Microphonic tube noise?

[BobV55]

Hi all - new member, new Class 5 owner, with a question about an odd noise...

Recently, I noticed an odd noise that occurs only on certain notes...the most prominent seems to be on the B (D string, 9th fret). It doesn't sound like a cabinet vibration, it has more of a "metal/glass" sound to it. In the following video (not mine), you can hear the exact sound at the 1:30 mark:

[youtube][/youtube]

I use the amp in a home studio setup - the volume is only set to about 2 or 3, treble about 7, bass and mids south of 12, so it doesn't take a lot of volume to promote the sound at all.

The amp is the new style, with the three piece back and tube retainer bracket with O-rings installed...the amp is completely stock, having had no mods or changes at all.

I absolutely love the tone this amp gives me...you just cannot get that with a digital modeling amp. If my theory is right about the noise being a tube (and I'm hoping one of the experts here can verify that), I'm curious as to what tubes others have chosen to use in the amp so as to not lose that great tone that it has.

Thanks in advance for your time and expertise!

[JCM900MkIII]

Does it sound as if it is an empty coffeecup with a spoon in it, dancing on the table???

Then it is very likely a microphonic pre-amp tube.

[exotl]

Mine had exactly that noise - after swapping the stock EL84 it disappeared completely.

[BobV55]

Thank you both for your replies! I love the description of a "spoon in an empty coffeecup dancing on the table"...you captured it perfectly!

Interestingly, you've both described the noise perfectly, yet in one case it's most likely a preamp tube, and in the other, the power (EL84) tube was confirmed to have been the culprit.....I'm thinking about visiting the tube store The Tube Store and looking at the matched sets they offer for the Class 5. Of the four sets offered, I'm leaning toward their Premium package, particularly where their preamp tubes are described as "The plates are manufactured out of a premium metal imported from Germany and supported with extra thick mica spacers to insure against microphonics"

The Premium set is $72.90, which isn't unreasonable...I can obviously save the original tubes to have on hand as backups.

Thanks again for taking the time to ready and reply...I felt it was a tube by the "dancing coffeecup" nature of the sound, but it's very reassuring to have the confirmation!

[JCM900MkIII]

Unless I would go for NOS tubes (New Old Stock, vintage tubes) I wouldn't spend that much on tubes.

EL84 = $12-$20 (for new production tubes)
ECC83/12AX7 = $7-$25 ($25 for "gold" or "gold plated" tubes)

And b.t.w. "matched tubes" are not required in the Class 5. I think the store has a "pre selected set which they think sounds good in the C5".
I have no problems with that (a selected set) but claiming you need a matched set because of technical specs/requirements is a no go.
Last time I would buy anything at that shop...

[BobV55]

Thanks for the alert, JCM900MkIII - I found that store by a Google search for "Marshall Class 5 tubes", but after I made that post yesterday, I did some more reading on here, and found good reviews for Doug's Tubes on Long Island, NY. I visited his site, and wound up ordering 2 JJ/Tesla 12AX7's ($22) and a Mullard EL84 ($16), which should be here by Thursday. The prices were far more reasonable, and although folks are as particular about their tubes as they are their strings, these brands seem to be popular in general. They did have a Mullard NOS EL84 as well, but I didn't feel the need to drop $100 on a single tube for home recording purposes.
As a 40+ year bass player with a home studio who's adding guitar to the "resume", I'm grateful to have found this site and the helpful members here...it reminds me of the old Tascam forums, of which I was an early member until the founder passed on, and the doors got closed for good. This site is a valuable resource for a Marshall "noob" like myself!

[JCM900MkIII]

Cheers!
I hope you enjoy your C5

And yes, great site!
Even silly questions get serious answers here (posted some silly ones myself).

[BobV55]

Just a follow up, along with thanks, to both JCM900MkIII and exotl for thier help...the tubes I'd ordered from Doug's tubes arrived yesterday, and I had a chance to install and test them this morning. That noise is now completely gone, and the tone has improved...it's noticably brighter, almost more "voice like" in timbre....much less low end density, with all dials exactly as they were before the switch. I tested with the LP Studio straight into the amp, no pedals in line. I probably should have changed one at a time, in order to isolate which was the culprit, but decided to just swap the set, and save the originals as backups.

[exotl]

Good to know you got it fixed. When shaking the tube close to my ear I can clearly hear the same kind of noise from inside.