delta plate minus screen relationships - pentode

[jpfamps]

The Glen Kuykendall video was rather good. I'm sure I saw him using the volume controls and even stepping on a distortion pedal, so it's not as if he's achieving that whole dynamic range with "touch".

Glen definitely uses the volume controls on the guitar, but I'm pretty certain he plugs straight into the amp for those demos, which I also thing are great.

I have to admit I find the phrase "touch sensitivity" practically meaningless.

Do you simply mean that the amp doesn't compress/limit the signal? If so this can be measured.

[Steve Conner]

To me, touch sensitivity means that the amp converts changes in input level into changes in harmonic content, over and above the changes that you get from the guitar itself. When playing single-note lines it gives you the same expressive capabilities that a sax or trumpet player has: the harder you "blow", the brighter and more aggressive the sound gets. Any decent tube amp will do it, except maybe the modern high-gain ones.

[J M Fahey]

Yes, that's about it.
I also suspected him stepping on a pedal (probably a clean boost one) but reading the comments (suggest you do, they clear things up) he emphatically said it was not the case, that he just stood in a different way.
Fully agree on his using the (passive) volume pot all the time, it's "within acceptable rules", also switching from a full-on pickup to a quite padded one .... obviously with a "real" (10%) Log pot which means 20dB down when set on "5", a *huge* variation.
The basic way to get such "guitar only" control on sound, no pedals involved, is to set the amp so it clips playing loud but cleans when picking light , with volume set on 5.
Setting the volume on 10 or switching pickups means a 20dB boost.
He also gets real close to the speakers, on the edge of feedback.
So close in fact, that moving 1 foot either way means getting in/out of feedback.
He also shows "bowing the strings across the frets" when note starts to decay ... which by the way adds tasty expressive vibrato.
I have seen people with this kind of control using a humble Twin Reverb/Super Reverb, etc.
I'm also sure he has a (small) treble compensation cap added to his volume pot, so when clean (on 5) he also gets bright and jangly, instead of dull.

None of the above is understood by a kid (or an adult) with a Dual Rectifier or a Metal Zone, the exact opposites.
Oh well.
As I said, he got incredible "body" control , definitely after long years of experimenting.

[Alan0354]

Basically yes. But remember it's Musician's lingo, not Tech Speak.
And unrelated to what we were discussing earlier.
A goor example of incredible touch sensitivity:

Beware that I attribute most of it to amazing "hand" technique and to this Musician knowing *very* well his tools (guitar and amp).

That sounds pretty good. That's how we old timer did a lot, you need to crank the amp up and back off the guitar volume. You usually cannot do it in the cascade gain amp as they have so many stages and caps to ground to drown out all the goodies. Again Mesa come to mind that is exactly opposite to touch sensitive.

[Alan0354]

So, higher "input sensitivity" means a shorter grid base, less input signal before clipping?

The Glen Kuykendall video was rather good. I'm sure I saw him using the volume controls and even stepping on a distortion pedal, so it's not as if he's achieving that whole dynamic range with "touch".

What is grid base? Sorry for the ignorance.

[Alan0354]

I still don't get what is grid base? Is it a resistor or what? I take that it's a circuit like Gird Stop is a resistor in series with the grid.

[Steve Conner]

I think it refers to a measurement taken from the tube curves. The change in grid voltage between cutoff of plate current, and onset of grid current. I'm not sure though, it is not a widely used term. I think I only ever saw it mentioned once in a WW2-era British textbook. Help? Merlin?

[J M Fahey]

I humbly ask everybody who writes something technical to try to use the standard meaning of tech words, because newcomers don't know better and start repeating them or quoting each other.
Sometimes I get questions and really don't understand what they are talking about.

[Merlinb]

I still don't get what is grid base?

The grid base is equal to the cut-off voltage of the valve (at a given anode voltage).

For example, an ECC83/12AX7, with 200V on the anode, requires a grid voltage of about -3V to put it into cut-off. We would say that its grid base is 3V.
At the same anode voltage, an ECC82/12AU7 needs about -16V. We would say that its grid base is 16V.

The ECC82 therefore has a 'longer grid base' than the ECC83 (although I always think it should be a 'wider grid base'!)

The grid base is therefore also equal to the maximum peak-to-peak input signal you could apply without clipping. So the bigger the grid base, the bigger the signal you could shove in, or in other words more headroom.

The term is more common than you think. Although some textbooks don't use it at all, it is common in many others, British and otherwise. You'll probably start seeing it everywhere now you've heard about it!

It comes from the mutual characteristic graph, since it refers to the 'base' of the triangle formed by each curve. In the example below you can see the grid base for Va = 50V is about 3.5V: