20-04-2013, 11:39 AM
At long last I received all the Resistors. I must have chosen the two most incompetent Suppliers on the planet.
Anyway, I fitted a full set as there seemed little point ignoring the couple that were in tolerence.
It looked very pretty, so I fitted it back in the 'scope along with its new Valves. I also joined A4 to -150v as the Schematic says that's where it should be during the scan, and there's no guarantee that the Timebase will be running.
So, fire it up, wait 90 Seconds, and ........... nothing, no oscillation
Well, there must be something else wrong, so I measured the voltages - see attached.
A2 - +300v - is a bit low but not enough to stop it I wouldn't think.
The RH Half of the 12AU7 looks to be hard on. I expect the -143 on the Grid is Grid Current. The other voltages around there - A6 etc - I supect come from that -150, although I haven't disconnected anything yet to find out.
The above cuts the LH Half off pretty solidly.
The voltages on the 5763 look about right bearing in mind the other voltages, and it is conducting.
There is HT on both sides of R501 so the Transformer isn't O/C.
So, that all looks pretty normal to me for a 'not oscillating' start-up condition.
The 1n across the Transformer is new, but I haven't changed C501. It measures Ok and it is Ceramic, but ......
All suggestions gratefully recieved.
Alan
Anyway, I fitted a full set as there seemed little point ignoring the couple that were in tolerence.
It looked very pretty, so I fitted it back in the 'scope along with its new Valves. I also joined A4 to -150v as the Schematic says that's where it should be during the scan, and there's no guarantee that the Timebase will be running.
So, fire it up, wait 90 Seconds, and ........... nothing, no oscillation
Well, there must be something else wrong, so I measured the voltages - see attached.
A2 - +300v - is a bit low but not enough to stop it I wouldn't think.
The RH Half of the 12AU7 looks to be hard on. I expect the -143 on the Grid is Grid Current. The other voltages around there - A6 etc - I supect come from that -150, although I haven't disconnected anything yet to find out.
The above cuts the LH Half off pretty solidly.
The voltages on the 5763 look about right bearing in mind the other voltages, and it is conducting.
There is HT on both sides of R501 so the Transformer isn't O/C.
So, that all looks pretty normal to me for a 'not oscillating' start-up condition.
The 1n across the Transformer is new, but I haven't changed C501. It measures Ok and it is Ceramic, but ......
All suggestions gratefully recieved.
Alan
