Hello from Cuba

[Miguel Lopez]

Good weather?.......oh yes, and don't forget the hurricanes.................

[Nowhere-Man]

I can now see Miguel's point about broken transistor legs. I haven't worked on radios modern enough to use boards, but I have already found the legs can get very brittle over time. My valve radio PCB board has some very brittle capacitor leads and, I suspect, one or two dry joints.
On the Soviet East German radios also they use very thin wire and the closest I can compare to it is telephone wire, except this latter is a bit thinner. Even so, two twisted telephone wires would pretty much equal the East German wire. And equally as brittle. This wire solders very well indeed but the wire itself is a bit brittle and stiff.
In my free time, actually, I have revised my basic transistor theory as I'd forgotten most of it. The usual stuff such as PN junctions. The book I was using had an angle that given the resistance of each PN junction differs hugely due to the forward or reverse bias, the power amplification in watts is considerable.

[Miguel Lopez]

Recently a friend of mine gave me a couple of Soviet radios that he had getting dusty in a corner of his house. They are one Spidola and one VEF Spidola. They are in good shape, althought they have no transistors at all, and both of them lack the turret knob. I will be working on them soon, and I will share the advances (or set backs) in a thread dedicated to this.

[Nowhere-Man]

Sounds like a challenge to get the transistors but I'm sure you'll succeed.
Later when I upload a pic I'd appreciate your advice. I have two disconnected aerial winding wires on my Auriga. There are three windings on the ferrite rod but I'm not sure which busbar terminal to resolder. The other two windings are fine.
I was struck by how small the tracks are. I guess you need good eyesight and steady hands.

[Miguel Lopez]

I have two disconnected aerial winding wires on my Auriga.

As the Astrad Auriga seems to be a VEF-12 with another name (let's guess that), and the VEF-12 is very, very similar to the VEF-206, here I show you the layout of the later. Check the connections of the aerial coils there.

[Nowhere-Man]

That's fine, Miguel. I can work it out with the diagram.

[Nowhere-Man]

Anyone have any thoughts on testing transistors already in circuit? According to the theory I read last week (refresher stuff), with the PNP transistor, each junction is either forward or reverse biased. One way will be the so-called "holes current" flowing towards -. The other way should be a larger current of electrons flowing to +. This description is about 1959 (that's how old my books are). On that basis, couldn't you set the meter on milliamps in series with the emitter and looks for a large current?
Basically I am a bit weak on transistors as most of my effort has been with valves. I know some people here do lots of transistor work although I assume most of it will be PNP Bipolar types.

[Crackle]

Transistors are not so forgiving as valves. I would remove it from the circuit and buy yourself one of those £10 transistor testers http://www.ebay.co.uk/itm/LCR-T4-ESR-Met...SwYIxYBcn6.
They test capacitors and all sorts.

Mike

[pwdrive]

Anyone have any thoughts on testing transistors already in circuit? According to the theory I read last week (refresher stuff), with the PNP transistor, each junction is either forward or reverse biased. One way will be the so-called "holes current" flowing towards -. The other way should be a larger current of electrons flowing to +. This description is about 1959 (that's how old my books are). On that basis, couldn't you set the meter on milliamps in series with the emitter and looks for a large current?
Basically I am a bit weak on transistors as most of my effort has been with valves. I know some people here do lots of transistor work although I assume most of it will be PNP Bipolar types.

Measuring the in circuit voltages on the transistor can sometimes reveal things, the emitter to base voltage for a germanium transistor is generally around 0.25 to 0.3 volts DC, for a silicon transistor it's normally around 0.6 to 0.7 volts DC.

Measuring transistor junction resistances in circuit can lead to a false diagnosis due to parallel resistive paths which generally exist in the circuit.

Lawrence.

[Terry]

That mention of holes brought back a memory.

In 1965, Bush released their first hybrid TV, the TV135. We also had a visit from a Rank Bush Murphy field engineer that year.

He said that some of the older engineers (I was but a youngster then!) were having difficulty understanding these new-fangled transistors.

Valves, he said, are easy to understand. The cathode emits electrons, which exist. Now these electrons are attracted to the anode. Simple.

A transistor, on the other hand has holes but these holes don't really exist. Now these holes, they move ...!

As Lawrence said, you can recognise germanium and silicon types by the voltage drop across the base/emitter junction - provided, of course, that it is forward biased. In some small signal applications the voltage for a germanium type can be even lower than the figures Lawrence quoted, down to around 150mV.

If you have a data sheet showing voltages you should be able to use that information to deduce the transistor types without even touching the set!

There are two flavours of transistor that you should be aware of: PNP and NPN types. As a generalisation, most germanium transistors are PNP and most silicon transistors are NPN - but notice that I said most - not all! Silicon transistors have by far the greater numbers of PNP types mixed in with the NPNs.

The collector circuits of PNP types are fed from the negative supply rail with the emitter circuit being returned to the positive supply and if you see the positive supply rail is connected to the chassis, that is a sure sign that most, if not all of the transistors are PNP.

NPN types are more like valves in their powering arrangements - collector positive, emitter negative.