Filament voltage standards for tubes (valves)

Anybody know why there were different filament voltages for rectifiers (5 volts) and various small-signal tubes (6.3 or 12.6 volts).
Why didn't one size fit all?
Roby
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Roby wrote:

There are a lot more voltages than those for filaments and heaters for vacuum tubes. Some of the original tubes were designed to run from batteries, and their voltages started at 1.5V, the so-called A battery. 6.3 V tube heaters ran from early automobile batteries with 3 cells in series. The 12.6 V tubes were for the present generation automobiles with 6 cell, (12V), batteries. The 5V for rectifier filaments was just a convenient voltage for a winding on the power transformer.
There are a few that ran at 2.5V, 2.8V, and a bunch of rectifiers at 5V. There were even 18.9, 25, 35, 45, 50, 70, and 117V heaters. The most famous of these were the ones used in the AD/DC five tube receivers in which the heaters were all in series across the 117V line.
When I worked at Bell Labs in 1950, one of my jobs was pumping the tubes that were used in TAT3, one of the early telephone trans-Atlantic cables. It had vacuum tube repeaters about every forty miles. The heaters of all of these were connected in series! It required a few kilovolts DC at each end. The amplifiers were powered by the voltage drop across the heaters. These heaters ran on about 24V DC for each tube.
--
Virg Wall

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That was back in the West Street era. That must have been a fun place to work back then. Just a few minutes by subway to the Theatre District.
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John Gilmer wrote:

Indeed! Just a short walk to Greenwich Village and some of the well known clubs that had lunch specials. The ferry ride from Hoboken was fun also. I moved to Murrey Hill in 1950 and then to California, (North American Aviation), in 1951. I miss NYC, but wouldn't want to live there. :-)
--
Virg Wall

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Popular in Europe (don't know about US, 120V would be a problem) were the 300mA heater tubes/valves, which were all designed to run in series (part numbers all starting 'P'). TV sets with perhaps 15 tubes had them all in series across the mains, with a power resistor to make up any difference between the mains voltage and the total heater voltage and a thermister to limit the inrush current. Different sized tubes/valves used different voltages, so that the power required was delivered from the 300mA current. There was also another standardised current which I don't recall clearly -- might have been 150mA, but the the 300mA ones were far more common in commercial products.
--
Andrew Gabriel

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Was the A battery ever a physical size (like AA, C, D cells) or just a designation for the filament battery?

Wow. Whose job was it to replace a burned-out tube? :-) How many voice channels could one circuit handle and how long did they last? I'd hate to calculate a MTBF for a thousands-mile circuit with a tube amp every 40 miles...
--
-Mike

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Michael Moroney wrote:

It was the designation for the filament supply. The "plate voltage" was supplied by the B battery, and the bias voltage was from the C battery.

From:
http://www.iscpc.org/cabledb/atlan_page.htm
TAT-3 Transatlantic No. 3     Out-of-service: retired 1986, 23 years of Service Tuckerton, New Jersey, U.S.A. -- Widemouth Bay, England - 6,515km at 414 + 414 KHz Maintenance Authorities: AT & T, British Post Office
http://www.tycotelecom.com/AboutUs/HistoryTelecom.asp
In 1962, they invented SD analog technology, which enabled bi-directional transmissions rather than requiring a separate cable for each "direction" of traffic. This technology, which also increased bandwidth, was used by Tyco Telecommunications to build TAT-3, the third transatlantic telephone cable, and allowed simultaneous transmission of 148 circuits.
Now, of course, fibre optic cables are used.
I skipped that part of technology, but worked in communication satellites since 1960. They still use vacuum tubes--TWTA's, (Traveling Wave Tube Amplifiers), as the RF output amplifiers.
--
Virg Wall

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I wouldn't imagine there are too many TWT's left, though there could be. Virtually everything I know of (a few hundred earth stations in Alaska) has long since been converted to Solid State Power Amplifiers (SSPA's).
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@barrow.com
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"Floyd L. Davidson" wrote:

TWTs are still used for sat uplink and higher power ENG vans. CATV AMS relays used them, but they are probably being phased out.
There is supposed to be an abandoned C-band uplink near here, and I think it was the one used by "Captain Midnight" to jam HBO years ago. The company went out of business and I'm told there is still a chain link fence with barb wire around the studio building and large AFC transmit dish. I'm trying to track it down because its the only Microdyne built Sat uplink, serial #1 for my collection of microwave equipment.
--
Former professional electron wrangler.

Michael A. Terrell
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...
Any place where reduced maintenance is a cost savings, will phase them out! :-) That is basically the reason SSPA's are universal in Alaska now, because of the number of unmanned sites that are so expensive to put a pair of hands on the equipment.

