tube substitution in vox ac4tv

stromero01

Member
Messages
101
If i put a lower gain preamp tube (say a 12AU7 in place of a 12AX7) will it allow the power tube to work harder without a significant gain in volume? Going further, if I put a JJ EL844 in place of an EL84 would the net result be more power tube distortion at a lower volume? Thinking of doing this in a Vox AC4tv.

thanks.
 

rbutt88

Member
Messages
41
i own and used a vox ac4tv for a while. A lower gain preamp tube will reduce your overall volume, it won't necessarily let the power tube work harder though. Depending on what tube you change to you may just be able to turn the volume knob up higher before break up.

Are you wanting to get more output tube distortion than preamp tube distortion? Ultimately what i found after my tube swaps, is that this amp has a decent clean but is a low watt amp designed to breakup pretty quickly.

If i understand correctly the amp is designed to get the preamp tubes distorting quickly so to what extent you can counteract this i dunno.
 

JackOrionWas

Member
Messages
48
I just put a sylvania jan 5814a (12au7) NOS dated june 71'. It's a beautiful tube with dark grey plates and thick mica's. This tube is a perfect match for the Ac4tv if your looking for power tube break up. There is a significant volume drop, so to get the amp to break up you have to dime it. It will render the amp strictly a bedroom practice/ acoustic band amp. Forget about live drums.

What you get back in return is a much more dynamic touch sensitive feel. A glassy almost tweed tone. The amp is dead quiet now as well and it can now be used very effectively for recording. As far as tone goes it's a vast improvement, at least with the nos tube I'm using. Gone is the fizzy distortion, in is a just past the verge of break up.

I boosted the volume with a Diamond Boost/EQ pedal and was able to get some volume back but thats not the point with this tube swap. I haven't thrown my OD (maxon 820) at it yet, though I did try a swart atomic boost, and it seemed to take away what the tube was doing on its own. The diamond clean boost was much better.

Again this mod makes sense if your using this amp as a home/recording amp. One thing that may or may not be of concern is heat. It really sounds best pegging the volume but it heats up pretty good, and it sounds like it!! Yet remains dead quiet, amazing.
 




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