STEP 1
I have checked most of the chassis against the MK circuit diagram, and so far it all looks original.
I removed the valves and dial globes so I could check the transformer on no load. Slowly wound up the variac while watching ammeter, to half mains voltage. Measured secondary TX voltages and appear OK. No smoke or heat. Left on no load 30 mins.
Replaced dial globes and wound up to half mains again - no problems - left on for 60 minutes.
The TX windings and leads need attention, but removing could cause more damage. Before I wind uo to full mains voltage, can I spray with polyurethane or something else ?? Hard to locate small quantity elect varnish ??
My next major step is to replace all R's and C's and wiring - basically a total rebuild.
Cheers

I have used Jaycar PCB clear spray for lots of things.
If it's safe to spray on PCB assemblies, its probably safe to spray on wire.
You may as well get a can of spray, a can of contact cleaner/lube and a can of cleaner and have them on hand all the time.
Fred.

The wiring is usually rubber of the lowest grade and crap. Only replace the paper and electrolytic caps. The tuning Gang and its coils are a matched set. If you replace the Mica caps, especially those on the coils the result is liable to be catastrophic. The ones on the coils are rarely marked and put their to get the coil in spec.

Even that the resistors are old, there are only a select few that wander off, normally high, or open. My standard is 10% off it goes. Do not run 5Y3 sideways.

There is reference to damage in August Silicon Chip on my HMV42-71. For not the first time, I cut the damaged wire close to the transformer, spliced in new wire with suitable voltage rating and covered the splice with shrink tube.

For a Mar 300g CRC pressure pack. "Urethane Seal Coat" Code 2044 (Red) there is another colour. I got it from an industrial supplier.

"Seal Coat" is odd here inland: Only get Bunyips.

You may need to replace the "fly lead" on the detector 6B* cut it off; do not unwire the can. Remove the top screws don't touch the middle one. May be mounting bolts in the pan? To take the cover off. The sleeve looks to long recycle, or use shrink tube all along the terminal. You leave the new wire long to act as a "snake" to get it through the hole and the cover back on.

Photo uploaded to Post 16.

Looking at the photo Brad has now posted. It confirms something I will never do, unless its known to be going (just) (come in with fault) and that is power it with wax paper caps and old electrolytics in situ albeit one ecap, is not original.

The speaker transformer can be rough checked by cracking a 9V transistor radio battery across the primary.

Also note that with some tubes, running them at low volts can poison the cathode.

A cap with purple is usually on the AGC and often 1.75Meg You will have to go to the low wattage types to get 1.8Meg if its out of spec?

That is a common oddball AGC value: One can imagine some bunny sifting through a bucket full of duds looking for these "carefully selected /specific value resistors".

Marc

STEP 1
Tidied up chassis and examined/tested most components. Have decided to replace all R's, C's and wiring - complete rebuild. Removed valves and dial globes for test of TX on open circuit. Slowly wound up variac to half mains voltage - no smoke or fire - ran for 30 mins. TX voltages seem about right. Re fitted dial globes and mains again up to half - loaded OK - ran for 60 mins.
I don't want to remove TX from chassis, as it could do damage. Before using full mains voltage, I would like to apply some insulation to core and leads. Can I mask up and spray with polyurethane?? Hard to get a small quantity of elect insulation varnish.

Cheers
Rob

Pic sent to Brad - thanks Brad

You'd be better off to remove the transformer. You are going to do a full rewire anyway and it's more likely to get damaged if you leave it on the chassis.

Soak it for a day fully immersed in oil-based polyurethane, marine grade, turps clean-up. Don't use the water-based type. Waste of time just spraying it. The stuff you need is made by Cabots and it's available at Bunnings.

Test the speaker transformer primary with an ohm-meter. It should read about 200 ohms.

If it's OK, it is a candidate for a mask and spray (or pour) because you can't remove it undamaged from the speaker without drilling out the rivets and if you do that, no matter how careful you are, tiny iron filings will jump straight into the speaker annular gap and ruin it. Voice of painful experience here!

Let's hope the speaker transformer tests OK. The only safe way to remove it is to tear it off the rivets and then carefully cut the rivets away with side cutters. Not fun.

