Series vs parallel tube circuits

[cstenger5]

So I'm still very new at this, so all of this may seem basic, but I'm pretty curious about this. I see a bias in the downloads section toward the use of parallel 12ax7 wiring. And when I say that, I just mean that I've noticed it a lot more often in these circuits than I have when clicking all over the internet trying to soak up schematics of amps I like.

My assumption going in, is that we're using two triodes in that situation to better do the work of one. Im inferring that each triode is processing half of the signal, and so the output is roughly the same, at least in terms of volume, as using a single triode. Of course, there's at least a 50% likelihood I'm wrong...

I know from running series circuits in parallel, which is a way I've played through a few old fenders, you get a little bit of a different character than you would out of just the single, series preamp. So my question is, what was the reason for going that route with so many of these 18 Watt designs? Do we get more headroom? Less headroom? Different harmonic structure (or whatever)?

How about if we married up zp's Lite IIb with the tmb channel from Josh's TMBs, In what I assume would be parallel-series? What happens there?

These are the things I sit and think about while I'm at work, wishing I was instead at my workbench .

[JMPGuitars]

The parallel triode is a little fuller and maybe smoother than a single triode. There may be a slight increase in gain, but not necessarily perceivable.

If you look at my EF86 Xtra circuit, or the Tremolo TMB, or my preferred Lite 2b(ish), there's different reasons why. The higher gain of the first two options gets smoothed a bit from the parallel dual triodes, but in the Lite 2b(ish), it's mostly for that slightly thicker tone. In the Tremolo TMB, it's also being used to drive the tone stack.

You should look at ZP's Parallel/Cascade switch mod. That gives you the choice for higher gain with the triodes cascaded in series, or flip the switch for the triodes in parallel.

Thanks,
Josh

[cstenger5]

Thanks Josh!

[colossal]

The parallel triode is a little fuller and maybe smoother than a single triode. There may be a slight increase in gain, but not necessarily perceivable.

Yes, for sure. Gain will increase slightly, miller capacitance will double, and better signal-to-noise ratio. The sound is definitely fuller and a bit richer to my ear, if you will. It is my preferred channel on these amps for Volume and Tone knob work with a Les Paul. The cascaded variants are awesome, don't get me wrong, but I do like that Normal channel.

[JMPGuitars]

The parallel triode is a little fuller and maybe smoother than a single triode. There may be a slight increase in gain, but not necessarily perceivable.

Yes, for sure. Gain will increase slightly, miller capacitance will double, and better signal-to-noise ratio. The sound is definitely fuller and a bit richer to my ear, if you will. It is my preferred channel on these amps for Volume and Tone knob work with a Les Paul. The cascaded variants are awesome, don't get me wrong, but I do like that Normal channel.

I don't remember if I ever sent you my Xtra TMB circuit, but it has the best of both worlds. I put it up in the downloads section.

Thanks,
Josh

[cstenger5]

Yes, for sure. Gain will increase slightly, miller capacitance will double, and better signal-to-noise ratio. The sound is definitely fuller and a bit richer to my ear, if you will. It is my preferred channel on these amps for Volume and Tone knob work with a Les Paul. The cascaded variants are awesome, don't get me wrong, but I do like that Normal channel.

I don't remember if I ever sent you my Xtra TMB circuit, but it has the best of both worlds. I put it up in the downloads section.

Thanks,
Josh

This is the first circuit (anywhere) that says HELL YES to me, based on the the characteristics I'm looking for in an amp and what you all have described. I know there's not a ton of love for the Mojotone stuff here, but their 18TMB with a few simple mods for more gain gets me almost there, with no complaints at all. I'm excited to do this one. Turret board and turrets have been ordered, and many of the components are on hand from my planned Matchless/Vox build and leftovers from previous builds.

[JMPGuitars]

This is the first circuit (anywhere) that says HELL YES to me, based on the the characteristics I'm looking for in an amp and what you all have described. I know there's not a ton of love for the Mojotone stuff here, but their 18TMB with a few simple mods for more gain gets me almost there, with no complaints at all. I'm excited to do this one. Turret board and turrets have been ordered, and many of the components are on hand from my planned Matchless/Vox build and leftovers from previous builds.

I like a lot of Mojotone's products. The issue is with their build docs and layout designs. Some people have no issues, but many people have a lot of issues (as you can see by searching mojotone on this site).

I'm sure you'll enjoy the Xtra TMB. I certainly do. The Tremolo TMB is also awesome, as you'll see when you build that one. Side by side, they make a crazy pair. I'll probably make a PCB for the Xtra TMB at some point. It gets a bit expensive ordering the PCBs though, so I'm not in a rush.

Thanks,
Josh

[TriodeLuvr]

My assumption going in, is that we're using two triodes in that situation to better do the work of one. Im inferring that each triode is processing half of the signal, and so the output is roughly the same, at least in terms of volume, as using a single triode.

The real reason is often that the designer had an extra section with no purpose. Connecting it in parallel creates a facade of usefulness, whereas leaving it dangling looks like a faux pas. This technique doubles the Miller capacitance of the stage, but that has little effect in instrument amps due to their limited high frequency response.

Jack

[JMPGuitars]

The real reason is often that the designer had an extra section with no purpose. Connecting it in parallel creates a facade of usefulness, whereas leaving it dangling looks like a faux pas. This technique doubles the Miller capacitance of the stage, but that has little effect in instrument amps due to their limited high frequency response.

Jack

I disagree. It makes an audible difference in guitar amps. See what colossal said above from his perspective as well.

Also, as I mentioned previously, parallel triodes have a smoothing effect when used after another gain stage. You can hear this difference as well.

In either case, you can make the function switchable and see if you can hear the difference or not.

Thanks,
Josh

[Bieworm]

I guess that's what I hear in the TremTMB then.. it's nasty, but in a gentle and mature way

[cstenger5]

I guess that's what I hear in the TremTMB then.. it's nasty, but in a gentle and mature way

How I like my women.

[Bieworm]

I guess that's what I hear in the TremTMB then.. it's nasty, but in a gentle and mature way

How I like my women.

Nice !

[zaphod_phil]

Yes, for sure. Gain will increase slightly, miller capacitance will double, and better signal-to-noise ratio. The sound is definitely fuller and a bit richer to my ear, if you will. It is my preferred channel on these amps for Volume and Tone knob work with a Les Paul.

Same again here. I've often gigged with my Lite IIb, which has inputs, both for single triode and parallel triodes. I've always ended up using the parallel input, because of its fatter tone, as well as slightly bigger gain.

[cstenger5]

Same again here. I've often gigged with my Lite IIb, which has inputs, both for single triode and parallel triodes. I've always ended up using the parallel input, because of its fatter tone, as well as slightly bigger gain.

Do you prefer separate inputs to a switch? I think I'd personally prefer that, due to the fact that there's no relayed switching.

[colossal]

Same again here. I've often gigged with my Lite IIb, which has inputs, both for single triode and parallel triodes. I've always ended up using the parallel input, because of its fatter tone, as well as slightly bigger gain.

Do you prefer separate inputs to a switch? I think I'd personally prefer that, due to the fact that there's no relayed switching.

I've built them both ways and now I don't even bother with the single triode input option or wire the amp to support it. I would probably do two separate jacks though, unless I was building for someone that just had to have the single/parallel option and was switching inputs and guitars all the time. Then I would probably use a toggle switch.

If it helps you, on a personal note, I have run the gamut of building amps bristling with switches and now build these amps with the absolute least amount of anything in or around the signal path.