20-08-2012, 07:51 PM
The start of this little saga was the purchase of a Pye Black Box Transistor amplifier last week. It was cheap and I figured it would make a useful general purpose amplifier and a spare for my Transistor Black Box.
So, what do I need? Signal Generator, AVO, Scope and a Load. Might as well use my TF893A. I bought this a year or so ago, gave it a quick check and stored it away. It's all passive so there's not much to go wrong, is there? I thought I'd better give it the once-over just in case so I connected it directly to the Low Impedance Output of my trusty Advance J-2. Everything seemed fine until I switched to the Yellow X1 Impedance Range Multiplier, when the meter sank to zero. The Yellow X1 is where all the useful Low Impedance Speaker type Impedances live. Ah, well, can't be too difficult.
It's very easy to expose the innards - remove two screws and swing the panel upwards. Out with the AVO and trace the wires. Fine up to the transformer on one side but only up to the switch on the other. A magnifier and strong light revealed all - the switch contact for that range is completely missing, presumably broken off due to some previous misuse.
And how did I miss it before? The old Pictures I took show it set to the Black Ranges.
I'm not sure at the moment what I'm going to do about it. Changing that contact is a possibility, or a replacement wafer - it's two pole eight way. Anyone got anything suitable?
And the amplifier? That works fine apart from a slight bit of hum and a peculiar transfer characteristic due to it's original use in the Black Box.
Alan
So, what do I need? Signal Generator, AVO, Scope and a Load. Might as well use my TF893A. I bought this a year or so ago, gave it a quick check and stored it away. It's all passive so there's not much to go wrong, is there? I thought I'd better give it the once-over just in case so I connected it directly to the Low Impedance Output of my trusty Advance J-2. Everything seemed fine until I switched to the Yellow X1 Impedance Range Multiplier, when the meter sank to zero. The Yellow X1 is where all the useful Low Impedance Speaker type Impedances live. Ah, well, can't be too difficult.
It's very easy to expose the innards - remove two screws and swing the panel upwards. Out with the AVO and trace the wires. Fine up to the transformer on one side but only up to the switch on the other. A magnifier and strong light revealed all - the switch contact for that range is completely missing, presumably broken off due to some previous misuse.
And how did I miss it before? The old Pictures I took show it set to the Black Ranges.
I'm not sure at the moment what I'm going to do about it. Changing that contact is a possibility, or a replacement wafer - it's two pole eight way. Anyone got anything suitable?
And the amplifier? That works fine apart from a slight bit of hum and a peculiar transfer characteristic due to it's original use in the Black Box.
Alan
