I forgot this part,

A white toroid might work. The color white means its a powdered iron and not ferrite. The only problem with a toroid is it's not tunable. Though you might add or subtract a turn to get the right value with a toroid. You can look up any toroid chart on powdered iron to get the material specs. For HF work, I've seen white, and yellow used.

Best,

Will


> 
> 
> Joe,
> 
> Precision Paper Tube Co. made a lot of those adjustable forms that 
> most used for variable inductors. You could get these either PC 
> board mount or chassis mount. The chassis mount goes in a round 
> hole with a small metal clip around the top neck of the form. You 
> need to tell them what ferrite material you want for the slug and 
> then wind your own coils. These coils are calculated the same as a 
> toroidal impedance transformer is. The only difference is by using 
> the slug, the impedance coupling is changed by moving the slug in 
> and out. Sometimes Oceanstate Electronics carry these too.
> 
> You can change this by using an air wound bi-filar transformer and 
> tune it by a padder capacitor like an Arco 302 or 304. Generally 
> the 302 is used. If more capacitance is needed, you can add a 
> silver mica cap at 500V in paralell with the padder or go up in 
> model number to the 304 or greater. The Arco caps are mica 
> compression caps and the 302 is around 50-100 pF if I recall. This 
> is the method I use to tune grid driven amps and works for G-G too. 
> A simple Pi circuit can be used also with an air coil. You just 
> need to know the input imprdance you want.
> 
> Oceanstate Electronics
> 
> http://www.oselectronics.com/
> 
> Best,
> 
> Will
> 
> 
> >
> > I'm working on a "classic" W6PO 144 MHz 8877 amp 
> > (http://web.wt.net/~w5un/8877-1.htm) .  The input tuning circuit 
> > calls for L1 to be wound on a 1/2" diameter form with a white 
> > tuning slug (CTC 1538-4-3) .   Does anyone know where I can find 
> > this particular form?  Or a reasonable replacement?  The amp 
> > currently just has the coil and some unknown ferrite rod stuck in 
> > the middle and can't get the SWR between the amp and driver below 
> > 3:1.
> >
> > Thanks
> >
> > joe n6kk
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> 
> 
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