil.
I felt that this way I could poke a bit with the sharp razor edge to locate one of the windings in the waxy coil.
So I very carefully poked at a few of the top windings until my meter showed contact. So then I carefully pulled this up a tiny bit and cut it in two. Then I uesd the meter to find wich part was the good part connecting to the pin on the coil form.
The print indicated that the winding should be about 8 ohms and I was reading very close to that so I knew I had enough of the winding to work properly.
I took a short length of 22 or 24 gauge stranded wire and soldered it to this new found stub.
Then I carefully positioned the remaining wire around the form and up to the dead pin and soldered it in place. Then I used a piece of duct tape to swaddle the connecton to the hair wire around and against the coil form safely.
Now with fingers crossed I reinstalled the coil and rewired all connections.
I turned on the juice.... and as the tubes slowly warmed I was holding my breath.... but then it came alive!. Yes tere it was...mucic RF ..great!!
Now what in the world caused that coil wire to break deep under the wax especially at this time?... I'll never know. But I can only suspect that somewhow maybe it happened as I was working under and around there. Who knows?
Anyway I am very thankful that I was able to salvage that coil. I don't know where or how I'd be able to find another one that would work properly.
Do any of you guys know if I could have bought a generic one from AES or somewhare else and made it work without too much difficulty?
Zenith 6D614 only has broadcast band. You could use a Universal Osc Coil, P-C70-OSC from AES.
http://www.nostalgiaair.org/PagesByModel/101/M0025101.pdf
There is an open ended winding in your oscillator coil. It can be replaced with a 50 pf cap as used in some radios. Check different schematics.
Norm
:I've been rebuilding and restoring this old Zenith 6d-614 lately. And I've recapped it, replaced most of the wiring including inside the IFs... and cleaned and sanded the chassis and repainted the case as you can see here:
:http://www.pbpix.com/radio/consoltone1.jpg
:http://www.pbpix.com/radio/consoltone2.jpg
:
:But along the way, things happen that can baffel the best of us.
:I am very close to having this thing finished and trying to get it all put back together to put up on Ebay by Sunday.
:So last night I attempted to do a few final stages. I had, the previous evening, removed the tuning condenser to wash it as usual. So after a day's drying I put it back in the circuit last night. Now to make sure of my steps I had even made a drawing of every connection in that area below the oscillator and antenna coils. I followed it to the letter during re-install.
:
:However ....when I turned the radio on there was total silence!
:
:I tested the center tap on the vol control and the audio was fine.
:I fed modulated 455kc in the RF stage and that was fine too. A nice clean 400hz tone with sufficient volume... but no radio signals.
:
:So I put the scope probe near the oscillator coil to see it it was running... nope!
:Well why? Every re-connection was done perfectly.
:
:So I spent several hours retracing every single wire in that area to see if it agreed with the schematic just in case my own hand drawing was wrong.
:
:http://www.nostalgiaair.org/PagesByModel/101/M0025101.pdf
:
:And YEP... all connections were fine. But the oscillator was still dead.
:
:I tried removing a few things to check their connections and when I lifted one side of the AVC cap I noticed the oscillator was running.
:.. but weirdly because there was still no real radio signals just squealing hetrodynes here and there.
:
: So I measured the osc freq on my freq counter and it was way off...
:At this point I thought that maybe while I was washing the tuning condenser ....perhaps I moved the trimmers enough to throw things off like this... so I tried tweaking them to bring the oscilator ack into range but no dice.
:
:Well now what?, I thought to myself... here I am, almost finished, and this new puzzle happens and now I'm on sort of a deadline as well. ( glad I hadn't already put it up on Ebay expecting to finish it before the auction end... or I'd be dead.)
:
:So I could only slowly begin to now suspect the oscillator coil itself.
:.. but I couldn't determine which of the 5 pins on it are which windings ...so I was really stuck.
:
:I was hoping I could find another similar Zenith in my stock pile of radios around here to compare with or at least to steal the oscillator coil from. (assuming the coil is the problem in the first place...lol)
:
:... So luckily I have a file drawer with schematics for every single radio in the shop..... even all those many radios out in the garage still waiting to be worked on.
:
: I always make a schematic print-out with a photo of every radio I buy the day I buy it and file it.
:
:So as I was perusing my Zenith file, sure enough, I found a model 6d029 that has the identical circuit:
:http://www.nostalgiaair.org/PagesByModel/062/M0025062.pdf
:
:Well that meant I could pull that radio apart to compare ... but as I looked closer at this schematic I was greatly relieved to see that they show a nice clear drawing of the oscillator coil and each pin designation. Wow what luck!
:
:So now I check it against my problem radio to be sure I have mine properly connected and it seems I sure do.
:
:So now it's time to check for continuity of the each winding to be certain the coil itself is good.
:
:But I had no reason otherwise to suspect it because although I was working all around it and moved it a bit a few times... there was no physical signs anywhere on the coil of broken leads or damage from my tools... it looked just fine. In fact each hair wire lead from the windings were all still complete in tact and still nicely covered under wax as they lead up to each terminal pin and still beautifully wrapped on each pin and nicely soldered.
:
:But when I ohmed them out for continuity I found that one winding was open!!
:
:Well this is good and bad. Good to find the problem but bad because what can I do to fix it?
:
:I was hoping it was a bad solder contact but that was not the case.
:Each lead on the bad winding led into a mass of black wax. So I used my solder iron to melt some away and sure enough out pops the bad broken disconnected lead end...only about an inch or two away from the solder lug... but I could not see the part it broke off of anywhere!!!
:So I carefully worked with 3 pair of eye glasses and my eye loop using a tooth pick to dig at that wax for the longest time.
:
:I never found the other half.
:
:I finally had to take he bull by the horns. So I used my exacto blade and connected one lead from my ohm meter to it. The other lead to the other pin on the coil.
:I felt that this way I could poke a bit with the sharp razor edge to locate one of the windings in the waxy coil.
:So I very carefully poked at a few of the top windings until my meter showed contact. So then I carefully pulled this up a tiny bit and cut it in two. Then I uesd the meter to find wich part was the good part connecting to the pin on the coil form.
: The print indicated that the winding should be about 8 ohms and I was reading very close to that so I knew I had enough of the winding to work properly.
:
:I took a short length of 22 or 24 gauge stranded wire and soldered it to this new found stub.
:Then I carefully positioned the remaining wire around the form and up to the dead pin and soldered it in place. Then I used a piece of duct tape to swaddle the connecton to the hair wire around and against the coil form safely.
:Now with fingers crossed I reinstalled the coil and rewired all connections.
:I turned on the juice.... and as the tubes slowly warmed I was holding my breath.... but then it came alive!. Yes tere it was...mucic RF ..great!!
:
:Now what in the world caused that coil wire to break deep under the wax especially at this time?... I'll never know. But I can only suspect that somewhow maybe it happened as I was working under and around there. Who knows?
:Anyway I am very thankful that I was able to salvage that coil. I don't know where or how I'd be able to find another one that would work properly.
:
:Do any of you guys know if I could have bought a generic one from AES or somewhare else and made it work without too much difficulty?
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I guess I'm just not experienced enough with this stuff to think that just because it was designed that way doesn't mean it can only work that way.
Maybe I'll just order up one of those coils to have around and experiment with it a bit.
I really appreciate that Norm... again thanks..