| Author | Message | ||
| Mike Flynn |
I just got this from a friend. It has the silver badges on it. I had some tubes I never used kicking around and I was thinking of using a Mesa Boogie 12ax7-a in the pre-amp. Is this an ok tube to use? i noticed that in the amp currently is a 12at7. Is that possibly just a different version of a 12ax7????? any help would be appreciated. also, can i just switch out this tube myself or is there any type of biasing that would need to be done? | ||
| vcamargo99 |
Yes it's OK to use. The tube is actually the Phase Inverter (PI). As far as I've ever heard, the original tube in your amp should be a 12ax7. A lot of Fender amps players use a 12at7 in the PI. Perhaps the previous owner used that logic. I tried it (HD130) with the 12at7, but did not notice any difference tonally. If anything the 12ax7 might drive the power tubes a bit harder. In the past I would use the 12at7 in the PI slot of my old Fenders to gain a bit more "clean head room". No Biasing is needed when you change that tube. However, it wouldn't hurt to check the bias to make sure it is running at the optimum setting. | ||
| Mike Flynn |
Thanks a ton. I tried the 12ax7a and it actually sounded a lot better. I noticed a little more gain, a little more warmth and a little more low end. Maybe the 12at7 was dead or on it's last legs. | ||
| edward solberg |
I'm not sure if this is the correct thread to post this note (it is the most recent in the tube subject area) or whether it is right to crow about my recent exceptionally good fortune. I am now the proud possessor of a virgin pair of Sylvania 6ca7's and an Amperex 12ax7. I know they are mid seventies because I bought them at that time. a month ago or so I was cleaning out my garage and stumbled across my "whatzit" bag of emergency parts/ (forgive the pun) "bandaids" for my guitars and amps if a break down should occur. last time I saw that bag was in 1975 when I unloaded it with my equipment after a tour of the west coast (san diego to vancouver, bc) with my blues band as warmup for a big name blues act. we played a lot of dates and halls; I was exhausted when I got home and unloaded in a hazy mental-fog. I forgot all about that emergency kit. figuring it lost, I made up another and moved on. imagine my surprise when, in the midst of a really crappy chore, I stumbled upon these virgin, 1970s tubes. I said something like "holy shit, batman..." after standing there slack-jawed for a minute or so. amazing! (is there another superlative greater than "amazing"?) you know I forgot all about garage cleaning and immediately ripped out my shitty chinese tubes and retubed the 210-sixty five with the real deal. the sound was simply incredible and, with the garage door closed, I cranked it up to 9 master/6 gain and neutral tones (6/6/3) and began riffing away on my 335. I quickly turned the amp down to reasonable volume levels and continued playing my butt off. I had forgotten just how good these amps could sound--they sound great with crappy tubes; with the "correct" tubes for the factory-circuit....!!!!! words fail me (and I am a very wordy bastard). the old lady couldn't get me to come in for supper I was having so much fun. I had planned on replacing my Ruby el34's with a pair of the jj e34l tubes michael k. is so hot for; but now....? I guess the jj's will just have to wait for another 20 or 30 years--bummer (yeah, right). e | ||
| mike kaus |
Nice find. I've got a bunch of them in the basement. Probably eight pairs or so, I bought them when they were $2.50 or so(and thought, damn, that's high just for a tube!) and now have quite a stock for the future. I do use the JJ's right now but might be putting a pair of Sy's in for a while as I'm trying to find a problem in mt 2-10. It's amazing to "find" these treasures when you're not looking for them. | ||
| ed solberg |
ain't that the truth, michael? find yourself with a disgusting chore to placate the little dictators who run our lives and discover treasure; well it takes a lot of the sting out having to do the chore... also it is a great excuse for blowing the chore off for little reprieve from the salt mine. e | ||
| edward solberg |
oh, and are you still being troubled by excessive top end on your combo? I was under the impression that the 15-inch JBL had solved that problem. ed | ||
| mike kaus |
WEll, it does solve THAT problem but I'm going to look into revoicing the front end a little so that I can use it without the 15. That's just one more thing that I have to freaking carry! The other day, I did swap the front end caps around and now the front end seems overloaded and distorts early so I'm going to have to scope it and find where THAT's coming from. It never ends. I'd like to be able to use it again(I've been using the JBL twin since) because it's smaller but right now it's un-usable. Ive been using it as a test amp in the basement for pedal mods so that I have something to try them through. What a waste. Anyway, after this week, I plan on getting into the workshop and seeing what's going on with it. I've alway felt the front end was too hot as it reaches full undistorted volume on like 3 and after that DOES break up. And it's NOT biased too hot and distorting in the final so it's coming from the front end so I have to find that. Oh well, one of these days. Mike. | ||
| Edward Solberg (edward_solberg) Username: edward_solberg Registered: 05-2006 |
that sounds way TOO hot, mike. mine doesn't even begin to crunch until I hit around six, and full breakup occurs between seven and eight. those are gain numbers with the master set at 8/9. damned shame you can't use that amp. If I recall correctly, you've got more than a little bit of time invested in that amp as well as a new pair of weber cali's. anyway, regardless of how much time or dinero one has invested in their MM, it's just too nice an amp to leave sitting on your basement workbench. good luck with the signal tracing. e tried to post this a couple days ago.... thank the powers that be that we now have a registration-type site. hopefully, we can keep the spam and "other" links off of our board. |
Tue, 03/25/2014 - 09:29
#1