tube weirdness

[django1]

I have a little tube pre amp made by sometime forum member billnchristy. I had not noticed before but with certain tubes, notably Mullards and Russians, the pre amp sort of acts like a microphone. If I tap the pre amps metal cover I get a very metallic ringy sound out of the speakers. With my favorite tubes, the Hitachis, nothing. Unfortunately the Hitachis have developped a bit of a crackle and seem to be very rare. What gives we the mike effect?

Also can a volume pot become noisy over time?

[HAL]

I have a little tube pre amp made by sometime forum member billnchristy. I had not noticed before but with certain tubes, notably Mullards and Russians, the pre amp sort of acts like a microphone. If I tap the pre amps metal cover I get a very metallic ringy sound out of the speakers. With my favorite tubes, the Hitachis, nothing. Unfortunately the Hitachis have developped a bit of a crackle and seem to be very rare. What gives we the mike effect?

Also can a volume pot become noisy over time?

The term is a microphonic tube and it is not uncommon. Better tubes usually have less of the issue. Sometimes tube dampers like Herbie's Audio Lab can help.

Yes, pots can become noisy over time. Ones that are not sealed can get dirty. Using an electronics cleaner without silicone can sometimes remove the dirt and remove the noise source.

[django1]

It seems you know everything:). Thanks! I guess the tube thing got worse because I have been using a Virtue 2 amp as a power amp. The amp I usually use has variable volume .

Two questions: How to identify better tubes? Do those tube dampers work?

[dvenardos]

No answer on the tubes, but if it helps you can switch the jumper on the Two and use its volume control. All other things being equal it is better to have only one pot in the mix.

[django1]

No answer on the tubes, but if it helps you can switch the jumper on the Two and use its volume control. All other things being equal it is better to have only one pot in the mix.

I was thinking the same.. Enjoying the amp btw :applause:!

[HAL]

The only thing for checking microphonics is testing the tubes in the unit. Do not tap the tubes directly as that can cause other damage. Lightly tapping the unit would be good.

You can try the tubes you have with silicone damping rings that many people offer to see if they work to reduce the ringing. This maybe the simplest way to check the other tubes to see if it helps.

[dvenardos]

Big or little difference from your Bill and dweekie amp?

I was thinking the same.. Enjoying the amp btw :applause:!

[django1]

Big or little difference from your Bill and dweekie amp?

That is kind of hard to say because the streamer is also new in the system. But the bass is very notably improved. Nice tight, pretty wonderful bass. If I have time over the weekend I am going to A B it with a buddy. Just to make sure I don't fall prey to you sales skills without reason:).

[InfernoSTi]

What tubes are they? There are sometimes military equivalents that are more rugged and have a finer grading process. As a result, often they have fewer microphonic issues. A few examples of this are the CV (British), JAN (American), and EV (Russian) tubes.

The CV4024 Mullard is a British military 12AT7.

The 6N14N-EV is a Russian military EL84.

The Joint Army Navy (JAN) tubes often have the same designation as the civilian equivalent and the manufacturer can be determined (RCA, GE, etc).

The military tubes are also sometimes "long life" tubes (particularly the Russians), an added bonus. I've used the CV4024 in place of the 12AT7 and liked it very much. Perhaps this is something to research depending on the exact tube your pre-amp uses.

John

[etcarroll]

Tubes are microphonic to a greater or lesser extent, they benefit from dampers. I use Herbie's in my pre and phono pre, 5 tubes total, makes a noticeable difference for the better.

[django1]

The tubes are the very inexpensive 6j6.

I couldn't decide if HAL was pulling my leg with that Herbie tube damper. Herbie's got some funny stuff. Maybe I'll give them a try...

[HAL]

No, I have one in my Dodd Audio Battery Tube Buffer on my 6H30P-DR dual triode.

[django1]

No, I have one in my Dodd Audio Battery Tube Buffer on my 6H30P-DR dual triode.

And I assume there was a noticeable result? Cool.

I am just looking at some tubes and I forget if the extra letters mean anything. Are 6j6a or 6j6wa the same as 6j6?

[HAL]

Since all tubes are microphonic to some extent, I like to make sure they are all damped. In my case it was a small difference, but worthwhile to me.

The 6j6 may respond a lot more to the damping. The high temperature silicon rubber rings are inexpensive and a good place to start.

[django1]

Big or little difference from your Bill and dweekie amp?

Very big. :D