Best way to impliment a parallel stage

[iknowjohnny]

So i took the extra triode stage and used it to parallel the last stage, both the last and the extra stage being in the same tube, V2. So i have 3 stages, the last one paralleled just before the tone stack. The tones stack being plate fed. I tried what i read here about parallel stages, that being 1/2 the plate, cathode, and any grid stoppers and double any bypass cap. Didn't sound as good. So now it's just paralleled the simplest way....plates, cathodes and grid tied together with the same 100k plate, 820R cathode with a 1uf bypass.

the question is, would there be a clearly better way to do this such as paralleling the input stage instead? Or anything else that would yield better tone? Better tone is subjective of course, but i just look for commonly considered "good" details like harmonic richness, thickness, sustain, clarity, etc. And i intend to buy a new tag broad and parts to rebuild it since it's so shoddy from endless experimentation. So i want to make sure i implement this the way I like best so i don't lay out the board a certain way then want to change it in a month. So i'm just asking for any thoughts as to what might well be a much better way to implement this, be it at the input instead of where it is, doing it differently than just directly connecting the cathode plate and grids like i did, or any other things i haven't thought of.

[ampgeek]

Just a quick thought here.

Take a look at the Bassman 5F6A plan and envision tying the norm and bright channel grids together in parallel. It is commonly done, externally, with a jumper cord.

I have built a handful of those (some with a defeat switch) and the increase in all the characteristics you mention running in parallel is evident. Being able to dial in some of each flavor via the volume knobs great.

Not sure that this example fits your vision perfectly. But...it could provide some grist for the mill!

Cheers,
Dave O.

[tubeswell]

Paralleling the input stage can definitely be an improvement, from two main angles I can think of off the cuff:

1) you can halve the plate resistor and cathode resistor values and get the same gain as a single triode stage that has twice those resistor values, but with a lower noise:signal ratio than you get with a single triode (because the plate resistor noise component is less, and it is less in the all-important and most-influential (1st) stage); and

2) with the setup in 1) you also have half the output impedance that you would have with a single triode, preserving more bandwidth and having better ability to drive any following tone stack load without losing as much signal clarity etc, so you get more of the guitar pick-up tonal qualities in the signal.

[guitarmike2107]

I don’t like paralleled triodes in later stages, I built an amp that had three paralleled stages and the harmonics/overdrive was ok, but when I made the second two stages just single triodes it sounded much better..

[rsalinger]

I don’t like paralleled triodes in later stages, I built an amp that had three paralleled stages and the harmonics/overdrive was ok, but when I made the second two stages just single triodes it sounded much better..

What are the basic procedures (rules of thumb) for changing a single triode input stage into a paralleled triode stage?

...and inversely, changing a paralleled triode stage into a single triode?

Paralleling the input stage can definitely be an improvement, from two main angles I can think of off the cuff:

1) you can halve the plate resistor and cathode resistor values and get the same gain as a single triode stage that has twice those resistor values, but with a lower noise:signal ratio than you get with a single triode (because the plate resistor noise component is less, and it is less in the all-important and most-influential (1st) stage); and

2) with the setup in 1) you also have half the output impedance that you would have with a single triode, preserving more bandwidth and having better ability to drive any following tone stack load without losing as much signal clarity etc, so you get more of the guitar pick-up tonal qualities in the signal.

Are there any schematics/layouts that illustrate this? Sorry for asking... It's just that this is a new concept, to me. And, I'd like to learn more about it.

Thanks,
Rob

[iknowjohnny]

What are the basic procedures (rules of thumb) for changing a single triode input stage into a paralleled triode stage?

It's just a matter of connecting the unused stage to another one by wiring the plates together, the cathodes together, and the grids together.

