28-11-2011, 01:32 PM
Following a bit or arm-twisting by Alan B I came back from Golborne with a P75.
The seller had very sportingly pointed out that the output valve was "soft" and given that it looked like a bottle of milk sorting that out would be my first job.
I hadn't got an EL41 so bunged an EL84 in. Silence was the result, and I mean silence of the type which if I hadn't been able to see the heaters I would have been checking the fuse and switch.
I connected the grid terminal to my bench amp and got weird and horrible noises such as are seldom heard even in a jazz band.
I didn't know if my amplifier was playing up so had another go at getting the valve going. It eventually transpired that Pye had wired it in an odd way using a terminal which Mullard say isn't connected to anything.
This too made the same howls but with help from Alan we diagnosed an electrolytic cap was failing to do its decoupling duties. Connecting a 0.1μF one across it dealt with that.
This morning I set about fitting a permanent 9-pin base; another Golborne purchase.
I carefully noted down the existing connections but when I came to do the re-wiring found they made no sense - even I knew there couldn't be a resistor direct from the anode to cathode - b***** silly rim-locks. I ended up working from the diagram is got it right first try.
I'll next be cracking on with the case.
- Joe
The seller had very sportingly pointed out that the output valve was "soft" and given that it looked like a bottle of milk sorting that out would be my first job.
I hadn't got an EL41 so bunged an EL84 in. Silence was the result, and I mean silence of the type which if I hadn't been able to see the heaters I would have been checking the fuse and switch.
I connected the grid terminal to my bench amp and got weird and horrible noises such as are seldom heard even in a jazz band.
I didn't know if my amplifier was playing up so had another go at getting the valve going. It eventually transpired that Pye had wired it in an odd way using a terminal which Mullard say isn't connected to anything.
This too made the same howls but with help from Alan we diagnosed an electrolytic cap was failing to do its decoupling duties. Connecting a 0.1μF one across it dealt with that.
This morning I set about fitting a permanent 9-pin base; another Golborne purchase.
I carefully noted down the existing connections but when I came to do the re-wiring found they made no sense - even I knew there couldn't be a resistor direct from the anode to cathode - b***** silly rim-locks. I ended up working from the diagram is got it right first try.
I'll next be cracking on with the case.
- Joe
