Noise on '69 Superbass

[surfguy13]

Hi Guys

I thought I must pick your brains on this one. I have a stock '69 Superbass, only changes are a matched quad of JJs.

I've noticed that when a note is decaying (particularly on the 'D' when hitting a 12th fret harmonic) the is a sound that I can only describe as being like small pieces of glass moving around inside a valve. A sort of 'tinkling' sound.....'scuse the technical terminology!

It's no big deal and not really noticeable at volume, in fact it isn't at all, but I can't work out what it is. Could it be exactly what it sounds like.....a dodgy valve? I have had this exact same thing on my '63 Fender reverb tank (an old one). I assumed it was the rectifier valve and got a replacement but it wasn't that. Still have the (slight) noise when a note is decaying.

The amp is extremely quiet, working perfectly with no issues at all. It has 3 old Brimar preamp valves which may be the originals. I can post photos if that would help?

Any help would be much appreciated!

Cheers

Guy

 

[sct13]

I am not an amp tech, but I toy around with building some...

Firstly eliminate the guitar as the cause...I say this because you mentioned a "D" note, you may have some fret buzz or some sort of bridge anomaly.

Secondly (if firstly doesn't work) swap around the preamp tubes and see what changes.

Thirdly (if secondly fails to reveal the problem) Power tubes...

I have a 68' JMP 50 and I was getting a horrible noise at the end of the notes. Found to be the tubes get looser and looser from vibration and heat. It didn't have power tube spring holders, I installed those and so far the problem has not returned. So keep your trouble shooting simple at first

Good Luck.

 

[surfguy13]

Great advice......many thanks.

I've had this issue before with slight distortion on decaying notes but this one definitely feels like it's amp related.

I've ruled the guitar out....tried 3 now and no difference.

As soon as I have some daylight tomorrow I'll try swapping the preamp valves first and then, if that doesn't work out, try the power valves. I'll report back.

I have no power amp valve retainers on this head so that seems like a really good suggestion to fit some. Makes perfect sense. I have lubed the valve pins and valve bases as I know that a poor connection can cause this type of problem.

Wish me luck........

I am not an amp tech, but I toy around with building some...

Firstly eliminate the guitar as the cause...I say this because you mentioned a "D" note, you may have some fret buzz or some sort of bridge anomaly.

Secondly (if firstly doesn't work) swap around the preamp tubes and see what changes.

Thirdly (if secondly fails to reveal the problem) Power tubes...

I have a 68' JMP 50 and I was getting a horrible noise at the end of the notes. Found to be the tubes get looser and looser from vibration and heat. It didn't have power tube spring holders, I installed those and so far the problem has not returned. So keep your trouble shooting simple at first

Good Luck.

 

[sct13]

keep me posted....

oh and good luck

 

[Georgiatec]

I've had this with EL84's in my 2061x, but not with EL34's. I took out the power tubes and if I shook them gently one of them produced a faint rattle. Replaced the tube with one that didn't rattle and the problem was solved. As with your problem the rattle was only present at certain frequencies (G on mine). I suspect you have the same issue. Find the dodgy tube and swap it out and see if the noise goes away.

 

[surfguy13]

Right......have swapped preamp valves and power valves and also cleaned valve pins and valve bases.

The problem seems to have reduced dramatically but whether it's gone altogether I honestly can't say. Sounds ridiculous I know but when I'm 'listening' for a noise I start to question what the noise started out sounding like and whether it's gone or not.

I think there is still some noise and when playing at volume last night there did seem to e a vibration, kinda like glass rattling around inside a glass container (make any sense?) but whether this was something else vibrating or the guts of the amp I honestly don't know.

I also have a dodgy bulgin socket connection....well, did have until I rewired it....and that did seem to be causing some strange unwanted noises and buzzing.

I reckon maybe I need to change the output valves and rule them out completely as if it's going to be valve realted that's bound to be the culprit!!

I am not an amp tech, but I toy around with building some...

Firstly eliminate the guitar as the cause...I say this because you mentioned a "D" note, you may have some fret buzz or some sort of bridge anomaly.

Secondly (if firstly doesn't work) swap around the preamp tubes and see what changes.

Thirdly (if secondly fails to reveal the problem) Power tubes...

I have a 68' JMP 50 and I was getting a horrible noise at the end of the notes. Found to be the tubes get looser and looser from vibration and heat. It didn't have power tube spring holders, I installed those and so far the problem has not returned. So keep your trouble shooting simple at first

Good Luck.

 

[surfguy13]

I've had this with EL84's in my 2061x, but not with EL34's. I took out the power tubes and if I shook them gently one of them produced a faint rattle. Replaced the tube with one that didn't rattle and the problem was solved. As with your problem the rattle was only present at certain frequencies (G on mine). I suspect you have the same issue. Find the dodgy tube and swap it out and see if the noise goes away.

I suspect this is an extremely good idea!! As I don't have access to a valve tester changing one output valve at a time seems like an excellent idea and I don't need to buy a quad!!

Yeah, that's the problem exactly.....just certain frequencies. Problem is, as I said in my last post immediately above, it's so bloody difficult to isolate vibration noises from the amp.

 

[sct13]

Another thing is take it off the cabinet. Get a longer cord and play through the cab without the head on top of it and see if it goes away.

 

[damienbeale]

I've had this with EL84's in my 2061x, but not with EL34's. I took out the power tubes and if I shook them gently one of them produced a faint rattle. Replaced the tube with one that didn't rattle and the problem was solved. As with your problem the rattle was only present at certain frequencies (G on mine). I suspect you have the same issue. Find the dodgy tube and swap it out and see if the noise goes away.

Not a very relevant test for EL34's unfortunately. You'll find quite a few types have heater filament rattle that does not affect them in operation. Tesla's can be REALLY noisy, but sound grrrreat!