What construction flaw factor causes a Western Electric "B" grade 300B tube?

[grataku]

The question is WHY would WE attempt to go for volume instead of brand integrity. The idea is to recreate perfection, not to improve on it.

 

[Windcrest77]

Someone needs to do a curve trace of one of these "high" current tubes to see what you are getting. If the grid or filament are off center, then one would expect to see "roll-over" or flattening of the curves at the HV end, giving high 2nd Harmonic.

I'm planning on doing that. But I have to learn how to adjust the parameters in the eTracer, if I have to at all? Do you think I can just choose the file for a 300B and trace it like a normal 300B? I would think I should tell it to run through a wider range of bias values, of course leaving the plate V values the same. Maybe I'm over thinking it and I should just trace it using the parameters of a normal 300B, then decide if I want some curves outside the normal ones added.

 

[grovergardner]

I might give these B-stocks a try in my Elekit TU-8600R 300B SET, which runs 360V plate voltage.
Is there any reason to buy the Hi-IB over the cheaper Low-IB B-stock tubes for the Ekekit, which has the "new active automatic bias"?

"Unlike traditional cathode bias, where a resistor and capacitor are placed at the cathode to set the bias voltage, the TU-8600R employs a separate, dedicated bias power supply and an active circuit. This circuit senses the plate current (with the current detection moved from the cathode side to the B+ power supply side for improved sound quality) and actively controls the grid voltage to maintain optimal bias."

You should check with Viktor. I know he advised against using Sophia 300Bs in the 8600. And with good reason. A friend of mine kept trying to use them in his 8600 and broke it--twice.

 

[drjlo]

Was he trying to use Sophia 300B 2.5V version in the Elekit 300B amp? Regular Sophia 300B tube should present no compatibility issues..

 

[grovergardner]

No, it was the 5V version. It drew too much current, either for the filament regulator or the autobias, I wasn't clear which. Either way, they did indeed blow the board, twice.

 

[Windcrest77]

I might give these B-stocks a try in my Elekit TU-8600R 300B SET, which runs 360V plate voltage.
Is there any reason to buy the Hi-IB over the cheaper Low-IB B-stock tubes for the Ekekit, which has the "new active automatic bias"?

"Unlike traditional cathode bias, where a resistor and capacitor are placed at the cathode to set the bias voltage, the TU-8600R employs a separate, dedicated bias power supply and an active circuit. This circuit senses the plate current (with the current detection moved from the cathode side to the B+ power supply side for improved sound quality) and actively controls the grid voltage to maintain optimal bias."

If that amp automatically adjusts it's bias using normal tubes it may not have enough "range" to auto-bias these back to the set bias. It may "keep trying" but never reach the set point because the designer never expected someone to plug in a tube like this, its range of auto adjust may only be +/- 5% or so. With a direct bias amp where you control the bias fully is probably the main candidate for these tubes I would think.

 

[Windcrest77]

Here is the direct-bias project schematic I'm designing for why I bought these tubes in the first place, if anyone is interested: I'm going to keep this schematic revising on post #1 as I move along. Next week I hope to get the time to post curves.

https://www.diyaudio.com/community/threads/ambitious-direct-bias-pse-300b-with-dual-psus.427124/