Mellower Than a 12ax7 in V1 for a Mini Rec?

[KiwiJoe]

I'm not a high gain player; rarely push the gain on the red channel past 10 o'clock (but I do like to push the power section and run the master up between 1-3 o'clock). So, I was thinking of putting something like a 12au7 or a 12at7 in V1 to soften the preamp up a bit, so that the gain would be the same at noon or 1 o'clock as it is now at 10 o'clock with the 12ax7, basically in hopes of getting more fine adjustment over a narrower range of overall gain available.

Anybody tried such a thing?

 

[kguitars]

Hi, I ended putting a 12AX7 back in V1. 12AU7, 12AY7 lacked punch and quite a bit of volume loss. 12AT7 and 5751 were ok. I think this amp needs a 12AX7 or 5751 at least. I have two 5751s in my TA-30 and it sounds great and haven't noticed any significant volume loss.

 

[Blaklynx]

Try 5751 in V1 and a AT7 in the PI slot. Mr Ray Vaughn used a 5751 in V1.

google 12at7 in PI position to read up on what others think.

Another nice tube in the PI slot is Sovtek's 12AX7LPS. I have a Sylvania 5751 in V1 and Sovtek's 12AX7LPS in the PI slot in my Rectoverb. Sounds good.

 

[KiwiJoe]

Thanks, guys. I'll give a try to the 5751, and 12at7 and 12ax7LPS.

Question though - PI I assume to mean "phase inverter" Which one is that? They're all "V" something. Would it be V4, what's referred to in the Owners Manual as the "phase splitter/driver"? http://www.manualslib.com/manual/525235/Mesa-Boogie-Mini-Rectifier-Twenty-Five.html?page=21#manual

 

[green_henry]

I swapped in a 12AT7 in my Blue Angel, and it cleaned up a lot of the noise. I'd recommend sticking with Boogie tubes; I tried some JJs and was not happy.

 

[MrMarkIII]

Thanks, guys. I'll give a try to the 5751, and 12at7 and 12ax7LPS.

Question though - PI I assume to mean "phase inverter" Which one is that? They're all "V" something. Would it be V4, what's referred to in the Owners Manual as the "phase splitter/driver"? http://www.manualslib.com/manual/525235/Mesa-Boogie-Mini-Rectifier-Twenty-Five.html?page=21#manual

Yes. The phase inverter/driver/splitter is almost always the 12AX7 closest to the power tubes. Example: If V4 is the first power tube, then V3 is the phase-whatever. (Example means not necessarily any specific amp.)

 

[Dreamtheaterrules]

Joe,

Let me know how it works out.

 

[bandit2013]

The 12AT7 in my RA100 was okay but a bit noisy. I guess when they get old things may change. I did some shopping around on 12AT7 and found many of the NOS tubes to comparable in price to the current production versions. RFT12AT7 will have a deeper tone than a JAN/Phillips 12AT7. As for the PI tube, I have used a NOS JAN/GE 5751 (will cost more than current production) with good results. I prefer Sovtek LPS with matched triodes for the PI. Since the Mini Rec is driving EL84's the gain structure and character is quite different than say EL34 or 6L6 or 6V6. I would experiment with standard 12AX7 in V1 and drop the gain V2 with a 12AT7. You can try a 5751 in V1 but may be bright depending on what tube you get (military grade JAN will be bright). I had similar issues but with a different amp that used EL84. A 12AT7 helped to reduce the abundance of gain. (reference Carvin V2MC, by no means is it similar to any Mesa so I am only making reference to the amp since it also uses EL84 but 4 of them for 50W).

 

[elvis]

SPAX7

 

[KiwiJoe]

UPDATE: After talking to the leading amp builder/modder here in NZ I bought an Electro Harmonix 12AY7 (gain factor 55.6) and and a JJ ECC83MG (gain factor 76.85) last week. He tests every tube he gets and explained that these things can be all over the place, not just between different brands but within the same brand, tube type, and batch. He has 5751s, which he said he'd be more than happy to sell to me, but he said that often they offer no real gain reduction over a 12AX7 and are often hotter.

I should specify my particular set-up just to be clear that this may not work for anybody but me. But if somebody has a similar set-up and tonal taste, this may be helpful.

