rodl2005 Posted October 10, 2008 Share Posted October 10, 2008 (edited) My ampeg V4BH is s'posed to have these tubes in these pos.'s (sorry for the BAD diagram - but I hope U get the idea BACK of AMP ------------------------------------------------------------------------------------------------------------ 6L6/5881 CHASSIS section O O O O 12AX7 12AU7**** O O --------------------------------------------------------------------------------------------------------------- FRONT of AMP -------------------------------------------------------------------------------------------------------------- Inside pre amp section 12AX7 12AU7#### O O }my amp had a 12AX7 inside pre amp section where the 12AU7 is located ------------------------------------------------------------------------------------------------------------- NOW I bought MY V4BH NEW & IT came with only ONE 12AU7 in the position marked with the Asterix's **** I assume this is the Phase splitter tube. According to the service manual-THANKS Jerrold- & the manual my tech got too- it's s'posed to have TWO 12AU7's!!!!!!! One where it's marked ****(where it was in my amp) & one where it's marked with '####' where there is/ & was when I bought it NEW, a 12AX7 in it!! Anyone know what the REAL story is/ why MY NEW V4BH would've been shipped out with a 12AX7 in the ### marked valve spot??? I'm gonna get a 12AU7 & put it in there asap, but it seems to work OK with a AX7 in there now????? Anyone got any ideas???? Thanks for looking! Rod ps-sorry for AWFUL diagram Edited October 10, 2008 by rodl2005 Quote Link to comment Share on other sites More sharing options...
escholl Posted October 10, 2008 Share Posted October 10, 2008 it's really nothing to worry about. the 12ax7 is just a 12au7 with a higher voltage gain...that's why it works fine, as it's not *technically* a direct replacement but it's near enough as makes no difference. As far as i know, pretty much all of the 12a dual-triode series are more or less interchangeable without doing any harm, although they've all been designed for different applications (not all audio) and so will give you slightly different results...some overdrive better than others, or are lower noise, etc, etc...but then again, the same can be true between two different brands of the same exact model. again, it's nothing to worry about. Quote Link to comment Share on other sites More sharing options...
rodl2005 Posted October 16, 2008 Author Share Posted October 16, 2008 Yep cheers. I got a cuppla JJ pre amp tubes a 12AX7 a 12AU7 & a 12AT7 so will try 'em all out & post my results when I get time! Thanx Quote Link to comment Share on other sites More sharing options...
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