ampeg pre-amp revalve

[Dan_Nailed]

[quote name='mike257' post='305663' date='Oct 13 2008, 04:54 PM']As an idiot question (I've never dabbled with the insides of my amp) do I need to be concerned with biasing if I do this, or can I just throw the new ones in? I think my SVT3 would benefit from this, it's sounding a bit lifeless lately.[/quote]

You never need to bias preamp tubes, they don't suck enough juice to require it. In fact I'm pretty sure it's impossible to do.

The 12AU7 in an SVP-Pro is the driver tube, that pushes the "poweramp" section and is last in the chain, position 5 of 5 on an SVP-Pro. It won't add any grit really, to change that characteristic you need to change the V1 tube, 1 of 5, as this is THE most significant tone shaper tube. Changing V1 has the most effect on overall tone, should I say, as it's the first tube your signal hits before the rest of the preamp does it's business. The 12AU7 in the SVP-Pro IME experience dictates more the punchiness of the amp, not any grit, although if you have a dirty midrange then you may notice the 12AU7 have an effect. It's all down to your setup and tonal preferences. Basically and in general, if you want more grit, change the V1 tube for a higher gain one. If you want less, go for a lower gain 12AX7 or even a 12AT7.

Edited March 20, 2009 by Dan_Nailed

[largo]

If it helps, I found a TB article on this stating that 4 x JJ ECC83S tubes to replace the 12AX7's and a JJ ECC82 to replace the 12AU7 works really well.
Hotrox can do all these valves for well under £50. www.hotroxuk.com

[symcbass]

The JJ's are a very good replacement for the money. I also managed to source a NOS Mullard 12ax7 & 12au7 for less than a fiver, in v1 & v5 made a big difference to the warmth of my amp. Just my findings, but the JJ's are very good for the price.

[coasterbass]

Afternoon,

I need to give my Ampeg SVP a bit of a wash and brushup and wanted to check something with you all.
Its got a bit noisy - electrical hum at turn on, and our engineer says he can hear noise in the DI when I'm playing.
I'm thinking it'll need a bit of a resolder (its a 1998 model if I recall) and I was going to revalve it whilst I'm at it.

Watford valves has come up many times - but do they just sell you the valves or can you send it to them to overhaul your amp as well ? Failing that, are there any recommendations for someone who will do the full package in the London/North Surrey area?

Thanks

Nick

[coasterbass]

Quick bump just in case anyone has any advice?
Cheers

[colinmk]

Having a strnage problem with my svp pro pre or possibly power amp. Seem to be lacking bottom end? I play high up on my bass a lot of the time but the songs I play low down seem to have much less level in comparison. another guy who borrowed my head at the weekend said he found the low end to be kind of muffled and lacking and had to turn the bass control right up and even the graphic EQ lows right up. Something is up surely, can this be due to a faulty valve or something? It still sounds great to my ears on the higher up notes. I have a crest ca9 power amp.

[wazz]

i replaced the valves in my svt3pro to ones recommended by Watford valves and I'm pretty sure I didnt notice any difference.
Was a couple of years ago now though.

[Tee]

I wonder if i'd notice a difference if i changed the valve (a single 12au7) in my Ampeg B200R. No doubt the stock 12au7 is nothing special, but if i put something nice in there, would i notice a slight change in tone?

[Dood]

[quote name='Tee' post='793578' date='Apr 1 2010, 06:32 PM']I wonder if i'd notice a difference if i changed the valve (a single 12au7) in my Ampeg B200R. No doubt the stock 12au7 is nothing special, but if i put something nice in there, would i notice a slight change in tone?[/quote]


If the stock valves are anything to go by, then yes - I think you would notice a subtle difference - but then - you may have a big difference depending on your choice of valve. I think a Mullard (if you can find one) would sound great - or any of the Telefunken clones, such as the JJ's mentioned above would be a good choice. Ruby valves get good reviews (I think) - and also GT (Groove Tubes)

At the end of the day - it's probably gonna cost you little to find out - and is a good opportunity to get the vacuum cleaner out and have a hoover round too!

[Dood]

[quote name='colinmk' post='793423' date='Apr 1 2010, 03:52 PM']Having a strnage problem with my svp pro pre or possibly power amp. Seem to be lacking bottom end? I play high up on my bass a lot of the time but the songs I play low down seem to have much less level in comparison. another guy who borrowed my head at the weekend said he found the low end to be kind of muffled and lacking and had to turn the bass control right up and even the graphic EQ lows right up. Something is up surely, can this be due to a faulty valve or something? It still sounds great to my ears on the higher up notes. I have a crest ca9 power amp.[/quote]

Yes, this could be a problem with one or more valves messing about. Do you notice any additional noise or 'plinking' noises through your speakers when the power amp is turned up?

