As per my previous blog, I've been thinking about what to do with the PM-2 rebuild, rebuild as is or rebuild to the most recent service bulletin.
After some discussions with other Collins restorers who gave some great advice, I have decided to rebuild to the service bulletin PM-2 Service Bulletin 1.
This improves and extends the input voltage limits, relocates the electrolytic capacitors to under the speaker and under the tagboard, rather than having them all mounted underneath the tagboard, I'll also upgrade the diodes and put 105 degree capacitors in as usual. I will also take the opportunity to change or rebuild C7 which is a dual 40uf electrolytic capacitor on the +275 V line. Not decided if I'll restuff the original can or find a suitable modern equivalent - I've used 50uf/500v dual ones from Cricklewood electronics previously to good effect.
If you saw the previous blog post you will have seen that the tagboard was not re-useable - it had been overheated badly and repaired (poorly) several times.So decision made - the first thing is to re-create/remake the tagboard - I always try to make it as close a possible to the original so I sourced a suitable piece of 3 mm Phenolic resin sheet, I couldn't quite find the right colour its a too dark but the right thickness. I also found the right tags from RS Components, or very close to the original ones under part number 433-589
So after some careful measurement of the original board and some drilling I had this ;
I'm no expert and as you can see the phenolic resin sheet is a little brittle and I clipped one corner (top left) but overall not too bad. From this, the tags/pins need to be pushed into the holes. The pins come with a punch which helps to do this as otherwise, you will damage the pins.
So after some careful work, I ended up with this ;
So now I'm ready to start putting together the board ready for the rebuild, but that will be in another blog post.
Overall just under a couple of hours of careful but pleasurable work to get this far, though its not a race !