How to rebuild a I.F. Can

8/7/2011 8:14:50 AMJesse Hancock

Hello all.. Its been quite a while since I posted on the boards.. I finally got around to checking the last project that I was asking questions about. I found that the first IF can is OPEN on the GE202 that Im trying to restore back to health. My question, is there a way to repair a can thats open? If so , could someone direct me to a site, or some information on how to do this? I have a long time radio engineer friend who told me there is, but we dont see each other enough to get this information when I need it, and I would like to get started on this. Help from anyone would be GREAT !

8/7/2011 9:20:41 AMWalter

:Hello all.. Its been quite a while since I posted on the boards.. I finally got around to checking the last project that I was asking questions about. I found that the first IF can is OPEN on the GE202 that Im trying to restore back to health. My question, is there a way to repair a can thats open? If so , could someone direct me to a site, or some information on how to do this? I have a long time radio engineer friend who told me there is, but we dont see each other enough to get this information when I need it, and I would like to get started on this. Help from anyone would be GREAT !
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Carefully remove the IF transformer from the chassis and then the shielding to expose the winding. Many breaks can be found on the outer portion of the winding or in the lead to the IF terminal. Hopefully the break will be obvious. The first thing is to locate the break and then decide the best way to repair it.

8/7/2011 9:25:26 AMJesse Hancock

::Hello all.. Its been quite a while since I posted on the boards.. I finally got around to checking the last project that I was asking questions about. I found that the first IF can is OPEN on the GE202 that Im trying to restore back to health. My question, is there a way to repair a can thats open? If so , could someone direct me to a site, or some information on how to do this? I have a long time radio engineer friend who told me there is, but we dont see each other enough to get this information when I need it, and I would like to get started on this. Help from anyone would be GREAT !
::
:
: Carefully remove the IF transformer from the chassis and then the shielding to expose the winding. Many breaks can be found on the outer portion of the winding or in the lead to the IF terminal. Hopefully the break will be obvious. The first thing is to locate the break and then decide the best way to repair it.
:

I removed the cover from the can and I found at least two breaks. Where the winding actually connects to the terminal. I just dont know if there's two connections to each terminal or just one!

8/7/2011 9:26:27 AMJesse Hancock

::Hello all.. Its been quite a while since I posted on the boards.. I finally got around to checking the last project that I was asking questions about. I found that the first IF can is OPEN on the GE202 that Im trying to restore back to health. My question, is there a way to repair a can thats open? If so , could someone direct me to a site, or some information on how to do this? I have a long time radio engineer friend who told me there is, but we dont see each other enough to get this information when I need it, and I would like to get started on this. Help from anyone would be GREAT !
::
:
: Carefully remove the IF transformer from the chassis and then the shielding to expose the winding. Many breaks can be found on the outer portion of the winding or in the lead to the IF terminal. Hopefully the break will be obvious. The first thing is to locate the break and then decide the best way to repair it.
:

I removed the cover from the can and I found at least two breaks. Where the winding actually connects to the terminal. I just dont know if there's two connections to each terminal or just one!

8/7/2011 9:27:20 AMJesse Hancock

::Hello all.. Its been quite a while since I posted on the boards.. I finally got around to checking the last project that I was asking questions about. I found that the first IF can is OPEN on the GE202 that Im trying to restore back to health. My question, is there a way to repair a can thats open? If so , could someone direct me to a site, or some information on how to do this? I have a long time radio engineer friend who told me there is, but we dont see each other enough to get this information when I need it, and I would like to get started on this. Help from anyone would be GREAT !
::
:
: Carefully remove the IF transformer from the chassis and then the shielding to expose the winding. Many breaks can be found on the outer portion of the winding or in the lead to the IF terminal. Hopefully the break will be obvious. The first thing is to locate the break and then decide the best way to repair it.
:

I removed the cover from the can and I found at least two breaks. Where the winding actually connects to the terminal. I just dont know if there's two connections to each terminal or just one!

8/7/2011 9:25:20 AMWalter

:Hello all.. Its been quite a while since I posted on the boards.. I finally got around to checking the last project that I was asking questions about. I found that the first IF can is OPEN on the GE202 that Im trying to restore back to health. My question, is there a way to repair a can thats open? If so , could someone direct me to a site, or some information on how to do this? I have a long time radio engineer friend who told me there is, but we dont see each other enough to get this information when I need it, and I would like to get started on this. Help from anyone would be GREAT !
:

Carefully remove the IF transformer from the chassis and then the shielding to expose the winding. Many breaks can be found on the outer portion of the winding or in the lead to the IF terminal. Hopefully the break will be obvious. The first thing is to locate the break and then decide the best way to repair it.

8/7/2011 5:35:06 PMEdd

Sir Jessee . . . . .

On that unit along with the model 200 series, I am seeing ONLY 4 terminals on each IF transformer and its two coils, with their and start and finish leads . . . therefore no ambiguity.

