Using "leakage" for lack of a better term. I'm hoping to get some ideas here, as this one is baffling me. Here's what's going on:
The problem:
I'm getting varying degrees of audio "leakage" from one input source to another. For example, if I have an audio source hooked up and playing through AUX, when I turn the input selector to, say, PHONO, I can still hear the AUX source faintly coming through my speakers.
I am seeing that anything line level hooked up to any of the inputs can be heard clearly when it's correlating source is selected on the input dial, yet it can also be head faintly (at differing degrees, and through either left only, or both speakers), when I turn the selector dial to any other source & turn the volume up.
FM signal does not appear to be bleeding into other sources - i.e., FM broadcasts can only be heard when I select either FM or MPX. However if I have an aux source hooked up and playing at line level, I can hear both that source as well as FM broadcast when I have it set to either FM or MPX.
I'm hearing some static through open PHONO sources too, which doesn't seem to be associated with FM, because when I found a clear broadcast signal, that broadcast doesn't bleed into the open PHONO channel - it just sounds like white noise static, instead.
What's been done so far:
The power supply on this unit was recently updated - all caps replaced, selenium rectifier replaced with silicon diode, all connections tested, and unit performed without any problems after update. All tubes were checked out & two PHONO tubes replaced - again, the unit performed well afterwards, but with some weak PHONO issues & a burned out MPX light. So, tested and verified that the MPX transistor was dead and replaced it. Also replaced 2 cracked "bumblebee" coupling caps (.1uF 300v) on the phono pre-amp tubes (both channels) as well as 2 toasted 1K 3W resistors (1 had drifted to 800 ohms).
It was only after these repairs that I noticed the audio leak. First thought was that some deoxit may have been accidentally sprayed on the input selector wafers & caused shorting. So tried gentle (no touch) cleaning of wafers with 99% alcohol, and letting it dry for 2 weeks before powering on and testing again - no change.
So, this is where I am with it. Anyone have any ideas? I don't want to mess with the input selector any more than necessary, as I don't want to risk damaging the wafers. Could this "leakage" be coming from somewhere other than the input selector switch? I'm only really assuming that it *may* be the source of the problems, but I can't be sure of it. Also worth noting is that while I replaced the power supply myself, all other repairs were done by an experienced vacuum audio specialist. We're both baffled, though, so I'm putting this out there in the hopes that someone may have experienced this issue before, and/or can offer some advice as to what to check next. Thanks!
The problem:
I'm getting varying degrees of audio "leakage" from one input source to another. For example, if I have an audio source hooked up and playing through AUX, when I turn the input selector to, say, PHONO, I can still hear the AUX source faintly coming through my speakers.
I am seeing that anything line level hooked up to any of the inputs can be heard clearly when it's correlating source is selected on the input dial, yet it can also be head faintly (at differing degrees, and through either left only, or both speakers), when I turn the selector dial to any other source & turn the volume up.
FM signal does not appear to be bleeding into other sources - i.e., FM broadcasts can only be heard when I select either FM or MPX. However if I have an aux source hooked up and playing at line level, I can hear both that source as well as FM broadcast when I have it set to either FM or MPX.
I'm hearing some static through open PHONO sources too, which doesn't seem to be associated with FM, because when I found a clear broadcast signal, that broadcast doesn't bleed into the open PHONO channel - it just sounds like white noise static, instead.
What's been done so far:
The power supply on this unit was recently updated - all caps replaced, selenium rectifier replaced with silicon diode, all connections tested, and unit performed without any problems after update. All tubes were checked out & two PHONO tubes replaced - again, the unit performed well afterwards, but with some weak PHONO issues & a burned out MPX light. So, tested and verified that the MPX transistor was dead and replaced it. Also replaced 2 cracked "bumblebee" coupling caps (.1uF 300v) on the phono pre-amp tubes (both channels) as well as 2 toasted 1K 3W resistors (1 had drifted to 800 ohms).
It was only after these repairs that I noticed the audio leak. First thought was that some deoxit may have been accidentally sprayed on the input selector wafers & caused shorting. So tried gentle (no touch) cleaning of wafers with 99% alcohol, and letting it dry for 2 weeks before powering on and testing again - no change.
So, this is where I am with it. Anyone have any ideas? I don't want to mess with the input selector any more than necessary, as I don't want to risk damaging the wafers. Could this "leakage" be coming from somewhere other than the input selector switch? I'm only really assuming that it *may* be the source of the problems, but I can't be sure of it. Also worth noting is that while I replaced the power supply myself, all other repairs were done by an experienced vacuum audio specialist. We're both baffled, though, so I'm putting this out there in the hopes that someone may have experienced this issue before, and/or can offer some advice as to what to check next. Thanks!
