I've been silent because I've been trying to determine where to shield and how to shield without causing a short.
While thinking about that I did some more research:
- I put my iphone in through the Tape Monitor jacks and didn't have the problem.
- I also don't have the problem when I turn on the Hi Filter switch.
- In looking at the grid on V3, the voltage was going negative w.r.t ground when I turned the treble all the way up. It was a sudden change in voltage when I crossed some invisible threshold at about 4 o'clock on the treble control. It only happens on the right channel. Don't know if this is due to reverse grid flow or some other odd tube behavior.
- Loudness switch didn't have any affect on the behavior.
- Volume didn't have any affect on the behavior.
- I replaced the ceramic caps (C9, C10, C11, C12, C31, and C32) around V4 and V3. I was hoping I had a leaky cap, but that didn't have any affect - but it made me feel good that I crossed that off.
- Found a problem with the shielded cable to one side of the Hi Filter switch - It had a non-infinite resistance between the conductors. Created a twisted pair of wires and replaced the grounded cable. I expect that it was overheated at some point - maybe when I was replacing the ceramic caps.
- I've gone through and tried to add some spacing near crowded wires behind the faceplate near the controls that Dave mentioned. (Maybe this is the dressing that Dave mentioned.)
None of this seemed to matter much to the problem.
While in there I fixed the headphone identity issue. I've added a second CL-80 to the other leg coming in from the wall. I've been watching my wall voltage and it is running 120-121VAC, so I figured the approx 3V drop I get from two CL-80's will allow me to avoid having to use a variac or bucking xfrmr. I'll be running the primary of the PT at 117-118VAC which I hope is safe for this old unit.
Today I just gave up (at least for the near future) and put it all back together and slid it into the case I got for it. I've got it hooked up to my Dual 1226 w/M91 Cart and my Iphone is running in to the Aux. I hooked it up to some 1985 Heresy's that I recently picked up cheap.
Anyway, I'm playing some blues through my iphone into the Aux input with the Heresy's and I rotate the treble switch all the way over and what the heck? The problem is gone! Well, maybe putting the control panel shield and the bottom plate back on put enough shielding in place that it did what Dave was telling me to do all along!!!!
Anyway, I've done a lot of the mods on this one, but I did not do the EFB or the common/ground fix to the output transformers. It started as a total wreck with rust all over, broken/missing switches, and a blown output trannie. I can't even summarize everything that was fixed or replaced. I received a lot of help and some parts from my friends here on AK to make this right.... I want to thank everyone for all their help on this one. I'm calling it done (for now). Listening to it right now and wow! Creamy is what I'd call it and it has enough grunt to make the Heresy's sound full which is saying something as they were bass shy when I played them through my Marantz.
Here is the final product. Thanks guys!!!! You know who you are. (Special mention to Dave and Larry and Matt.)
Now I'm on to the other ratrig - my Fisher KM-60 tuner that will eventually sit next to it. The chassis on the KM-60 is in even worse shape. If you want to compare - take a look at post #1 in this thread. Here's a glimpse of the next ratrig.