high frequency intermittent noise

James, searching at eBay for "RCA shorting plugs" (without the quotes) will lead you to a number of sellers offering them at low cost.

Good point by Ralph (Atmasphere) re the possibility that the amp doesn't provide grid stopper resistors in its design.  If that proves to be the case, James, I would think that if you explained the situation to Vladimir he could have them installed at modest cost.  It would just involve the addition of a physically small low power resistor in series with the grid of each tube.

Good luck.  Best regards,
-- Al
 

@kosst_amojan,

As sure as I am that it’s cell phone noise, I’m almost certain it’s not that tower.

Re: On-site Cell Tower Interference
« Reply #2 on: October 03, 2012, 10:03:56 pm »

It’s highly unlikely the cell site will induce RFI problems with any properly designed audio equipment, or any other system inside the building.

First, cellular/PCS sector antennas are highly directional. Directly below the antenna is a major null with signal levels easily being 50-70dB below on axis carrier level (based on antenna type and design) before building attenuation is considered.

First, cellular/PCS sector antennas are highly directional. Directly below the antenna is a major null with signal levels easily being 50-70dB below on axis carrier level

@kosst_amojan,

So for cell phone reception in the apartment building there may be equipment to compensate for the "null zone"? If so, would you expect the equipment, or antenna, placed on each floor?

Also if james1969 placed his cell phone in areas on his audio system as you did on yours he should pick up the same RFI noise as you did, correct?

Another question.
What if the apartment building has some type of building automation system that is remote controlled by a digital transmitted signal? Could that cause the same type of RFI noise?

That is GSM noise-your (or someone nearby) cellphone is being "polled" or is polling the basestation nearby....earthing(use copper pipe in bathroom or kitchen) may well fix...if not then chokes on power cables is another avenue to explore...and of course keep mobiles charger off hifi circuit.

I would assume he could do what I've done. If there's some point of weakness that might sniff it out. Referring to Atmasphere's post about resistors, the one thing an F5 has is resistors. No caps on the amps at all. Just 8 big filters in the PS. That may explain it's rejection when placed near the amps. I accidentally neglected to put a CL60 on the ground though. That may explain why I get it through the power supply. 

You may be into something with the building system. Some security systems use cell connections to avoid the possibility of wires getting cut or just running more wires period. 

I found a set of RCA shorting plugs. I turned everything off except for one mono block, inserted the RCA shorting plug, and the noise is still present.

I tried a different power cord, and the noise is still present.

I tried an XLR cable between my power amp and preamp, the noise is still present.

I have ferrite beads (made of material 61) on order.