Bopwer bubbly bositive and sovtek tubes!

Why B+?

Battery positive? Buggy plus? Power Bubbply plus? Bobber Bubby positive?
Why does not the simply V+ be sufficent? Or P+, or PS+ !? :?
Or shall i say "what" B+?!

Next:
A typical classic compressor vari mu swings between 240V and 45V
at anode, (plate), this indicates highly non linear behaviour at the
lower voltage range. (easy, steady now folks, im still building my
first vari mu compressor) depends on the B+ applied offcourse,
or what B+ offcourse.

This indicates that the current passing trough the tube also changes,
how does this fit with the idea of having a "constant" catode current?

Next:
Tubes was made by many manufacturers im looking for datasheets for
the sovtek (new sensor) 12AX7LPS and the 6SL7GT, i do have several
datasheets for these but they differ a bit depending on manufacturer,
so what would be resonable realible figures for these tubes?.

old tube circuits used two DC power suplies and a AC power supply for the heaters. So, A+ was the grid bias, and the B+ was the actual B+ we use today, the high voltage for the plates...

According to Langford-Smith 4th Ed. the A-battery supplied the filaments, the B-battery the plate and screen circuits, and the C-battery the grid bias.

> Why B+?

A 1920 radio needed three batteries. To avoid user confusion, they were called A, B and C.

> A typical classic compressor vari mu swings between 240V and 45V at anode, (plate), this indicates highly non linear behaviour at the lower voltage range..... This indicates that the current passing trough the tube also changes, how does this fit with the idea of having a "constant" catode current?

What constant current? There is no constant current source in a classic vari-"Mu" limiter.

For fixed load impedance, a tube's gain varies with current. In most amplifiers we don't want that, so we bias them to flow the same current all the time. The signal is represented as a variation of durrent: we need to keep the variation much smaller than the bias current so the wave gets the same gain on positive and negative peaks. If we want to change gain, we do it with linear accurate resistors, not by messing with the tube.

In a limiter we need gain control action much faster than you can switch resistors. We use the "flaw" of tube amplifiers: gain is a function of current. This works really well because we can change current very fast with very little control power.

> im looking for datasheets for the sovtek (new sensor) 12AX7LPS and the 6SL7GT, i do have several datasheets for these but they differ a bit depending on manufacturer

All tube datasheets are bogus. The curves are usually quite wrong at lower currents. The numeric data looks precise but if you fine the military specs you will find that most parameters vary 30% from tube to tube. Datasheets help you find a tube that might work, and parts-values that will get you in the ballpark. Then you have to build and test it, discover what really happens. Then you have to get a crate of 1,000 tubes and see how many don't work right, and if a parts change will make more of them work right. Then you can go into production.

[quote author="PRR"]> Why B+?

A 1920 radio needed three batteries. To avoid user confusion, they were called A, B and C.

Thanks to all for the explenation of B+.

What constant current? There is no constant current source in a classic vari-"Mu" limiter.

I have been miss ledd by a tube paper! It mixed a pre amp
with a vari mu!

For fixed load impedance, a tube's gain varies with current. In most amplifiers we don't want that, so we bias them to flow the same current all the time. The signal is represented as a variation of durrent: we need to keep the variation much smaller than the bias current so the wave gets the same gain on positive and negative peaks. If we want to change gain, we do it with linear accurate resistors, not by messing with the tube.

In a limiter we need gain control action much faster than you can switch resistors. We use the "flaw" of tube amplifiers: gain is a function of current. This works really well because we can change current very fast with very little control power.

have to build and test it, discover what really happens. Then you have to get a crate of 1,000 tubes and see how many don't work right, and if a parts change will make more of them work right. Then you can go into production.[/quote]

How boring, but i suspected it to be bad however i have gotten reports of nice matching between tubes of the Sovtek 12AX7LPS series, but i have no idea what LPS stands for. A manufacturer who usually match 12AX7
have switched to LPS and dont have to match any more. I dont know anything more than that about the issue.