Members blackba Posted July 1, 2005 Members Share Posted July 1, 2005 Has anyone messed around with the preamp tubes in an ampeg SVT III or IV pro. I really like the SVT III pro, but I can't help wonder if a preamp tube change might improve it a bit. Mine still has the stock groove tubes in there, so who knows who actually makes them. Link to comment Share on other sites More sharing options...
Members the_big_geez Posted July 1, 2005 Members Share Posted July 1, 2005 You can swap these around pretty much willy-nilly. The 12a_7 series tubes are all interchangeable. The 12AX7 has more gain than others, like a 12AT7 or 12AU7, but they all plug in just the same and no modifications are necessary. The funny thing I've noted about amps over the years is that if it calls for something like a 12AU, and you put in an AX, you wind up turning some of the controls DOWN to get back to where you would be if you'd just stuck with the stock tube... Makes it all semm like an excercise in futility to a certain extent. A recommended 12AX7 replacement is the 5751, which is a smoother, more linear tube. Link to comment Share on other sites More sharing options...
Members blackba Posted July 1, 2005 Author Members Share Posted July 1, 2005 That's not really what I was asking, but thanks. I am wanting to know how changing brands of tubes will affect the sound. I agree with you on the 5751's, the GE 5751's sounded great in my fender deluxe reverb. Link to comment Share on other sites More sharing options...
Members Decker Posted July 1, 2005 Members Share Posted July 1, 2005 Although 12__7 tubes can usually be swapped without damaging anything, you really should have a clue about what you are doing. The 12__7 series all have different gains, meaning their amplification factors are different. 12AU7's have a gain of 20. 12AT7', gain of 40. 12AY7's, gain of 60. 12 AX7's, gain of 100. 5751's are similar to 12AX7s, but have a gain of 70. That explains why different tubes will require different gain settings. Also, they like to work at different currents. A 12AX7 is usually run at a current of 1 ma, give or take. But a 12AU7 is "happier" (meaning running in a more linear fashion) at 5 ma or so. The current draw is set by the cathode resistor. Different tubes rarely work well with the same cathode resistor value. These tubes also have different heater current draws, so subbing a 12AU7 for a 12AX7 could overload your transformer. Not likely, but possible, expecially if there are several tubes. Regarding your original question, yes a different brand of 12AX7 can change your tone. I think that the Groove Tubes are made in China. Try a NOS (new old stock, meaning made years ago but never used) tube from an American or European manufacturer. Check out Angela Instruments (www.angela.com) or Antique Electronic Supply (www.tubesandmore.com) or Triode Electronics for a selection of NOS. I think that NOS kills anything currently manufactured, but YMMV. Link to comment Share on other sites More sharing options...
Members blackba Posted July 1, 2005 Author Members Share Posted July 1, 2005 Thanks for the suggestions I am really looking for specific tube recommendations from people who have this amp or an SVT IV pro. I agree, I like NOS tubes better, but I have a few of EH, EI elite, JJ, JAN phillips, GE, chinese 9th 12AX7's, 12AT7's and 12AU7's lying around. So I am looking for advice on what others are using and what to try 1st. Link to comment Share on other sites More sharing options...
Members blackba Posted July 4, 2005 Author Members Share Posted July 4, 2005 bump Link to comment Share on other sites More sharing options...
Members blackba Posted July 5, 2005 Author Members Share Posted July 5, 2005 bump.... Link to comment Share on other sites More sharing options...
Members Matteran Posted July 6, 2005 Members Share Posted July 6, 2005 try the electro-harmonix 12ax7, or JJ first. Link to comment Share on other sites More sharing options...
Members KeroseneTrewthe Posted July 6, 2005 Members Share Posted July 6, 2005 I posted in a thread my recent results. Cant find it right now. Do a search. I'll post it if I find it. Link to comment Share on other sites More sharing options...
Members blackba Posted July 6, 2005 Author Members Share Posted July 6, 2005 Originally posted by KeroseneTrewthe I posted in a thread my recent results. Cant find it right now. Do a search.I'll post it if I find it. I found this, was this what you meant: http://acapella.harmony-central.com/forums/showthread.php?s=&threadid=962629 but this one helped more http://acapella.harmony-central.com/forums/showthread.php?s=&threadid=968297 I am a big fan of the EI elite 12AX7's in guitar amps, I just will have to see if I have any left. Link to comment Share on other sites More sharing options...
Members KeroseneTrewthe Posted July 7, 2005 Members Share Posted July 7, 2005 Originally posted by blackba but this one helped morehttp://acapella.harmony-central.com/forums/showthread.php?s=&threadid=968297I am a big fan of the EI elite 12AX7's in guitar amps, I just will have to see if I have any left. Yeah, thats the one. I actually like the Groove Tubes better than the EH tubes. More smooth tone. The EH's are just too gritty for my taste. Link to comment Share on other sites More sharing options...
Members blackba Posted July 7, 2005 Author Members Share Posted July 7, 2005 Originally posted by KeroseneTrewthe Yeah, thats the one. I actually like the Groove Tubes better than the EH tubes. More smooth tone. The EH's are just too gritty for my taste. Did you get the groove tube mullard reissues, or just the standard groove tubes? Mine claims that it came with groove tubes, but I am sure it doesn't have the mullard reissues as they weren't out when I bought the amp a few years ago. Link to comment Share on other sites More sharing options...
Members KeroseneTrewthe Posted July 7, 2005 Members Share Posted July 7, 2005 Originally posted by blackba Did you get the groove tube mullard reissues, or just the standard groove tubes?Mine claims that it came with groove tubes, but I am sure it doesn't have the mullard reissues as they weren't out when I bought the amp a few years ago. Nah, just the regular GT. Link to comment Share on other sites More sharing options...
Members some old guy Posted November 14, 2019 Members Share Posted November 14, 2019 ive got an svp pro preamp that runs into a genz benz gbe750, and i also have an svt3 pro... both sound good with valves 2,3 and 4 being 5751 (ehx or tung-sol ), ruby 12ax7 ac5, and jj ecc802s (long plate 12au7) respectively. the svp has mesa spax7 in positions 1 and 5, the svt3 currently has a jj ecc803s (long plate 12ax7) in v1 and a long plate gold lion in v5 and its sort of good enough... ive tried all sorts of v1, v5 combinations in the svt3 to make it sound as good as the svp and genz benz but never quite match it... go figure... Link to comment Share on other sites More sharing options...
Members Girlgia Posted November 15, 2019 Members Share Posted November 15, 2019 You can swap around these two. Link to comment Share on other sites More sharing options...
Members some old guy Posted November 26, 2019 Members Share Posted November 26, 2019 just an update... i took that long plate jj back out of v1 - too much mud - tried a mesa 12ax7a, it was very mid, then a tung-sol which sparkled but i had to run my bass with the treble right off and still not much bass at the speaker so i went back to a ruby 12ax7 ac7 - i believe its much the same as a gold lion short plate - that i used to run before i started chasing more volume from the amp. conclusion? (1) forget the extra volume, keep the tone (2) the svt3 is not a very loud amp, excellent for practise or small gigs, or as an outstanding guitar amp (3) the svp-pro preamp is the preamp from an svt2, not an svt3 so im saving my bikkies to get an svt2pro... Link to comment Share on other sites More sharing options...
Members lug Posted November 26, 2019 Members Share Posted November 26, 2019 Try out an SVT IIP, predecessor to the SVP Pro. I have both and the IIP sounds better to my ears, although the out put is noticeably lower than the Pro. Link to comment Share on other sites More sharing options...
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