Pilot Problem - UK Vintage Radio Repair and Restoration Discussion Forum

kestrelmusic · 22nd Sep 2023, 5:46 pm

I am working on a Portadyne MU5 which has the same chassis as the pre-War Pilot Little Maestro.

The 2nd IF Transformer secondary is open circuit. Unfortunately the broken wire is broken off where it enters the coil and is, of course, utterly inaccessible.

This is a rather unusual IFT, uncased and mounted below the chassis on a twin preset capacitor.

There's no room on top of the chassis for a conventional IFT, even a small 1960s-style one. I wondered about removing the coils and former from a stock one, but they all seem to be slug-tuned and there would be no way of adjusting the slugs once the thing was in position.

Any thoughts on this most welcome!

Station X · 22nd Sep 2023, 6:03 pm

Rewind it? "Scramble" winding between a pair of cheeks should be OK. You could probably reuse the existing wire.

G.Castle · 22nd Sep 2023, 6:36 pm

Measure the inductance of the good coil and purchase two moulded axial types of the nearest value to that measured, (Epcos ones are suitable).

Solder them across the twin capacitor such that they are physically parallel to each other, and with enough leadout left on them so that the distance between can be adjusted to alter the coupling if necessary. I've found a good starting point is about 6mm gap.

That dodge has saved a few sets for me, the same method can be used for the capacitive adjusted IF cans too.

Regards,
Greg.

G6Tanuki · 22nd Sep 2023, 6:56 pm

Could you perhaps arrange to use the OK winding as the anode circuit and then arrange a capacitor to feed the grid of the next stage??

If you do this it would be a good idea to remove the failed windings to avoid any unpredictable 'suck out' effects that could steal RF energy from the tuned winding.

kestrelmusic · 23rd Sep 2023, 10:36 am

Quote:

Originally Posted by Station X

Rewind it? "Scramble" winding between a pair of cheeks should be OK. You could probably reuse the existing wire.

Many thanks for this suggestion. It worked!

Now on to the RF stages...

22nd Sep 2023, 5:46 pm	#1
kestrelmusic Hexode Join Date: Feb 2008 Location: Wrexham, North Wales, UK. Posts: 448	Pilot Problem I am working on a Portadyne MU5 which has the same chassis as the pre-War Pilot Little Maestro. The 2nd IF Transformer secondary is open circuit. Unfortunately the broken wire is broken off where it enters the coil and is, of course, utterly inaccessible. This is a rather unusual IFT, uncased and mounted below the chassis on a twin preset capacitor. There's no room on top of the chassis for a conventional IFT, even a small 1960s-style one. I wondered about removing the coils and former from a stock one, but they all seem to be slug-tuned and there would be no way of adjusting the slugs once the thing was in position. Any thoughts on this most welcome! Attached Thumbnails

22nd Sep 2023, 6:03 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 20,662	Re: Pilot Problem Rewind it? "Scramble" winding between a pair of cheeks should be OK. You could probably reuse the existing wire. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

22nd Sep 2023, 6:36 pm	#3
G.Castle Heptode Join Date: Dec 2020 Location: Swaffham, Norfolk, UK. Posts: 520	Re: Pilot Problem Measure the inductance of the good coil and purchase two moulded axial types of the nearest value to that measured, (Epcos ones are suitable). Solder them across the twin capacitor such that they are physically parallel to each other, and with enough leadout left on them so that the distance between can be adjusted to alter the coupling if necessary. I've found a good starting point is about 6mm gap. That dodge has saved a few sets for me, the same method can be used for the capacitive adjusted IF cans too. Regards, Greg.

22nd Sep 2023, 6:56 pm	#4
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,479	Re: Pilot Problem Could you perhaps arrange to use the OK winding as the anode circuit and then arrange a capacitor to feed the grid of the next stage?? If you do this it would be a good idea to remove the failed windings to avoid any unpredictable 'suck out' effects that could steal RF energy from the tuned winding. __________________ I can hear an Owl.