Ever Ready Skymaster (Late) - UK Vintage Radio Repair and Restoration Discussion Forum

nigelr2000 · 16th Nov 2016, 7:45 pm

I had a look at one of these today and as usual AF117 whiskers reared it's ugly head proved by a dead radio till I tapped the Oscillator transistor (TR1) it then burst into life for a short while.

Well I had a look in my random transistor box and found nothing germanium to do the job so just for a laugh I stuck a BC640 silicon straight in.

Imagine my surprise when I powered it up and radio 4 blasted out (literally) made me jump so if you get one of these dead I can now confirm a BC640 is a good substitute in this position, also I mounted it from underneath so joined a couple of the AF legs together and used the screen hole in the PCB to support it so from the top it looks original.
Not sure if the other 2 can be replaced in the same way though.
Circuit snip enclosed

Stylo N M · 16th Nov 2016, 9:54 pm

Hi nigel,

it does apear that it is for small low level amplification aplications, silicon transistors can work quite effectivly, as long as you get it right without to much gain, and as long as you don't mix up the pnp with npn, you can get away with quite a bit.

A drawer full of general purpose transistors, like the BCxxx ranges, can get you out of a whole heap of trouble.

paul.

16th Nov 2016, 7:45 pm	#1
nigelr2000 Heptode Join Date: Nov 2008 Location: North Walsham, Norfolk, UK. Posts: 900	Ever Ready Skymaster (Late) I had a look at one of these today and as usual AF117 whiskers reared it's ugly head proved by a dead radio till I tapped the Oscillator transistor (TR1) it then burst into life for a short while. Well I had a look in my random transistor box and found nothing germanium to do the job so just for a laugh I stuck a BC640 silicon straight in. Imagine my surprise when I powered it up and radio 4 blasted out (literally) made me jump so if you get one of these dead I can now confirm a BC640 is a good substitute in this position, also I mounted it from underneath so joined a couple of the AF legs together and used the screen hole in the PCB to support it so from the top it looks original. Not sure if the other 2 can be replaced in the same way though. Circuit snip enclosed Attached Thumbnails

16th Nov 2016, 9:54 pm	#2
Stylo N M Heptode Join Date: Jul 2012 Location: Derby DE1, Derbyshire, UK. Posts: 626	Re: Ever Ready Skymaster (Late) Hi nigel, it does apear that it is for small low level amplification aplications, silicon transistors can work quite effectivly, as long as you get it right without to much gain, and as long as you don't mix up the pnp with npn, you can get away with quite a bit. A drawer full of general purpose transistors, like the BCxxx ranges, can get you out of a whole heap of trouble. paul.