This being true for either the 1st or 2nd IF transformer, with no excess baggage of internally built in fixed mica capacitors included within the housing . . . which could confuse a person.

Thank goodness that they were easily detected with the outer end of a winding giving you “free” wire.

But only the wisp of an accessible wire end is needed to make connection to, if it is being a start of a coils winding, where you can tin the tip of the wire piece and bring the “eye of a needle” shaped piece of micro sized bare copper wire up to it and a drop of solder will then unitize the connection again and give you some spare lead length again to connect over to the terminal.

73's de Edd

::Hello all.. Its been quite a while since I posted on the boards.. I finally got around to checking the last project that I was asking questions about. I found that the first IF can is OPEN on the GE202 that Im trying to restore back to health. My question, is there a way to repair a can thats open? If so , could someone direct me to a site, or some information on how to do this? I have a long time radio engineer friend who told me there is, but we dont see each other enough to get this information when I need it, and I would like to get started on this. Help from anyone would be GREAT !
::
:
: Carefully remove the IF transformer from the chassis and then the shielding to expose the winding. Many breaks can be found on the outer portion of the winding or in the lead to the IF terminal. Hopefully the break will be obvious. The first thing is to locate the break and then decide the best way to repair it.
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8/8/2011 5:03:25 AMJesse Hancock

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Got the if can repaired.. It was indeed open with two breaks all on the outside where it was easy to fix.. The Humm, that I had previous is still there, but is now more pronounced! The I.F. Can went from showing open to a nice 5.9 ohms, I know it should be 5.5. but im ok with what it shows now. But to find out the source of this humm, just need to trace through and make sure everything is showing continuity, correct?
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:Sir Jessee . . . . .
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:On that unit along with the model 200 series, I am seeing ONLY 4 terminals on each IF transformer and its two coils, with their and start and finish leads . . . therefore no ambiguity.
:
:
:This being true for either the 1st or 2nd IF transformer, with no excess baggage of internally built in fixed mica capacitors included within the housing . . . which could confuse a person.
:
:
:Thank goodness that they were easily detected with the outer end of a winding giving you “free” wire.
:
:
:But only the wisp of an accessible wire end is needed to make connection to, if it is being a start of a coils winding, where you can tin the tip of the wire piece and bring the “eye of a needle” shaped piece of micro sized bare copper wire up to it and a drop of solder will then unitize the connection again and give you some spare lead length again to connect over to the terminal.
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:73's de Edd
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:::Hello all.. Its been quite a while since I posted on the boards.. I finally got around to checking the last project that I was asking questions about. I found that the first IF can is OPEN on the GE202 that Im trying to restore back to health. My question, is there a way to repair a can thats open? If so , could someone direct me to a site, or some information on how to do this? I have a long time radio engineer friend who told me there is, but we dont see each other enough to get this information when I need it, and I would like to get started on this. Help from anyone would be GREAT !
:::
::
:: Carefully remove the IF transformer from the chassis and then the shielding to expose the winding. Many breaks can be found on the outer portion of the winding or in the lead to the IF terminal. Hopefully the break will be obvious. The first thing is to locate the break and then decide the best way to repair it.
::
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8/10/2011 10:27:10 AMSteve Bento

This might be a good point to use a signal tracer to help locate the exact stage where the hum is being introduced into the signal chain. Sounds like it could be a shielding or grounding problem. Once you know the stage, check the resistances at each pin of the tube from that stage and compare it to the calculated resistance at each pin. If you don't know how to find it, let me know and I can tell you.

:Got the if can repaired.. It was indeed open with two breaks all on the outside where it was easy to fix.. The Humm, that I had previous is still there, but is now more pronounced! The I.F. Can went from showing open to a nice 5.9 ohms, I know it should be 5.5. but im ok with what it shows now. But to find out the source of this humm, just need to trace through and make sure everything is showing continuity, correct?

8/10/2011 11:01:11 AMNorm Leal

Check loop antenna connections. Be sure the RF stage grid has a path to AVC line.

http://www.nostalgiaair.org/PagesByModel/613/M0007613.pdf

Norm

:This might be a good point to use a signal tracer to help locate the exact stage where the hum is being introduced into the signal chain. Sounds like it could be a shielding or grounding problem. Once you know the stage, check the resistances at each pin of the tube from that stage and compare it to the calculated resistance at each pin. If you don't know how to find it, let me know and I can tell you.
:
:
::Got the if can repaired.. It was indeed open with two breaks all on the outside where it was easy to fix.. The Humm, that I had previous is still there, but is now more pronounced! The I.F. Can went from showing open to a nice 5.9 ohms, I know it should be 5.5. but im ok with what it shows now. But to find out the source of this humm, just need to trace through and make sure everything is showing continuity, correct?
:
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8/10/2011 1:41:07 PMEdd

Sir Jessee. . . . .

Hmmmmmmmm . . . . you certainly must not have palsy . . . . with the successful repairing of that IF transformers inner and minute intracacies . . .Taaa Daaaaa !

Exactly HOW much down is your main ~125VDC B+ and its sub ~88VDC B+ voltages from those given values . . . . and DO confirm that you were having your metering mediums NEGATIVE lead being on the floating ground buss.. . . . and NOT using the sets chassis ground for that referencing.

Also is the negative of the filter capacitor to a good connection into the floating B- buss and not being made near any connections that the 12SQ7 1st AF amp is near, in case a previous repair person made filter changeouts and moved their grounding position(s) where an undesirable ground loop might have been created in a 1st audio region.
Also, that the old can / capacitor set is not still in circuit and having new electrolytics just shunting across the old sections ?

FORBID . . .that they didn't make the very common assumption that the low/bottom side of a volume control is always ground and have connected in there.

An optimal physical position for it / them to be connected to. . . . (in case 2 separate units are involved now) . . . would be at the very BOTTOM lead (B-) of the 150 ohm cathode resistor of the 35L6 AF output tube.

Soooo the Hummmmmmmm is there irregardless of the volume control position . . . of particular interest is hummmmmm being present, while being at its at its minimum-um-um position.

Confirmed . . . on your having the loop antenna connected in circuit. A usually a fallacy of being open circuit, will result in picking up only the strongest station(s)...... and it typically will be having a warbling / "talking underwater" intonation of its sound.

Quickee-quickee . . . analytical troubleshooting procedure :

Take maybe like a 20-47-50 mfd at 150VDC Eeee-lectrolytic capacitator in hand and then turn on the set.

Be sure the cap is shorted out to initially be totally discharged, place the negative of the sub cap to B- buss and the caps + lead goes to the plate of the 12SQ7 . . .brace for the initial . . . .POP . . . . what say now . . . chum . . .got any hummmmmm ?

If still having that hummmm level, discharge the capacitor and use the same ground again, but THIS TIME place the caps+ to B- ground and the caps negative to the 1st grid of the 35L6 for about 5 seconds of evaluative time to then see if the hummmmmmm disappears.

IF not, then the hum must be coming in from insufficient filtering of the power supply.

Now, just exactly WHAT were you doing just above ? ? ? . . . well . . . when you ran the volume control to absolute minimum, you should have shut down any incoming HUMMMMM from the sets RF front end stages and the final detected audio sourcing . . . .ergo . . . the problem is further on to the right , down the AF processing circuits trail.

That placing the source of the hummmmm untroduction, being AFTER being amplified by the 12SQ7.

When you placed the filter across the plate of the 12SQ7, that huge amount of capacitance "dead shorted" any present AC audio or hummmmmm directly to ground. That further confirmed the hummmmmm not being amplified by the 'Q7 nor creeping in from its power supply source. . . . seems that the offending trouble source is yet further on to the right.

Now one slight last circuit eccentricity before we move on to the examining and testing the B+ supply sourcing, a last hidden possibility is associated with the negative feedback loop circuitry tied in from the cathode of the 35L6 tube back into the 1st audio amp circuitry .

To wit . . . see the cathode of the 35L6 and its cathode, where above its 150 ohm cathode resistor there is inserted a series 47K and .01 capacitor network that has their other ends feeding to a series 1K resistor with its other end then finally ending up at the low end of the volume control WHICH is being held ABOVE B- level with yet another 1K resistor(R9).

Place a jumper lead a short across that R9 resistor to see if it has any effect upon your hummmmm problem.

If that proves fruitless, we have covered the AF aspects so take that ? 47 ? ufd electrolytic subbing capacitor again and jumper across the C21 B 88V supply filter capacitor . . . . . any hummmmm abatement ?
Then since we are stepping up to a HIGHER voltage threshold, merely move its positive lead up to then be shunting the main C21A capacitor.

How about the HUMMMMMM situation of the last two tests ?. . . . . what say you ?. . . .standing by for results. . . . .

73's de Edd

:Check loop antenna connections. Be sure the RF stage grid has a path to AVC line.
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:http://www.nostalgiaair.org/PagesByModel/613/M0007613.pdf
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:Norm
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::This might be a good point to use a signal tracer to help locate the exact stage where the hum is being introduced into the signal chain. Sounds like it could be a shielding or grounding problem. Once you know the stage, check the resistances at each pin of the tube from that stage and compare it to the calculated resistance at each pin. If you don't know how to find it, let me know and I can tell you.
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:::Got the if can repaired.. It was indeed open with two breaks all on the outside where it was easy to fix.. The Humm, that I had previous is still there, but is now more pronounced! The I.F. Can went from showing open to a nice 5.9 ohms, I know it should be 5.5. but im ok with what it shows now. But to find out the source of this humm, just need to trace through and make sure everything is showing continuity, correct?
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