[ARC5] Cleaning MFP resin.

[Richard Knoppow]

    Kerosene is pretty benign but is inflammable, so use some care. I 
don't think it will dissolve MFP lacquer. I've never found anything that 
is very active to it and I've tried most common solvents. Naphtha is a 
good solvent for grease and oils and pure naphtha does not leave a 
residue. Naphtha will not attack plastics. Turpentine may work on some 
materials. Deodorized turpentine is sold as "white spirits" AKA Stoddard 
Solvent. Works on some things and was developed as a dry cleaning solvent.
    I would avoid solvents like Acetone, Xylol, MEK, all of which will 
dissolve some plastics.
     I am surprised that the MFP became gooey, usually it dries out and 
cracks.
    MFP is supposed to prevent oxidation but if it forms cracks moisture 
gets under the coating and causes exagerated oxidation.  The green stuff 
on the wires is almost certainly copper oxide, i.e. verdigris.
    I suspect the stuff around the filament leads on the sockets is also 
oxidation perhaps from hydrolysis. If not too bad you may be able to get 
it off with an oxide remover like Barkeeper's Friend or Zud made into a 
paste and used with a toothbrush.
     Bakelite is generally pretty tough but can also be moisture 
sensitive. It depends partly on the type of filler used. Bakelite is 
made from a plastic resin mixed with a filler. The filler can be all 
sorts of materials from ground up cardboard to ground up mica (low loss 
type, usually dark yellow.
    A google search for "history of crystal oscillators" will get you a 
lot of hits. Until WW-2 making crystals was a sort of cottage industry. 
Crystals were made but no one knew the best way. On the outbreak of war 
it was found that crystal controlled radio transmission was absolutely 
vital. Before long it was discovered that many crystals did not work so 
a rush research project was started to find out why. Also, the source of 
crystals was not adequate to make good ones.  After a time it was 
discovered that excellent crystals could be grown synthetically. Many 
defective crystals were ground up and used as a basis for growing new 
ones. Also, such practices as acid etching the surfaces to make them 
more active and also to obtain precision adjustment of frequency were 
introduced as was silver plating the surfaces instead of using air 
spaced mountings. By the end of the war crystal manufacture had been 
very highly perfected. Despite this many of the same small businesses 
continued to be the primary suppliers although most had grown enormously.
     My own BC-221 (I think an AK with AC power supply) is quite stable. 
The standard is sealed and looks like a metal octal tube. It has a 
trimmer to match it to a primary standard such as WWV, however, mine is 
in a wooden case so the trimmer is not accessible without removing the 
unit from the case. There is a shift in temperature and frequency once 
the unit is back in the case so getting exactly zero beat is tedious. 
Once there it stays there provided the meter is allowed to come up to 
temperature. Metal cased ones may not be as critical.
     I still find my BC-221 useful and quite accurate in comparison to a 
good counter. Of course, you can use it with a counter as a beat 
detector.  It is also something of a work of art mechanically. Worth 
some effort to get going again. I suspect you may have some open 
connections due to oxidized wire or solder connections.
    I have a collection of papers on crystal manufacture but don't know 
where I got some of them. I don't think this list accepts attachments 
but if you are interested I could forward some to you via private e-mail.

On 10/1/2017 9:18 PM, Leslie Smith wrote:
>    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

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL