joegarcia Posted November 19, 2009 Share Posted November 19, 2009 Tried my new amp today for the first time (thanks again Gareth!) and it's fantastic. However, when I really dug in I got a 'bottoming out' sound which sounded like nasty speaker breakup. It's not speaker breakup and the drive led was coming on, there seemed to be no good middle ground with the gain control between being too quiet and distorting in an unpleasant way. I know there are compressor/limiter options but I'd like to know if anyone knows what 12ax7's might get more headroom out of the preamp. I've been told Philips are good for this but they cost an arm and a leg. Any suggestions? It needs five of them so can't be [i]too[/i] pricey. It has EHX in at the moment I think. Was thinking of putting ECC81's in there as they are lower gain but am worried it won't drive the poweramp hard enough. Any ideas? Quote Link to comment Share on other sites More sharing options...
maxrossell Posted November 19, 2009 Share Posted November 19, 2009 What bass are you playing? Is it active? If not, did you try rolling off the bass volume a little? Quote Link to comment Share on other sites More sharing options...
joegarcia Posted November 19, 2009 Author Share Posted November 19, 2009 [quote name='maxrossell' post='658821' date='Nov 19 2009, 02:11 AM']What bass are you playing? Is it active? If not, did you try rolling off the bass volume a little?[/quote] Yea, it's an active bass but I tried with a passive too. Rolling off the bass stopped the breakup but then it wasn't bassy enough I spent a long time playing with eq and different gain structures but couldn't get enough crushing low without nasty breakup. I don't mind it not being clean at all but it's not a pleasant kind of distortion really. Thinking about these: [url="http://www.watfordvalves.com/product_detail.asp?id=644"]http://www.watfordvalves.com/product_detail.asp?id=644[/url] Quote Link to comment Share on other sites More sharing options...
maxrossell Posted November 19, 2009 Share Posted November 19, 2009 [quote name='joegarcia' post='658825' date='Nov 19 2009, 02:18 AM']Yea, it's an active bass but I tried with a passive too. Rolling off the bass stopped the breakup but then it wasn't bassy enough I spent a long time playing with eq and different gain structures but couldn't get enough crushing low without nasty breakup. I don't mind it not being clean at all but it's not a pleasant kind of distortion really. Thinking about these: [url="http://www.watfordvalves.com/product_detail.asp?id=644"]http://www.watfordvalves.com/product_detail.asp?id=644[/url][/quote] Is it 83s in there right now? Quote Link to comment Share on other sites More sharing options...
joegarcia Posted November 19, 2009 Author Share Posted November 19, 2009 Think so yea. Can't actually look as it's tucked away in my rehearsal room unfortunately. Quote Link to comment Share on other sites More sharing options...
maxrossell Posted November 19, 2009 Share Posted November 19, 2009 You could try 5751s. They're low-gain. Groove Tubes are £13.50 a pop. Quote Link to comment Share on other sites More sharing options...
maxrossell Posted November 19, 2009 Share Posted November 19, 2009 [url="http://www.watfordvalves.com/product_detail.asp?id=1564"]http://www.watfordvalves.com/product_detail.asp?id=1564[/url] There you go. Quote Link to comment Share on other sites More sharing options...
joegarcia Posted November 19, 2009 Author Share Posted November 19, 2009 Does it still have the same output as a normal ECC83 though or is it lower gain on the way in and out? Basically, will it be quieter overall? Quote Link to comment Share on other sites More sharing options...
maxrossell Posted November 19, 2009 Share Posted November 19, 2009 The 5751 has the same plate resistance as the 12AX7, but the gain factor is only 70 compared to 100 for the 12AX7. Quote Link to comment Share on other sites More sharing options...
joegarcia Posted November 19, 2009 Author Share Posted November 19, 2009 How would they compare with the Philips I linked to above you reckon? Quote Link to comment Share on other sites More sharing options...
maxrossell Posted November 19, 2009 Share Posted November 19, 2009 [quote name='joegarcia' post='658837' date='Nov 19 2009, 02:47 AM']How would they compare with the Philips I linked to above you reckon?[/quote] To be honest, I'd say that if you went for a 12au7, which has a gain factor of something like 20, you'd lose all of the fat warmth and valve character of the amp. If you're worried that the 5751 might still be a bit too gainy, you could go for a 12at7 instead, which breaks up less. It really depends on the extent of the problem you're having. If it's only breaking up a tad more than you want it to, just cut the gain by a third, it should be plenty. Or if you want to get really far into it, you could mix and match, maybe three 5751s and two 12au7s. I dunno, it's your call. Quote Link to comment Share on other sites More sharing options...
maxrossell Posted November 19, 2009 Share Posted November 19, 2009 Actually I just checked - as standard, the amp has four 12ax7s and one 12au7, so right now you're running at an average gain factor of 84. You could reduce that to 68 if you just yank one of the 12ax7s and jam another 12au7 in there. Save you replacing the lot, as well. And if it's still too gainy you could just do the same again. Quote Link to comment Share on other sites More sharing options...
joegarcia Posted November 19, 2009 Author Share Posted November 19, 2009 Cool, sounds like a plan! Thanks for your help. Quote Link to comment Share on other sites More sharing options...
joegarcia Posted November 19, 2009 Author Share Posted November 19, 2009 Think the model SVTII I have has five 12ax7's and three 12au7's actually... Quote Link to comment Share on other sites More sharing options...
rodl2005 Posted November 19, 2009 Share Posted November 19, 2009 U ARE talking about the SVTII not the 2PRO right???? I got a SVTII & find this interesting. I've never even tried to swap around any preamp tubes in mine & the last time I opened her up was when I got it over from the US- to swap the 110V to AUS's 240V Since then she's worked SUPERBLY-never missing a beat & sounding SUPERB. I must take a look! Quote Link to comment Share on other sites More sharing options...
Dood Posted November 19, 2009 Share Posted November 19, 2009 Derek from Watford Valves always recommended Harma Diamond STR ECC83's and Jan Philips ECC82's for all my Ampeg gear. Gotta say, they are just awesome valves! Have a chat with Mr Rocco directly as he does know a bit about his valves too! Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted November 19, 2009 Share Posted November 19, 2009 How've you establish that it isn't speaker breakup? Guessing you are down to A, so your amp might be pushing stuff into your cab that its just not happy with. Even though its a beasty cab, there is stuff there below its port tuning which can upset it. Quote Link to comment Share on other sites More sharing options...
joegarcia Posted November 19, 2009 Author Share Posted November 19, 2009 [quote name='Mr. Foxen' post='659104' date='Nov 19 2009, 12:18 PM']How've you establish that it isn't speaker breakup? Guessing you are down to A, so your amp might be pushing stuff into your cab that its just not happy with. Even though its a beasty cab, there is stuff there below its port tuning which can upset it.[/quote] Because it wasn't nearly as loud as I've gotten with the Sunn and the peak led was lighting up. Gonna phone Watford Valves now. Quote Link to comment Share on other sites More sharing options...
joegarcia Posted November 19, 2009 Author Share Posted November 19, 2009 Bugger. Just spoke to Watford Valves, spoke to an expert on Ampegs by the sounds of it. He reckons it's the power valves are either dud or need rebiasing Either that or the diodes have gone. Quote Link to comment Share on other sites More sharing options...
Shaggy Posted November 20, 2009 Share Posted November 20, 2009 No expert whatsovever, but in my experience farty noises / nasty distortion / lack of vol is [b]always[/b] the power valves: decent preamp valves pretty much go on forever. As a first step just try taking them out, checking the contact pins are clean, and re-seating them firmly. I know Molan had the same trouble recently, not sure what the outcome was. At least if/when you have to replace all the power valves there's only 6 - one reason I got an SVT rather than the Mesa 400+ with 12 of 'em! Quote Link to comment Share on other sites More sharing options...
rodl2005 Posted November 21, 2009 Share Posted November 21, 2009 SO - please help me here & sorry if I'm seemon dopey- probly coz I am ;-) - but U ARE speaking re AMPEG SVTII (non-pro) ones in prod from '89-'92 . I've got a '92 model IIRC. LOVE it!! Quote Link to comment Share on other sites More sharing options...
joegarcia Posted November 23, 2009 Author Share Posted November 23, 2009 My one is one of the early 'pro' ones with blue lettering. Same internally to the last few non 'pro' ones I think. Quote Link to comment Share on other sites More sharing options...
umph Posted November 23, 2009 Share Posted November 23, 2009 [quote name='joegarcia' post='658817' date='Nov 19 2009, 02:05 AM']Tried my new amp today for the first time (thanks again Gareth!) and it's fantastic. However, when I really dug in I got a 'bottoming out' sound which sounded like nasty speaker breakup. It's not speaker breakup and the drive led was coming on, there seemed to be no good middle ground with the gain control between being too quiet and distorting in an unpleasant way. I know there are compressor/limiter options but I'd like to know if anyone knows what 12ax7's might get more headroom out of the preamp. I've been told Philips are good for this but they cost an arm and a leg. Any suggestions? It needs five of them so can't be [i]too[/i] pricey. It has EHX in at the moment I think. Was thinking of putting ECC81's in there as they are lower gain but am worried it won't drive the poweramp hard enough. Any ideas?[/quote] run the master flat out and turn the input gain right down, the preamps are really hot on svt's and they tend to break up really quickly if your not careful with the input. Also you could try changed the first valve for a 12au7 or 12at7 to reduce the gain. svt's are really easy to bias yourself are both the bias lights on the back green? Quote Link to comment Share on other sites More sharing options...
joegarcia Posted November 23, 2009 Author Share Posted November 23, 2009 [quote name='umph' post='662516' date='Nov 23 2009, 11:31 AM']run the master flat out and turn the input gain right down, the preamps are really hot on svt's and they tend to break up really quickly if your not careful with the input. Also you could try changed the first valve for a 12au7 or 12at7 to reduce the gain. svt's are really easy to bias yourself are both the bias lights on the back green?[/quote] Already had the master up full with the preamp as low as possible. No, the bias was out (red lights), guessing this is the issue really although perhaps the power valves are on their way out too. I already have a newish set of Harma 6550's to put in, hesitant to revalve and bias myself though. Is it really that simple? I kinda know how it's done but just not too confident and don't want to damage anything. Quote Link to comment Share on other sites More sharing options...
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