Amp Repair, urgently!

Jelly 292

Hi,

I got a 2x12 valve amp making some bad buzzing/humming noises and probably needs new valves also.
I need it fixed urgently for upcoming gigs.

The only number I can find is for Aladins Amps, I rang but they said they are on holiday till Tuesday 7th August (?)

Is there any other (quick) service like this around Dublin?

Voodu Child

2 golden rules of valve-amp ownership.

1) Before you go near a tech/repairman, always check/change the valves. 99% of valve amp problems are caused by dud valves. If you bring it to a tech and it's just bad valves, he'll charge you through the nose anyway and probably make up a fault.

2) Always keep a spare set of valves (FULL set). There's nothing worse than running around town looking for valves at the last minute, when you have an upcoming gig and your amp is shot.

In relation to your problem OP, get a good preamp valve (that you know is good - i.e. brand new), and swap it one by one for the existing ones. 90% of the time, hissing or noise problems will be fixed this way.

Jelly 292

Thanks, I was going to do this my self but no nothing abut amp electronics.

Im a technician but am weary about fiddeling with the valves myself.

Could you run thru the basic do's and donts please? and do I need to re-bias ,what ever that is?

Can I source decent valves in Dublin?

duhkha

you might need to have the valves biased as well which you'll probably need a someone who knows their sh!t to do. afaik martin nolan is better and cheaper than aladdin. 8316168, he's in beaumont.

Voodu Child

What's the amp?

Jelly 292

Thanks, JCM900 2x12

Voodu Child

Well, the simplest thing you can do for the moment is get a hold of a couple of spare preamp valves (ecc83 or 12ax7). Borrow a few, or pick them up in any of the shops in town. They're not expensive so you might as well buy a few, handy to have more than you need.

All you need to do is a straight swap, there's no rebiasing or anything with preamp valves. Just take each one out in turn and replace it with a good one. If it doesnt fix the problem, put the original one back in, and move onto the next one.

As usual DONT OPEN THE AMP CHASSIS UP. You should be able to get at the preamp valves from the back of the amp. You might need to remove a wooden panel or something, which is fine, but NEVER open the steel amp chassis itself. Dangerous for beginners

If swapping the preamp valves doesnt work, you might as well move on to an amp tech. It sounds like changing the power-valves might be a bit above you.

Jelly 292

OK cool, thanks Voodoo. I will have a crack at the Pre Amp Valves and see what happens.

I got a quote from an amp tech and it was €€€ ofr a full service, I hate not knowing how to do things!

From looking at you Sig I am getting corrupting thoughts about your F-50 running through the marshall's 2x12 cab.

If its around next week (after I find sumplace to live and see what funds are like) I may come back to you

Voodu Child

Jelly 292 wrote:

OK cool, thanks Voodoo. I will have a crack at the Pre Amp Valves and see what happens.

I got a quote from an amp tech and it was €€€ ofr a full service, I hate not knowing how to do things!

From looking at you Sig I am getting corrupting thoughts about your F-50 running through the marshall's 2x12 cab.

If its around next week (after I find sumplace to live and see what funds are like) I may come back to you

Yeah, amp techs are a rare breed here, and it can cost an arm and a leg to get an amp looked at. So if you can learn to change valves, fuses etc yourself, you can save the amp tech for genuine serious problems.

FWIW, part of the reason I mainly play Boogies (apart from the tone!) is:
1)They're very reliable, and
2) When something DOES go wrong, the're very easy to take apart and service. Especially when you're paying by the hour, this is major plus. Unfortunately, the likes of modern Marshall's (not the older stuff) and even ENGL are full of logic chips and cramped flimsy PCBs, and even a skilled tube-amp tech would shudder at the thought of trying to repair one. Hence many hours to fix, and big $.

Jelly 292

yep, my marshalls back side does seem a faily simple old school affair. Shoud make things a little easier for me

The back of a Mesa Boogie is Art imho

Jelly 292

Just an update if your intrested:

I got some Pre amp valves, 3x Marshall ECC83's, swapped these in and still a loud hum but a noticible improvement in tone.

I was a bit dissapointed by this so yesterday I said fek it did some googleing and got 4 x5881's, Sovtek's as these were the only ones I could find in Dublin.

I removed the old Power Amp Valves which were knackerd upon inspection, burn marks on glass and I noticed one was not even lit, logo worn off the glass. They were Sovteks and Electro Harmonix,different sizes, mongrel mix of valves!

So I swapped in my new 5881's crossed my fongers and turned the amp on and bingo! No hum and a great sound, mega loud. I had not noticed how poor the amps volume had become over time.

I think I have gotten away with not Biasing them, under bias-hum/noise and over bias -harsh sound/crackle and pops apparently.
I have none of this and the amp was fine last night for 5 hours odd of practice

Apparently Electro Harmonix Valves are Sovteks which may explain why I got away with not baising.

So happy bunny. Morale of the Story as posted here- change your valves!!

Cheers for the help:)