12ax7 ID/Help

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12ax7 ID/Help

Postby brandon_cur on Tue Aug 27, 2013 5:31 pm

Hey guys,

I finally decided to get two pairs of old glass for the preamp of my Plexi (50w Bass) and had a few questions. I'm curious as to whether I got ripped off or not, and where these tubes might fit best into my amp.

First, I got 2 Electrochrome 12ax7. They have seamed glass tops, half crescent cutouts in the gray plates, halo getters, and labeled with the Phillips Ontario plant code. I bought these for 15 a piece.

Second I got 2 Mazda-labeled BVA 12ax7 with made in England on the back. According to what I've found these are Brimar tubes. The codes indicate they were made in the early 60s...? (3C1) I got these for 17 bucks a piece. They test at 1400/1800 and 1700/1500 on an Amplitrex AT1000 where new value is 1600-1600

Right now I have some no name Chinese preamp tubes in it. I subbed in a Tung Sol RI in V1 and it sounds way more open and musical. I plan on putting these in for recording sessions - I'll replace the other Chinese with Tungsol for regular use. Can anyone tell me what positions benefit from what type of tube? I just want to set my amp up for classic British Rock tone.

Any help would be appreciated.
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Re: 12ax7 ID/Help

Postby OldSchoolDave on Tue Aug 27, 2013 6:25 pm

brandon_cur wrote:I'm curious as to whether I got ripped off or not,


No, you didn't :-P .

brandon_cur wrote:...and where these tubes might fit best into my amp.


As a general rule, the most bang for the buck is upgrading V1 - the first tube in the preamp section. Next "most improveable" spot is usually the Phase Inverter (closest to the power tubes), but V2 may win depending on the circuit in question.

In any case, you've got plenty of nice tubes to experiment with. I've found Brimars to be more aggressive than Mullards, but YMMV. Which should go in which socket all depends on the sound you're after.

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Re: 12ax7 ID/Help

Postby brandon_cur on Tue Aug 27, 2013 11:02 pm

Thanks Dave.

They are all pretty bright and aggressive tubes. The tones are for more complex and 3d sounding. There is a lot of depth to the mids and the amp seems to breath better. They all sound very good - The Canadian Amperex are a bit cleaner and sparklier than the Brimars. They have a great aggressive midrange tone and are pretty gainy. I'm gonna spend some more time rolling them around.

I'm hoping to snag an old long plate mullard for recording. I really, really liked both tubes much more than the Sovteks and Shuguang I had before. The Tung Sol RI actually compares pretty well to the NOS tubes. Not quite as full and lush but still, bright and aggressive.
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Re: 12ax7 ID/Help

Postby OldSchoolDave on Tue Aug 27, 2013 11:17 pm

brandon_cur wrote:I'm hoping to snag an old long plate mullard for recording.


Don't disregard a Telefunken or Bugle Boy, if you happen to stumble across either in your search.

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Re: 12ax7 ID/Help

Postby dtw576 on Wed Aug 28, 2013 12:13 pm

brandon_cur wrote:I'm hoping to snag an old long plate mullard for recording.

I've occasionally used long plate Mullards for the PI since they tend to be more linear in their response than a normal I61 or I63 short plate. And don't forget to try a 12AT7, I particularly like the military Mullard CV4024, in the PI position. Some folks even like the 5751 in the PI for the same reason. The reduced gain in V3/PI makes for a smoother gain structure in 1987's from my experience. Not sure about in a 1986 (bass). Telefunkens are linear, but bright, from my experience. Got some in my stash and that is where they tend to stay. And since you seem to enjoy swapping preamp tubes around, throw a 5751 or 12AT7/ECC81 in your V1 position and see how close a Marshall can come to sounding like a Fender. Almost eerie. :shhh:
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Re: 12ax7 ID/Help

Postby master keeper on Fri Sep 06, 2013 7:21 am

dtw576 wrote:
brandon_cur wrote:I'm hoping to snag an old long plate mullard for recording.

I've occasionally used long plate Mullards for the PI since they tend to be more linear in their response than a normal I61 or I63 short plate. And don't forget to try a 12AT7, I particularly like the military Mullard CV4024, in the PI position. Some folks even like the 5751 in the PI for the same reason. The reduced gain in V3/PI makes for a smoother gain structure in 1987's from my experience. Not sure about in a 1986 (bass). Telefunkens are linear, but bright, from my experience. Got some in my stash and that is where they tend to stay. And since you seem to enjoy swapping preamp tubes around, throw a 5751 or 12AT7/ECC81 in your V1 position and see how close a Marshall can come to sounding like a Fender. Almost eerie. :shhh:


smoothplates are my no1 choice for PI in marshalls, they seem to have the magical property to make the tone very clear and creamy at the same time.
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