First thing to try is to reseat the valves. Turn off the power for a good half an hour, then pop out each valve in turn and push back in to it's socket after a clean. Be GENTLE but firm! - Next step if it doesnt help - will be to look at replacing the valves I think. Any idea how old they are? Or - better still - can you pop the lid and tell us what they are? If they turn out to be naff valves (not assuming anything) - then yes, an upgrade will be like night vs day!

[colinmk]

[quote name='dood' post='793729' date='Apr 1 2010, 09:09 PM']Yes, this could be a problem with one or more valves messing about. Do you notice any additional noise or 'plinking' noises through your speakers when the power amp is turned up?

First thing to try is to reseat the valves. Turn off the power for a good half an hour, then pop out each valve in turn and push back in to it's socket after a clean. Be GENTLE but firm! - Next step if it doesnt help - will be to look at replacing the valves I think. Any idea how old they are? Or - better still - can you pop the lid and tell us what they are? If they turn out to be naff valves (not assuming anything) - then yes, an upgrade will be like night vs day![/quote]

These are valves from watford Ecc83 str harma and 5814a philips. I'll try reseating tomorrow. It is fairly noisy when turned up but I have a Rivoli with 60's humbucker and assumed this was quite noisy anyway. I'll clean the connections too.

[Dood]

[quote name='colinmk' post='793884' date='Apr 1 2010, 11:40 PM']These are valves from watford Ecc83 str harma and 5814a philips. I'll try reseating tomorrow. It is fairly noisy when turned up but I have a Rivoli with 60's humbucker and assumed this was quite noisy anyway. I'll clean the connections too.[/quote]

Hmmm! Sounds strange! That's the same configuration I put in my old SVP - as recommended my Derek @ Watford valves.

Preamp valves don't wear anywhere as quickly as power amp valves - so unless they are very old?? Hopefully it's not a problem elsewhere.. there are sections of the schematic, that, should a component on the bass side of things go open circuit, could cause a lack of bass - but it has been far too long since I calculated filters to give you a rough guesstimate of the effects of different faults in the design. Hmmmmmm.....


Tell you what you could try - first plug your bass in to the input and connect your power amp to the effects send. Note the tone and volume etc (preferably with all the tone controls at 12 o'clock) - then plug your bass in to the effects return and power amp in to the output. There will defintely be a volume difference - but see if you get a massive difference in bottom end one way or the other. The first way round will IIRC give you 4 valves and all the tone controls, the other way round is half of the fifth valve on it's own (connected to the master volume) - which in my opinion is a noisey hissy part of the SVP design. My preference was always to run the send in to my effects - then the effects output would go straight to my power amp. My 'master volume' was then the line driver on the effects unit instead. It cut down extraneous noise a great deal. Mebbe try that too and see how you get on?

Sorry if this doesn't read to well - once again, I should be sleeping, not feeding my bass chatting addiction!

[colinmk]

[quote name='dood' post='793963' date='Apr 2 2010, 01:27 AM']Hmmm! Sounds strange! That's the same configuration I put in my old SVP - as recommended my Derek @ Watford valves.

Preamp valves don't wear anywhere as quickly as power amp valves - so unless they are very old?? Hopefully it's not a problem elsewhere.. there are sections of the schematic, that, should a component on the bass side of things go open circuit, could cause a lack of bass - but it has been far too long since I calculated filters to give you a rough guesstimate of the effects of different faults in the design. Hmmmmmm.....


Tell you what you could try - first plug your bass in to the input and connect your power amp to the effects send. Note the tone and volume etc (preferably with all the tone controls at 12 o'clock) - then plug your bass in to the effects return and power amp in to the output. There will defintely be a volume difference - but see if you get a massive difference in bottom end one way or the other. The first way round will IIRC give you 4 valves and all the tone controls, the other way round is half of the fifth valve on it's own (connected to the master volume) - which in my opinion is a noisey hissy part of the SVP design. My preference was always to run the send in to my effects - then the effects output would go straight to my power amp. My 'master volume' was then the line driver on the effects unit instead. It cut down extraneous noise a great deal. Mebbe try that too and see how you get on?

Sorry if this doesn't read to well - once again, I should be sleeping, not feeding my bass chatting addiction![/quote]

Hi Dood,
been busy this month and forgot to go back to this thread....your advice about going from the effects send into the power amp cuts out the noise almost completely, does this suggest that it may be the '5th' valve that is faulty or just maybe the output of the preamp is dodgy? I put my old valves back in to see the difference but it's pretty similar. I suppose I can just go straight out of my delay unit to the power amp then. I'm going to check again tonight though what the bottom end is like between each set of valves. The DI out seems to work perfectly though as I recorded with this a couple of weeks ago and the bottom end is fine. Played a gig at the start of the month and the sound eng was complaining about the noise out of the pre out into the DI for front of house so it's not just at my house either. Thanks for your help so far, wouldn't of thought to use the effects loop!