Ouch. We used to have a lot of jokes about "Serial Number One", because we had a lot of them, literally (and figuratively). Our first Scientific Atlanta SCPC equipment, installed in the mid-70's, had 155 precision Bourne trippots per channel spread across three circuit packs. The manuals originally gave instructions for adjusting 3 of them, and later 3 others were added. It was essentially a breadboard design rushed directly into production because the State of Alaska was willing to buy it *now*.
But *that* particular ES would indeed be a real catch!
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@barrow.com
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snipped-for-privacy@world.std.spaamtrap.com (Michael Moroney) wrote:

WECO, the manufacturing arm of the Bell System, made some equipment that used good design engineering to a degree that was sometimes mind boggling.
How about vacuum tube amplifiers where the tubes were *very* likely to last 20 years! I never worked on a submarine cable, so I can't speak to the specifics of the situation above, but I did see tubes that were more than 25 years old and still functioning!
The basic trick was to to use 24 volt filaments, and then actually run them at seriously reduced filament voltages. That doesn't allow for much gain, but when only 1-6 dB was needed needed, they didn't design a circuit with 30 dB of gain and cut it back. They reduced the filament voltage until the tube would barely warm up, barely have any gain, and *never* wear out!
The A4 Channel Bank used with L carrier starting back in the late 1930's was an example where that was done. I don't remember exactly which tube were used, but they were 300 series triodes, like 310's, 311's, or 312's, if I remember right.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@barrow.com
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Floyd L. Davidson wrote:

These particular tubes were asembled at Bell Labs West Street, which is why, as a new junior engineer, got the job of pumping and activating them!

These were based on a design that had been on life-test for over twenty years.

The filament or heater voltage has nothing to do with the gain!!! An amplifier with 1-6 dB gain would be worthless!! Read some basic electronic books.
You've got the basic physics very wrong here. A cathode, or filament emits electrons, and has to run at a temperature where this happens. If the temperature is too low, the cathode surface will not emit the ammount of electrons to support the tube's current. If too hot, the active part of the cathode is depleted rapidly. Another problem for long life is the poisoning of the cathode surface by residual material within the tube.
--
Virg Wall

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Giggle snort...
Some circuit don't require *any* gain. And if you don't think the filament voltage would affect gain (technically it is the transconductance that changes, but that amounts to gain in practical circuits), just try running most tubes at say about 1/2 the normal filament voltage and see how much gain they (don't) have!

Exactly. Now... remember all the nice little "cathode activity" tests that were built into many circuits in L carrier systems? Put a voltmeter across a resistor in series with the plate circuit, thus measuring plate current, and then lower the filament voltage a specified amount. The plate current will drop, and if it goes too far down, the tube should be replaced because the "cathode activity" is too low.

And of course if a circuit is designed to operate at the lowest functional cathode surface temperature, the tube will last *significantly* longer than if it the normal temperature is maintained.

More significant with some tubes than with others though. "Gassy" tubes were common.
One cause of such failure, with certain types of tubes, was applying high voltages to various elements before the filament/cathode was fully up to temperature. Generally that applied only to transmitting tubes, but was also significant with some receiving tubes such as the 416 lighthouse microwave tubes that were used in the TD-2 microwave systems installed in the late 40's and early 50's which changed the nature of long distance in the Bell System.
For such tubes a switch was provided to turn on filaments first and then, after a delay, another switch for the high voltages. Failure to wait long enough would destroy a tube that had more than perhaps 4-6 months of filament time. Some equipment had timers to ensure the delay. Some equipment used variacs to slowly bring up the voltages and allow precisely setting them too. Filament voltage on many transmitting tubes is very critical, as if it is slightly low performance suffers and if it is slightly high the tube's life is shortened significantly.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@barrow.com
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Floyd L. Davidson wrote:

LOL is more like it!!

Some circuits don't even require tubes. :-)

Every drug store had a testor like this in the 40-50's. A very few actually measured gm.

The circuit desigh has nothing to to with the "lowest functional cathode surface temperature", whatever that is.

Which is why getters are used and during activation, induction heaters are used to out gas all tube elements.

The TD-2 tubes has such a small cathode-grid spacing that the grid could pick up cathode material and become emissive. I used similar tubes in the design of the ARSR, (Air Route Survellance Radar).

Really? ;-)
--
Virg Wall, P.E.
K6EVE, FCC Radio Telegraph Operator's Certificate T2-HQ-8354
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Ain't that the truth. At least you gave up on being serious, for the most part.

Being silly, are you? There are many applications where tubes are used in circuits that do not require gain. And as little a 1-6 dB is of course *very* common in telecom designs.

Yes, many of them did in fact test tubes with something very similar to that.
The point to learn though, is that your original statement above is incorrect, because *you* got the physics wrong.

