Valve amp problem - looking for advice.

[StewartB]

Hoping I might get some advice on my amp problem. It's a Traynor YCV40 which has the common configuration of three 12AX7 preamp tubes and two 6L6 / 5881 power tubes. The preamp tube sockets are PCB mounted and the power tube sockets are chassis mounted. The amp is maybe 10 years old and I'm not the first owner.

 

The problem is that when playing certain notes/frequencies (notably D & G in particular) the amp makes a buzzing noise that I firstly thought was just a wall panel in my music room resonating at specific frequencies. I then realized that was not the case and did some tube swapping with the preamp (12AX7) tubes. That seemed to fix the problem.

 

A couple of weeks later I fired it up again and after about an hour of playing the same problem came back. It is particularly bad on the Gain channel, not quite so bad on the Clean. Thinking about statistics and probability, it seems that the preamp tube may not be the issue and am guessing that one or other of the following could be the cause: -

 

1. Faulty/cracked preamp tube socket?

2. Intermittent fault with a resistor or capacitor?

 

I don't know much about tube amps so I'm hoping the forum might have experienced this type of issue before and can give me some advice. Assistance appreciated,.......................

 

Stewart

[m-theory]

Thinking about statistics and probability, it seems that the preamp tube may not be the issue

If you're thinking prob and stats, it's more likely to be that same preamp tube again, given the drastic inconsistencies and tendancy for premature failure of today's small bottle tubes.

 

If replacing it fixed the problem the first time, try it again. Just because you replaced it doesn't mean the new one can't be bad.

 

You can do at least SOME testing, with regard to tube microphonics (although, this problem may be filament rattle, too). With the amp on, warmed up and ready to play, take a pencil or chopstick and lightly tap on each tube individually. You'll hear SOME tapping, but if it's excessive, and especially if it sets off additional noise, you've found an excessively microphonic tube that needs replacing.

 

This noise could also be caused by a loose screw or two in the cabinet. It's not at all uncommon for screws to work themselves a bit loose over time, and for certain frequencies/volumes to set up an oscillation that creates a buzz or rattle in the cabinet. These can be tricky to pinpoint, unless you can get the offending signal fed into the amp for a long enough period for you to track down the source of the noise.

 

I see no reason to believe that the problem is either of the two possibilities that you've mentioned, frankly. Good luck. My #1 guess is a faulty preamp tube again.

[RSDx]

 

If replacing it fixed the problem the first time' date=' try it again. [b']Just because you replaced it doesn't mean the new one can't be bad.

[/b]

You can do at least SOME testing, with regard to tube microphonics (although, this problem may be filament rattle, too).

Yup - had me a couple of power tubes for my VJr w/ filament rattle , both bought new from the local mom'n'pop store....they had no problems exchanging them (one at a time, obviously) until I finally got one (different brand) that didn't do it. The 2 I returned sounded fine and worked as intended, just had the annoying "rattle....." This incident turned me off to Sovteks, although it's likely not brand dependent, just (bad) luck o' the draw.

[StewartB]

If you're thinking prob and stats' date=' it's more likely to be that same preamp tube again, given the drastic inconsistencies and tendancy for premature failure of today's small bottle tubes.

 

If replacing it fixed the problem the first time, try it again. Just because you replaced it doesn't mean the new one can't be bad.

 

You can do at least SOME testing, with regard to tube microphonics (although, this problem may be filament rattle, too). With the amp on, warmed up and ready to play, take a pencil or chopstick and lightly tap on each tube individually. You'll hear SOME tapping, but if it's excessive, and especially if it sets off additional noise, you've found an excessively microphonic tube that needs replacing.

 

This noise could also be caused by a loose screw or two in the cabinet. It's not at all uncommon for screws to work themselves a bit loose over time, and for certain frequencies/volumes to set up an oscillation that creates a buzz or rattle in the cabinet. These can be tricky to pinpoint, unless you can get the offending signal fed into the amp for a long enough period for you to track down the source of the noise.

 

I see no reason to believe that the problem is either of the two possibilities that you've mentioned, frankly. Good luck. My #1 guess is a faulty preamp tube again. [/quote']

 

Thanks guys. Will do as you said and check tubes/screws before grabbing the soldering iron. Thanks again.

 

Stewart

[BoBoBlues]

Thanks guys. Will do as you said and check tubes/screws before grabbing the soldering iron. Thanks again.

