18-11-2015, 04:48 PM
UPDATE:
Something strange happened today when testing voltage around the X78 Frequency Changer. Like most of the tube bases under the chassis, this was tricky to get at. In such circumstances I tend to tape the red probe of the meter so only the very tip is conductive. This avoids any accidental bridging of voltages in cramped areas. I was seeking out the Triode Hexode H.T. anode and, on finally locating it, the voltage showed up on the meter. This was on spec. However, the signal strength improved dramatically and I was getting really good sound. Speaker volume shot up and tone improved. On removing the probe, volume would drop and audio output would be not as good. Could this be a result of the load on the anode or was conductivity simply improved? I'll investigate.
All testing so far indicates the output stage and power supply stage aren't so bad at all. I suspect the areas I need to look at more closely are the Mixer/Oscillator part of the circuit.
It should be noted the tube bases are "rickety". I cleaned up the pins and it would be nice to re-solder some base wires with new wire if I can get access.
Something strange happened today when testing voltage around the X78 Frequency Changer. Like most of the tube bases under the chassis, this was tricky to get at. In such circumstances I tend to tape the red probe of the meter so only the very tip is conductive. This avoids any accidental bridging of voltages in cramped areas. I was seeking out the Triode Hexode H.T. anode and, on finally locating it, the voltage showed up on the meter. This was on spec. However, the signal strength improved dramatically and I was getting really good sound. Speaker volume shot up and tone improved. On removing the probe, volume would drop and audio output would be not as good. Could this be a result of the load on the anode or was conductivity simply improved? I'll investigate.
All testing so far indicates the output stage and power supply stage aren't so bad at all. I suspect the areas I need to look at more closely are the Mixer/Oscillator part of the circuit.
It should be noted the tube bases are "rickety". I cleaned up the pins and it would be nice to re-solder some base wires with new wire if I can get access.
