[R-390] Cleaning Chassis and rebuliding -Long

[G4GJL@aol.com]

Today I did some more work on the current BLUE STREAK project here. (Not the=
=20
1960s Missile Project but the St Juliens renovation!)

Here are some notes on my achievements, which are related to chassis cleanin=
g=20
but do not answer directly Jims question. Im afraid I do not have the mail=20
you mentioned, Jim.

I have the rebuilt St Juliens receiver working very well, astonishingly so i=
n=20
fact. Especially as it was a pretty badly corroded and sand laden example=20
from the massacre. I have been working on it on and off for about four month=
s=20
now.

I washed the IF, PSU and audio decks in hand washing soap and warm water,=20
with plenty of pure tap water wash off, then dried them in the clothes airin=
g=20
cupboard for about two weeks.

 I took great care not to get the IF transformers wet, but other than that=20
the chassis and components were all cleaned and came up beautifully. I was=20
amazed by the amount of dirt and grit washed off into the bowl after the=20
initial cleaning.

Last weekend I stripped the RF deck of its transformers and painstakingly=20
dismantled and cleaned every face of every paxolin cheek in each transformer=
.
 I remember Nolan saying that he found the deposit on these surfaces to be=20
conductive, so I didnt want to take any chances here!.=20

I used a QTIP (Cotton bud, here in UK) to clean inside each coil former and=20
around the ceramic caps. I used methylated spirit for this work, taking care=
=20
not to get too much on the coils themselves. I used a fresh cotton head for=20
each face so as not to cross contaminate from one piece to another.

During the RF deck cleaning I found the wrecked 2-4MC antenna transformer. I=
t=20
had me foxed as I could not get at the fixing screw on that particular unit.=
=20
It was obscured by debris inside the can. When I finally got the transformer=
=20
off the chassis I found the remains of three slugs and the broken former=20
lurking inside. Totally useless!

The RF deck was washed with kerosene, and thoroughly cleaned. The metal was=20
perfect under all the dirt that had built up on it. The deck is a Collins, a=
s=20
are most of the transformers. I re lubed the moving parts and used Molyslip,=
=20
applied with a Qtip on the sliding faces and bearing surfaces of the slug=20
racks.

On re assenbly I straightened all the slug springs . I didnt have any talcum=
=20
powder to hand at the time so I have left applying talc until later, if at=20
all.

A major worry was the coax relay. It was very badly tarnished and showing=20
powdery corrosion in places. I guess that my radio had its back to the sea a=
t=20
St Juliens, as the rear of the set has taken the brunt of the corrosion and=20
dust ingress.=20

One of the coax relay coils was open, so I decided to strip the relay, clean=
=20
and rebuild, which I did today.

I used Goddards Silverdip, which is a silver jewellry cleaner available from=
=20
supermarkets here in UK and possibly internationally.=20

I dumped the silver parts into the liquid and scrubbed them with a=20
toothbrush.... the Silverdip has magic properties and restores a clean silve=
r=20
finish to most parts after about five minutes immersion. (BTW it is only=20
about =A32 a bottle, enough for about 4 R390s). So having rewound the magnet=
=20
for the whip antenna channel and re assenbled the relay parts, I now have a=20
pretty good looking coax relay at the back of my set.

I also changed the selenium (?) rectifier for the relay supply, as I found i=
t=20
had one poor leg. I guess this might be why one of the relay coils has gone=20
open in the first place. I replaced it with a silicon equivalent, using the=20
old rectifier mounting bracket for the new one. I added a 100volt 100uF=20
electrolytic across the dc side of the relay rectifier. I found that this=20
reduced the hum from the relays when they are energised. A tip worth noting!

I recapped the audio deck and added 47uF 400 electrolytics beneath the=20
chassis to the audio decoupling components. What an incredible uplift in=20
audio output and quality.....Definitly worth doing that on any set with=20
30year plus elecs in it.

The EAC IF deck seems ok, so no recapping there yet except for trhe dc=20
blocker berfore the Mechanical filters...just a precaution! I used 0.01 2kV=20
disc ceramic as it was to hand and fitted in easily.

I was hoping to report the repair of the 200kc Calibrator crystal, but alas=20
that was not to be..... The crystal was loose inside the HC6/U can, and=20
therefore the calibrator would not lock. I opened the crystal and attempted=20
to resolder it to its mounting posts. I used a heat gun and LMP solder  Any=20
way, my attempt failed as the crystal now oscillates at 275kc. I guess it ha=
s=20
cracked under the heat. I thought it was a long shot any way!


So, in finishing the receiver is working well on all excepy the 2to4 MC=20
banbs, but without a calibrator. The PTO needs stretching, but I will tackle=
=20
that next week. In the mean time the rig is back in my shack and I am=20
listening to it for a while!

More updates later.

73

Pete
G4GJL