30-12-2011, 06:32 PM
Well, the Home Straight turned out to be a bit further away than expected.
As I reported last time one of the resistors on the Tag Board - R10 according to the Pye info - appeared to be damaged and another one was overheating. Also, the voltage readings I got were nonsense, one even being negative. Clearly something was seriously wrong. I'm of the school which says 'what have I done'. Well, I'd reconnected it all, so I took all my notes and pictures and checked everything. The problem was quite straightforward, I'd swapped over the White and Slate wires. Having put them in the right places the voltages looked much more promising, although a bit high, which is where the Variac comes in, and the smoking stopped. Putting the Detector and Output valves produced a very faint hum, and touching the Gram input produced a healthy buzz. Finally, installing V1 and doing a bit of twiddling produced Radio 4, at good volume. I was quite chuffed
So, a few comments:-
Attached is a marked up Circuit, just in case we have a fire.
I haven't done anything about R10 yet.
The voltages on the diagram are what Pye says they should be. I haven't measured them yet.
The 'Gain' control is a bit odd. The volume increases as the knob is turned clockwise and then decreases as the Pot kicks in - R12 and C20 are ganged. Also V1 screen voltage is probably high which may well affect the 'Reaction' side of things.
The tuning is a bit 'double humped', but it is Long Wave, and there is the R10 problem.
The sound from the speaker is good so the Field coil and the Transformer are fine.
I haven't figured out yet which position of the switch is really LW, MW and Gram.
So, perhaps the Home Straight is in sight - hang on Joe.
Alan
As I reported last time one of the resistors on the Tag Board - R10 according to the Pye info - appeared to be damaged and another one was overheating. Also, the voltage readings I got were nonsense, one even being negative. Clearly something was seriously wrong. I'm of the school which says 'what have I done'. Well, I'd reconnected it all, so I took all my notes and pictures and checked everything. The problem was quite straightforward, I'd swapped over the White and Slate wires. Having put them in the right places the voltages looked much more promising, although a bit high, which is where the Variac comes in, and the smoking stopped. Putting the Detector and Output valves produced a very faint hum, and touching the Gram input produced a healthy buzz. Finally, installing V1 and doing a bit of twiddling produced Radio 4, at good volume. I was quite chuffed
So, a few comments:-
Attached is a marked up Circuit, just in case we have a fire.
I haven't done anything about R10 yet.
The voltages on the diagram are what Pye says they should be. I haven't measured them yet.
The 'Gain' control is a bit odd. The volume increases as the knob is turned clockwise and then decreases as the Pot kicks in - R12 and C20 are ganged. Also V1 screen voltage is probably high which may well affect the 'Reaction' side of things.
The tuning is a bit 'double humped', but it is Long Wave, and there is the R10 problem.
The sound from the speaker is good so the Field coil and the Transformer are fine.
I haven't figured out yet which position of the switch is really LW, MW and Gram.
So, perhaps the Home Straight is in sight - hang on Joe.
Alan
