Whistling tube (12AU7)

Hi all,

Just joined and have briefly combed through the forum but couldn't find anything on pre-amp tubes that whistle: high pitched whistle or squeal and some may liken to a boiling kettle.

For my Rogue Audio Sphinx V1 amp, I recently bought 10 pairs of NOS 12AU7 from 3 different sellers: 2 local shops and 1 online seller. I have at least one whistling tube from all 3 sellers though they all tested fine.

What causes the whistle?
Is a whistling tube as good as trash or will it improve with use?

I can stand a little noise and hiss but the whistling is just to annoying and distracting to bear.

Thx in advance!

 

Any one?

 

Tubes are likely micro-phonic. All tubes have some micro-phonics, your whistling tubes are at the high-end of micro-phonics.

 

Just to be clear, whistling heard through the system via the speakers, or from the tube itself?

 

This is NOT a microphonic effect. Your amp is simply going into oscillation. While one particular tube may seem to trigger this effect, it is NOT actually the tube itself which is truly at fault here. It is the fault of the design of the amp or preamp which is running that tube right on the ragged-edge of stability.

I've encountered this problem with some tube amps and preamps. Particular tubes just seem to push certain designs right over the edge and into instability, and yet these exact same tubes can run perfectly inside of other amps! So don't throw those tubes away thinking that they are bad! They are simply a really bad match for your amp.

If I were you I'd contact Kevin Deal at upscale audio. He is one of the best at helping you to identify tubes which will actually work well inside of a given amp.

 

Thank you all.

To Otlset: the whistling is heard via the speakers, NOT from the tube itself.

To TarnishedEars: thanks, and what you said sounds similar to the reply I got from Rogue Audio though they didn't spell it out quite literally.
They just said "the tubes may perform better in another product" and that's it, which may be implying the situation you described.
And then I asked them for a recommendation, tubes they know for sure would match, they mentioned some brands but told me to specify to the tube seller the tubes have to be pre-amp grade and tested for low noise.
But the ones I use ARE, supposedly, pre-amp grade: RCA clear tops, Sylvania 6189 and 5814, Telefunken, etc.

The bottom line is that it seems I won't know for sure until I actually try them in my unit.

 

Rogue may or may not be able to help you. But I'd be willing to bet that Kevin Deal at Upscale Audio probably can. Just because the tubes are preamp grade means NOTHING when it comes to oscillation. Preamp grade merely means low noise, and low microphonics. But Oscillations are a different animal which are not necessarily related to either of these qualities.

What you need is somebody who has experience with your amp. Best would be somebody who has encountered this issue before with your amp, and who found a solution.

 

If whistling, or oscillation, is a compatibility issue, and all this is occurring electronically, then it must be something measurable.
And if that's true then there must be tubes that carry certain specs that satisfy the requirements of a finicky amp.
But nobody discusses tube compatibility this way.
After all, we're not discussing which tubes sound best with which amp, we're talking about which tubes can function NORMALLY with an amp.
That's what I don't get.

 

Does the pre-amp "whistle" in one or both channels?

 

Depends on the tubes.
In the case where only the L channel whistles, swapping the tubes would result in R channel whistling.

 

Tubes that whistle in your amp may not in other amps.

 

Rogue Audio suggested that I try tubes of current production, so I did.
I bought a new pair of reissue Gold Lion 12AU7 over the weekend.
The guy at the shop (also the authorized Rogue dealer) pointed out that since the Sphinx is of a modern design, there's a chance that it may be over-taxing the old tubes (higher voltage?) and he agreed that new tubes should be the way to go in my case.
Well, they are. The new Gold Lion tubes exhibit a lower noise floor, clean sound... couldn't be happier.
At first I thought the treble wasn't as bright as the RCA clear tops, but after listening to a few familiar songs, I concluded that it could be me.

Will give them a week or two and see.

Guess I'll have to sell all my NOS tubes then.

 

Can it carry a tune?

 

You mean the new Gold Lion tubes? So far so good is all I can say for now.