Ampeg BA-115HPT Tube Rolling Question

Old Fart · #1 09-24-2011, 02:45 PM

I did the search and saw a discussion from about 2 years ago which did not conclusively settle the question. This amp supposedly has a 12AU7 preamp tube. There is evidence that Ampeg approves the use of a 12AX7, which is a tube with considerably higher gain than the 12AU7. I have some 12AX7's lying around and am tempted to roll them, to see what they sound like.

Has anybody done this? Has anybody taken a 12AU7 tube out of an Ampeg BA-115HPT and replaced it with a 12AX7? If so, have you subsequently had this amp turned way up, volume-wise?

Old Fart · #2 09-24-2011, 06:38 PM

Bump. Nobody has done this?

JimmyM · #3 09-24-2011, 06:49 PM

They tell me what tubes to use and I stick with them. I figure they're there for a reason.

Old Fart · #4 09-25-2011, 08:47 AM

Ampeg mentions the 12AX7 tube, along with the 12AU7, in the manual for this amp but the wording of that reference is inconclusive. Also, the 12AU7 in my amp is likely a Groove Tube unit, which are not the best tubes. It is very possibly out of spec. Other 12AU7's would likely improve sound, but I don't have those. I just have 12AX7's.

JimmyM · #5 09-25-2011, 11:14 AM

Couldn't find the manual, but a 12ax7 is likely going to make the gain stage really hot and go into overdrive quicker. You could try it for funsies and see what you think, though. Also, I've bought a few Groove Tubes in my day and really haven't had a problem with them. Ya, you pay a little extra for the rebranding, but they do sort them out and pull the obviously bad ones ones at least.

Old Fart · #6 09-25-2011, 11:27 AM

Yeah, that is why I am being cautious. Overdriving a solid state output stage does not end well. Clipping kills.

JimmyM · #7 09-25-2011, 11:33 AM

Quote:

Originally Posted by Old Fart

Yeah, that is why I am being cautious. Overdriving a solid state output stage does not end well. Clipping kills.

You're not necessarily going to overdrive the output stage. That's why amps have volume knobs.