12AT7 phase inverter in Marshall TSL? And another question.

Kommerzbassist

Thunderbirdologist
Hi,

just messing around a bit... what would a balanced 12AT7 do in the V4 of my amp compared to the standard 12AX7?

Also... I always thought V1 was the first gain stage, V2 was the drive channel driver or something and V3 the "normal V2" until recently, when I heard something different (V1, V2 are gain stages and V3 is the drive channel/effect tube). Marshall doesn't quite give you any info on that so if anyone has some firsthand info on that, I'd appreciate it. I've always had the same tube type in V2 & V3 so I didn't care too much, but as I already said, I'm in for something new :friday:

thanks
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

Is this your amp? http://www.schematicheaven.com/marshallamps/jcm2000_tsl100_100w.pdf

Schematic Heaven has a couple of TSL schematics but not necessarily yours. Both of them show V4 as the phase inverter. I haven't had enough coffee yet to figure out what V3 does...

The short version is that a 12AT7 has a mu of only 70 compared to 100 for a 12AX7. That's the theoretical maximum amount of voltage amplification IRRC. However, the 12AT7 puts out much more current than a 12AX7. That's why it's frequently used as a driver for a reverb transformer (BF Fender). All other things being equal, the 12AT7 will send a reduced voltage swing to the grids of your power tubes.

What are you trying to accomplish? If you're trying to reduce preamp gain a bit, experimenting with a 5751 in the V1, V2 and V3 spots might make more sense. The 5751 is very similar to a 12AX7 but with the mu of a 12AT7. Relatively cheap for NOS too.

BTW I'm not a believer in the "balanced triode" marketing stuff. Great if you're working with an tube driven stereo, but guitar amps aren't supposed to be hi fi.

Hope this helps,

Chip
 
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Re: 12AT7 phase inverter in Marshall TSL? And another question.

I've got the TSL 60... I know V1 is V1 and V4 is the phase inverter, my question is just whether V2 is V2 or V3 does what a "normal" V2 would do (2nd gain stage ;) )

Actually I just thought because the AT7 puts out more current it might push the power tubes more resulting in more... driiiiive :firedevil But obviusly I'm mistaken here.
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

what kinda tubes are in there now?

if they're jj's or something there are hotter 12ax7's out there. The Chinese ones are probably my favorite, real chunky
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

You need a hotter 12AX7 to drive the power tubes more and the effect won't be all that noticeable IMHO.
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

Oh I have Chinese ones in there.
I use TAD tubes which are basically "selected" out of the normal batch and matched in case of the power tubes... they have all the popular ones... like Chinese... the JJs... Sovtek... you name it, relabled after selection.

But it's routine replacement time so I think I'm gonna go...

V1: TAD 7025/ECC83 HIGHGRADE (RT030)
V2/V3: TAD ECC83-Cz (RT003, JJs basically)
V4: TAD 12AX7A/ECC83 (RT001, Chinese ones)
Power: TAD E34L-Cz (RT152, JJs)

I was really just thinking whether those 12AT7s others could give me some kinda magic edge, but I think there's no other black magic than the good old crank to 11.
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

A common mod back in the day was to use a 12AT7 in the PI to clean up a Marshall a bit, so this would probably be counter productive if your goal is actually more drive.
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

A 12AT7 has like (I forget if it's) 60 or 70% of the gain of a 12AX7, and I have never heard of it putting out more current.

Every amp uses the triodes in a different fashion, so you really need a Tube Layout from Marshall to know what each triode is doing, unless you wanna trace that schematic.

I called up MESA/BOOGIE when I was changing preamp tubes for the first time, and Michael emailed me the tube layout.
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

A common mod back in the day was to use a 12AT7 in the PI to clean up a Marshall a bit, so this would probably be counter productive if your goal is actually more drive.

