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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Mu stage driver

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#41
Hello Koonw,
Thanks for your replies.
I tested 4 tubes and the story is the same for all.
My kitchen lab,i use a little switching power supply :
XlYXj.jpg
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#42
I Found where the mistake was:
The screen wasn't at the good potential.It was wired at the ground instead of the O v pentode.So for the pentode screen voltage wasn't 100v.
Now current value is 5ma.You showed me the way! Thanks!
 
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#47
An other trouble:distortion:
At 500hz it's ok (see picture)
At 1000hz little spikes have apared on the curve.
At 10000hz it's very ugly .
I think it's my ceramic capacitor 10nf
I calculated it with the effective Rcf(7,83 MΩ that i calculated and capacitor value should be 4,7nf for 4hz)
Is it wrong ?
Or should i calculate it with 470kΩ?
Both resistors are parallel...
An other question :The gain :
Input :0,1v for 1 division =0,2v
Output :10v for 1division=40v
Where is the mistake ?
QbVRl.jpg
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#48
It appears that you are connecting the signals directly to the scope's channel inputs.

1. If your generator has a 50 Ohm output, terminate it with 50 Ohms (A 47 Ohm resistor will get you close).
If your generator has a 600 Ohm output, terminate it with 600 Ohms (A 620 Ohm resistor will get you close).
Without any termination, you are driving the generator into 470K Ohms, essentially no load, the generator output will be 2X the generator's voltage setting.

2. Make sure the scope channels 1 and 2, are both set to Probe = 1X
 
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#49
I think the screen resistor is too low as it draws too much current that causes the distortion, use Rs of 10K is better. Or increase the bias of top pentode should help.
 

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  • 6f12p Mu stage 5mA-2.png
    6f12p Mu stage 5mA-2.png
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#50
The coupling capacitor in upper tube should be reduced as you already pointed out as effective Rp is greater now. Still think you need to bypass the screen to cathode with a capacitor.
 
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#53
RC constant for Tp1/Tp2 (0.0001µ/1000Meg) has very little loading on signal and frequency response down to 10Hz, is ideal for measuring the tinny difference of gyrator. But there is no coupling capacitor here. The gyrator has 164M effective Rp, more than 10 times the pentode for bottom triode.
 

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  • 6f12p-t hybr mustage 5mA.png
    6f12p-t hybr mustage 5mA.png
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#54
Hello , thanks for this post.
The interest of using the mu follower with 6f12p is there is a pentode and a triode in the same tube with very good characteristics.
I have a project with gyrator builded with an irf710 MOSFET and a DHT tube.
I want to learn LT Spice. I eard that there is a freeware version,right? Where should i start? Please.
 
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#58
Koonw said:
RC constant for Tp1/Tp2 (0.0001µ/1000Meg) has very little loading on signal and frequency response down to 10Hz, is ideal for measuring the tinny difference of gyrator. But there is no coupling capacitor here. The gyrator has 164M effective Rp, more than 10 times the pentode for bottom triode.
Click to expand...


Correction: Load should taken out on source top of 300 Ohms. Effective remeasured Rp is (?), sorry about that.
 
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