Amp problems

Neo#

I bought a tube amp about 5 months ago. A Marshall. After a couple of months I noticed an annoying sound coming from it sometimes. A whistling noise high pitched. Could the tubes have dyed already? Sometimes its not there. It has been looked well after with the correct usage of the standby switch and all that. Im wondering whether I should bring it back to the shop just in case its a more serious problem or whether I should just buy a new set of tubes and plug them in. But would the amp need to be biased then?:mad:

feylya

High whistling like feedback or something different? Do the tubes look different from each other

Voodu Child

1st point of action is defintely new valves. The shop may do something for you alright, ring them to ask. Sounds like a microphonic preamp valve to me, thats what id change first if the shop didnt help.

Eoin Madsen

Neo# wrote:

I bought a tube amp about 5 months ago. A Marshall. After a couple of months I noticed an annoying sound coming from it sometimes. A whistling noise high pitched. Could the tubes have dyed already? Sometimes its not there. It has been looked well after with the correct usage of the standby switch and all that. Im wondering whether I should bring it back to the shop just in case its a more serious problem or whether I should just buy a new set of tubes and plug them in. But would the amp need to be biased then?:mad:

Is it a combo or a head? And what model, out of curiousity?

When the amp is on, tap each valve lightly with a pencil. All valves are slightly microphonic, so when you tap the three ECC83/12AX7s (the smaller valves, often with the metal tube over them) you should hear the tapping a little in the speaker, if the volume is up. They should be successively louder the earlier in the signal path they are (and they should be physically in order of their position in the path). If tapping any of the valves sets off the high pitched whistling then you most likely have a valve problem. Because of the interrelationship between the valves, it sometimes helps to rearrange the three ECC83s a bit (only remove them when the amp is turned off) to track down the offending valve.

Also, ideally avoid touching them with your fingers. Skin-oil on the glass is not especially good for the valve. The amp needs to be biased any time the powerstage valves (the big ones) are replaced.

I'd suggest replacing the stock valves irrespective of whether there's a problem, since you'll almost certainly notice an improvement if you change to higher quality valves. Shop online though, you won't get great valves in Ireland, certainly not for the price.

Neo#

Its a Marshall TSL 601. So its a 60 watt combo. The valves do look the same. Same stock ones. Yeah the noise is like something is shaking like mad. A metalic like whistling noise. The back of the amp has a cover so it will take a little bit of work to remove it with a screwdriver. Ill try that tomorrow Eoin to see if there is a faulty valve. Is there a place in Dublin that will bias the amp? Maybe that amp repair place I see in resources. Im thinking I might as well replace the power ones too. There might be an improvement in sound.

Quattroste

I thought that if you were replacing the Power Tubes with the same type/output value(not sure of the lingo) then the bias doesn't need to be reset. That's what Eurotubes told me.

fitz

Neo# wrote:

I bought a tube amp......I noticed an annoying sound coming from it....

Neo# wrote:

Its a Marshall TSL 601.

There's your problem right there.

Eh, what Eurotubes said is pants.
You'll need to re-bias every time you replace the power valves really.

This problem is more likely to be pre-amp valve mind you, and you'll probably get more of a noticable improvement in your sound by replacing them than replacing the power valves. Start there.

I'd recommend Harmas for a more vintage sound, and JJ's for a more modern, higher gain sound.

Let us know how you get on.

NeMiSiS

Try even just reseating the velaves, if it got a a bit of a bang.. It might not be well.
TK

Eoin Madsen

Quattroste wrote:

I thought that if you were replacing the Power Tubes with the same type/output value(not sure of the lingo) then the bias doesn't need to be reset. That's what Eurotubes told me.

This is incorrect. All valves even within a type (EL34, KT66 etc) are different, hence the need to test and match them into pairs or quads of similar valves. You could try and get matched valves to suit your previously set bias, but this is sort of the more expensive and difficult way of approaching it. And tbh, even then it would still be good practice to recheck the bias since the values do drift. Obviously an amp is probably not going to explode if you don't rebias, and keeping within the same type of valve is going to reduce the chance of a significant over- or under-bias which might cause rapid death of the valves... but never the less, no reputable valve dealer is going to suggest anything but having an amp biased when replacing power valves - if only to cover their own ass.

Are you sure you didn't take him up wrong? It would be reasonably accepted practice not to bother adjusting a cathode biased amp like one with an EL84 powerstage.

Eoin Madsen

Neo# wrote:

Its a Marshall TSL 601.

There should be 4 of the smaller ECC83/12AX7 valves, and 2 x EL34 powerstage valves.

Quattroste

Sorry lads but the info I got on the Biasing was from the Mesa forum so cannot be taken as truthful. I was mixing it up with info I received from Eurotubes.(below)

"The Lone Star Special amps as you stated uses a quad of EL84's, a 5Y3 and five 12AX7's. They are fixed bias at a pretty cold setting so I would use a warmer quad of the JJ EL84's and five of the JJ ECC83S's with one of them being current balanced for the phase inverter position in V5 which is the closest preamp tube to the middle two EL84's in the back row. This will eliminate any dead spots due to phase cancellation. The JJ's have a very deep tight low end, a natural harmonically rich mid and a smooth sweet high end with a nice sparkle that's not brittle so they are a nice upgrade from the stock tubes."

How does one get their amp biased???

Neo#

Eoin Madsen wrote:

There should be 4 of the smaller ECC83/12AX7 valves, and 2 x EL34 powerstage valves.

Yup. I tried the pencil technique and all is well. Nothing unusual. I took out all the valves and set them up differently so Ill see later. Cant crank my amp up at the moment.

And Fitz, youre just jealous. What amp have you got?????:p

Eoin Madsen

Neo# wrote:

And Fitz, youre just jealous. What amp have you got?????:p

Yeah... Fitz has an AC30 and a Sound City 120, so it's not jealousy I'm afraid.

If the problem continues even after resitting the valves then try the pencilling with the amp at a higher volume. After that I'd suggest replacing the entire set of valves anyway. If that still fails to fix the problem you'll have to bring it to a tech (you may have to do this to get it biased anyway, so you can do it all in one go). There's a number of other things characterised by high pitched squealing, but other than the valves none of them are fixable unless you know your way around the inside of an amp.

The power supply capacitors in guitar amps hold considerable charge often long after the amp has been turned off, so I would not recommend you go poking around inside on your own.

When you're tapping around in there give the transformers a knock while you're at it, just on the off-chance.

Neo#

Ha ha fair enough its not jealousy. Ill get my coat. Yeah Ill repace the whole set. Would different tubes dramatically alter the amp tone because I like it currently. Im thinking of ordering matched valves from thetubestore.com. Which types would you recommend out of interest?

Neo#

I just cranked the amp and its still there. Aggghhh! Its only when I play it really loud. Its like there is something loose inside. My old solidstate never had any problems. Other than sounding like a piece of crap.:D I guess these are the problems ya get with tube amps.

Eoin Madsen

You know, there could just be something loose inside!

Changing valves won't alter the tone dramatically but it will alter the tone. To be honest, upgrading from stock, you're talking clear improvements -tighter bass and smoother treble, that sort of thing. Stock valves are invariably the cheapest ones the manufacturer could find.

I buy valves from Watford Valves in the UK (http://www.watfordvalves.co.uk). You pay a little more, but their matching and quality control are exceptional. And they have a huge selection of valves. I'd suggest you email a few places anyway, and get different quotes and recommendations of valves for your amp.

What kind of music do you play?

Neo#

What I play varies. Mostly Rock stuff. Led Zeppelin, Chili Pepper esque. Watford Valves seem to be the business. Ill order from them so. Thanks.