Ok that ends all. I don't want no 12AT7 anymore... no clean sounds... noooo :firedevil
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

2 distinct signal paths:

"clean": V1a - tone stack - V2b - effects loop/reverb - V3a - V3b - V4(a&b)

"dirty": V1a - V1b - V2a - V2b - effects loop/reverb - V3a - v3b - tone stack- V4(a&b)

V3 is a recovery stage and cathode follower and is common to both channels

V4 is the phase inverter

effects loop & reverb are solid state
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

A 12AT7 has like (I forget if it's) 60 or 70% of the gain of a 12AX7, and I have never heard of it putting out more current.

Tube data sheets:
12AX7
mu or "amplification factor" equals 100
maximum plate dissipation equals 1.0 watts

12AT7
mu or "amplification factor" equals 60
maximum plate dissipation equals 2.5 watts

5751
mu or "amplification factor" equals 70
maximum plate dissipation equals 1.0 watts

New production 12AT7s cost less than a 5751, but NOS 5751 cost a bit less. Stevie Ray Vaughan supposedly liked 5751s for whatever that's worth.

There may be some advantage to using a higher-current output tube in the phase inverter spot (e.g. 12AT7 in BF Fenders), but generally a 5751 is closer to a 12AX7 except for reduced gain.

Chip
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

Bump for this thread please!! I’ve been playing around with nos tubes in my tsl60 and right now I have a pretty “winning” mix imo...I have a Raytheon 12DF7 in v1, a Mazda France Silverplate in v2, a Miniwatt/Dario Mazda France 1958 longplate in v3, and a 58-59 Mullard Blackburn longplate in v4. My power tubes at the moment are new production Genalex Gold Lion KT77’s, but I have a pair of Mullard XF1 EL34’s that I’m going to put in there...Waiting until after the holidays for that since I need to take it down to the shop and have the owner/tech do a quick re bias after putting the new ones in... I’m extremely happy with the mix with the 12DF7 in v1...There’s just not a tone setting that sounds bad...Can go full bass and treble with the mids completely scooped, all knobs at noon, bass noon, mids at 7/8 of 10 w/treble at 9-10...Pretty much anything without dropping the treble below the 5 of 10 mark! I’m just trying to figure out where to go from here...I’m thinking of maybe getting another 12df7 to put in either v2 or v3(will prob just sub them in the different spots and see what sounds best)

But the big question would be this...Could/should I try out a 12at7 for the phase inverter v4 spot?? Or could a 12au7 work as well? I always hear about the phase inverter spot, but what exactly does it do and how does it effect the overall tone of the amp? I guess the question is with things being pretty much how I want them to be, would it makes sense to try out a non 12ax7 type tube in the v4 spot, or just go with another 12DF7 for v2 or v3?(heck could even try it in v4, but I kinda like the Mullard in that position(had switched things up just to try and put the Silverplate Mazda in v1, the Miniwatt Dario in v2, the Mullard in v3 and the Raytheon 12DF7 in v4...Was ok, but definitely preferred the other config! Maybe should try switching the two Mazda France tubes positions, just to see if there’s any extra treble...)There’s definitely enough bass and warmth to the amp, though I’m always looking for a way to get a little extra “sizzle” out of the amp!!

Thanks for any answers, it’d be nice to hear what the op ended up doing and how it worked out! The tsl60 can sound absolutely beautiful with the right tubes, I’ve had mine since 2000 and never did anything with it until like 4/5 months ago...It’s like a completely different amp and just can’t stop playing it!! If anyone wants to hear it, send me a message and I could send you my YouTube name, or could put a link up, but just didn’t want to randomly do that in this post! Also have a jvm1c that I put all nos tubes into, Plus changed out the crap 8 inch speaker for a 10 inch Celestion G10 greenback...It sings now! I play in stereo using an Xotic Stereo X Blender, love the extra choice of using that instead of a Supro Coronado(again w/nos preamp tubes) since the Supro is such a LOUD 35 watt clean amp...makes a great platform for fuzzes though...Anyways, just trying to figure out where to go from where things are now :)
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

12DF7 are really rare beasts and only known of Raytheon brand. A very low noise version made for recording mic preamps. Just for **** and giggles i would try the Mullard in V1. It has the distinct Trademark Marshall Sound.
You can really use anything in v4 spot, even noizy or tubes prone to feedback. i prefer some hotter Chinese tube to drive the output tubes more.
Really, the Mullard is a waste of tubes in the V4.
 
