Leo and his 420V 6V6

[Helmholtz]

3db is commonly referred to as the 'half power point'.

Yes, with power (and with on-axis SPL) +3dB means times 2 and -3dB means divided by 2.
Discussion is about the audibility of doubling (or halving) amp power.

[g1]

Yes I understand the concern to be the audibility of the 3db. But the 'half power point' is something that is more likely to be found when doing google search regarding 3db and is also why it is used in bandwidth graphs. Also historically linked to RF and transmission.

[Chuck H]

3db is commonly referred to as the 'half power point'.

This is an important distinction. A change in overall volume is actually less noticeable than a change to some part of the mix I think. Otherwise we wouldn't bother with minute differences in pickup design or HPF capacitor values in amps. And I'm sure there's a bigger chance to notice any change within the more hear-able frequencies. Like, say, 400Hz to 5kHz. Try changing the bright channel cap on an old Fender from 47p to 68p. There's barely over 1dB of difference in HF at 10kHz. Though it sort of ramps that way starting at about 3kHz. I promise you'll hear a difference because I've done just this. Or, on the same amp try changing the treble cap in the tone stack from 250p to 330p. No more than 1dB difference at frequencies ramping from the mids to the lower HF. And it makes such a difference that anyone that doesn't hear it must be tone deaf. Ask Dumble about that one! Our brains are tuned to hear even subtle changes in timbre between midrange and lower HF frequencies because that's how we recognize human voices and animal sounds. It was a part of our survival kit for a hundred thousand years. Our old member Steve Conner use to poo poo small changes in design that didn't represent a change of at least 3dB on the premise that it wasn't audible otherwise. I never argued it with him because:

1) I don't have the psychoacoustics chops to hold up my end of that conversation.

2) It was Steve Conner!!!

Since I (use to I suppose) build custom designs for people and tweak each one to make it the best it could be for THAT particular amp, sometimes with only small changes to a few things, I very much believe that a few small changes can make a big difference.

[K Teacher]

So, what's the final verdict here?

Is it worth to fry the 6V6's running them @ 420V to get +1.96dB output (22W vs. 14W) or do like Valco did, and have them to last decades?

Or it's just marketing and bragging rights?

[Chuck H]

So, what's the final verdict here?

Is it worth to fry the 6V6's running them @ 420V to get +1.96dB output (22W vs. 14W) or do like Valco did, and have them to last decades?

Both. It depends on which amp you want

Seriously though I don't think there's a huge tonal advantage to running 6V6's at high voltages so if you aren't trying to eek out a couple of extra watts it's not worth it. But maybe you ARE trying to eek out a couple of extra watts. A Deluxe Reverb with an efficient speaker can sometimes keep up live where the Valco can't. To the point that if that's the goal there's no point trying the same efficient speaker with the Valco because it's just not going to get there. So why not just use 6L6 tubes instead (he hypothetically asked)? Because a guy like Leo was building amps in tiers of price and power. Then everyone wants to see "improvement" and so it goes that these designs exist. And a Deluxe Reverb doesn't sound like a Valco and vice versa.

[35L6]

I've heard it said that 20 watts is all you need but in a recent thread the poster said it was not in his band . If you go from not enough to just enough it's a big change . You do have to remember that the difference only happens at full volume . The 14 watt amp is as loud as the 20 watt amp until you get to the top and there is no more . Then the 20 watt amp has a little more . It's very situational .

[Chuck H]

Yes. Very situational. A guitar player for a metal band that doesn't even mic the drums can't possibly get by with twenty watts. They need more because of the frequencies they use in their tones. More mid scoop and now the guitar doesn't cut through. I've even seen fifty watt amps come up short in this situation.

Then take a little blues gig at a coffee house where the tone will be as much in the mids as possible and five watts is unruly

That's why the most popular guitar amp configuration for working musicians in average bands has always been two big bottles (usually 6L6's) in a 1x12 combo with reverb, at least two channels and a master volume. (<period) It's a little too much for some gigs if you like to crank your amp but it'll get the job done and you won't find yourself short on the next gig because you only have a twenty watt amp.

My personal amp is a 2x el84 with an efficient speaker. It won't handle most gigs. I built the same design for a working musician that liked the amp. His has 4xel84's for obvious reasons.

