Problem with the tubes?

T

the_young_once

budget-conscious
Joined
Sep 9, 2009
Messages
38
Reaction score
0
Location
Singapore
Hi all,

ran into some problems recently and was hoping someone here could help me out with a problem with my tube amp--this is my first venture into valve amplification so am at a loss here! :confused:

My amp (bought used) uses 4x EL34, 2x 12AT7 and 2x 12AX7, all Sovtek; lately I have been getting a slight distortion on my left channel, especially with quieter tracks, saxophone in soft jazz songs---there is this (for lack of better description) phlegmy sound in the voice/instrument, only the left channel affected, anyone has an experience with such problems, could point me in the right direction?

I had a hunch it was the tubes acting up, so I swapped all around (geez, forgot how many permutations), the EL34 tubes, but problem still comes from the left--so I reckon must be the smaller tubes, true enough, switching the places of the respective 12AT7's and AX7's cured my left channel, but (maybe it's my mind playing tricks on me), i still feel some of that irritating phlegmy distortion on and off somewhere in my music;

what is going on here? Any help guys? If I were to get replacement tubes, do I have to replace them ALL at a go? Really clueless here, help much appreciated :)


cheers,
Kenny
 
Hi Kenny,

Are you getting a rustling sound?

What amp are you using and how much use has it had?
 
Hi RobHolt,

thanks for the reply! :) I wouldn't say rustling, it's not a noise, more of a distortion (heard very clearly on solo instruments and voice), kind of like when you hook up an amp with too low power to drive super hungry speakers, the thing just won't sing, distortion instead
(when I was younger, did some experimenting like using a car audio head unit internal amp to try to fire up floorstanders at home)-----that kind of distortion, even at low volumes it's there;

I am on a budget when I got this amp about 2 months ago? From the way it looks it probably had many years of mileage done on it already, I tried searching up the specs on the 'net but no luck, it's so obscure I'm inclined to think it's a DIY job of an amp?
All chrome, exposed tubes and transformers on the top deck, only Power, Volume L, Volume R, (yes it's those independent volume types) and the source selector on the front face;
the only words on it read: "Thunder (presumably the brand) Vacuum Tube Deluxe Stereo Power Amplifier"

Don't get me wrong I didn't get this for the sake of joining the valve-amp bandwagon blindly: I was on a very tight budget, and this amp had more clarity and more importantly a much better soundstage than my Arcam Alpha 5+ which I was upgrading from, after a long audition, I took it :D

back to the issue, it's very much like a "phlegmy" distortion, as if the singer had to clear his/her throat, it drives me up the wall man..
 
Since you've narrowed the problem down to the small signal tubes I'd be inclined to just replace them.
Standard Sovtek or Ei will only cost you around £8 a pop, and you should always have spares.

One thing that would help us are some internal shots.
Leave the amp unpluged form the mains for an hour and take some internal pics if you can.
That way we can spot any leaky caps or fried resistors.
 
Thanks then, yes I probably think it's the smaller tubes, as I mentioned 2 pieces of 12AT7 and 2 pieces AX7, after swapping their places, the problem seemed to go away, or suppressed at least;

got to go get a set of them, maybe later today, 8 pounds apiece? mmm, I'm not local, actually in Singapore, given that as a gauge, that should be just under SGD $20 apiece for me, argh.. oh well;

Also, RobHolt, is there any online resource that I can read up about tube maintenance? I been searching all over but most pertain to tube GUITAR amps, as a newcomer to this I wanted to know about things such as:
- average tube lifespan
- signs/symptoms your tubes are going to go (any visual?)
- if they do go, do they all go at once? does one affect another?
- how to narrow down to find out which one is the troublemaker (if there are no visual cues already)

things like that, nevertheless thanks for your help! :cool: Internal shots, that would have to wait a bit, but I'll try
 
Hi Kenny,

This is a good resource for all things tube:

http://wduk.worldomain.net/forum/index.php

Register at World Designs and search the forum - lots of good general information.

Small signal tubes should last for many years, decades even, but you do get the odd bad tube and that could be the problem.
Power tubes last less time, typically a few years if run regularly near full capacity.

Without an expensive valve testing machine, swapping as you've tried is probably the best diagnostic as often problems are visible to the eye with small tubes.

A good uk site to buy tubes is Hot Rox. I've used them many times and they seem fine. UK though so there is shipping:

http://www.hotroxuk.com/

Regards,

Rob.
 
Rob, you are the man, thanks so much for the really prompt response and good info, I will check these resources out;


cheers,
Kenny
 
Hello Kenny,

Here's another very good, reliable and informative on-line shop to purchase valves. Reasonable prices, and shippng costs are not too crazy either.

http://thetubestore.com/

Do enjoy your quest!

Regards,

Vincula
 

Latest posts

Back
Top