Issue with rebuilt 38-690 audio transformer - Printable Version

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+--- Thread: Issue with rebuilt 38-690 audio transformer (/showthread.php?tid=12610)

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RE: Issue with rebuilt 38-690 audio transformer - Diverted - 07-01-2015

It appears that way, I guess. Thank you for being patient. Now, another stupid question on my part:

I'm confused about part 172, marked "tweeter field" on my schematic. Obviously this part is open, and I'm assuming it's the main speaker field coil. However, why is it marked "tweeter field" on the schematic? Obviously I wouldn't be thrilled about having the coil on that massive speaker rewound, but would do it if I needed to. The main speaker's field coil reads about 4.2K ohms. Don't know how far off that is, as there are no resistances given on the schematic for it.
Again, thank you for your patience.

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RE: Issue with rebuilt 38-690 audio transformer - morzh - 07-01-2015

If it says tweeter coil, it is tweeter coil. 4.2K is not open and it says right there in the sch 4300 ohms. (yes it is given in the sch, just take a good look).
So, disconnect your tweeter, measure its field one more time, it will likely show full open.
Again, open means just that, open, no finite resistance present.
Check the wires just in case they are broken, but likely you will have to have your tweeter field redone.

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RE: Issue with rebuilt 38-690 audio transformer - Diverted - 07-01-2015

Thanks, Walrus. I can stomach that a heck of a lot more easily than having the big speaker field coil done. I will check in the morning. For now, going to bed and will likely dream of speakers, multimeters and OLs. Thanks for the help, I'll let you know and will try to make it as clear as possible

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RE: Issue with rebuilt 38-690 audio transformer - morzh - 07-01-2015

Suerte!


PS. For testing purpose, you could use a big 470 ohm resistor with proper power dissip rating (possibly 10W) to put instead of tweeter coil, this way you can have sound and do other stuff while your tweeter is being redone.

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RE: Issue with rebuilt 38-690 audio transformer - Diverted - 07-01-2015

Well, I fixed the problem.
YOu were on track with the tweeter field being open. Only it wasn't open; both tweeters tested fine. So I started tracing the wire from the speaker wiring harness all the way through the chassis, into each tie in point. Everything checked out OK on the first field coil. When I got to the second, one of the two field coil wires showed no continuity. The only thing thta that could be was a chafed or corroded wire. So I cut it out, removed the clamp holding the wiring bundle to the chassis and Bingo. Under the clamp, the wire was abraded in that spot and though it wasn't separated, it read open. Solder a new one to the pin, rewired, restored continuity to the tweeter field and cautiously started up the radio.
HOLY COW this radio cranks! Sounds fabulous!
Morzh, I can't thank you enough for helping me through this. It would have been a hard thing to spot if not for your guidance. I'm in your debt, and will post updates as I continue to go through the set.
Imagine that ... an abraded wire!

Ted

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RE: Issue with rebuilt 38-690 audio transformer - morzh - 07-01-2015

(07-01-2015, 12:57 AM)Diverted Wrote:  Imagine that ... an abraded wire!

Ted

Ted


My post #32

>>> ...disconnect your tweeter, measure its field one more time, it will likely show full open...... Check the wires just in case they are broken.....     






Yes you always have to allow for the less likely (albeit favourable) scenario




Glad it worked, I am sure it is fun to listen to. Hope to find me one one day.

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RE: Issue with rebuilt 38-690 audio transformer - Diverted - 07-01-2015

I hope you do too. It's a beast. Very intimidating, but it's an impressive thing.

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