*Mini Rec with Mini Rec slant cab, V30, 25W setting, both channels
*Epiphone Dot, stock pups (which, after 2 years I'm thinking seriously about a set of DiMarzio 36ths; the Epi neck pup can be a bit woofy (muddy) with OD, and I think both pups are hotter than what I'd like (so this tube experiment may change again after new pups).
*I'm in a trio (guit, bass, drums) that plays a really eclectic mix of blues, blues-rock, and jazz. Think: Little Feat meets Miles Davis. I like the pure virginal cleans, the crunchy cleans, and a lead tone much like Larry Carlton's back in the mid 70s-early 80s when he was using a Boogie Mark I (yeah, I know, just get a Mark I or a RI :lol: )

So I put the 12AY in V1, and it's wonderful. I didn't notice a real volume drop on Ch 2 "vintage", but I did on Ch 1 "clean". However, I can turn up the volume to compensate and match (roughly) with Ch 2. It's not that big of a deal for me, though. We don't have any songs really where I need to switch from clean to OD. Clean songs stay clean for the most part.

What I did notice was that I now have a lot more fine control over the gain in OD. With my trio I set the master at 2-3 o'clock and was running the gain at around 9 o'clock; any higher and it was just too saturated for me. I like a "clean" sounding OD with lots of sustain yet really nice note separation. Now with the 12AY, the gain doesn't get saturated until it's up around 3 o'clock where it really comes on like a hair trigger. So now my gain setting is closer to noon with the same master setting. I do a lot of guitar volume rolling, and with the pots rather low (3-4) I can get a nice clean with a soft touch, dig in and get a bit of growl, and when I want "more" I can roll the pot up to suit.

With the clean setting, master is up around 3 o'clock, gain just past noon. With guitar pots no higher than half open, it's virginal clean all the way. With the pots open, it will get a bit hairy if I dig in, but still stay clean with a lighter touch.

Overall both channels are now very nice and "open" sounding with very little compression.

I did try the ECC83 in V2 (with the 12AY still in V1) and I didn't like it. It was actually worse than having the full compliment of 12AX7s in there; very fizzy at just about any gain setting with the guitar volume rolled up a bit. I may try it in the V4/PI slot and see how that sounds, and I will give it a go in V1. Right now, I am digging the 12AY7 in V1.

 

[Dreamtheaterrules]

Great update Joe. Glad it's working out for you. Rock on!

 

[YellowJacket]

I was just doing to suggest running more 'vintage' style pickups since the crunch will get a lot 'softer' or 'rounder' when the front end of the recto isn't hit as hard. It's kind of the opposite of a boost pedal, where the idea is to blast the front end and saw off as much of the wave as possible.

 

[KiwiJoe]

I was just doing to suggest running more 'vintage' style pickups since the crunch will get a lot 'softer' or 'rounder' when the front end of the recto isn't hit as hard. It's kind of the opposite of a boost pedal, where the idea is to blast the front end and saw off as much of the wave as possible.

I agree. Like I mentioned, the 12AY7 makes a huge difference, but I think a set of DiMarzio 36ths or Lollar Imperial "low winds" are in my near future, just for that final touch. I don't know what the specs are on the stock Epiphone Alnico Classic pups, but I suspect they're hotter than a traditional PAF. My mate's '64 335 is a lot mellower through my amp on the same settings.

I really suspect I'm being a bit fussy; this is all just an exercise in *very* fine tuning of an amp that I am really happy with. It's like I'm 99% of the way there, just trying to extract that last 1%.

 

[afu]

I'm tired and feeling a bit fuzzy, but something about the difference in the clean channel occurred to me.

If it's similar to the clean in the bigger amps, It has it's EQ controls after V1. This style of EQ loses a lot of gain and using a lower gain tube would make that brick wall a little harder to climb.

Vintage mode has negative feedback in the phase inverter which reduces the overall gain a bit before it hits the power tubes, but the preamp's heavily distorted third stage, then the cathode follower into the EQ, and having the master volume follow the EQ, makes for a very large signal to still pass through the FX loop buffer and on to the inverter stage. In other words, it builds a lot more size to come down from and the gain reduction at V1 will be more subtle.

