My limited goals are to look again at the anode and cathode values that we changed in the driver bias mod. Maxx chose one set of values and Sonic chose another.
I see.
Because B+ is so low, none of the load lines are not so good. Luckily the swing needed is not that big. Always good to practise drawing load lines.
A gyrator load would allow for a flat load line, combined with CCS tail at desired anode current, even at 150V B+. Not sure about stability inside a gNFB loop, also probably wouldn't fit inside the chassis.
Re: CCS mod I will be following Sonic's design for the CCS closely because we have both made similar mods with similar values
Good idea.
Sorry, just preliminary attempts to elicit very general comment as to plate current values etc which I'm not sure about.
I would shoot for 1 to 1.3 mA of Ia in your scenario. Enough to get the tube really conducting, and to offer at least some drive to the following coupling cap.
I didn't know about the specific phraseology "ultralinear"
Here's a schematic:
So g2 (screen grid) is not connected to a DC supply (pentode mode), it's not connected to the anode (triode mode), but rather somewhere inbetween. UL requires a special tap on the OT primary, usually at 17% of the primary turns.
Curves are somewhere between triode and pentode (or beam tetrode) mode. Compare the different mode curves:
http://www.audiomatica.com/tubes/6l6.htm
17% was more or less arbitrarily chosen as a nice point, there have been also different tap arrangements. The closer you move the tap to the anode side, the more the curves resemble triode mode, and the closer you move it to B+, the more the curves resemble pentode or beam tetrode mode.
In technical terms you are introducing a local feedback loop that has part of the primary in it. The point of this was to achieve some better THD performance of the triode mode while retaining some of the higher power output of the pentode mode.
It's still used in some bass guitar amplifiers and retro type PA amplifiers, but I wouldn't recommend UL for serious best results HIFI use. It still has lots of pentode mode odd harmonics present. (Adds 'bite' to bass guitar sound.)
I was not absolutely sure that same tubes by different manufacturers were identical in every respect.
Not in every respect, but for voltage and current purposes and load line purposes, yes, they are identical.
Or, as identical as any tubes of the same type, within one manufacturer. Remember these curves say AVERAGE for a reason. They were made as composites, typically taking readings from a hundred different tubes.
If the type was meant for home use, they might include tubes with +-20% specs in that average. If it was special quality for industry or military, maybe only +-10%.
There is bound to be great variance in anode resistance and sometimes even µ (though that is a bad sign for quality) among any tubes, within or between manufacturers.
Modern people think with modern standards. These were not the standards when tubes were developed and mass manufactured.
The reason tube rolling works in some circuits, is just that; there is a lot of variance. If the circuit is "balanced on a tipping point", small variance one way or another can change the behavior of the circuit. Smart design avoids this.
Anode resistance is the big one usually, it affects distortion behavior, but different capacitances can affect 'tone'. If your circuit can deal with the capacitances, all tubes "sound the same".
He should know your still learning.
Yes I know. The way you learn is that somebody points out the correct information when you use terms incorrectly. Leaving somebody in a state of mistake is not a favor to that person.
Don't thank him for being a crab.
My posts are written more or less like an engineer. Aside from clear joking, any emotional tone you infer is your own projection.
Do not use such language in the future to refer to me or my writing.
