Accidentally hit a choke coil with my soldering iron… how screwed am I?

[Madeline12]

*sigh* Of course, the last capacitor I needed to replace on my first repair I’ve been working so hard on, I accidentally singed one of the coils connected to pin 6 of a 6T8 socket in my Stewart Warner TV. According to the schematics, it’s the choke coil rated at 15 ohms. It looks pretty burned/black sadly… I believe these coils NEED insulation so… I’m curious if rewinding this is even doable knowing how thin the wiring is. Any ideas how to fix this possibly?

Photo of the coil pre-fry and repair below:

[Madeline12]

I can also provide a photo of the damages if needed.

[Yamamaya42]

Originally Posted by Madeline12

*sigh* Of course, the last capacitor I needed to replace on my first repair I’ve been working so hard on, I accidentally singed one of the coils connected to pin 6 of a 6T8 socket in my Stewart Warner TV. According to the schematics, it’s the choke coil rated at 15 ohms. It looks pretty burned/black sadly… I believe these coils NEED insulation so… I’m curious if rewinding this is even doable knowing how thin the wiring is. Any ideas how to fix this possibly?

Photo of the coil pre-fry and repair below:

look in the SAMS for pos replacements for the coil.
there is often listings under miller / merit / meissner and others on the list.
most of which can still be found on evil-bay for fair prices.
winding your own will be next to impossible w/o the correct rig to do so.

The SAMS should have all the info to find a replacement, including the microhenry rating and resistance and if its wound on a resistor.

[Madeline12]

Originally Posted by Yamamaya42

look in the SAMS for pos replacements for the coil.
there is often listings under miller / merit / meissner and others on the list.
most of which can still be found on evil-bay for fair prices.
winding your own will be next to impossible w/o the correct rig to do so.

The SAMS should have all the info to find a replacement, including the microhenry rating and resistance and if its wound on a resistor.

I have, and there are no replacements listed in the table. There’s columns for Meissner and IRC, but none specifically are listed for this coil. Microhenry rating is also not specified in the SAMS or the service manual.

[Yamamaya42]

does it still test at 15 ohms?
not sure if this is the right SAMS
but it says
https://www.earlytelevision.org/pdf/...sams_64-12.pdf

l34

rf choke 507373 15 ohms

SOMEONE may be able to look it up in an old cross ref book.

[Yamamaya42]

also, if this is the right SAMS, this set seems to be series strung, and has a 19t8, is that correct?

[Madeline12]

Originally Posted by Yamamaya42

does it still test at 15 ohms?
not sure if this is the right SAMS
but it says
https://www.earlytelevision.org/pdf/...sams_64-12.pdf

l34

rf choke 507373 15 ohms

SOMEONE may be able to look it up in an old cross ref book.

Not sure where you found that model… the tv I’m working on is a 9121A. It is the same Stewart Warner Part number (507373), but has no other replacement part numbers associated in the SAMS you shared or in the SAMS associated with my TV. I will test it momentarily

[Madeline12]

Originally Posted by Yamamaya42

does it still test at 15 ohms?
not sure if this is the right SAMS
but it says
https://www.earlytelevision.org/pdf/...sams_64-12.pdf

l34

rf choke 507373 15 ohms

SOMEONE may be able to look it up in an old cross ref book.

Welp… it appears I’m an idiot and didn’t think of doing basic diagnostics to begin with. Yes, readings are still hovering around 14.9-15 ohms. I brushed off a bit of the char and it looks like the damage isn’t tooooo bad… very minor to be frank.

This is what I get for being a bit panicky… looking silly. But at least I know I don’t have to begin a possibly endless hunt for a new coil. Thank you.

[Yamamaya42]

Originally Posted by Madeline12

Welp… it appears I’m an idiot and didn’t think of doing basic diagnostics to begin with. Yes, readings are still hovering around 14.9-15 ohms. I brushed off a bit of the char and it looks like the damage isn’t tooooo bad… very minor to be frank.

This is what I get for being a bit panicky… looking silly. But at least I know I don’t have to begin a possibly endless hunt for a new coil. Thank you.

to keep it that way, it's best to cover the damaged area with some kind of enamel like corona dope, which is made to protect coils and such,

https://www.amazon.com/MG-Chemicals-...008OA7CAE?th=1

it's not cheap, but does the job.

in a real pinch, clear nail polish may work, but corona dope is much better for protecting the coil in the long run.

[Penthode]

Has anyone thought what that portion of the circuit is doing? It looks weird to me.

It looks like a feeble attempt at providing further AM limiting. The plate of the limiter is capacitively coupled to the 19T8 diode plate. The choke coil is simply an RF choke to preventing the sound IF being bypassed fully to ground.

It looks as if this is an attempt to further IF limit any residual AM reached the sound detector. I am especially curious the placement of the 10uF electrolytic: the IF rectification of the diode should place a negative voltage on the diode plate corresponding to the peak negative excursion of the IF signal. This means the 10uF capacitor is reverse polarized.

Makes me think that it would work better if that coil was open!

[Madeline12]

Originally Posted by Penthode

Has anyone thought what that portion of the circuit is doing? It looks weird to me.

It looks like a feeble attempt at providing further AM limiting. The plate of the limiter is capacitively coupled to the 19T8 diode plate. The choke coil is simply an RF choke to preventing the sound IF being bypassed fully to ground.

It looks as if this is an attempt to further IF limit any residual AM reached the sound detector. I am especially curious the placement of the 10uF electrolytic: the IF rectification of the diode should place a negative voltage on the diode plate corresponding to the peak negative excursion of the IF signal. This means the 10uF capacitor is reverse polarized.

Makes me think that it would work better if that coil was open!

This is not a 19T8 tube. It’s a 6T8 technically… and I’m not sure frankly, it’s just how I’ve followed the schematic. Maybe someone can provide further input.

[Yamamaya42]

Originally Posted by Madeline12

This is not a 19T8 tube. It’s a 6T8 technically… and I’m not sure frankly, it’s just how I’ve followed the schematic. Maybe someone can provide further input.

it's highly likely that the circuit in your TV is wired the same way in both sets the one I found on the ETF site and the one you are working on, and since 19T8 and 6T8 are the same tube save for heater voltage, it looked to me like the circuit may be some kind of AM limiter. but not sure, someone with more tube knowledge may know.

[Madeline12]

Originally Posted by Yamamaya42

it's highly likely that the circuit in your TV is wired the same way in both sets the one I found on the ETF site and the one you are working on, and since 19T8 and 6T8 are the same tube save for heater voltage, it looked to me like the circuit may be some kind of AM limiter. but not sure, someone with more tube knowledge may know.

Here’s a snippet of mine, shows positive to ground. Not sure if it’s helpful or if it needs to be zoomed out.

[Yamamaya42]

Originally Posted by Madeline12

Here’s a snippet of mine, shows positive to ground. Not sure if it’s helpful or if it needs to be zoomed out.

As mentioned, it looks like it's exactly the same as in the SAMS that I posted!

[Penthode]

... same as the Sams posted except that the electrolytic is backwards.

It looks as if it is another example of Sams making an error! Sams, especially on the early drawings,makes lots of mistakes.