[mhuss]

> 700v
I've never seen design max specs for a common grid power tube configuration. Common grid config is primarily a voltage amplifier (as opposed to common cathode which is a power amplifier and common plate which is a current amplifier). Just speculating, but I imagine the anode dissipation would be much less then a typical power amp. Also, the schematics I've seen don't specify the idle collector/cathode voltage, it may be significantly high.

[edit] Oops, a little late to the party

[Helmholtz]

Common grid config is primarily a voltage amplifier ...

I don't agree.
A common grid amplifier uses the cathode as input.
Cathode input impedance is low, so requires drive current and voltage, in other words drive power.
On the contrary a common cathode amplifier only needs a drive voltage.

[mhuss]

Cathode input impedance is low, so requires drive current and voltage, in other words drive power.
On the contrary a common cathode amplifier only needs a drive voltage.

I was speaking of input versus output results, not input requirements. If you apply power to a CG amp input, you get voltage gain but not current gain. It acts like a reverse impedance converter, low to high impedance (which is perfect to get BJTs driving traditional tube output transformers.) Sort of the inverse of the CC connection.

[pdf64]

... Our old member Steve Conner use to poo poo small changes in design that didn't represent a change of at least 3dB on the premise that it wasn't audible otherwise. ...

I don’t recall Steve’s 3dB thing being that a change of less than 3dB wasn’t audible?
Rather it was more the case that a change of less than 3dB was too insignificant to be concerned about. eg the 3dB thing was akin to a filter, to avoid the designer wasting time worrying about low impact stuff.

[Chuck H]

I don’t recall Steve’s 3dB thing being that a change of less than 3dB wasn’t audible?
Rather it was more the case that a change of less than 3dB was too insignificant to be concerned about. eg the 3dB thing was akin to a filter, to avoid the designer wasting time worrying about low impact stuff.

I'll buy that. As I remember it he felt 3dB was the threshold where it at least mattered. So that makes sense.

[The Dude]

I think this is down to a person's hearing and some other factors. I was taught in tech school that 3 dB is the minimal amount of change for the human ear to perceive a difference. That said, I do believe that some can hear a 1dB change. There are factors. At what frequency or bandwidth? At higher frequencies, especially with age and some hearing loss (even minimal), it probably takes more of a change to be audible as opposed to a person who still has great hearing. Fletcher Munson curves also come into play and 1 dB change at a lower volume likely has a different perceptibility than 1 dB change at an already high volume. Since this is usually brought up here in the context of a guitar amp at max volume, some of the variables are somewhat solved (what approximate volume and what approximate bandwidth). Speaking for myself, I certainly wouldn't go through a whole lot of trouble tweaking an amp for a gain improvement of less than 3dB. I honestly don't think most people would hear the difference, and if they did, it would be for proving a theory but wouldn't make any real world difference.

[Chuck H]

The little tweaks... Less than 3dB. Exercised in several places in a design can add "polish" that makes an attractive difference that can be heard in a couple of ways. One is that these little tweaks taken in their entirety make a more significant difference than any one adjustment. Another is that a musicians discerning ears hear it and like it. Now they can play without thinking about the little things. Nothing but art coming out on the other side. Maybe everybody can't hear it but if it makes a difference to the guy creating the music it ultimately demonstrates in their performance. This is a powerful thing. Speaking for myself it's those moments when I don't have to think about my tone that are the best. Some amps rise to the top for good reason. Part of it is a musicians familiarity with the tools at hand and what to do. But this implies that the actual amp make/model is insignificant. There are examples and circumstances where this IS the case. Still, some amps have floated to the top. Some famous classics (our earrs are trained to some degree) and some modern. I guess what I want to get across is that it still makes sense to create personalized circuits and designs. Which has always been a part of this forums mission. I still believe it matters.

[The Dude]

That brings to mind something I ponder often. I'll first stipulate that different folks like different tones and what's good is very subjective. BUT, I often wonder why we like the tones we do. What if the music we grew up with sounded COMPLETELY different from a guitar tone perspective? Would we favor completely different tones? Is there something magical about the sounds we like, or are we searching for something we are used to hearing or have heard? If no one ever recorded a distorted guitar sound and it never became desirable, would we still chase that sound? The same for other aspects of "tone"- do we like a certain sound because it's inherently good and instinctive, or is it because we heard other people do it?