12AT7 phase inverter in Marshall TSL? And another question.

I’d also suggest the Mullard in V1 however I don’t think putting it in he PI is a waste of a tube. I have one in my Quickrod’s PI slot and I love it there. Although, it is typically used in the V1 slot.
I can’t explain on a technical level what the PI does but I know it somehow splits the signal to the power section in a push/pull type amplifier, like the Marshall. I don’t feel as if it makes a huge difference to the tone of the amp, rather it affects the feel of it. It seems to make my amp a bit more syrupy and feels great when you dig in to it....if that makes sense. It’s tough to describe.
I generally like a long plate tube in the PI as well.

Also:
If you are happy with what you hear from your amp....don’t go messing with a good thing.
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

would lower the gain and sound thin and like crap!
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

I’d also suggest the Mullard in V1 however I don’t think putting it in he PI is a waste of a tube. I have one in my Quickrod’s PI slot and I love it there. Although, it is typically used in the V1 slot.
I can’t explain on a technical level what the PI does but I know it somehow splits the signal to the power section in a push/pull type amplifier, like the Marshall. I don’t feel as if it makes a huge difference to the tone of the amp, rather it affects the feel of it. It seems to make my amp a bit more syrupy and feels great when you dig in to it....if that makes sense. It’s tough to describe.
I generally like a long plate tube in the PI as well.

Also:
If you are happy with what you hear from your amp....don’t go messing with a good thing.

I've noticed changes in frequency response from switching PI tubes. For example I like the Sovtek 12AX7LPS due to how full it sounds; it can be a huge help in lower wattage amps like my Marshall Mini Jubilee.
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

I tried switching things around and putting the 12DF7 in different spots, but(to my ears) it’s absolutely to die for in v1! I just tried a new mix and took the Mullard out of the tsl and put it into the jvm1c as it’s v1...Now, it’s too late to be rally jamming at this time of night, but (super low volume) first impressions are very good with the Mullard Blackburn in the v1 slot of the lil 1 watt....I’m really bummed because I wanted to put in a set of the 6085’s for the “power tube” section, but there isn’t enough clearance for one of the two tubes because of the speaker(though I don’t know if it could have fit w/the 8incher I replaced ) But I’m not going to get rid of the g10 greenback because of 1 tube...Adding the 10 was a huge improvement in tone, so gotta look for a different 12au7 matched pair!! Oh, so v1 is the nos Mullard Blackburn 58-59 longplate, nos Mullard CV4004/12ax7 in v2, a pair of RCA Cleartop 12au7’s for the power tubes(thinking about upgrading them just to see if it’ll make any kind of difference) and a GE Pewter Plate 12ax7 for the “v3”(I’m guessing phase inverter spot...) Hoping it sounds as good at higher volume as it does right now, the Mullard really seemed to bring up the gain and smoothness of the lead channel, but there’s still enough “sizzle” to the top end tha I really like!

