Different Pentode Connections

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Paul Barker
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#1 Different Pentode Connections

Post by Paul Barker »

F.E. Terman (1937) Radio Engineering 2nd Ed. pgs 148-149 McGraw Hill, New York and London.

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Mike H
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#2

Post by Mike H »

Very interesting!

I presume the high-mu variation (fig. 2) comes about because the total area of the two combined grids is larger, or more wires, or the gaps are smaller, whatever. :?:

I remember reading that although the optimum grid position & configuration for a particular mu might be calculated, it's still only up to a point, the remainder being by "try it and see" :D

Generally, higher mu requires being closer to cathode and more turns of wire, or something like that.
 
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Paul Barker
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#3

Post by Paul Barker »

The screen grid is further from cathode which I believe makes it higher mu. connection 4 interests me, at least the cathode part of it. But the other text whiuch gave more explanation about the space charge operation did mention a catch, which I have forgoten the details of. It may be available power is markedly reduced.

The inverted operation is really not worth discussing in the normal sense as there is less gain than a cathode follower.

steve Bench found the best use of it as an SE OTL amp but due to the very low power output it requires multiple valves and seems a lot of trouble to go to. but when used inverted valves are much more linear. Just must less powerful aswell. Oh and very low output impedance.

One day I may build an inverted 6080 amp with loads of valves.

In Beam Tetrodes the better triode connection option 1 of connecting suppressor to anode with screen is not aavailable.

In theory EL34 and 813 should make better triodes, but probably only the original ones not the modern production. The success or quality of an EL34 was in perfect alignment of the suppressor. The Beam Tetrode has no such issues so is easier and cheaper to make. Recent manufacturers probably don't take the trouble to align the suppressor exactly the way the original manufacturers did, when they knew the art as originators of it.

As you can see from this text in 1937 they knew a lot more than is common knowledge in the valve community today. Only Steve Bench brought these issues to our attention. But the majority I can quickly tell don't study Steve's pages, or else they wouldn't be so dumb.
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Paul Barker
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#4

Post by Paul Barker »

the manufacturers data for the 46 explains it best, and as a picture paints a thousand words, those in the know will see the stark difference in mu when g2 is incorporated with g1 as a control grid, and the entirely different curves. Whereas triode connected with g2 anode connected it looks like a normal triode.

the 46 may make an interesting candidate for space grid connection of g1 control g2.

These two images also show Phil's problem. His valve is probably like the 46 designed for class B push pull operation, so he has had to bias it grid positive to get anything out of it at all. Whereas when he connected it as a triode his curves would have more aproximated the 46's triode curves and so positive bias no longer pertinent.

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What Phil should really be doing with his valve is using it in push pull, one half of same valve pushing other half pulling.
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pre65
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#5

Post by pre65 »

I already have the 832a double tetrode push pull amp, my first amp build as it happens.

That was built nearly six years ago.

My how time flies. :)
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#6

Post by steve s »

if anyone wants the terman book i have a spare..

must be worth a the price of a beer at the next meet..
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andrew Ivimey
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#7

Post by andrew Ivimey »

Yes please Steve. But can you give it to Philip who can pass it on to me as I can't make it to Owsterberg.
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