2. amps-preamps
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Tube Whine noise...Please Help

Hi everyone.

As a newbe to tubes I am having a problem that I need some help on. I just received my Musical Design SP-2 preamp and while it sounds wonderful, occationally there is a high frequency whine/whistling noise coming from one or both speakers. The SP-2 uses 2 6922 that the previous owners said were NOS RCA types. I want to know if the tubes went bad and needs replacing or if there is another problem that I need to look for. Thanks
speedracerucr
jig
160 posts
 
Odds are that the tubes installed have thermionic emissions, i.e. the sound you are hearing. Try a different pair and see what happens.
slipknot1
1,423 posts
 
Jig is correct. Some 6922/6DJ8 tubes are more prone to microphonics than others. If you have some spares to swap, try that. Sometimes the use of tube dampers can help with that. Herbies Audio Labs HAL-O tube dampers are very good at cutting down microphonics.

The high pitched "ringing" you hear from these tubes might be from microphonics being caused by vibrations in the tube.
bob_bundus
1,834 posts
 
(1)Yes it's microphonics alright. Using a pencil-eraser, gently (very very gently) tap on the tube envelope to find out which is the offender.

(2)Let's HOPE that the tubes exhibit a thermionic emission behavior; that's normal & is how they all work! Filament heats the cathode which emits electrons past the control-grid toward the collector plate. Without any thermionic emissions you'll get no usable output.
speedracerucr OP
16 posts
 
Thanks for the replies. So if it is indeed microphonics, what options do I have to eliminate it. The ringing is pretty annoying. Even when no music is playing and the tube preamp is left on, the ringing will occur sometimes. Am I correct to assume that I will have to switch out my tubes for ones that are not microphonic? Also will Herbe's Hal-O dampers help?
slipknot1
1,423 posts
 
I have had good success with HAL-O's. I also have had good luck when buying new tubes getting the low noise "LN" variety. It may not eliminate it, but it could greatly reduce it. In my previous post, I left out the "in" in front of correct.

Thermionics are what makes the glass bottle work, to make the music go round-n-round
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