Look, if you don't have a clue about how any of these designs worked, and never saw one of them, just say so. But cease making abjectly stupid statements.
The purpose of reducing the filament voltage was *precisely* to lower the filament/cathode (whatever the electron emitting element was) to a temperature that would just barely allow it to function. That resulted in an extremely stable long lived vacuum tube circuit, as opposed to one that required the tube to be changed every few years.

Yep.
That and the extremely thin layer of oxide on the cathode. That layer was something like 0.0005 inches. The cathode to grid spacing was only 0.0006 inches.
Yes, 416B's were popular. But none of the other uses had the massive effects that the design and implementation of the TD-2 microwave network that was installed by the Bell System. The difference was that in the 30's and 40's, as we can still see in vintage movies, everyone who made a long distance call to grandma had to shout "Hello Hello, can you hear me!" into the phone three times before grandma realized that someone actually was on the line. By 1955 or so it was possible to almost speak normally on a cross-country telephone call from just about anywhere to anywhere else in the country. That was enabled by the 416B tube.
(And is was Pulse Code Modulation, finally fully implemented 1980's made it possible to whisper into a phone and be heard!)

Matter of fact. Even if you had forgotten about it (or never knew for all I can tell).
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@barrow.com
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Floyd L. Davidson wrote:

How many systems have *you* designed?

There is an optimum temperature and it's not where the cathode "just barely functions".

Close, but no cigar! See:
Morton,J.A., "A Microwave Triode for Radio Relay". Bell Laboratories Record, May, 1949.

The L-3 Coax system worked pretty well, too.
One of the neat things about the TD-2, was that it was single sideband and put into use with only one sideband used. When traffic warranted it, a simple change doubled the capacity.
The three stage 416A amplifier had a gain of 18 db at a bandwidth of 20 megacycles at the 0.1 db points. The output was set at 27 dbm.
--
Virg Wall--Long time vacuum tube designer.

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What *I* have done has nothing to do with your babbling!

Where ever did you get the clue?
I said the temperature is dropped to where it barely functions. That certainly would not likely be optimum! But optimum in one respect does not necessarily equate to optimum in another. If you want optimum lifespan for the tube you do not optimize for maximum gain, cathode emissions, or any number of other equally life shortening parameters.

Your cigar is wet. Citing something that doesn't support your claims is *not* going to endear you to anyone. Not quoting anything to support what you claim, but instead rattling off other interesting but irrelevant information from your source is just nonsense on your part.
See "Principles of Electricity applied to Telephone and Telegraph Work", 1953 Edition. p239.
"The oxide coating of the cathode is .0005" thick." "The cathode-grid spacing is .0006"." "The grid wirs are spaced a thousand to the inch and are .0003" in diameter." "The plate-grid spacing is .012"."

But distinctly did *not* allow the Bell System to network the entire country, _until_ they put it on microwave. Keep in mind that L carrier was designed in the 1930's. It was not the innovation that had the most dramatic effect, though it certainly added to it.

Dual redundant channels was not exactly new or inovative.

Hey, you made fun of amplifiers with 1-6 dB of gain... are you aware that the last stage in that particular bit of hardware is an amplifier with only 3 dB of gain? And the second stage is 6 dB? Only the first stage fits what you claimed... :-)

Virg, we're all getting old and forgetting a lot of this stuff... *Don't* go on memory. Look things up and verify what you think you remember before posting it.
I don't know about you, but I'm *not* sorry that I don't work with vacuum tubes any more. In fact, the same goes for individual components, be they transistors or even IC's. I like working with entire card level components, with embedded micropressors...
When I was a teenager I dreamed up designs that would have filled three floors of a large building, and required all of Hoover Dam to power. I could only dream about them. Today I whip something like that, totally in software, in an hour.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@barrow.com
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in article snipped-for-privacy@barrow.com, Floyd L. Davidson at snipped-for-privacy@barrow.com wrote on 5/3/05 5:43 PM:

A lot depends upon what you mean by "gain." A cathode follower, the equivalent of a modern emitter follower, had a voltage gain less than one. Nevertheless, it provided a power gain from a high impedance source because it can drive a lower impedance load than the source could.
Bill
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I personally used a drug store tube tester as late as 1973. And I worked at a steel mill where the instrument shop kept a tube tester around till well into the 1990's, because there was at least one tube-based amplifier in the plant.
Bill
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The problem with tube testers, and the drug store variety were by far the worst, was that they rarely indicated whether a tube was good or bad! I.e., only if the filament was burned out or there was an internal short, was the "bad" indication was valid.
Otherwise there was rarely a better test for a vacuum tube than to plug it into the circuit in question, and see if it worked. If it didn't, it might (or might not) work in another circuit.
That was true of brand new tubes straight out of the box just as much as for tubes in operating equipment.
Which is to say, rather than a tube tester, the usual practice was to have a large caddy of tubes for use as "swapping spares".
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@barrow.com
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