Valve amp Servicing

[Johnnyc]

Hey guys,

Does anyone know where I can find someone to service my Ampeg SVT-VR? Probably needs a new pre amp valve so I thought it'd be a good time to get it serviced too. I emailed Surrey Amps but got no response so far. Also what's the general opinion on carrying on using the amp when one or more of the pre amp valves are on the way out? Is it a no go? Just sold my back-up amp too so great timing eh? =/


Cheers

Johnny

[Johnnyc]

Wow ok yeah just noticed the sticky about amp techs. But the question about still using the amp in this state remains valid.

[JapanAxe]

What makes you think there is a problem with your preamp valves? Power valves are more likely to die, as they have to work a lot harder.

You could just buy a set and swap them out yourself, but if another fault has caused damage to them, then you may trash them too. If you are ever in Swindon you are welcome to bring the head and I will put them on my Orange valve tester. DISCLAIMER: I AM NOT AN AMP TECH!

[Mr. Foxen]

Sometimes preamp valves die, its pretty much an at random, rather than a wearing out sort of deal. Start with symptoms if you want help figuring. If it is pre valves, just getting some spares and swapping about will tell you, cheaper than a tech bench fee, as long as your time is free. How old is the SVT, some have trouble with caps dying, even 90s ones.

[Johnnyc]

I'm sure it's a pre amp valve as the distortion occurs no matter what volume I use the amp at, and I'm getting a fair bit of general white noise. Plus I only recently changed all the power valves to Sovtek 6550WE's. It's a 2007 SVT so I wouldn't expect much to be wrong with it; one of the pre valves has been running really bright since I bought it & now it's started to distort I guess I actually have to sort it out. I guess that's probs the best option then, I'll just buy some valves and swap the bright one out and see if it fixes it.

cheers

Johnny

Edited April 19, 2013 by Johnnyc

[Mr. Foxen]

Brightness of the preamp valve won't tell you much, its jsut the heater in it, and in some valves its more exposed than in others.

[BILL POSTERS]

[quote name='Johnnyc' timestamp='1366393515' post='2052080']
I'm sure it's a pre amp valve as the distortion occurs no matter what volume I use the amp at, and I'm getting a fair bit of general white noise. Plus I only recently changed all the power valves to Sovtek 6550WE's. It's a 2007 SVT so I wouldn't expect much to be wrong with it; one of the pre valves has been running really bright since I bought it & now it's started to distort I guess I actually have to sort it out. I guess that's probs the best option then, I'll just buy some valves and swap the bright one out and see if it fixes it.

cheers

Johnny
[/quote]

Not an amp I'm familiar with, but if there is one, try feeding a signal, from an ipod or something like, into the FX return. if its still distorted your problems not in the pre amps.

[Johnnyc]

Ok cheers for the advice guys, seeing as I'm sorting this out rather than taking to a tech I did a bit of homework on what is actually inside my amp (what a novel idea!) Turns out the valve that has been glowing brightly is one of the "driver" valves, a 12AX7. I've ordered a Harma Retro 12AX7 from Watford valves so I'll switch that out when it arrives and see if it fixes the problem.

In the meantime,

[quote name='BILL POSTERS' timestamp='1366621325' post='2054845']
Not an amp I'm familiar with, but if there is one, try feeding a signal, from an ipod or something like, into the FX return. if its still distorted your problems not in the pre amps.
[/quote]
Bill, if I try that little experiment with the FX loop will the driver valves come into play? They're after the pre amp but before the big 6550's in the power stage I believe.

[BILL POSTERS]

[quote name='Johnnyc' timestamp='1366642071' post='2055318']
Bill, if I try that little experiment with the FX loop will the driver valves come into play? They're after the pre amp but before the big 6550's in the power stage I believe.
[/quote]

Almost certainly, yeah.

To prove the point, you could try it with the driver valve/s removed, if you get no sound at all the answer is yes.
Not a familiar amp, but I thought there was a mod for SVTs to use 12AX7s, or am I just out of date ?

[basstheface]

If you need to take it to a specialist, I recommend John Kelly (previously owner of Kelly Amplification). Based in London N1, he's a nice guy, honest and knows his stuff. He recently serviced my AMPEG V4B. His number is 020 7359 8001.

