Some help? Rectifier:power tube relationship vs. Bias

[Mango Moon]

I think the breakdown in communication here is that I am focusing on your earlier assertion that =C= tubes might be hotter than your Grooves, and you are more concerned with if you turn up the current will the tube break up sooner. Is that fair? I feel like we are somehow speaking to crossed purposes. If i am confusing the issues I am sorry.

Enzo,

Thanks again for your responses, and nope, there's no real fault of your own here whatsoever. Rather I think it was me that muddied things a bit by contrasting or even mentioning the two different makes (or specs) of tube (i.e., =C= vs. Groove). All I was really trying to get at was, once a given (specific) make and model of replacement tube is chosen (SED =C=), isn't it plausible to pre-select a 'late' breakup pair (as opposed to 'early' breakup), based on the vendor's preliminary published bench test results, assuming that the testing device and test parameters he used were the same for both sets?

THAT was the 'just' of my question and I think its since been answered. Now, why or how my questions seem to evolve into such laborious journeys as this one has, I'm not quite sure (I think its just the nature of the internet and the electronic interface as opposed to open conversation amongst friends), but it must also have something to do with my own poor choice of words or the indirect way in which I articulate the question(s), and I take complete responsibility for the latter.

Anyway, the question does indeed appear to have been answered, and thus, I (we) can all now move-on.

Many thanks Enzo! Many thanks All!

[Mango Moon]

Changing out the rectifier tube for a 5AR4 probably raised all of the voltages in the amp a little. That would include the screen voltage of the power tubes, and screen voltage affects idle current just the same as bias does.

Steve,

Thanx to you also for your expressed views and feedback here, but please note, I never changed the rectifier. All tube evaluations conducted and all questions posed of the membership (per above) related to an amplifier with the very same (Ruby) 5AR4 rectifier installed at all times.

[Mango Moon]

Changing out the rectifier tube for a 5AR4 probably raised all of the voltages in the amp a little. That would include the screen voltage of the power tubes, and screen voltage affects idle current just the same as bias does.

Steve,

Thanks to you also for your views and feedback here. I'm grateful. Also, please note that I never changed the rectifier. All tube evaluations that were conducted and all questions posed of the greater membership here relative to same were conducted with the very same (Ruby 5AR4) rectifier in-place. So that wasn't a factor in the equation.

[Steve Conner]

Oh, sorry, I just read

For grins, I swapped-out the Ruby 5AR4 rectifier

and somehow I got the idea that you swapped out the rectifier.

Either way, all of my other points (which are basically what Enzo said too ) still hold. There is lots of manufacturing variation between tubes, and the different tube vendors' grading systems don't compare with each other.

[Mango Moon]

Yes Steve, understood. Thanks again.

[booj]

From Enzo -

OK, within a given make of tube, the hotter ones - the ones with naturally higher currents - will be easier to break up.

I'm thinking opposite. Lets say you set your bias up for a #5 tube. You stick a "hotter" #10 tube in its place. It will draw more current. So how do you re-set the bias to run the #10 tube? You increase the amount of negative voltage to the grid. You also increase the window in which the grid signal operates, effectively reducing the amount of breakup for the same amount of input signal.
Putting a #1 tube in place of the #5 would create a lower current flow. The bias would have to be adjusted for less negative voltage, which would decrease the window the signal voltage has to operate in, meaning earlier breakup.
just my .02 worth