16-03-2012, 07:31 PM
(This post was last modified: 29-08-2012, 04:41 PM by Robert Darwent.)
Rebuilding the coil-pack
I modified the existing A22 circuit diagram to reflect the different bands offered by an A22T, the donor parts and the calculated padder and tracker capacitors for each range;
The following diagram shows the layout for the A22T coil-pack;
I began with the slightly easier 'Aerial' side of the coil-pack, adding the three coils one at a time and soldering the required connections between the bank of trimmers running down the side of the board and the band-switching wafer mounted in the middle. Working carefully and methodically, I successfully completed this side of the coil-pack;
Continuing on in exactly the same fashion, I rebuilt the 'Oscillator' side of the coil-pack. This section was more difficult, due to having to accomodate the additional large padder capacitors in the limited space available;
Note; the two large 6800 pF 1% mica capacitors. These are connected in series to make-up the calculated, non-standard, 3400 pF padder value required for the S2 oscillator range.
Finally, I should add that none of the original coils and padder capacitors were used in the rebuild and have been carefully stored. Even the medium wave coils came from the scrap A23 chassis. Therefore, if so desired, the coil-pack could be converted back to a standard A22 model.
Next instalment: Chassis restoration.
I modified the existing A22 circuit diagram to reflect the different bands offered by an A22T, the donor parts and the calculated padder and tracker capacitors for each range;
The following diagram shows the layout for the A22T coil-pack;
I began with the slightly easier 'Aerial' side of the coil-pack, adding the three coils one at a time and soldering the required connections between the bank of trimmers running down the side of the board and the band-switching wafer mounted in the middle. Working carefully and methodically, I successfully completed this side of the coil-pack;
Continuing on in exactly the same fashion, I rebuilt the 'Oscillator' side of the coil-pack. This section was more difficult, due to having to accomodate the additional large padder capacitors in the limited space available;
Note; the two large 6800 pF 1% mica capacitors. These are connected in series to make-up the calculated, non-standard, 3400 pF padder value required for the S2 oscillator range.
Finally, I should add that none of the original coils and padder capacitors were used in the rebuild and have been carefully stored. Even the medium wave coils came from the scrap A23 chassis. Therefore, if so desired, the coil-pack could be converted back to a standard A22 model.
Next instalment: Chassis restoration.
