The Fine Things are Always Hand Made
I'm working on a late AW23 that is driving me a bit crazy. It is dead...even putting my finger on the 1st AF input grid only gets a very small sound. If I connect a known working set to the same P/S and speaker, it plays great. All voltages in the audio stages are spot on. Interstage transformer tests fine. The volume control is very scratchy (only makes a slight sound in the speaker), I've swapped it with a modern unit to test - still doesn't play. I'm really looking for ideas...
Also: the -20 bias voltage and associated divider. What are the correct voltages going down the divider network? I'm reading -20; -9; -5 and -2.5. Also, the noise limiter should read -9.5, but I'm reading about half that (less than -5). All resistors check within tolerance.
Same interconnect cable? or two different cables?
Thinking broken wire or high resistance connection.
I have the following: Green wire -20v, red tracer -7.5v, yellow tracer -4.5v, black tracer -3.0v. A little off on these shouldn't make the set dead. Do you use a signal generator? run a coax to a 0.1 uF cap and use to probe into audio grids. a volt or so into top of VC should get you strong audio.
You have my number, Bill
There's an old Steven Segal action movie where the bad guy says "assumption is the mother of all f***-ups". I assumed something....when I restore a set, after recapping and the usual restorative work, I always go through and test all the tubes on my I-177, clean them and make sure they are all good. So tubes were "out of mind" during this troubleshooting session. Bill's note nudged me into going back to the basic signal tracing...went through the amp stages with a 1V PP 1KHz sine wave...all stages checked out. So I set up the signal generator to the IF freq and started back from the last stage...at the 3rd IF - nothing...so I check - wow, that 3rd IF tube is cold (and the set has been on for 15 minutes now). Sure enough, open filament for that 39/44. Swap another one and the set takes off. Since it's on the bench, I rechecked all the alignment, buttoned it up and it's back in the Valencia playing great.
Never assume the tubes you tested just a few hours (bench time) earlier are good...honestly, I've seen dead tubes but never a couple hours after testing in an I-177...
Kent, its' possible that the 39/44 has a broken filament, but depending on the position you have the tube in (right side up vs upside down or sideways) that the filament is making contact. I had this happen ONCE many years ago,
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