[ARC5] Cleaning MFP resin.

[Leslie Smith]

  Hello All,

  I have a BC-221 treated with mould and fungus protection spray.  
  (Mold if you use the Webster dictionary).
  After 70 years the MFP is soft and starting to run everywhere.  
  I find I can remove it with kerosene on a cloth.
  What damage will kerosene cause to (or on) the chassis?

  I notice weird corrosion on the bakelite socket in the crystal
  oscillator circuit.
  Between pins 1 and 7 (if I count correctly) the bakelite has been
  badly corroded.
  Pins 1 & 7 are heaters.
  Around other pins there is little corrosion - the bakelite appears
  pristine.    Generally bakelite is robust.
  What's going on here?

  On the ceramic octal socket (used to mount the DC-9 crystal) some
  liquid (perhaps MFP) has run along the rubber coated wires.   I see a
  green colour on the cloth-covered wire - rather like verdigris.  
 It may well be verdigris.  The xtal oscillator didn't work.

  I wanted to measure the drift in frequency after 70 years, but I gave
  up on that.  I have one or two more BC-221s and I'll make that
  measurement later.  Since the '221 is a secondary standard I think it
  will be interesting to know how stable this standard is.  (This is
  particularly interesting, because (as I understand it) the BC-221
  design was done (or at least the LM-xx design) was done in the
  mid-30s.  Access to counters (or any quick calibration) wasn't easily
  had - unlike today, when we can measure to within 1Hz in 10 seconds.  
  I'm interested to know understand the process and accuracy from that
  time.)

According to the LM-xx manual, the 1000kHz crystals were spec'd to
within 30Hz of stated frequency.
In my book, grinding a crystal by any means and measuring to within 30Hz
demands a good degree of skill.
Naturally, I'm curious.  How did they do this - and do it (perhaps)
10,000 times?



73 de Les Smith
   vk2bcu at operamail.com