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2359glenn | studio
Nov 15, 2018 at 6:22 PM Post #23,356 of 39,986
Question for Glenn...

Why is it desireable to tie the cathode and grid3 together, in a C3g?

image.jpeg P
 
Nov 15, 2018 at 6:26 PM Post #23,357 of 39,986
Also, for @UntilThen -

After tubes had been in for 20 mins....I heard what you reported with FDD20, the "sharp" upper mids/lower treble.
Had in FDD20/6BX7/6AS7...

Removed 6BX7 a no more sharpness from FDD20/6AS7...

Also more gain, so looks like FDD20 Is not a perfect match for 6BX7...


:)
 
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Nov 15, 2018 at 6:58 PM Post #23,360 of 39,986
JazzVinyl said:
Yes, not quite the same...looks like grid3 and grid2 are swapped and grid3 is not tied to cathode as in C3g...

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Click to expand...

Yes grid 3 is tied to the cathode.
In the pentode valve / vacuum tube, the suppressor grid is generally maintained at a low voltage, often connected directly to the cathode. Its function is to create a lower voltage region between the screen grid and the anode. It suppresses the secondary emission where high energy electrons hitting the anode at high speed have a tendency to bounce off. This effect causes a kink in the response curve of tetrode valves. In this way it enables the pentode to provide a high amplification factor along with the ability to operate at high frequencies.
 
Nov 15, 2018 at 7:05 PM Post #23,361 of 39,986
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Nov 15, 2018 at 8:06 PM Post #23,363 of 39,986
2359glenn said:
Yes grid 3 is tied to the cathode.
In the pentode valve / vacuum tube, the suppressor grid is generally maintained at a low voltage, often connected directly to the cathode. Its function is to create a lower voltage region between the screen grid and the anode. It suppresses the secondary emission where high energy electrons hitting the anode at high speed have a tendency to bounce off. This effect causes a kink in the response curve of tetrode valves. In this way it enables the pentode to provide a high amplification factor along with the ability to operate at high frequencies.
Click to expand...

Very nicely explained! Thank you.
 
Nov 15, 2018 at 8:30 PM Post #23,364 of 39,986
Nov 15, 2018 at 8:32 PM Post #23,365 of 39,986
2359glenn said:
The EL11s should sound better in the C3g socket as long as she wired them straight through as a pentode.
And they are not triode wired like in a FA amp. Looking at the circuit board I see trace jumping a couple of pins maybe I am seeing something that isn't there.
Click to expand...

Yup I wrote to confirm and they understood what is required.
 
Nov 15, 2018 at 9:26 PM Post #23,368 of 39,986
 
Nov 15, 2018 at 9:27 PM Post #23,369 of 39,986
And while we are on the topic of pentodes and mesh plates, what about this beautiful 1952 National Union JAN tube 6SG7GT?
s-l1600.jpg

Looks beautiful and $4.50 each.
But I think that both of these mesh plates are just stamped mesh and not true metal wire mesh - don't know, but some people say that real mesh sounds better (don't know if that is true either).
 
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