[Boatanchors] SP-600 Toroid

[James A. (Andy) Moorer]

I rebuild the torroids as follows:

I start with a core from Micrometals. A T37-6 or T44-6 will do. If your eyes 
are good, you could use a smaller one.

I wind it as follows:

Tap 1 followed by 4 turns
Tap 2 followed by 10 turns
Tap 3 followed by 4 turns
Tap 4

The original was 2-10-2, but that doesn't put much voltage on the output. 4 
turns puts about 1.5 VRMS. Note that whatever you feed it with has to put 
out that voltage.

I then cover the whole thing with epoxy. I hold it to the PC board with 
nylon washers with a #6 screw and nut.

Remember not to twist the wire together when you bring out the taps. That 
just adds capacitance (bad!).

I have restored a number of JX-17's (I'm not sure how many) and I have never 
seen one without a broken T-35. You can't just glue it together - when it is 
broken, it also breaks the magnetic circuit. Note that this means that you 
can't put two standard JX-17's together and expect it to work, since both 
their T-35's will be broken. With this replacement in both receivers, you 
can. I have tried it and it works pretty well.

I believe the problem is that the torroid was made early in the history of 
ferrite materials and they didn't take stresses from thermal cycling into 
account. A little humidity in the air plus a red-hot tube receiver and *pop* 
goes the transformer.

This coil does not resonate - it is just an autotransformer.

Hope this helps.

James A. (Andy) Moorer
www.jamminpower.com

----- Original Message ----- 

>
> I have an SP-600JX17 apart and found a broken toroid.
> The toroid is T35 in the FCU, in the plate of the 6AH6
> crystal oscillator/HFO Buffer stage.
>
> I considered epoxying the pieces of the core back
> together, but a substantial amount (about 1/3 of the
> circumference) is missing.
>
> Does anyone know of a replacement or have permeability
> data on the core?
>