|
Due to email received, mostly private about the DJ
coil mods especially the ferrite approach, the required information
follows.
Models using the BCB capacitor board, total series
capacitance 24nf need an inductance on the main ferrite core winding
of 54 - 53 uH for 135 - 138 khz. Pick a ferrite or iron powder core
about the same size as the amidon T200 or larger and wind the reqd
number of turns to get the above inductance value. My core needed 43 turns
of 1mm enamelled wire. I use these cores for my LPF
capable of running several hundred watts RF
output and they never get warm.
Pull out the capacitor board and connect
the above coil in series to pin 5, also join the connectors labelled 7
and 8, connect a sig gen and scope in parallel to the input of coil and earth
lead to pin 1 (as per original connections in cct diagram) for main coil. Tune
the sig gen around 135 - 138 khz for min amplitude display, series resonant
procedure, and adjust the inductor turns to the exact resonant freq
rqd. If the C board value is as above then it will be easy to arrive
at the desired resonant freq with the above inductor value. Two taps on the
coil permits freq adjustment from 135.7 - 137.8 khz.
The beauty using the above procedure allows
all adjustments to be made externally from the unit and when replaced it is spot
on, no freq changes or going off resonance because of metal case proximity
as happens with the air wound coils.
The ferrite/iron coil because of the small size can
actually be mounted on the capacitor board, there is ample room at the top end,
and convenient to adjust if necessary.
For the link winding follow the same procedure as
above but only about 4uH is required, more details if required.
For the lower band models proceed as above but the
C board BCA needs to be modified for a total series C of 24
nf.
Have fun de
Mal/G3KEV
| 