Triodes Pentodes and Irishmen WARNING LONG READ

[TheRecordFable]

I found this in my F-50 manual and thought it was a fun read...

 

ON TRIODES, PENTODES & IRISHMEN:

With apologies to Friends and Relatives from the Emerald Isle - who will make their appearance soon enough - the humor which

follows is dedicated to the memories of Spec McAuliff and Fae (Rafael) McNally, two of the True Greats.

As their numerical references suggest, the terms Diode, Triode and Pentode indicate the number of elements within the vacuum tube

i.e. two, three or five. All tubes also require a filament or heater which is not included in the count. Its purpose is to excite electrons

from the cathode coating by raising the temperature such that they are able to boil out of the electron-rich coating material and form

a cloud of free electrons in the vacuum space surrounding the cathode.

Although the term filament and heater are often used interchangeably, there are specific differences: A filament is a directly heated

cathode where cathode coating is applied directly to the heating element. Examples are 5U4 twin diode rectifier and 300B triode

amplifier tubes.

A heater, on the other hand, is a heating element which is separate from the cathode and is usually inserted within the tubular cathode

sleeve. Examples are 12AX7 twin triode amplifier and 6V6 or EL84 beam power pentode tubes. In all cases this fundamental aspect

of each tube\’d5s construction is clearly visible, especially when the heating element is glowing red hot.

The cathode, then, would be considered the first numbered element because it is the source of the electrons. The word itself is from

the Greek literally meaning completely down, which implies a sense of central origin - like the center of the earth where Tone begins.

It might be said that an ecstatic audiophile experiences a positive catharsis, his soul being purified when his system transports him to

Audio Nirvana. The only trouble with taking this positive imagery too far is that the cathode is, unfortunately, negative... at least

electrically speaking. However this is easily remembered since virtually all musicians and audiophiles have also experienced the

more common negative catharsis when they emerge from the emotional rebirth kicking and screaming in rage and frustration.

Once heated, the intrinsically negative electrons are energetic little fellows of almost no mass. Thus they may be accelerated almost

instantaneously and will travel through a vacuum a nearly the speed of light. Being of like, negative charge, they tend to repel one

another and thus within the electron cloud surrounding the cathode, there is much jostling and elbowing as each one tries to maintain

his distance from all the others... unless there is a strong and universal attraction from an outside influence.

Visualize, if you will, a group of sub-atomic Irishmen milling about and in a repellent, negative state of mind. All are scowling and none

wants to have anything to do with the other. Now introduce a strong attraction say, a public bar, and you can easily picture an orderly,

if rapid movement of the lot in a single direction. This is what happens when a positively charged element called the anode or plate is

introduced into the vacuum.

The plate is the large metal element most prominently visible through the glass of an electron tube. It is the outermost element of a

tube’s structure and it surrounds all the others. The cathode is at the center radiating electrons outwards. As higher and higher

positive voltage is applied to the plate, the attraction for the electrons surrounding the cathode is increased and with nothing standing

in the way, full uninhibited flow to the plate occurs...sort of like removing the doors and offering free drinks to the crowd of surly

Irishmen milling around outside. As electrons flow to the plate, the space charge will continually be replenished by further ‘boiling’ of

the hot, electron-rich cathode as you can easily imagine other Irishmen impatiently taking up the places of those who’ve gone inside

- until the entire village is deserted.

Now, where do they come from and how do they emerge? Well, a grand and elegant lady once showed me how to revive flat

champagne: She dropped a raisin into the glass. There was a dramatic and immediate increase in effervescence with the introduction

of a cathoding surface. Thousands of tiny bubbles suddenly appeared - and continued to flow from the raisin. Of course the bubbles

were made up of gas dissolved in the beverage, but the analogy makes it easy to visualize the loosely bound electrons dissolved in

the rich cathode coating as they effervesce from its heated surface.

But back to the electron flow. If the electrons are strongly attracted to a positively charged plate, then it follows that they are strongly

repelled by a negatively charged plate and they are. Thus, if an alternating current - such as comes from a transformer - is applied to

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the plate, electrons will flow only during the times when the plate is positively charged. During periods of negative plate charge,

ON TRIODES, PENTODES & IRISHMEN: (Continued) electron flow is stopped and the space charge of electrons remains compressed

in the area around the cathode.

Thus a diode tube - one with a cathode and an anode - is mostly used to rectify alternating current into direct current by passing it

without restriction, but in one direction only. This also explains why closing time is stricly enforced at Irish pubs: During normal

operation, the traffic flow is similarily unimpeded and uni-directional toward the bar and this process rectifies the work-day negativity.

It goes without saying that no one leaves as long as the atmosphere around the bar remains positively charged.

TRIODES:

This section is a continuing technical treatise on the workings of Irish Pubs but to make it easier for the layman to understand, it is

explained in terms of vacuum tube technology. Enter the original bar - free beer and no doors. Well, it turns out that some control over

the flow can be a necessary and useful advantage. This led to the invention of those swinging louvered saloon doors which are open

at the top and bottom. They are patterned after the control grid of the vacuum tube, which is a loosely wound coil of thin wire located

between the cathode and the plate.

