I'm at work now, so I don't remember any model numbers off the top of my head, either for the scope or the plugins. I forgot that my pictures showed the scope 
I noticed that, 3 or 4 little holes. It'll be hard to get the probe's ground in there, maybe if I borrowed a lead from my DMM. So I can trust the frequency and amplitude of that signal?
Thank you. It's heavy! I got it for $75 at a surplus store, probably because the last calibration sticker is marked 1994, and the focus is fuzzier than other scopes I remember. But, this is good enough for what I need for now, I think. All other scopes in that store were $250 - $400.
I noticed that, 3 or 4 little holes. It'll be hard to get the probe's ground in there, maybe if I borrowed a lead from my DMM. So I can trust the frequency and amplitude of that signal?
Thank you. It's heavy!
I got it for $75 at a surplus store, probably because the last calibration sticker is marked 1994, and the focus is fuzzier than other scopes I remember. But, this is good enough for what I need for now, I think. All other scopes in that store were $250 - $400.More strange voltages.
* My speaker cables have about 2V (measured against safety ground) on them even when not connected to the amp. This looks like noise picked up from the power cabling, because it changes as I move the cable and unplug components. This signal is common-mode to both leads of the speaker cable, and I don't see any signal betwen the leads (except what looks like RF hash if I turn the timebase all the way up).
Is this normal? Is it something I should worry about?
* And this is more worrisome - my 2-prong receiver's line level connectors are all at 35V to safety ground. The HT and audio systems share a subwoofer. The sub is 3-prong, but it looks like its audio circuitry is isolated from its safety ground. As a result, the interconnects coming to my amp have their ground lead at 35V to my amp's ground. I accidentally ended up with one hand on the IC and one hand on my amp's chassis, and I'm pretty sure I felt a tingle. If I connect the ICs to the amp, everything goes to 0V.
Does that sound normal? I'm not sure what effect that 35V will have, if any. Or is it just that when I connect the IC to the amp, that gives the audio circuitry inside the receiver a ground reference, and that's all that's happening here?
* Other stuff that's probably RFI - with the timebase in the .1us range, I can see many strange spiky waveforms at many points in the amp. I don't get anything when the probe's lead is held in the air close to the chassis, so I'm guessing the noise is coming in on the mains. I go get some fuzziness when I move the probe close to the interconnect though. Other than that, I can pick up this noise even across two ground points.
On the bright side, I solved one of my earlier problems. The cap from the 6SL7 filament transformer CT to ground took care of those spikes in the speaker output waveform, and also removed the buzzing sound from the speakers. Now all I have is a pretty faint 120Hz hum (about 5mV p-p). I also used the scope's internal calibration outputs to test things out - all 4 voltage amplifiers are pretty accurate. The timebase is slightly off (with the calibration control all the way over), and I think that's good enough.
Saurav
* My speaker cables have about 2V (measured against safety ground) on them even when not connected to the amp. This looks like noise picked up from the power cabling, because it changes as I move the cable and unplug components. This signal is common-mode to both leads of the speaker cable, and I don't see any signal betwen the leads (except what looks like RF hash if I turn the timebase all the way up).
Is this normal? Is it something I should worry about?
* And this is more worrisome - my 2-prong receiver's line level connectors are all at 35V to safety ground. The HT and audio systems share a subwoofer. The sub is 3-prong, but it looks like its audio circuitry is isolated from its safety ground. As a result, the interconnects coming to my amp have their ground lead at 35V to my amp's ground. I accidentally ended up with one hand on the IC and one hand on my amp's chassis, and I'm pretty sure I felt a tingle. If I connect the ICs to the amp, everything goes to 0V.
Does that sound normal? I'm not sure what effect that 35V will have, if any. Or is it just that when I connect the IC to the amp, that gives the audio circuitry inside the receiver a ground reference, and that's all that's happening here?
* Other stuff that's probably RFI - with the timebase in the .1us range, I can see many strange spiky waveforms at many points in the amp. I don't get anything when the probe's lead is held in the air close to the chassis, so I'm guessing the noise is coming in on the mains. I go get some fuzziness when I move the probe close to the interconnect though. Other than that, I can pick up this noise even across two ground points.
On the bright side, I solved one of my earlier problems. The cap from the 6SL7 filament transformer CT to ground took care of those spikes in the speaker output waveform, and also removed the buzzing sound from the speakers. Now all I have is a pretty faint 120Hz hum (about 5mV p-p). I also used the scope's internal calibration outputs to test things out - all 4 voltage amplifiers are pretty accurate. The timebase is slightly off (with the calibration control all the way over), and I think that's good enough.
Saurav
Calibrator ?
I have 2 7603 frames - neither had been calibrated for a decade and both calibrators were within 1%. This was serious kit when it was made but your milage may vary. I have a paper service manual if you need some specific info but I won't be wanting to scan the whole thing
these can be readily bought online (pdf).
Don't worry about noise from unconnected wires / ungrounded circuits. The 1 / 10 M input impedance and wide bandwidth lets anything connected act like an antenna. My AC voltmeter reads 10V RMS with 1 metre of unshielded wire attached (10M input)
Either use the scope earth to pull the signal ground to earth or use a differential amplifier (BTW a 7A22 diff vertical amp can be bought for peanuts in the US and does microvolt sensitivity - well worth buying)
Sorry I can't help with what to expect inside a tube amp (except high voltages!).
PS.
Pull the probe tip off to expose a tiny wee pointy thing to stick into the calibrator sockets - no need to connect the gnd wire.
Dave
I have 2 7603 frames - neither had been calibrated for a decade and both calibrators were within 1%. This was serious kit when it was made but your milage may vary. I have a paper service manual if you need some specific info but I won't be wanting to scan the whole thing
these can be readily bought online (pdf).Don't worry about noise from unconnected wires / ungrounded circuits. The 1 / 10 M input impedance and wide bandwidth lets anything connected act like an antenna. My AC voltmeter reads 10V RMS with 1 metre of unshielded wire attached (10M input)
Either use the scope earth to pull the signal ground to earth or use a differential amplifier (BTW a 7A22 diff vertical amp can be bought for peanuts in the US and does microvolt sensitivity - well worth buying)
Sorry I can't help with what to expect inside a tube amp (except high voltages!).
PS.
Pull the probe tip off to expose a tiny wee pointy thing to stick into the calibrator sockets - no need to connect the gnd wire.
Dave
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