02-03-2014, 06:35 PM
Let me first apologize for misstating my shadowmeter issue. The vane remains slightly deflected with MAXIMUM signal. I can bend the light bracket to center the shadow, and the shadow will narrow substantially with tuning-- it just won't be at minimum width unless the vane centers perfectly when tuned accurately.
I was going to illustrate that with photos, but unfortunately the radio went tango uniform last night (any Air Force folks out there?). No audio--no apparent signal.
Nevertheless, here's a 20-second video of the shadowmeter. Power starts when the light comes on, the vane deflects maximum left and then returns slightly towards center. The vane remains in the position it is when the video stops. This is with no shunt, no antenna, and no apparent signal. I think this is normal.
https://picasaweb.google.com/coldrb/Febr...directlink
Now, to get the radio working again. While doing nothing but turning the tuner knob, the radio went silent. Nothing but a slight hum out of the speaker. No evidence of any signal received or amplified.
I have only a rudimentary understanding of electronics, but I did my best to diagnose until 2 a.m. The only anomaly I have found is the 6A7 oscillator/detector shows zero voltage at the oscillator grid. All other tube socket and power transformer voltages are the same as before the set died
I have double-tested the 6A7 with both transconductance and emissions tester; verified the appropriate continuity through the input transformer, output transformer, oscillator transformer; and randomly tested a number of other components. As you can see, I'm now flailing aimlessly at the problem and need some direction.
So, given the sudden failure and zero oscillator grid voltage (It was -22 V), can someone give me some direction in diagnosing the problem?
I have a legible schematic posted here:
https://picasaweb.google.com/lh/photo/gv...directlink
Grateful for Guidance,
Winky
I was going to illustrate that with photos, but unfortunately the radio went tango uniform last night (any Air Force folks out there?). No audio--no apparent signal.
Nevertheless, here's a 20-second video of the shadowmeter. Power starts when the light comes on, the vane deflects maximum left and then returns slightly towards center. The vane remains in the position it is when the video stops. This is with no shunt, no antenna, and no apparent signal. I think this is normal.
https://picasaweb.google.com/coldrb/Febr...directlink
Now, to get the radio working again. While doing nothing but turning the tuner knob, the radio went silent. Nothing but a slight hum out of the speaker. No evidence of any signal received or amplified.
I have only a rudimentary understanding of electronics, but I did my best to diagnose until 2 a.m. The only anomaly I have found is the 6A7 oscillator/detector shows zero voltage at the oscillator grid. All other tube socket and power transformer voltages are the same as before the set died
I have double-tested the 6A7 with both transconductance and emissions tester; verified the appropriate continuity through the input transformer, output transformer, oscillator transformer; and randomly tested a number of other components. As you can see, I'm now flailing aimlessly at the problem and need some direction.
So, given the sudden failure and zero oscillator grid voltage (It was -22 V), can someone give me some direction in diagnosing the problem?
I have a legible schematic posted here:
https://picasaweb.google.com/lh/photo/gv...directlink
Grateful for Guidance,
Winky