In a Triode the plate is always positively charged with high voltage D.C. and even though the grid is blocking the path, those negative

electrons can still FEEL the strong attraction - just as the Irishmen can see in through the louvers of the bar doors. They know what

pleasures lie beyond, but to get there requires overcoming the negative influences controlling the access. This negative influence is

typically called a Bias. In electronic terms that means the grid is supplied with a voltage which is slightly MORE NEGATIVE than the

already negative electrons. The more negative the Bias, the more it tends to neutralize the attraction of the plate and repel the

electrons back toward the cathode.

The Irish can be similarily charged with Bias, but unless you are Irish yourself, this type of Biasing may be more difficult to understand.

The effect is similar though: The more negative the Bias, the more it impedes forward progress. Generally speaking though, the

electronic Bias of the grid is easiert to overcome, and for two main reasons: First, the Bias is set - like the bar doors - to allow some

passage. Second, the grid is mostly NOT THERE, like the louvered doors which are mostly open spaces. Unlike the plate which is

solid, the grid is like a coiled bed spring. It can create a repelling field but mostly it’s empty space in between widely seperated

windings of wire. It’s very easy to control the electrons as they pass through the grid’s force field: Changing the grid voltage only

slightly will have an enormous effect on how much current flows through... and that’s what AMPLIFICATION is: a small change in

voltage at the grid causing a large change in current flowing to the plate.

The purpose of the louvered bar doors is similar to that of the grid, namely, to give momentary pause while still revealing the promise

within. Hesitation mostly gives way to temptation, but there are those few stalwart Irishmen who think twice and decide to come back

later. Most just pause slightly then go on through. That is the purpose of the bar doors: to prevent everyone from crowding in all at

once - and as the door is made less of a barrier, wider spaces between the louvers, more of the bar’s attractive influence is felt outside

thus amplifying the customer flow and increasing the crowd at the bar.

PENTODES:

Occasionally though, bar doors - even the louvered type - were found to be too effective, and too many customers turned away.

Something further was needed to increase the attraction of the bar and overcome the resistance created by the door. Thus the cocktail

waitress was invented.

Once again the idea was inspired by the vacuum tube. It had been discovered in some tubes, often large power types, that the

distance to the plate was too great to attract enough electrons past the negative influence of the control grid. So another grid coil of

fine wire was inserted between the first grid and the plate. This was called the screen grid and carrying a highly positive charge, it

functioned as a bait for the plate.

In a properly designed power tube such as an EL84 or a 6V6, the windings of the screen grid are precisely aligned to fall in the shadow

of the control grid. This way the electrons responding to the pull of the screen grid are lined up in sheets as they pass between

windings of the inner control grid... only to find that they have been fooled! Once past the control grid and drawn toward the screen

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grid, they discover...there’s almost nothing there. The path they’re on has them aligned to zing straight through the spaces BETWEEN

ON TRIODES, PENTODES & IRISHMEN: (Continued) screen grid windings. So rather than a close and personal encounter, they

just fly on past - and once they’re out that far, there’s no stopping them. The influence of the plate takes over and - being solid metal

and of the highest positive attraction - it is at this final destination that the electrons congregate.

Thus the proper cocktail waitress - visible through the louvers - is scantily clad so as to be all the more effective at reinforcing the

attractive influence of her bar and by being located in between the door and the bar, she serves as bait to lure customers past the

door’s negative influence. Once through the door however, it is the rare Irishman who actually comes in personal contact with the

cocktail waitress as, for all intents and purposes, she - like the screen grid - turns out to be a vanishing illusion. Yet, having come this

far, the solid influence of the bar itself now takes over and attracts the customers to congregate, having happily reached their destination.

If you’re still following this and haven’t lost track of the count, you’ll know we’re still one element short of the five needed to make a

Pentode. This last part is a pair of beam-confining shields which being negatively charged, serve to direct the flow right toward the

plate. This is much the way a short entrance hall to the bar prevents wandering accidentally into the Men’s room on the way.

Once at the bar though, the circuit is complete and the process of soul-nourishing works its ritual magic. Biases having been overcome,

illusory nightingales having vanished, the spirits truly soar and the once surly Irishmen now are filled with warmth, wit and

kindred friendship, enjoying the music and glowing nicely with their heaters on.

With appreciative thanks to the inhabitants of the Land of the Leprechaun, we have now concluded our little diversion into the

mechanics of proper bar lay-out.

A feature article by Randall Smith

Designer / President

[SouthpawGuy]

One day an American tourist walked into an Irish pub somewhere in County Roscommon. Strangely enough, under the American’s arm was a healthy, Irish pig.

 

“If you don’t mind me askin,” says the bartender, “Where’d you get that animal from?”

 

“I won him in a raffle,” says the pig.

 

 

 

 

Top o' the mornin' to ye'

 

[TheRecordFable]

One day an American tourist walked into an Irish pub somewhere in County Roscommon. Strangely enough, under the American’s arm was a healthy, Irish pig.

 

“If you don’t mind me askin,” says the bartender, “Where’d you get that animal from?”

 

“I won him in a raffle,” says the pig.

 

 

 

 

Top o' the mornin' to ye'

 

 

[slider313]

Would that be a picture of Jimmy McDonough from The McDonough Five?

[Steiner]

Top o' the mornin' to ye'

 

 

And the rest of the day to you too, SPG!

 

I enjoyed the article's interjected analogies. It's good to see our Emerald Island inhabitant takes no offense to being called an electron!

[TalismanRich]

Fable, that's definitely a different take on electronics.

 

 

oh.. . and one final thing.. Southpaw.. I recommend you speak to your tailor.