05-15-2016, 05:31 AM
Well, I'm at a standstill. I've ordered 2 NOS 78's and a NOS 6A7 from the US - so thats probably going to be a couple of weeks away. I'm staring at it but seeing nothing helpful any more and getting a little annoyed at it, and myself. It for being such a PITA and me for getting annoyed at it for being a PITA. Its simple, yet I can't see the wood for the trees so I'm going to put it away and work on something else for a while.
One other very annoying 'feature' (we use this word in software engineering - undocumented feature - to justify bugs in our code) it has is that it always sounds like its tuned just slightly off-station. No matter how I tune or align it, speech has that hissy distortion that makes it sound very much like someone turned the tuning knob a little bit off frequency. Interestingly this is easier to hear if I am not in the room than if I'm right beside the set on the bench.
One thing I did sort, with the help of Marc from that other forum, was the SG voltage... which was way high. One of the two resistors generating that voltage had drifted way low since I first measured it (Should have been 16k, was around 14.8k when I first measured it from memory... was 12 when I measured it the other day (and yet no warning flag went off in my mind... sigh) and just over 9 sitting on the bench now. Replaced with 2 x 33k 1W in parallel. That knocked about 25V off the screens. It also seems to have knocked about 1V off the AGC line when I have a strong local station tuned in - but its still almost 3V which is too high for the shadow meter.
Maybe a 37-640 will be easier to work on... how hard can an RF sub-chassis be?
One other very annoying 'feature' (we use this word in software engineering - undocumented feature - to justify bugs in our code) it has is that it always sounds like its tuned just slightly off-station. No matter how I tune or align it, speech has that hissy distortion that makes it sound very much like someone turned the tuning knob a little bit off frequency. Interestingly this is easier to hear if I am not in the room than if I'm right beside the set on the bench.
One thing I did sort, with the help of Marc from that other forum, was the SG voltage... which was way high. One of the two resistors generating that voltage had drifted way low since I first measured it (Should have been 16k, was around 14.8k when I first measured it from memory... was 12 when I measured it the other day (and yet no warning flag went off in my mind... sigh) and just over 9 sitting on the bench now. Replaced with 2 x 33k 1W in parallel. That knocked about 25V off the screens. It also seems to have knocked about 1V off the AGC line when I have a strong local station tuned in - but its still almost 3V which is too high for the shadow meter.
Maybe a 37-640 will be easier to work on... how hard can an RF sub-chassis be?
There are no personal problems that can't be overcome with the liberal application of high explosives
