Tubes Asylum

When I knock at my Cary SLP-90, there are sound from one speaker...

153.20.24.68

[ Follow Ups ] [ Post Followup ] [ Tubes Asylum ] [ FAQ ]

seem like the pre-amp has picked-up the noise and amplified it. Only happen on the right speaker. Any ways to remove this problem? Thanks!

Follow Ups:

May be my description wasn't clear (pls read) Goldentube 18:47:25 09/25/00 (1)
What I mean is when I knock at any part of the chassis (not the tube itself), the sound will amplified via one of the speaker. What I worry is any thing wrong to the pre-amp.
The SLP-90 deployed 12ax7 as gain tube, 12au7 as follower and EZ81 as rectifier tube.
I've swapped the 12au7 to a new pairs but not the 12ax7. I'll try to swap the 12ax7 next.
Any advises is welcome!
Thanks!
- Re: May be my description wasn't clear (pls read) steven oda 23:15:23 09/25/00 (0)
  Offhand, I'd say one of your 12AX7's is going microphonic. You really don't need to replace it---yet. Just swap positions, one-by-one, until the tapping on the cabinet problem goes away (hopefully).
  Then, if all else sounds okay---you might not have to change the tubes. Just leave the present tubes in a configuration with the least noise problems.
  But, if you decide to buy another 12AX7 (if that truly is the problem)---be sure it's tested for noise.
  Good luck. Keep us posted.
  steve
Stop hitting it then (more) Kevin Deal 06:33:58 09/25/00 (0)
I saw the other comment asking you to tap on the tube. When you tap on a preamp tube it is supposed to make noise...tubes that have other jobs will not make noise no matter how much you hit them.
Unless you have a good understanding of why you are doing it and what you are looking for then why would you take a chance on hitting a hot tube...even lightly...and taking a chance of making it worse.
If the tube is truly microphonic, and if it is in a position where it would even make a difference if it was, then you will know it. It will be come apparent under normal use via distortion when you play music. Anything else is not an issue.
I would like to find the guy who came up with the little tester that was being sold a few years ago that was a funny shaped pencil designed to tap tubes. What a dumb idea!
In absence of that, don't go looking for trouble as you may end up creating it by looking.
Re: When I knock at my Cary SLP-90, there are sound from one speaker... Duncan Donuts 00:38:48 09/25/00 (1)
Don't knock the pre, then ;)
Also check your tubes. Maybe got one microphonic. Flick flick your hand on the tubes lightly and not so hard. MAybe you will find out why.
- Noisy pre-amp steven oda 11:56:28 09/25/00 (0)
  Duncan,
  I'd follow Kevin's advice. Whacking on tubes isn't a good practice. I find that swapping tubes from one socket to another (I'm kinda dense---so I keep track of each switch, on paper), may take the offending tube from a critical point (like the first gain stage) to a less critical stage. Then, the resulting tone might have less noise.
  If you have a spare tube, you can swap it with the present tubes until the the noise has reduced to a satifactory level.
  Personally, I find that 12AX7-types tend to be the worse offenders (since they have the highest gain). Sovteks, Ei, and unfortunately---a lot of the NOS US made 60-70's 12AX7's tend to get noisy. If this is the case, and you need a new tube, I'd be sure the seller tests the tube for noise, microphony, and symmetry across the twin diodes. It's worth the extra money---provided the service is done by a reputable dealer.

This post is made possible by the generous support of people like you and our sponsors:

Signature Sound

[ Signature Sound Lounge ]

You can not post to an archived thread.