Then that means I’ll also have to see what the tsl60 sounds like with the 12DF7 in v1 and the other 3 sockets being filled w/Mazda France tubes! Anyways, thanks for the info, I’m going to not do a 12at7 in v4...Either going to put the Mullard back in, or get another vintage Mullard tube and keep the Blackburn Longplate in the JVM1...I’m going for a classic to hard rock to “light metal” kind of tone...And the nos tubes are giving me that, but with a depth I couldn’t even imagine before I started “rolling” tubes! I’d like both amps to have a treble And harmonically rich lead channel distortion, but also want the clean channels to be able to take pedals, as I have like 7-8 different fuzzes to throw at it! Hoping the Wample Dracarys That’s on the way can take care of the hard rock/metal side of things when I’m not using the amp’s distortion...The 12df7 takes Fuzz like a champ, I’m very happy with how it’s responding to what is thrown at it! Have definitely experienced the most noticeable difference in to since putting that into v1, almost as much of a difference as when I put my first nos tube in there! With the amount of $ shelled out for guitars and pedals, it just makes sense to me to go for the big guns when it comes to tubes and to just go nos...I’m sure many may have differing opinions regarding preamp tubes, but to each his own! That’s y it’s so awesome to me that there are all sorts of 12ax7’s(and comps) out there that can be experimented with...And no matter what l, even if it’s not giving you the sound you’re looking for in a particular amp, it could do just that in another! And I just realized that with the Xotic Stereo X Blender that I can run the Supro, Jvm1c and the tsl60 at the same time! I have the jvm in the center, with the Supro to the left and tsl to the right! Sounds really cool to have a fuzz going through then all, as the variations in tone between the amps just adds up to a more complex and “richer sounding” tone! Also it’s really fun to have the jvm as a center channel that bypasses the Empress Echosystem, as I can have delays running on both the tsl and Supro, but the jvm stays without the effect...So it’s almost like what the “mix” function does, allowing you to hear the unaffected tone through the center and the delays in stereo bouncing of your ears from the left and right!!

Can’t wait for my 59RI to be finished so I can try out the new setup!(Seymour Duncan 59 Custom Hybrid in the bridge, with a Custom Shop Duncan hybrid in the neck, a 78 model screw coil and a Pearly Gates slug coil with rough cast, degaussing Alnico 5 got the mag! Plus a Doyle Coils full vintage harness....And hopefully something else I wanted to try, the Duncan Triple Shot system for both pickup rings...Hoping it’ll turn the 59 into a “do everything” kind of guitar with the coil splitting, series and in and out of phase stuff, all while keeping the benefits of the tone of the vintage style harness!!(mad sure to order 4 conductor wire so it could be something to attempt! Ok, will keep on this as the rig changes, but here’s a few vids!

https://youtu.be/aQV1XA43hBc

https://youtu.be/YtrRoz69T_E

https://youtu.be/gmZuVH3qsdY

A couple different vids w/different fuzzes, different guitars, etc...I’d recommend nos tubes any day! And am waiting to put in a matched pair of Mullard Xf1 EL34’s, just have to wait to take it to the shop for a quick bias check after switching out the new production Genalex Gold Lion KT77’s!(wish I could find a pair of actual nos, REAL Genalex KT77’s, just too rare and costly!!) Hopefully my experimenting will inspire others to try out some nos tubes, though I’d recommend starting small(like a v1 change) instead of a full, down the rabbit hole approach I’ve taken...The tsl60 is a much better sounding amp than I thought would be possible! Don’t write off your tired amp just yet!!;I only started playing with tubes over the last 3/4 months, I’ve had the amp since 2000! Merry Christmas, and everyone have a great New Years!!
 
12AT7 phase inverter in Marshall TSL? And another question.

Just a word of caution about the V3 (cathode follower) in the JVM amps. I’m not 100% sure about your particular amp but I used to have a JVM 210H. The V3 slot has a slightly higher voltage than the other preamp positions. Iirc, it has about 105v (?). In any case it’s pretty particular about what tubes will work there. I blew out a couple of tubes before I learned about the higher voltage. The JVM forum has a lot of info about it. Just be sure to check the spec sheet on whatever tube you run there. It seems that the spiral filament type tubes are especially prone to failure.
As always, ymmv. I ended up using a TAD 12ax7 as it can handle 180v.
 
Re: 12AT7 phase inverter in Marshall TSL? And another question.

I think the issue is mainly with the New Sensor made tubes with spiral filaments. 12AX7 spec for heater to cathode voltage is around 200V. The Sovtek made tubes with spiral filaments don't handle the higher cathode to filament voltages in cathode follower circuits despite meeting the spec on paper. Either that or it's a QC issue. But a techie can correct me if I'm wrong.
 
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