AEE Polyfoils are definitely polyester. Used by several TV manufacturers in the 60s, into the early 70s.

The factory was in Brookvale as was my office so I knew them right at the end. They were the last Oz cap maker to close.

Never seen a bad one of these.

AEE Miniprints were paper though. A copy of a European design. Bad.

What else would you like to know about AEE?

The ONLY paper cap made here in plastic tubes was UCC's "Hi-Qual 100". Replace on sight.

UCC "Di-Pol 100" are polyester, do not replace.

I replaced all three caps and noted that the old C11 24μF measured only 3μF when removed, compared to 30μF for the old C12. The C11 reading was different to the 34μF that it was showing when it was 'in chassis'.

I was hoping that this was the issue but about 30 mins into operation the heavy hum returned suddenly and the set got quite hot...so unless C11 has failed, I need another direction to look for the 'hum' culprit.

Are you sure you put the new one in the right way around?

Let's get some voltage measurements. Start with the main B+ and back bias.

Next thing to check is, pull out both 6BM8s and see if the hum goes away,

If so, put one in at a time to see if the fault is only in 1 channel.

Main 'B+' and 'back bias' are terms I can only imagine! I assume they are pins on the valve bases, so pin numbers would be good!

I turned on again and the hum is now loud and immediate...not even a 30 minute wait. I believe the hum is on both channels. C11 was faulty originally and I wonder if something has blown the new cap too.

Hmmm. If you don't understand those terms it's quite possible you did put that cap in backwards.

Run it for 30 seconds, then turn off. Are any of the caps you put in warm? Sure sign it's the wrong way around if so.

You can't "blow" the new caps except by putting them in backwards.

If they are cold, that's not your problem.

When you say the hum starts immediately, do you mean in less than 1 second after switch-on, or after about 30 seconds?

If the latter, go back to my previous post.

Haha...no, I double checked that the new caps were the same way around as those that were taken out. However the originals could have been incorrectly fitted. I know that the arrows point towards ground and one is directly connected to the chassis at one end so I know that one is ok. I'll remove the chassis and check again where the other two are connected in the circuit. .

The heavy hum comes in within 20 seconds of switch on. It is the first sound out of the speakers from a cold start-up.

OK, so follow my suggestions.

Took chassis out, checked the three new cap solder joints and found that one was broken. Re-soldered all of them for good measure and the hum has disappeared. Thanks for bearing with me on this one.