Maybe putting the tube in V2 will bypass the problem with the clean's EQ, by affecting it's second stage (make-up gain, but no impedance hurdle). It will still be lower, but not as much. It will also affect Vintage stages 2 and 3. That should make a huge difference with the distortion's character.



off topic a bit:

If you want Vintage to be a little more old fashioned, the resistor on the cathode of stage 3 is a consideration for modification. The stock value is 39k on it's big brother. A JCM 800 is around 10k. Somewhere between those, maybe? The relatively large size of that resistor makes the stage very nonlinear and it distorts with very little effort. Reducing it will actually make the overall gain (loudness) a bit higher, but the distortion will be a bit lower, but still distorted. I don't know that I'd do it, because it would be radical, but it's an idea. I wonder if that's one of the Voodoo mods.....

 

[KiwiJoe]

I'm tired and feeling a bit fuzzy, but something about the difference in the clean channel occurred to me.

If it's similar to the clean in the bigger amps, It has it's EQ controls after V1. This style of EQ loses a lot of gain and using a lower gain tube would make that brick wall a little harder to climb.

Vintage mode has negative feedback in the phase inverter which reduces the overall gain a bit before it hits the power tubes, but the preamp's heavily distorted third stage, then the cathode follower into the EQ, and having the master volume follow the EQ, makes for a very large signal to still pass through the FX loop buffer and on to the inverter stage. In other words, it builds a lot more size to come down from and the gain reduction at V1 will be more subtle.

Maybe putting the tube in V2 will bypass the problem with the clean's EQ, by affecting it's second stage (make-up gain, but no impedance hurdle). It will still be lower, but not as much. It will also affect Vintage stages 2 and 3. That should make a huge difference with the distortion's character.

Makes sense. I'll give that a shot. Thanks.

 

[YellowJacket]

Bare Knuckle Pickups have a model called the 'mules' which are a PAF style pickup with an Alnico IV magnet. It may be a great option for what you're looking for. I really like BKP with Mesa since the clarity and 'openness' of the pickups balances well with the 'thickness and complexity' of Mesa's gain tones.

 

[KiwiJoe]

Maybe putting the tube in V2 will bypass the problem with the clean's EQ, by affecting it's second stage (make-up gain, but no impedance hurdle). It will still be lower, but not as much. It will also affect Vintage stages 2 and 3. That should make a huge difference with the distortion's character.

BINGO! I did that last night, and the difference wasn't huge, but it was significantly "better", and, you're right, the difference between the clean and OD channel volumes isn't as drastic. Thanks so much for your help and insight.

One thing I can say is that the JJ ECC83MG just didn't work in any slot, even in V1 with the 12AY7 in V2). Just a fizzy mess, despite the lower gain factor.

So the 12AY7 in V2 with the stock 12AX7s in the other slots is the winner.

 

[KiwiJoe]

Bare Knuckle Pickups have a model called the 'mules' which are a PAF style pickup with an Alnico IV magnet. It may be a great option for what you're looking for. I really like BKP with Mesa since the clarity and 'openness' of the pickups balances well with the 'thickness and complexity' of Mesa's gain tones.

A bit pricey (here in NZ they're about $500 a set), but they're on my list of options. I think just about any traditional-style low-wind PAF replica will do the trick. The stock Epi Alnico Classics are 8.5 and 10-something, neck and bridge respectively. Just way to hot for my applications, and the neck is really muddy with OD.

 

[afu]

Maybe putting the tube in V2 will bypass the problem with the clean's EQ, by affecting it's second stage (make-up gain, but no impedance hurdle). It will still be lower, but not as much. It will also affect Vintage stages 2 and 3. That should make a huge difference with the distortion's character.

BINGO! I did that last night, and the difference wasn't huge, but it was significantly "better", and, you're right, the difference between the clean and OD channel volumes isn't as drastic. Thanks so much for your help and insight.

One thing I can say is that the JJ ECC83MG just didn't work in any slot, even in V1 with the 12AY7 in V2). Just a fizzy mess, despite the lower gain factor.

So the 12AY7 in V2 with the stock 12AX7s in the other slots is the winner.

Right on. I'm glad it worked out.