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Post by bountyhunter on May 15, 2024 2:53:18 GMT -5
I have a 68R receiver with a bad Ktran IF transformer. I was going to repair it but I think possibly my dog needed more iron in her diet because one of the ferrite slugs is missing so Barketts gets more of my money. I received the new part and my question is this, should I install new ktran as is? or should I remove the silver/mica and replace with mica capacitors, 100pf I think?
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Post by 2600 on May 16, 2024 0:42:41 GMT -5
Doesn't have silver mica. The internal capacitors are mica sheets with metal plates interspersed. An upside-down "V"-shaped steel spring holds tension against this stack of micas and plates. This style will have a brass rivet as the rim of the lower adjustment hole.
The top end of that rivet holds down the tension spring.
The styrene plastic frame shrinks and becomes brittle with age. Causes the spring tension to slack. The capacitor plates shift around randomly and cause the signal to drop out.
A new unused part hasn't yet been exposed to the radio's high temperatures, and may still be perfectly okay. Don't have experience with new K-Tran parts, only old worn-out ones.
Never had much luck removing this style internal capacitor. Just getting that brass rivet loose would crack the plastic body beyond repair. Well, beyond the labor I wanted to put into it. The capacitor in the 455 kHz IF transformers in a Tram D201 is a polystyrene axial cap that's 330pf. Never have discovered what the K-Tran's internal cap value is meant to be.
The K-Trans I looked inside have "cup" cores. A cup-shaped ferrite with threads on the outside. It covers the outside of each winding, not like the thin cores with a hex-shaped hole that threads inside the coil. They say this was done to magnetically shield each K-Tran from one next to it. Allowed the designer to place the IF transformers closer together without unwanted magnetic coupling happening between them.
Here's one guy's solution:
73
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air1
Ratchet Jaw
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Posts: 72
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Post by air1 on May 16, 2024 8:15:39 GMT -5
Been there, done that with K-Trans. Like Nomad said, if you don't know the value, you have to use different values until you get one that works. I just repaired one a while ago in a Johnson Messenger 223. I tried 330pf like Trams have, but the upper and lower slugs touched before the signal peaked. Tried a 220pf,same problem, finally ended up with a 100pf. Real pain in the neck having to take them in and out of the radio every time till you get it right, but it's all you can do unless you can find another one that works. Getting the rivet out to remove the old parts is sketchy. I usually drill them out, but like Nomad said, the bodies are brittle. Then you have to find a way to hold it all back together. I use superglue and it seems to work. You should try the one you bought first before operating on it.
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