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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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5th Dec 2013, 11:48 am | #1 |
Retired Dormant Member
Join Date: Dec 2012
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Mullard EF86 valve data sheet
I have been playing around with load lines, g1 bias points, effect of g2. Done some other reading re the g2 bypass cap and got very confused. The earthy end of the g2 cap can be connected to cathode or 0V. Gain reduction if not bypassed. Some where ultra linear was mentioned.
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5th Dec 2013, 11:55 am | #2 |
Hexode
Join Date: Apr 2008
Location: Ramsgate, Kent, UK.
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Re: ef86 mullard valve data sheet
Not quite sure what you are asking but if you are looking for a data sheet on the EF86 that contains characteristic curves then one can be found here:
http://frank.pocnet.net/sheets/030/e/EF86.pdf Adrian. |
5th Dec 2013, 12:00 pm | #3 |
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Re: ef86 mullard valve data sheet
Some circuits using the EF86 (e.g. Mullard 5-10,5-20) inject negative feedback at the cathode. This means that the cathode is not grounded. It creates a choice about where g2 should be decoupled to: cathode or ground. For full pentode operation it should be cathode.
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8th Dec 2013, 12:38 pm | #4 |
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Re: ef86 mullard valve data sheet
I've seen a circuit can't remember where g2 bypass C was connected to cathode RC. Wondered why? The AC signal at g2 would flow through g2 C and cathode bypass C's. A easy place to connect earthy end of g2 bypass C.
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8th Dec 2013, 3:13 pm | #5 |
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Re: Mullard EF86 valve data sheet
I do not think you are correct. The valve varies its current which is taken from the cathode so the best place to bypass g2 is staight back to the cathode, making the loop as small as possible. There is then no part of the g2 current going through the cathode bypass capacitor or the chassis.
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8th Dec 2013, 3:44 pm | #6 |
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Re: Mullard EF86 valve data sheet
The purpose of g2 is as a screen to spoil the Miller capacitance feedback path from anode to grid, allowing greater stage gain. In a pentode, this screening effect is shared by g2 and g3.
So we can expect the g2/g3 decoupling point to have to carry some current, which came capacitively from the anode. This is easy if the valve is being used as a simple amplifier. The issue gets more interesting if the cathode is not completely decoupled, and more interesting still if the cathode is a point where a negative feedback signal is applied. We then need to start viewing the valve stage as having a differential input and a differential output. They won't be balanced, of course. There isn't a single right answer to this issue. The decoupler should 'ground' to wherever the designer accounted for in his calculations. David
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21st Dec 2013, 2:53 pm | #7 |
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Re: Mullard EF86 valve data sheet
Many thanks to all. Should have replied with thanks a wile ago. Life has been a bit difficult recently. I am grieving for the passing of a love one .
Next move do some reading. To get some sort of idea. Looked at 5-10 input stage as suggested. g2c to cathode, cathode R fully bypassed & NFB. know wonder I was confused thanks all |
22nd Dec 2013, 3:18 pm | #8 |
Dekatron
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Re: Mullard EF86 valve data sheet
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