Filament voltage standards for tubes (valves)



The ones I remember did a lot more than that. They had a meter and at the minimum determined whether the tube could function at least as a diode. Some of the drug store types were equivalent to the testers used by servicemen.

That seemed to be the folklore.

Well, that partly explains how the Japs god ahead of us in consumer electronics. With reasonable quality control one should be able to mix and match.

Aside from everything else, it's a lot quicker to just exchange tubes than plug in a tester and test the tube.
If quality control was really that bad switching tubes could lead to nothing at all working.
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That was true enough. Due to availability issues, some tubes had way more performance than the circuit needed and would work forever. Other designs needed fresh tubes to work properly.
Best example I ever saw was the OLD Western Electric Theatre amplifer, I think it was the type 42. Used the 205 triode as the power amplifier and as the rectifiers, with grid and plate strapped. WE told you to run the 205s in the amplifier position until they were unsatisfactory, then put the spent tubes in the rectifier sockets. Whn the no longer worked as rectifiers they were COMPLETELY shot!

I never experienced this, at least not in entertainment equipment. Some test equipment used selected tubes, but by and large BRAND NAME new tubes were pretty much interchangeable. There was a big scandal in the late 1950's, however, where businesses were buying up used tubes, washing them, relabelling them and selling them as new. That may be the origin of that story.

As stated above, I never observed any real QC issues with name brand product.

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It wasn't so much "way more performance" as it was conservative circuit design engineering. Using two stages, rather than one, to get any given amount of gain and using feedback to stabilize the entire circuit are examples. With good design most circuits can operate without such great sensitivity the tube characteristics. But that wasn't true of all circuits, and of course it cost money to implement, so it didn't always happen.

A great example. WECO was famous for such designs. Working on the telephone carrier system they designed back in the 30's was still great fun even into the 1970's because of the excellent engineering.

Test equipment was one area where they weren't interchangeable. RF use was another. TV sets for example! And other uses for tubes meant for TV sets, such as the many Ham Radio transmitters that were designed using TV horizontal sweep output tubes. Many of those would work best with one or two brands of tubes, and some would not work *at all* with some brands.

Nope. Experience in the 60's and 70's with tubes used in commercial radio equipment.

It doesn't have to do with QC, and Japanese made tubes were no different. The problem is that a given tube type had a relatively small set of target characteristics which defined it, as compared to a much larger set of characteristics that affected its actual operation. The same production line, never mind two different production lines, generates significant variations in the second larger set. Transistors are even worse!
But manufacturer's did learn, and with transistors they came up with the solution. Rather than hundreds or thousands of tube types, there are tens of thousands of transistor types! The same production line would be manufacturing several different devices, and the difference was determined by testing them.
That continued to be done with IC's too, though to a lesser degree. For example the 80386sx, the cpu without the math co-processor, came off the same production as the version with a working co-processor... :-) (Hmmm... I wonder if the external math-coprocessor was just a cpu with a malfunctioning cpu and a working coprocessor???) And usually there have been a least a couple of different variations of clock rates for each cpu, again all off the same production line.
(None of which detracts from the actual fact that the Japanese had *much better* quality control for such manufacturing processes, and that did indeed give them an advantage.)

Mostly because it is a definitive test, while a tube tester is a wild guess in most cases.

You had to learn *how* to do it! People would randomly swap tubes and lose track of which ones started where. Bad! Swap a tube, and if it doesn't change, _put_ _the_ _old_ _one_ _back_.
That's hard to do perfectly every time though, and leads to another problem, for which there is a definite solution. Between swapping tubes and ending up with a mixture of used and new, the *bad* ones get mixed into the pile! Our initial solution was to toss the whole bunch the instant it was realized that any one of them could be bad. That wasted a dozen or so good tubes to avoid a bad one.
But a better idea came along... a bad tube should immediately be "marked". Yeah! Just bend all the pins flat. That was so easy to do that everyone in the crew I worked with found it an easy habit to form. (We shared rolling test equipment bays and tube stocks. Doing a full blown routine on a radio set might go through a couple hundred tubes each for one or two types, and another 50 for all others. So we're be grabbing spare tubes by the handful at a time.)
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@barrow.com
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And by that time you probably had to order your tubes from Russia! :)
--
Don Kelly
snipped-for-privacy@peeshaw.ca
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73 was definitely toward the end of the tube era tube sets were still being made. The tube era was extended by a few years with the "compactron" tubes which had 3 or more sections and something like 12 to 18 pins or so. The tubes were a lot more reliable by then too. The life limiting factor started to be components (like caps or transformers) that were damaged by the heat from the tubes rather than the tubes themselves.
As examples: I had a set last last from 1980 to about 2003. It had one repair when it was about a year old. It was mostly solid state but the picture sure wasn't.
Likewise, I have a working microwage thats over 25 years old.

