Microphonic 7044's

142.165.129.189

Posted on October 27, 2009 at 18:37:56

morrisonic
Audiophile

Posts: 29
Joined: October 25, 2009

I just swapped in a couple of 7044's into my 5687 preamp and to my shock and horror they are both as microphonic as hell. To bad since they sound quiet good. I've never experienced this before. The 5687's weren't microphonic at all and the 6n1p's in the amp can be whacked with a chopstick and don't make a sound!!!!Is this common with this tube?
Kelly

RE: Microphonic 7044's

coolhand

17:16:52 11/01/09

That's some good advise...

morrisonic

18:01:23 11/01/09

It may not be microphonics.

Allen Wright

04:33:47 10/28/09

Very true

FenderLover

08:17:48 10/28/09

RE: Microphonic 7044's, posted on November 1, 2009 at 17:16:52
coolhand Audiophile Posts: 220 Location: BBQ Area Joined: June 5, 2006	Have you tried a different brand of chopsticks ? I do find that the hardwood types do induce quite a bit more microphony than the lighter and more flexible bamboo types. ;-)

That's some good advise..., posted on November 1, 2009 at 18:01:23
morrisonic Audiophile Posts: 29 Joined: October 25, 2009	I'll hit the grocery store on Monday.....lol Kelly

It may not be microphonics., posted on October 28, 2009 at 04:33:47

Allen Wright
Manufacturer

Posts: 4737
Location: Schaffhausen
Joined: January 31, 2002

The 7044 is similar to a 5687 but is not the same - hence if your preamp was designed for 5687s, then it may become unstable with a higher transconductance tube like the 7044.

I have often found microphonics actually to be the tube oscillating at very high frequencies (tens and even hundreds of megahertz) which we of course can't hear - but somehow it appears as some form of noise in the audio band, often hum, but more often as a hugh senstivitity to vibration = microphonics.

"Stopper" resistors added right at the grid pins of the offending tube is the normal cure. I'd suggest starting at 1k and bringing them down in value if you can.

Regards, Allen

Very true, posted on October 28, 2009 at 08:17:48

FenderLover
Audiophile

Posts: 3313
Joined: July 31, 2007
Contributor
Since: May 17, 2009

I've even had substituted tubes induce instabilities. After adjusting the parameters (plate voltages and idle bias currents), tweaking with caps and feedback... certain subs MAY be better than the original. Good example is subbing a 12AY7 into an original 12AT7 position. Sometimes, the switch doesn't sound too good. But, adjusting parameters to suit the 12AY7 better, can really make that tube shine. I like this sub in many of my units. Though I admit, sometimes a 12AT7 just sounds better, no matter what is altered. These subs are very system dependent. And wholesale: "type A will always sound better than type B" thinking should be avoided.

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Microphonic 7044's

142.165.129.189