[R-390] Z503 replacement

[rbethman]

Todd old son,

This is ?great?.  I pose it with question marks for several reasons.

1) What percentage have an LCR meter?

2) What percentage have an HP-4342A Q Meter?

3) How does this change the alignment?

I pose these for the members of the list that really do NOT have all the 
specialized test equipment.

*THAT* is why I posted KNOWN sources for the Z-503!

Bob - N0DGN

On 4/2/2011 3:45 PM, ToddRoberts2001 at aol.com wrote:
> <SNIP>
>
> Hi All,
> A replacement Z503 was discussed on this list about 3 weeks ago.
> I have a spare NOS Z503 that I recently measured.
>
> The inductance of the coil L-514 measured 1.38-1.39mH (millihenries) using
> an LCR meter.
> The resonating capacitor C-563 measured 84pF.
>
> The Q of the coil and capacitor inside Z503 measured a meager 25Q at 410KHz
>   using an HP4342A Q-meter.
>
> It would be recommended to use a ferrite shielded inductor for a
> replacement to minimize stray effects of the shielding can.
>
> Mouser has some suitable small shielded inductors of 1.2mH and 1.5mH at
> current prices of $1.20 each.
>
> I have a similar 1.0mH shielded inductor from Mouser and it measured with a
>   Q of 170 at 455KHz.
> There was no change in inductance when I inserted the inductor inside the
> Z503 shield can.
> Unshielded inductors show a large change in inductance when inserted inside
>   the metal Z503 can.
>
> Using a fixed inductor would require a small trimmer cap to adjust to
> resonance. Mouser has
> suitable miniature trimmer caps that will easily fit inside the Z503  can.
> The assembly could be
> peaked with the can off, then replace the shield can as there will be no
> change of inductance with the can on.
>
> To match the low Q of the original inductor a resistor could be placed in
> parallel with the Mouser inductor and
> cap tuned circuit to lower the Q down to the 25-50Q range which should work
>   very close to the original Z503 circuit.
>
> 73 - Todd WD4NGG