To the other replies, thanks....sounds like i do need to use it up front if for no other reason than noise.

heres another question....in order to try it before i make a new turret board to replace the old one that is shabby from endless experimentation, i need to know if i like this enough. And the only way to try it is to wire the unused side of V2 to V1's input side. Aside from the fact there will be a bit of wire runs from V2 to v1, are there ant issues running sides of 2 different tubes together in parallel vs using the 2 sides of a single tube? I would only do it that way to try it, but when i make the new board i would lay it out to make both sides of V1 parallel.

[iknowjohnny]

Rob, here is a 18 watt showing a parallel stage ...

http://mhuss.com/18watt/schematics/18minwatt.gif

[Zippy]

To the other replies, thanks....sounds like i do need to use it up front if for no other reason than noise.

heres another question....in order to try it before i make a new turret board to replace the old one that is shabby from endless experimentation, i need to know if i like this enough. And the only way to try it is to wire the unused side of V2 to V1's input side. Aside from the fact there will be a bit of wire runs from V2 to v1, are there ant issues running sides of 2 different tubes together in parallel vs using the 2 sides of a single tube? I would only do it that way to try it, but when i make the new board i would lay it out to make both sides of V1 parallel.

+1 for putting it up front.

As to your question, it'll depend on how well matched the two triodes are - some prefer mismatch for "character". You certainly have more room to experiment with the effects of mismatch if you use two separate tubes.

[tubeswell]

@ Rob

Several of the Matchless amps also have parallel triode stages, esp at the V1 position

[guitarmike2107]

In theory I dont think there is a problem with using two triodes from two different tubes, but I do think there is a small interaction between two triodes in a bottle which may help it sound better if it was just a single tube.

Try it?

[Alexo]

In theory I dont think there is a problem with using two triodes from two different tubes, but I do think there is a small interaction between two triodes in a bottle which may help it sound better if it was just a single tube.

Try it?

Or the opposite: Sometimes there is an interaction between the two stages in a single tube that makes them sound worse if they are spread out in the circuit - signal from the plate of one triode can reach the grid of the next. This can be a doozey in a Fender build where you can't turn the volume down far enough to get zero signal, because it is bleeding into the tone stack recovery stage that happens AFTER the volume control.

[tubeswell]

In theory I dont think there is a problem with using two triodes from two different tubes, but I do think there is a small interaction between two triodes in a bottle which may help it sound better if it was just a single tube.

Try it?

Or the opposite: Sometimes there is an interaction between the two stages in a single tube that makes them sound worse if they are spread out in the circuit - signal from the plate of one triode can reach the grid of the next. This can be a doozey in a Fender build where you can't turn the volume down far enough to get zero signal, because it is bleeding into the tone stack recovery stage that happens AFTER the volume control.

Yep I agree, it is best to keep parallel and even cascaded triode stages in the same bottle if possible where they are next to one another in the signal path, because of the effects of h-k hum and even ground/B+ hum from different stages which may be decoupled at different points potentially causing unwanted feedback havoc etc. Not that it would necessarily be problematic all all cases, but that it is another layer of potential avenue for problems which I reckon is best avoided if at all possible. Others may beg to differ

[iknowjohnny]

Think i'm gonna pass on this one. Tried it on V1 and now i have it back to 3 stages no parallel and i think it's just cleaner and better like that. Well, learned something anyways. Thanks all.

[tubeswell]

Think i'm gonna pass on this one. Tried it on V1 and now i have it back to 3 stages no parallel and i think it's just cleaner and better like that. Well, learned something anyways. Thanks all.

how were the stages set up? With parallel stages, to get the same 'cleaness'/gain as a single triode, you have to half the plate resistor and cathode resistor values, otherwise you will just have more gain

[iknowjohnny]

I know, and i did it that way by simply paralleling the same values to half them (IE: parallel a 100k with the current 100k plate and a 1.5k with the same on the cathode. And i did it straight across like the 18 watt i posted. Just didn't like the tone. It changed the tone in ways i didn't like at all.
Besides, I have sozos arriving tomorrow and i want to be able to hear them compared to the current mallories with the amp sounding like i am used to.