 

Stewart

 

Stew, if you're willing to go in with a soldering iron, I'm sure you're going to ground all the B+ caps (discharge) before introducing a metal probe, right?

[StewartB]

Stew, if you're willing to go in with a soldering iron, I'm sure you're going to ground all the B+ caps (discharge) before introducing a metal probe, right?

 

Been away for a few days. Yes, if I was going in with the hot iron I know I have to dischare the positive side of each volatge marked cap to the chassis - or so I read.

 

Anyway, breaking news is that I now believe it is something unfortunately inside the amp head which is vibrating to specific frequencies. Two days ago I swapped all tubes around, kicked it gently a bit, and then had the bright idea of plugging in my Weber 115 speaker cabinet in, bypassing the amp's own speaker - no buzzing at all at those particular frequencies!! Should have thought of that first!!

 

Anyway, after checking all possble and visible screws, knobs, input / output jacks, the noise remains so having left it to discharge for what will be 3 to 4 days, I will have to remove the amp from the cabinet, go in, and tighten up every conceiveable source of the problem. Will try to avoid getting zapped.

 

Stewart

[K.E.B.1281734147]

So maybe it's the speaker or the way it's mounted? AFAIK the speaker shouldn't be tighten down too much as to warp it or something like that. Just tight enough to hold it. I'd check the mount before going into the chassis. Or, it could be a tear in the speaker itself. Just throwing out possibilities.

[wiggy]

I had a similar problem with an annoying noise from my BC30 when I cranked it above 10 O'clock. Sounded like something metallic was loose inside the amp and was rattling. I went through the amp with a fine toothed comb, check all the valve retainers, checked the valves themselves, tightened all the screws, made sure nothing was loose inside chassis. Nothing I did cured the problem.

 

This went on for weeks and was driving me absolutely crazy until one day, whilst at my guitar teachers place, I found the cause.

 

It was a tambourine on a shelf in his studio which was vibrating in sympathy with the amp at certain frequencies

 

The reason I never picked up that it didn't happen anywhere else is because the only other place I used the amp was at home and I never ran it above bedroom levels so assumed that it was the higher volumes causing a problem in the amp.

 

Just goes to show that the solution isn't always obvious.

[RSDx]

I still say it could be tube filament rattle .....in tracking my "noise" down, I removed the chassis from the combo cab, and the "rattle" went away - because the speaker wasn't rattlin' it...... possible the same when you ran yours out to an ext cab. It drove me crazy, and I was SURE it was something loose inside the amp itself (discounting the tubes...) ... was a power tube rattlin' all along ... in fact, it might've been someone here who steered me in that direction .... m-theory, perhaps??? (he knows his stuff )

[StewartB]

<br />I still say it could be tube filament rattle .....in tracking my "noise" down, I removed the chassis from the combo cab, and the "rattle" went away - because the speaker wasn't rattlin' it...... possible the same when you ran yours out to an ext cab.  It drove me crazy, and I was SURE it was something loose inside the amp itself (discounting the tubes...) ... was a power tube rattlin' all along ... in fact, it might've been someone here who steered me in that direction .... m-theory, perhaps???  (he knows his stuff  <img src='http://forum.gibson.com/public/style_emoticons/default/msp_thumbup.gif' class='bbc_emoticon' alt='' /> )<br />

<br /><br /><br />

 

Thanks KEB, Wiggy, & RSDx - all good ideas. I will definately play around with the combo speaker before puuling the head to pieces. Will also check out tube filaments. Thanks again guys. Will post again after I have had a couple of days to resolve the issue. Hopefully a good news post!

 

Stewart

[fuse]

I still say it could be tube filament rattle .....in tracking my "noise" down, I removed the chassis from the combo cab, and the "rattle" went away - because the speaker wasn't rattlin' it...... possible the same when you ran yours out to an ext cab. It drove me crazy, and I was SURE it was something loose inside the amp itself (discounting the tubes...) ... was a power tube rattlin' all along ... in fact, it might've been someone here who steered me in that direction .... m-theory, perhaps??? (he knows his stuff )

Yeah, you may be hearing tube rattle. A lot of guys with combos have gotten relief from those "tube damper" rings.

Good Luck

 

http://www.audiotubes.com/damper.htm

 

http://www.audioconnect.com/html/tube_dampers.html

 

http://www.elusivedisc.com/prodinfo.asp?number=MHEATDAMP