Never really had much of an issue drilling out the rivets, You only need to get the head, or tail off it. Properly covered there is no way anything can get into the front, or back of the cone. Of course you make sure that the drill cannot reach the cone. 132L Philips here needed a new speaker because a monkey put a drill bit into the cone.

Most of the damage to the transformer will be exacerbated by the rectifier and output tube and is why I put the heat shield between them on the 42-71. In most cases with a transformer, I have gotten away with crushing the brittle rubber wire's powdery rubber insulation then cutting & splicing and then cleaning & sleeving the joint with the woven tube, shrink tube, or both.

Where there are dissimilar metal joints, it does pay to spray them with circuit board lacquer to discourage corrosion.

Marcus, how do you stop the very fine drill shavings from being attracted by the speaker's magnet?

It isn't a drill through the cone that's the worry, that's easily repaired!

The example I'm thinking of was a 6" period Rola that was to go into a battery Airzone Radiostar (actually a Mullard version with that great grille treatment) that I was fixing as a wedding present for my son.

Despite wrapping the whole area with tissues and tape and going VERY slowly and carefully with a vacuum cleaner sucking the shards away as I went, those filings still got into the gap through the spider behind the cone and ruined the speaker.

Maybe you got lucky with aluminium rivets?

Actually in the case of the 132L it did stuff it, it was polling and now has a NOS 6" speaker out of a Mitsubishi Magna door in it.

There are a variety of ways to stop bits of the rivet ending up behind the cone, the simplest masking tape across the holes in the frame. A lap around the magnet sticky side out works wonders and a bit between frame & bracket sticky side facing the bracket also acts as a catcher. Lean the chassis back about 30 degrees.

This is all unnecessary if the tests indicated prove the transformer OK. Nothing needs to be disconnected to do that battery test method.

Across pin 3 plate & pin 4 screen of 6V6.

Finally got some noise out of Mickey KM. The noise is like severe static, but I think there are some short wave noises in the background at various positions on the dial. I assume it means Mickey needs a good tune up. I don't have the right gear to do same - only digital MM, basic cheap signal generator and oscilloscope. Most of the info on Youtube etc not very helpful to this radio novice - a lot of suggestions seem to say "don't touch".
No access to a valve tester, and fishy voltage at anode 6B8G - about 117 volts rather than circuit diagram showing 87 volts. Most other voltages appear about right.
Back to the drawing board for a while...........

Cheers

117 volts is fine at that position. Even 200 would be ok.

Severe static.. either an old carbon resistor about to die - or a mica capacitor, most likely on the anode of the previously-mentioned 6B8G.

Describe "severe static"!

Hiss?
Crackle?
Whistle?
Pink noise?

6B8 anode voltage will be high if it's being biassed off a bit by AGC which could happen if something is oscillating.

There should be a shield can on the 6B8 and it needs to make reliable contact with the chassis.

The ECH34 has a wire around the bottom of the red paint covered glass at the join to the bakelite base. It is vital that that wire makes reliable contact with the paint, which is metallic.

If the glass is loose in the base (remember Marcus's warning about pulling these of of the socket by the glass) then the contact will be broken. A silver or gold coloured metallic paint pen can often be used to repair this bond.

In most cases there is a wrapping of wire at the intersection of the base and socket. That wire should connect in most cases to pin one.

With a failure: Often you can expose the wire and sometimes get a tail to solder to. Otherwise wrap some fine wire (Silver wire or fuse wire) around it, take the tail to pin one, then use Jaycar CAT.NO: NM2831wire glue, or a conductive glue over the wrap.

I have also used the conductive metal glue to repair & replace the failed metallisation.

Watch that fly lead wire coming out of cans, it can fray & short, replacing it in toto is never unusual. You can salvage the terminal. But don't rush in.

A nice project Wodbore. These are a great little radio when they are working correctly.

If you are repairing this for someone else, DON’T try and “reform the electrolytic capacitors. This is just dodgy, they are well past their use by date and will not be serviceable, Good replacements are cheap and will ensure reliatble operation for years to come.
Keep things safe and do the job properly.
Good luck, it looks like fun.