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Bill Shymanski wrote:

About six months ago, my son found a B&K Dyna-Quik Dynamic Mutual Conductance Tube Tester. It has a tapped transformer which provides heater voltages from 1.5 to 50V. It is a true mutual conductance tester, using a regulated 1.5 V AC on the grid, and measuring the output with a built-in VTVM. It's complete with the tube settings manual, and according to the catalog inside the case, sold for $119.95 in 1967. It uses a "good-bad" scale, or can be set to measure the actual gm.
I haven't got around to trying it yet. I want to first test the four electrolytics in it to see if they need replacement or reforming. I still have several dozen old tubes which I can use to check.
I have a 1952 edition of the RCA "Radiotron Designer's Handbook", which was the early "bible" for vacuum tube circuit design up to the TV era. There's still a lot of good information on basic circuit components. I also have the three volume, loose leaf, RCA Tube Handbook with up-dates to about 1955. It includes receiving, transmitting, CRT and special tubes made by RCA. If anyone needs info on an odd-ball tube, made by RCA, I'll be happy to look it up.
As you know, tube amps are the rage with musicians, especially guitar amplifiers. Tubes are going for many times their original price, if they can be found at all.
-- Virg Wall
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in article B16fe.9754$ snipped-for-privacy@newsread2.news.pas.earthlink.net, VWWall at snipped-for-privacy@DEADearthlink.net wrote on 5/7/05 9:29 AM:

This is driving me crazy! Other than providing a favorable kind of distortion, whatever that is, in what way do tube amplifiers outperform solid state versions? Even if it is distortion that these crazy audiophiles want, what is the distortion? Why can that distortion be reproduced using solid state devices?
Bill
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http://groups.google.es/groups?selm=tpe123-0803992343330001%40192.168.2.5&hl=en
may provide insight.
Matt Roberds
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wrote on 5/7/05 9:29 AM:

Because tubes have a different sound than solidstate amps. I will not qualify as one better than the other but for the most part people just prefer the tube sound. In other words, there is a difference and a choice is made. This is more imporant in a guitar amp than in a hifi amp. In music the distotion is part of the sound that is desired, In Hifi there should be as little distortion as possible. The ctriterion for hifi can be meet with either tube or solidstate amp. For music where the distotion is much more pronounced the type of distotion is much more critical.
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in article cjrhe.28342$ snipped-for-privacy@twister.southeast.rr.com, Jimmie at snipped-for-privacy@carolina.rr.com wrote on 5/14/05 11:19 AM:

If distortion is wanted, there are analog and digital methods available to introduce distortion in a known way. A twin 2GHZ twin processor G5 computer using 64 bits could run circles around any audio signal that can be put into it.
It is difficult for me to understand why amplifier nuts, er.. perfectionists, do not delve into quantifying the distortions that do the best jobs for the music of interest. It should not be that difficult to make a function generator to duplicate the distortion of a tube. Moreover, that distortion could be made to vary dynamically according to the desire of the performer. In any event, how does the distortion survive the negative feedback in the amps?
Bill
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On Sat, 14 May 2005 19:15:50 +0000, Repeating Rifle wrote:

Teh technical term is "audiophools".

They fail every double-blind experiment. ...worse than Randi doing Uri. Audiophools like the "warmth" of toobz. On a cold winter night I prefer a fire in the fireplace, but...

One of the suggestions on sci.electronics.design was a "double-blind" experiment where a toob amplifier was recorded and played back through a decent SS amp (perhaps even with glowing filiments showing), and challenge the audiophools to tell the difference. Repeat experiment with black vinyl and CD. The fact is the ear isn't as good as either.
--
Keith

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in article Ivzde.3453$ snipped-for-privacy@newsread3.news.pas.earthlink.net, VWWall at snipped-for-privacy@DEADearthlink.net wrote on 5/2/05 5:23 PM:

I happened to be visiting Bell Labs Whipany, in 1956 I think, when the cable was dedicated.
Bill
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in article Ivzde.3453$ snipped-for-privacy@newsread3.news.pas.earthlink.net, VWWall at snipped-for-privacy@DEADearthlink.net wrote on 5/2/05 5:23 PM:

For most of the tubes, the number 6 in a 6SQ7 or 12 in a 12SQ7 designated the nominal heater voltage. Otherwise, tubes with the same designation except for the heater were supposed to be the same. Some tubes like rectifiers and output amplifiers required higher voltages for the heaters to produce the required electron emission.
In particular, many AC/DC sets use a 35L6 or 50L6 beam tetrodes for the output stage. In this cased, however, they were not analogs of the venerable 6L6.
Without further designation, these tuves had metal tube envelopes. For lower cost, smaller glass envelope tubes were used with a GT designation, such as 12SQ7GT.
Bill
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For the European numbering, it's the first letter... 'D' is 0.5-1.5V, 'E' is 6.3V, 'G' is 5V. For series operation, 'H' is 150mA, P is 300mA, U is 100mA.

Or the older glass ones with just a G designation, which I once heard someone describe as "female form shape" ;-)
--
Andrew Gabriel

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I don't know of any that use higher voltages to get better emission. Commonly they use low voltages and significant amounts of current though.
Rectifiers typically used 5 volts on the filament. As opposed to the typical "receiving" tube such as 6AK5 etc, which actually has a 6.3 volt filament, many transmitting tubes require 5.0 or 6.0 volts.

