Tube PHONO preamp interference - RFI, EMI, bad grounding?

@filipm thanks for posting those pics. Very interesting..yes, if you want to put it back together the way it was you may need a new 33 ohm resistor, but those are cheap enough. That one looks like a Vishay-Dale metal film, which are often found in audio because of how quiet they are.

I searched the web for images of the EAR 834p to see if I could find some that did not have the resistor, but of the ones that I found were a good enough pic to see the wiring in this spot of the EAR - all had the resistor there. So it seems intentional.

This one appears to have the same resistor as yours..(you may have to click the plus sign cursor once to increase its size)

This one does as well.

This one is a great pic, with what appears to be a "standard" (cheaper) metal film resistor between the ground post inlet and the IEC ground, and appears to be connected to the PCB ground plane directly (which would then match your EAR if I read things correctly).

Look at the first one again though at the RCA input jacks - there is some component they have bypassing signal to ground - a capacitor perhaps for noise filtering? Showing my inexperience here, I have not seen a capacitor that looks like that, perhaps one of the more expert folks on the thread can tell us what it is. Likely a custom mod (especially considering the Hovland MusiCap capacitors in there that I am reasonably sure are not stock given their cost).

I live near a major Air Force Base and occasionally get interference (although mostly on FM) from one of the radars on the base.  The periodicity of the noise to me is a giveaway that it is something causing a "sweep".  What that might be you are better to guess than me.

It sure looks like the resistor is in place on *this* particular unit:

picture of resistor

If you examine the schematic that someone else posted above, you can see there is a 33 ohm resistor shown in the schematic as a series element in a CRC filter for the filament supplies. I don’t know how you could have been measuring the resistance across that resistor, given your description of where you placed your probes, but if your probe was touching something that you could not see that was on one side of that resistor and the other probe was on the other side of that resistor, then you could have measured it inadvertently. Maybe you should retest that resistance between the two probes that you’ve earlier reported and which atmosphere remarked upon. That’s the only 33 ohm resistance that I cansee in the schematic, but of course you might be measuring the parallel sum of two or more other resistances.

@filipm Looking at that above linked picture, I can now see (rather clearly) what the little silver screw on the back does. As you mentioned Filip, it supports a shield - a shield that isolates the audio portion of the EAR, from the power supply portion.