Identify Transistor Radio (Ferguson 358BT)

[camtechman]

Whilst on the topic of equivalents for the AF117, I'm going to repeat an earlier warning post I made regarding the use of some AF127s.

Sometime back, when I first came across the AF117 problem and found out that the AF127 was a suitable alternative, I bought a large stock of the latter online from a German seller.

I used both the Mullard Data Book & the Towers reference book for the leadout data (given as L51/T072) but after fitting these AF127s the radio didn't work and after some testing & checking, the AF127's I'd bought were not the same leadouts as published.

The AF127 versions I'd bought were printed as an AF127-N version ! Fortunately, after much searching on the internet, I found data on it and, sure enough this N version is an L06 pinout !!

The difference between the L51 & the L06 is that the Base(b) & Emitter (e) leadouts are reversed !!!

Rewiring the AF127Ns in accordance to the L06 pinout the radio burst into life and the problem resolved.

Besides the 'N' suffix, the other obvious difference was that, although the case was a T0-72 in diameter, it was twice the height of a standard T0-72.

I've provided a comparison layout for the 3 versions and hope this helps.

Tony

[jonnybear]

If you want to use silicon transistors as replacement the nearest silicon to af*** series is BF450, BF451.
John

[jonnybear]

BF450 transistors seem to work well as replacements for the AF series, they are quite cheap £0.60p from Chricklewood.you will also need to replace those red and yellow plessey caps and the brown Hunts paper caps as well.
John

[Gulliver]

60p isn't bad, and I work just down the road from Cricklewood Electronics....but I got the BCC557B's for 6p each. The caps seem to be OK, as I had everything working temporarily after whacking the AF117's on the head with a screwdriver handle.

When time permits I will investigate this further. Thanks to everyone for the ideas.

[jonnybear]

Yes I except things were OK with the AFs but what you are replacing them with is a different animal, I have never used Bc*** in vintage transistor radios as the biasing is different. Bc*** tend to be used for switching where as Bf tend to be RF IF types.
John

[jonnybear]

Looking at the circuit diagram I have just received from S&P (Vintage Radio Service date), it looks like C10, C14, C15, C16, C20, C21, are all ceramic capacitors so should be all Ok if they are small brown or black Hunts Capacitors they will be suspect, if the electrolytics are Red/Yellow Plessey type C17, C22, C23 & C24 all 100uf I personally would change them for reliability, along with C12 8uf = 10uf now, if C23 or C24 fail they could take out the output transistors.
John

[julie_m]

According to the Mullard numbering scheme, audio-frequency transistors are generally numbered as though they were triodes (AC / AD / BC / BD) and radio-frequency transistors are numbered as though they were pentodes (AF / AL / BF / BL).

[Gulliver]

I used the BC557b's as several sites suggested them as good alternatives for the AF117's in radios. if that info is wrong I can replace them again with something else.

A more pressing problem, as I've mentioned I'm keeping the radio at work for the time being. I went to have a go at the transistors on my lunch break today and found that someone's been messing with it and the negative lead from the battery has been disconnected from the circuit board.

I am 95% certain where it should be soldered (underside of the board) but can someone please confirm before I potentially do some damage.

[camtechman]

Haven't you got the manufacturer's service docs there?

[crackle]

I would zap the original AF117's and put them back.

[jonnybear]

Negative wire Should go to the negative side of C24, second electrolytic in.
John