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Old 03-14-2013, 12:12 PM   #1
constructbot
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Changing tubes to increase headroom?

Hey guys,

I have a Vintage Modern 2266 50 Watt amp that I just use a clean pedal platform. I get my distortion from my pedals. I was wondering if changing the preamp tubes to tubes that have a lower gain level will increase the headroom of my amp? There are 12AX7s in there right now, would changing any of the tubes to a 5751 make any difference in headroom while keeping the volume output of my amp the same?
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Old 03-14-2013, 12:21 PM   #2
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I've experimented with 12AU7s and 12AT7s and my experience has been that while it does increase headroom, it also decreases output... Enough that it just didn't make sense for what I wanted to do. This was with a 15 watt Blues Junior though, so with a 50 watt amp the volume difference may not be as noticeable. I'd say try it out.
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Old 03-14-2013, 01:11 PM   #3
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^ agreed (in my limited experience, too). While you can probably affect the overall headroom a little with judicious tube choices, it's only going to do so much.

More efficient speakers can increase the volume a fair bit, too. Though different speakers sound different so if you love the sound of your current speakers...
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Old 03-14-2013, 01:28 PM   #4
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Really the best idea is to get an amp more suited to your needs. You can tweak things to get it closer, but my guess is you will never be totally satisfied.
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Old 03-14-2013, 01:32 PM   #5
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All good points here. My limited knowledge of the Vintage Modern tells me it is not the greatest clean platform. I'm also a 'get your grit from the amp and not pedals' guy so that may not help. I do have experience with the 5751 and although it is a great tube - I doubt you'd notice much difference. They are actually closer to 90% of the gain of a 12AX7. I'd get some 12AUs or 12ATs and experiment with those like Tubetime said.

And yeah - speakers make a huge difference. You may like something like a Classic Lead 80 - which are pretty transparent.
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Old 03-14-2013, 01:50 PM   #6
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Well the amp is actually a great clean platform for my needs. I'm definitely not looking to change my speakers, I've got a 1960AV cab. I'm happy with the sounds I'm getting, and the extra headroom is not a necessity, I just thought that maybe changing a pre-amp tube would be a cheap solution to get me just that bit of extra headroom. I guess I'll order a 12AT7 then and see where that takes me.
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Old 03-14-2013, 01:59 PM   #7
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I'd hold back on that, if clean headroom is what you want then you need to think about where in your amp you are generating distortion. Changing your phase inverter tube will probably do more good than anything - although, now i say it, a 12at7 is perfect for that. I forget the figures, but basically the phase inverter is used to alternate half the already amplified signal between your pair (or pairs) of power tubes in turn. Usually most companies except fender and the like will use a 12ax7, which has a higher voltage gain (basically useless in PI position) but a much lower current rating. This causes it to break down an distort in the preamp section, lowering your headroom. When you drop the gain before PI using a 5751, 12at7 and the like, you're really just trying to avoid overpowering the PI. A 12at7 on the otherhand has a MUCH higher current rating than your average 12ax7, meaning it can handle alot more signal before it starts to distort. The issue you'd have with headroom in that case would then be that this ampified signal will then be passed on to your power tubes giving you output distortion (which is awesome, but still distortion) - but at fifty watts i doubt that'll be a worry to you unless you fancy being deaf. So, what I'm saying is, try bunging that 12at7 in your PI slot (usually the last preamp valve before the power section) and your clean headroom should bump up a bit. It did wonders for me when i had a 30 watt EL84-tubed Hayden...until i caved and bought a fender deluxe reverb (because if you really want clean, you just get a fender).
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Old 03-14-2013, 02:13 PM   #8
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Looking at your amp's specs on the marshall site i reckon changing the Phase inverter to a 12at7 is the move to go. It has two (technically) gain-stage valves (both 12ax7), one that it switched in on the modern setting, giving you four gain stages as opposed to two, the issue you'd have in changing the v1 and v2 slots is that you'd be messing with the balance you have in the gain stages (the major 'tone' section) - you'd in effect totally change the characteristics of your amp's gain. the third valve is then another 12ax7 that acts as your tone recovery (tone stacks actually remove signal, which is then amplified again, rather than adding signal) changing to a lower rated valve here would literally do nothing, except lower you volume - so leave that alone!. The fourth valve is the PI, and i've been over that...so i'll shut up now.
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Old 03-14-2013, 02:14 PM   #9
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Thanks for all the information! I think a 12AT7 would be great, I'll order one tomorrow. Standard JJ's any good?
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Old 03-14-2013, 05:07 PM   #10
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Quote:
Originally Posted by tubetime86
Really the best idea is to get an amp more suited to your needs. You can tweak things to get it closer, but my guess is you will never be totally satisfied.


agreed.

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Originally Posted by 311ZOSOVHJH
All good points here. My limited knowledge of the Vintage Modern tells me it is not the greatest clean platform. I'm also a 'get your grit from the amp and not pedals' guy so that may not help. I


yeah that's what i was thinking. also i think the VM is (i think i read this somewhere, so don't quote me) 50 watts when cranked, whereas most 50 watt tube amps are rated at 50 watts clean. so that's probably not helping.
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