The solder paste you are talking about isn’t flux.
It’s a lot of microscopic beads of solder with flux added, and used for applying to PCBs through a stencil,
and then the solder is flowed with hot air once the part has been placed over the footprint that has the paste applied.
Solder flux is available from Jaycar at least in the form of a pen.

The downside to the solder paste is it’s shelf life, and keeping it under refrigeration, but for radio,
you’ll get a lot longer out of it than it’s quoted shelf life.

I have restored power supplies on only a few vintage radios but have restored/rebuilt several power supplies for telephone switchboards and other miscellaneous vintage equipment.

As a general rule (based on bitter experience) I never trust an old power transformer to still have its insulation intact or at least retain enough to not have shorted turns or a short to the frame when 230V AC is applied. Where possible I replace the old transformer with a new unit but particularly with vintage radios, a suitable replacement transformer is just not available. Then it is a case of applying lots of varnish and seeing if the damage can be repaired. I have never been able to repair a shorted turn problem but have heard that other collectors have had success soaking the windings in hot wax; can anybody comment on the effectiveness this method?

I always replace the mains power cord. I have never found an original VIR power cord where the insulation remained intact and has not hardened and fractured to make reuse very dangerous. Also I have encountered many early PVC cords where the inner insulation has lost the plasticisers and hardened. When these cords are bent it is possible to hear the inner insulation cracking and potentially allowing the conductors to touch. Oddly the other effect that can also occur is for something in the plastic (sulphur compounds?) to corrode the copper conductors. The result is that the conductor becomes thinner then either breaks or goes high resistance leading to hot spots or burning if the current is high enough. I have also encountered cases where a corrosive liquid has moved along the stranded conductors like a wick and oozed out to attack the termination point. These have included Ross Courtney terminals (didn't know that was what they were called), crimped lugs and plain old solder lugs. The copper parts became covered with green corrosion and the plated steel bolts rusted. I first thought that this was because someone had used a corrosive solder flux but when there was no evidence of solder, I tried stripping back the insulation on the cable. This revealed corrosion for a considerable length along the conductors, far more than any flux would have penetrated. I doubt that this would be news to most of the members of this site but it serves to reinforce the electrical safety warnings that Brad has posted.

My preferred source of replacement cords is a computer power cord with moulded 3-pin plug. (Supposedly these all meet Australian standards and are readily available.) I cut the IEC plug off (Jaycar also has cords without the IEC plug) and carefully trim back the outer cover to get at the inner conductors. When fitting the cord it is essential to use appropriate strain relief as mentioned in other posts.

My practice when attaching a stranded conductor to any terminal is to first tin the exposed copper strands with solder before crimping on a lug or putting the wire into a screw terminal. My belief is that this reduces the chance of the copper strands corroding/oxidising and ensures a low resistance, reliable connection. However I have heard that this is actually against the 'rules' for some unknown reason. Would anybody care to comment on this method to confirm or deny my theory or can anybody (Brad?) point me to the appropriate rule that states that this method is not allowed? (Note that I am NOT referring to fixed power wiring that is rightly the province of licensed electricians.)

Solder or not to solder is often a vexed question. Corrosion & vibration are the enemy. I have seen, even recently, a Wood Lathe where the bolt on earth has come adrift & a high resistance earth from corrosion.

I will often crimp & solder an eyelet, that way it cannot fail. One always leaves the mains earth wire a bit longer, based on the fact that if it is able to be pulled the earth will be the last to be torn off.

A lot of mains wires used to be soldered. One thing that will not happen to a good soldered joint easily is arcing & arcing creates heat.


Site is quite unstable tonight.

The only rule that I know of as far as appliances go is that a flexible cord must be anchored in an 'approved' way and the binding point for an earth wire cannot be a fastener for another component, such as a transformer. This is to say that the transformer must still be earthed if the appliance is not double-insulated but that earth attachment cannot be the first one. I am assuming that this rule is to allow for the fact that vibrations and harsh treatment can lead to nuts and bolts being loosened as described by Marc.

I personally don't see an issue with soldered earth connections if the joint is a good one. Yes, it is illegal in fixed wiring these days and clamps or BP connectors (as appropriate) must be used instead however for most people here, this is beyond the scope of vintage radio as most here will not be licensed electricians. In appliances, different rules and practices apply and the SAA Wiring Rules (AS/NZS 3000) doesn't apply.

For bolting a crimp lug to a chassis, it is simple. A bolt, a nut, a flat washer and a spring washer along with a drop of Loctite for those want to be really sure nothing will work loose or you could even use a nylock nut in place of the standard one.

Yes I've heard that tinning a flexible cable and fitting it to a screw clamp is unwise because the solder will creep under pressure and you'll end up with a loose joint. I have seen this in commercial equipment and installations and I had always assumed that the screw wasn't tightened enough in the first place.

A proper pressure swaged lug is the go. No solder and no crimped auto type lugs.
As tested many years ago by the Hydro electrical wise people pressure swaging had the least resistance and longest imunnity to corrosion. And they were dealing with 220kv plus, and heaps of current.
If soldering is a no no in the AUS wiring rules, it’s there for a good reason.
I personally cannot see why in a vintage radio situation where originally safety was relying on the isolation of the power transformer, an added chassis earth connection if properly restrained could not be soldered.
I would love to see some official documentation on this subject.
JJ

One of the things that does not happen other than with mainly Aircraft, that likely due to the volume, we do not normally collect & collate data on failures and cause. E.g in the case of an earth in anything electrical.......

Did it fatigue off; was it torn or cut off, did it fall of; did it burn off, or perhaps suffer a bonding issue due to corrosion? Corrosion can be moisture and electrolytic. Eg Aluminium against Steel will see the Aluminium eaten.

That's why a lot of sixties vehicles & Grey Fergies did thermostat housings & the cars both that & the water pump, if you failed to use a corrosion inhibitor.

Just revisiting this, and regarding the old Ross Courtney connectors, I note that the Aussie firm LX Electrical Accessories, based at St Marys, manufactures what it calls a fret lug:

https://scoresby.awm.mmem.com.au/lxplx705.html?rl=1

Actually a bit of solder on a crimped earth connector does stop it from corroding.

Glands mounted pointy end into the pan & with a zip tie as a double up are excellent cable clamps for many old radios.