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Old 24th June 2008, 10:47 PM   #51
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and (3-6):

Probably could find sorta related info in other books under "plate modulation".

Unfortunately, they don't give any references.

Couldn't find anything by that name in the RDH4.

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Old 24th June 2008, 11:25 PM   #52
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Thanks, Don. I can't get my scanner to work with my laptop (no Vista drivers) and I was trying to improvise something... Yes, that's the right figure.
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Old 25th June 2008, 12:00 AM   #53
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"Thanks"

Happy to help.


I've been looking thru the dual control tubes to see if anything is suitable for a single tube Mu=1 inverter. 6BU8 had the lowest gm3 of the bunch at 180 uMhos. But this is still likely an order of magnitude greater than 1/Rp, so not suitable for Mu=1.

Next idea would be to use two grids as plate and a grid in-between for control or visa-versa, but this is not looking workable either. The sequence of grids to plate generally have about an order of magnitude fall off in gm with each step out from the cathode, so cannot average two together to equal another.

Final idea would be to use a normal suppressor type pentode with a separately connected g3 terminal for control. (The dual control tubes have densely wound g3 grids, the normal pentode suppressor grids are quite sparse in contrast) Like EF86, but something with lower Rp maybe. Rp is a little misleading though, since a dense g2 grid could make both gm3 and 1/Rp small values. Its the ratio of gm3 to 1/Rp that matters for Mu=1. I would forget about inverted (neg. plate) operation since it lowers plate influence further. Just use low voltage g3 drive with positive plate output.

A desparate last resort for single tube Mu=1 might be to use a lowish Mu triode operated at very low current. Most triode Mu curves drop off badly at low currents. This would likely be noisy and rather non-linear though.

Don
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Old 25th June 2008, 06:48 AM   #54
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Default Electronic Designer's Handbook by Landee, Davis and Albrecht

Quote:
Originally #50 posted by smoking-amp
I looked in my Electronic Designer's Handbook by Landee, Davis and Albrecht and found this for "plate-driven tube" on pages 3-6 and 3-7:
Hello Don,
YEEP, thank you very much, this is excellent!
Can I use this attachment in my blog?
I am sure this will help understanding the coupling triode
(i.e. fourth circuit topology).


Kind regards,
Darius
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Old 25th June 2008, 02:46 PM   #55
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Hi Darius, "Can I use this attachment in my blog?"

Fine by me, I see the book was published in 1957, so is most likely out of copyright by now. I think Pete Millett's site has some link for checking on copyright status if you want to be certain.

One more thought on a single tube Mu=1 solution:
Lowering the filament voltage of a low Mu tube should decrease the space charge around the cathode, lowering Gm1 more than 1/Rp. So should reduce the Mu. You'll have to lower the operating current to stay within the reduced cathode sourcing ability. This should also improve the linearity of the tube some since "island effect" or "inselbildung" will be reduced as well.

Don
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Old 25th June 2008, 03:36 PM   #56
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Mu reduced in flament starved DHT? I would not be too sure about that...

Quoted from link above:
"The "data sheet" values for this tube are rp=10k, gm=0.8mS, mu=8. Reading the values from the above tube curves, near the datasheet operating point, I get rp=8.8k, gm=0.95mS, mu=7.5. Reading the values for the starved filament condition, again near the same operating point, the values are rp=13.5k, gm=0.63mS, mu=8.5. In a real circuit, there is a measureable increase in circuit gain as the filament voltage is lowered, consistent with the tube curves. The big difference, however is still the wide range over which the tube parameters are essentially constant. "
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Old 25th June 2008, 03:56 PM   #57
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I just noticed the same. Seems the Rp went up more than the gm1 went down. Well, try higher filament voltage then (use a cheap one).

How about putting a stack of donut magnets over the tube (for a cylindically symmetric design) to curve the electron pathes in spirals. No idea what that will do to the Mu.

Don
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Old 25th June 2008, 05:02 PM   #58
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Hello Don,

Quote:
Originally #55 posted by smoking-amp
Hi Darius, "Can I use this attachment in my blog?"

Fine by me, I see the book was published in 1957, so is most likely out of copyright by now. I think Pete Millett's site has some link for checking on copyright status if you want to be certain.
...
Don
ok, I made a link to this thread so far.

I am going to start a new blog hatetepe://line-pre.blogspot.com/ for the pre.
When it is finished (schematics) I open a new thread for discussion in the preamp.

Kind regards,
Darius
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Old 7th July 2008, 07:49 AM   #59
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Default Unity triode as phase inverter blog

Hello,
I just finished the blog for the phase inverter.
link

I took some photos of the triode section of the ECLL800.
Note the construction of the grid.

Scrolling down, you'll find the schematic for the pre,
this will be moved to the following blog.
CC

Kind regards,
Darius
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Old 8th July 2008, 11:23 PM   #60
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Default Re: Unity triode as phase inverter blog

Quote:
Originally posted by oldeurope
I just finished the blog for the phase inverter.
link
What are the main differences between the "gyrator" stage in your drawing and an ordinary mu-follower?

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