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Valve amp Servicing


Johnnyc
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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

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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!

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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.

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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 by Johnnyc
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[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.

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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 :o (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.

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[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 ?

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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?

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  • 3 weeks later...

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 :o

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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 by Johnnyc
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[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 by Mr. Foxen
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  • 3 weeks later...

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?

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