Best Tube to eliminate RFI

I have had tubes pick up RF in only one situation. However I suppose there must be some instances where it happens or the military would not have manufactured RF shields in such great numbers.

In any case, the shields I purchased were about $5.00 each, and helped to damp microphonics as well as pulling away heat. Pretty cheap experiment for Keithcady even if it fails.

Many suggestions posted here are valid and should be tried as well. Perhaps I misunderstood Keith, it sounded like he had tried various tubes, which improved the rejection of the RF.

When the solution is found I hope the results are posted. Good info for future reference what ever the source of the problem.

Thank you Albert, I've tried everything else. Made my own shielded and grounded power cord. Changed speaker wires and interconnects. In fact disconnected all of the interconnects from the system and the RF is still there. So the pick up is either in the amp or tubes. I tried the bws site but I haven't heard anything. I've e-mailed them I would be interested in knowing more about your Lloyd Walker product.

Bruce at BWS should still have the tube shields. If not, I may still have some around here that you could borrow.

The Walker kit is available from Loyd Walker, if not that too is here still in the original box.

You did not mention whether changing tubes had any effect on the RF. Also wonder if signal could come in from the power line. Shielded power cables won't help if the signal is carried along with the AC.

Have you tried an extension cord running from another outlet? Would be interesting to see if that changed anything.

Tubes don't pick up RFI, amps do. If the amp is properly laid out and using proper grid-stop resistors (similar resistors are found in all transistor gear) the amp will not pick up RFI.

I heard of a problem recently where RF was being picked up by gutters in the house! The customer lived near a radio station. Primitive diode junctions caused by rust in the gutters caused them to rectify the RF and vibrate. It took him a while to realize that the sound was coming from *outside* the house rather then from inside....

Ralph, certainly you know as much or more about tubes than anyone at this site. I know this personally from speaking to you on the phone many times. I believe you when you say a tube cannot pick up RF, I had this occur only one time and certainly it could have been something else (grounding, interconnect, etc..) that was causing the problem.

The one curiosity is why did the military manufacture so many RF shields for small signal tubes?