Grundig 80U

[Amie]

Amie
We can thank lawrence for the datasheet it will make the testing easier.
The teacher says get the DC bias correct first and then look at the AC. Consider the amplifier as a voltage divider with the load dropping voltage at a current controlled by the bias. Measuring the plate voltage will tell us quite a bit about the health of the circuit.



Measure the plate voltages and record them. We can look at them and see how healthy your circuits are.
1. If they are normal DC bias is well
2. No plate voltage indicates an open load OR screen supply.
   Missing screen voltage will put the valve in cut-off.
3. Equal DC supply indicates no drop across the load.
4. Abnormally low plate indicates high current which could be caused by a leaky coupling cap placing some plate voltage from the previous stage on the grid or a load increasing in value.
ETC.

Greg

Ok. So there was no volts on the triode anode, the 200K was replaced as it was OC. At switch on the pentode anode volts crashed and the resistor I'd just replaced fried 

I suppose from your fault finding guide points I should now replace the 2n2 capacitor. I'll do that tomorrow and report, I've cases to unpack now

Thanks all,
 Amie