12E1 in fixed bias - too much current!

[tjl]

12El tube can use 500vp , at pp mode, but screen grid is better use less than 200v , grid voltage -28 to -30v for normal operation, the screen grid is quite sensitive with higher voltage will causing a lot of plate current .

 

[MagicBus]

Hi MagicBus,
Better to be on the plate caps. A careful layout design helps to prevent parasitic oscillation as well.

Hi JohnTubeamp,
If you understand greek, you are "από μηχανής θεός" ! Anyway, you just helped me to troubleshoot an oscillation in my current project.
Many thanks!

 

[JohnTubeamp]

ΜagicBus, ναι καταλαβαινω και Ελληνικα, Ελληνοκυπριος ειμαι ))
Let`s return to English since not everyone here speaks Greek. I`m glad you solved the problem. What did you do to stop the oscillations? Just adding those plate resistors or something more than that?

 

[MagicBus]

First of all I'm not building something with 12E1. It's about this amp : Poor Man's TABOR. I had very little time today so I just tried 10 ohm plate stoppers and not even close to the cap but it works already. I"ll do better and update soon. Again, thank you.

 

[SM468]

Fixed bias 12E1 in my SE amp. Plate voltage at 450VDC, and the Screen Grids at 250V. Performance at 350V on the plate was nice but not impressive, anemic at low frequencies. While adjusting the negative bias voltage I did noticed the plate voltage sagging, especially under 5U4 rectifier setup. Once I changed to diode rectifiers, the plate voltage is not affected by varying the bias voltage. The 12E1 will glow red if the Screen Grids exceeds the maximum 300V specification. Variation of tubes may allow up to 340V but eventually you will see the glow as I have. So check the screen voltage (pin4) and the negative bias level if the tube is glowing red.

12E1 is not compatible with 6L6, El34, KT88 amplifiers when the operating plate voltage is above 300V without modifications.

 

[6A3sUMMER]

12E1 ABS’s data sheet:
10.08W filament
Plate 35 Watts
Screen 5 Watts
You might not want to stuff all 50.08 Watts in the glass envelope.
Curves 1 shows up to 300V screen, but it is based on 12us pulse, 1/400 duty cycle (4.8ms).
Curves 2 shows 150V screen, but it is based on 12us pulse, 1/400 duty cycle (4.8ms).

12E1 Mazda’s data sheet:
10.08W filament
Plate 35 Watts
Screen 5 Watts
You might not want to stuff all 50.08 Watts in the glass envelope.
Curves 1 shows up to 200V screen.
Curves 2 shows 150V screen.

Both the ABS and Mazda data sheets show maximum 400V difference between G1 and G2.
If you have -100V G1 bias, and +300V screen, you can not apply any signal swing to G1.

Just a few things to look at for the amp design, go for tube life, not for power.
Want more power, find another tube?

 

[Aladding]

Why not try ultralinear connection? The challenging part of this topology is that you have to let the screen work under overrated voltage, just as you use 807s in ultralinear mode for arond 30 watts output.

 

[artosalo]

Tested. Works very well.

 

[flint45]

Hi MagicBus a bleeder resistor from screen to ground may also help, it should prevent runaway