[tedmanzie]

i'd also like to recommend http://www.surreyamps.co.uk

[Johnnyc]

Ok so a bit of an update: I used the amp at rehearsal earlier this week, and I was getting some volume issues as well as the light distortion at times; the volume kept changing while i was playing, like it would seem really quiet so I'd crank it up on the volume knob to where normally it'd be rattling the windows and it would be just about usable, but then it would come back up to normal volume for a few seconds randomly in the middle of songs.
Earlier on today I received the valve I ordered so I replaced the driver valve that I thought was the issue, then switched the thing on. It was quiet still but with no distortion. Then I put it in standby to go through my pedal board, switched back on and it was proper loud, but with the distortion. (no pedals were actually on at that point except I was going through the stageclix)

Any ideas? Should I start on the pre amp valves?

[Mr. Foxen]

If you have one spare preamp valve start swapping them about to find which one is at issue. Also, if an amp is being quieter than it should, cranking the volume more is a terrible idea.

[Johnnyc]

Ok so I've just tried changing all the 12ax7's one at a time in the pre amp, no change. Is it worth ordering a 12au7 and trying those or is it time to take it to a professional?

Mr Foxen I guess it was a bad idea but it worked at the time

[Johnnyc]

The issue has now been found! 2 dead 12AU7's in the pre amp and a worn 12AU7 in the driver section. It would be the one type of valve I didn't try wouldn't it!

[BILL POSTERS]

At least theyre cheap and plentifull . There always seem to be ex TV guys selling ECC82s on ebay.

[Johnnyc]

Yeah that's true I picked up some JJ's for a tenner a pop, not so bad!

[BILL POSTERS]

[quote name='Johnnyc' timestamp='1368598928' post='2078919']
Yeah that's true I picked up some JJ's for a tenner a pop, not so bad!
[/quote]

Sounds a bit expensive to me tbh. But at those sort of prices it aint worth spending too long shopping around is it ?

[Johnnyc]

Yep I could probably have found them cheaper but I couldn't be arsed to look really. Just whacked on next day delivery too so hopefully they'll arrive in time for me to get the amp fixed for my gig tomorrow! Otherwise i'm gonna have to use my old Ashdown Mag 600

[Mr. Foxen]

Fancy old stock ECC82 are pretty easy to come b y cheaper than new ones.

[BILL POSTERS]

[quote name='Mr. Foxen' timestamp='1368621426' post='2079268']
Fancy old stock ECC82 are pretty easy to come b y cheaper than new ones.
[/quote]

Agreed. four old Brimars on ebay as we speak, doubt if theyll break anybodys bank.

[Johnnyc]

I could get a set of the Brimars on eBay for £20 a pop but would I actually notice the difference?

[url="http://www.ebay.co.uk/itm/12AU7-ECC82-BRIMAR-UK-NOS-/260695299591?pt=UK_Sound_Vision_Valves_Vacuum_Tubes&hash=item3cb2a69607"]http://www.ebay.co.uk/itm/12AU7-ECC82-BRIMAR-UK-NOS-/260695299591?pt=UK_Sound_Vision_Valves_Vacuum_Tubes&hash=item3cb2a69607[/url]

Edited May 15, 2013 by Johnnyc

[Mr. Foxen]

[quote name='Johnnyc' timestamp='1368629883' post='2079465']
I could get a set of the Brimars on eBay for £20 a pop but would I actually notice the difference?

[url="http://www.ebay.co.uk/itm/12AU7-ECC82-BRIMAR-UK-NOS-/260695299591?pt=UK_Sound_Vision_Valves_Vacuum_Tubes&hash=item3cb2a69607"]http://www.ebay.co.u...=item3cb2a69607[/url]
[/quote]

Won't notice the difference between them and the same Brimar ECC82 you can get on ebay for about £5. Not much point in getting same thing more expensive.

Edit: Actually, £5 ones are shorter plate, less microphonic.

Edited May 15, 2013 by Mr. Foxen

[Johnnyc]

Hmmm. Well this is interesting. Finally got my amp fixed and it was great for a few rehearsals and gigs... Now I think the same thing has happened again!

It crackled out on me yesterday and is even quieter than it was when it was in its broken state before. Would this indicate there is actually something else wrong with the amp that keeps blowing the valves?

[Mr. Foxen]

Are the valves blown? Was the amp serviced, the sockets cleaned, soldering checked etc? A drifted resistor can be hard on a valve.