Picked up one of these the other day. I thought I'd share the repair story if anyone is interested.
(no photos, sorry)

The case was immaculate, not a scratch or crack to be seen. The power plug had been cut off. According to the shop, it didn't work, which means buying it was a gamble. For that, I got a discount.

So, took the cardboard back off, top 2 screws missing. Bottom 2 screws also hold the chassis into the case. Pulled the knobs off, one on each side. One was broken long ago but had been sticky-taped together.

Withdrew the chassis, and a resistor fell out. It was an ancient brown IRC that had burnt out. According to the sticker the valve line up was 6A8G, 6AR7GT, KTG1, 6X5GT however the KTG1 had been replaced by a 6V6GT. The 6X5 had been disconnected and a pair of diodes wired in. Somebody had already replaced all the caps and some resistors, saving me a lot of work. However some things were no longer connected, and without a schematic I had to guess my way around.

Checked continuity of the output transformer and choke, both ok, so I felt it was ok to apply power. So, replaced the power cord and plugged in. Both dial lamps worked and there was a faint hum. Unrolled the 2m of antenna and connected it to the main aerial and could get some stations. However, with the antenna wire by itself it picked up nothing.

Tuning across the band, it seemed to tune from 450 to about 1400, and anything below about 600 produced a loud rumbling sound. So, the problem seemed to be a matter of mistuning. To cut a longer than necessary story short, somebody had screwed down a trimmer on the tuning capacitor. This wasn't noticed due to it being hidden under the dial. In the end a complete tuneup was done, and the 6A8 was replaced with a ECH35. After that it picked up lots of stations on the 2m antenna wire.

The next thing was to restore the 6X5 to service. The diodes produced just over 300V, dropping to about 220 after warming up, and the 6V6 got very hot. I wired back the 6X5 heater, removed the diodes, and found the 6X5 worked, but with about 50 less volts. A problem was that half of the heater had escaped and was pressing against the glass top of the valve. Because of this I decided to replace it with a modern version.

The cause of the hot 6V6 wasn't hard to find, the 500K grid bias resistor was up over 600K. Replaced this with 470K, however it was noticed that the resistor was dropping voltage across it which shouldn't happen. -20 volts at one end, -6 at the other. Tried 2 more 6V6's, these produced 0v at the grid. For whatever reason, the grid was connected to the anode via a resistor and series capacitor. Disconnecting one end of the capacitor restored the volts, now it was -13.6 at the grid. The voltage comes from a backbias supply, with 470 ohms to ground. I changed this to 390 ohm, and the voltage dropped back to -12.5, which is exactly what was needed.

Now the 6V6 ran cool, and we had more volts, not the 300 from the solid-state diodes, but sufficient. The speaker needs replacing but I didn't have a substitute handy, at the moment it makes lots of loud bumping at full volume, and a small part of the cone fell out, leaving a hole.

Last problem was to try stopping the motor-boating at the low end of the dial. I tried adding a 100μF capacitor across the previously-mentioned 390 ohm backbias resistor, and the problem was solved.

Further testing was done swapping the ECH35 with ECH33 and various 6A8G's. It proved conclusively the ECH valves are quite superior to the 6A8G. I'd recommend this upgrade especially for 4 valve radios.

A problem was that half of the heater had escaped and was pressing against the glass top of the valve

Ah, the infamous 6X5 heater worm. Some 6X5 designs were more prone to that than others, although I think circuit design came into play as well.

Does anyone have a schematic of this? I'd like to connect up the disconnected bits.

Also, seems that the original output valve is a KT61, same as in the 4A19 model. Probably explains why I couldn't find info on 'KTG1' anywhere.

If you unhide your email address via Control Panel, I'll send you the schematic.

BTW: It shows that in some versions the 6AR7 was replaced by 6N8, and the KT61 was replaced by 6M5. Not sure if both such replacements applied at the same time.

OK it has been unhidden.

Okay, sent.

Got it thanks