The 35L6 and 50L6 are identical to a 25L6, which is a "low-power 6L6" with a higher filament voltage. Of course there are a couple dozen or more "standard" variations on a 6L6, so it's hard to say that the 25L6 wasn't really a 6L6 just because it had slightly lower power ratings instead of slightly higher as most did. :-)

The metal envelopes were a fad that occurred in the 1930's, and continued on momentum only into the 40's. By that time nobody really wanted to make them. But the original 6L6, which was the first "beam tetrode" design and spawned hundreds of other similar tubes, was a metal tube. The first glass tubes to replace metal tubes (as opposed to glass tubes that had no metal counterpart) added a G suffix, but then other variations came along too and there are GA, GB, GC, GN, GS, GT, GX, and who knows how many others. Those would all be, for the most part, direct replacement tubes, though it wasn't uncommon to find circuits that did not work well with certain versions, or for that matter with tubes from certain manufacturers.
Suffixes with A also had a significant meaning, and for the life of me I can't remember what it was! Probably the ability to do a "slow warm up" with less of current surge.
WECO of course did not label tubes that way. Their designs were numbers, for example a 408, and then there might be be a 408A, 408B and so on as "improved" or sometimes "selected" variations were produced.
Tubes like the 6AK5 mentioned above (a 7 pin miniature) did not ever have a metal counterpart, and therefore did not have a G suffix. However, sometimes there were special selected variations of such tubes that might have suffixes like W for a ruggedized version. And there were identical tubes with 4 digit numbers too. A 5654 was a 6AK5, for example.
Some tubes were "selected" according the customer too! There were lots tubes that either had a prefix or a suffix of "WA", which were selected for the White Alice Communications System in Alaska. If I remember the number right, the 416B tubes we used were all labeled WA6280 (it might have been 6280WA though), and I seem to remember 5654WA tubes, but it may have been some other type.
--
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 5:00 PM:

The "classical" AC/DC set used a string of tubes requiring 0.15A for the heater. The ususal low power tube in the string ran at 12V. The output tube and rectifier tube required more heater power than could be obtained at 12 (actually 12.6 nominal) volts and 0.15A. Thus, the typical 50L6GT output tube used 50V and the typical rectifier 35Z5 tube used 35V. Three 12V tubes and these higher heater voltage tubes gave a string that required about 120V to run. The 35Z5 had a tapped heater that was used to obtain power for a pilot light.
The classical AC/DC used "bantam" octal tubes that were keyed to orient them with respect to the socket. The 6AK% was a later tube that did not use an octal base.

The metal tubes had the advantage of not requiring separate shields.

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But that is not a case of needing a higher voltage to get enough emission. That's a case of needing lower current because it is in a series string.

I'm not sure what you want to say threre. The original "All American Five" AC/DC radio had regular octal based tubes and was designed in 1938 or 1939. That was very popular in the 40's, but after WWII the use of 7-pin miniature tubes became the norm. There were variations: some used 6 tubes, some used loctal sockets. But they were all electrically almost identical and the design was so simplified that all totaled the radio had only about 50 parts if even the screws were counted.
A 1939 version would have used 12A8, 12K7, 12Q7, 35L6, and 35Z5 tubes, and may have been either metal or the G version with glass envelopes (for the 12.6 volt filament tubes).
Starting in 1945 sets were built using 7-pin minuature tubes; 12BE6, 12BA6, 12AT6, 50B5, and a 35W4 being a typical complement.
One of the first radios I ever played with was a Philco set that use loktal socketed tubes. It was battery operated. (In the late 40's my aunt and uncle lived in Forks, WN, and after he was killed in a logging accident my aunt moved to Bremerton and gave me that radio, probably because she no longer needed one that used batteries).
...

...
Not much of an advantage, particularly when compared with all of the disadvantages and the ease of installing a separate shield if needed.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska) snipped-for-privacy@barrow.com
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Before that, however, AC/DC sets used a string of 6 volt tubes with either a ballast tube or a resistive power cord to drop the remaining voltage. Ballast tubes ran VERY HOT! I have several sets with a 3-wire power cord. One hot wire has the resistance necessary to drop the filament voltage. The other hot wire is a normal copper conductor, used for the B+.
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
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in article PqWdnRnBVKj2 snipped-for-privacy@comcast.com, Ben Miller at snipped-for-privacy@worldnet.att.net wrote on 5/4/05 4:53 PM:

During WWII it was very difficult to get certain vacuum tubes. Popular Science gave a fix for using a mix of 6 and 12 volt tubes of the same kind except for the heater voltage. It used two power resistors and ended up using four times the original heater power. Talk about hot...
Bill
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VWWall wrote:

The filaments were powered by lead acid cells, so the filaments were rated at multiples of 2.1 volts per cell. The 1.5 volt tubes came later for portable, dry cell power. The 5 volt rectifiers require a separate filament winding, and are 2 or 3 amps at 5 volts. Its a tradeoff between operating current and a rugged filament. There were rectifiers with higher heater voltages and a separate cathode.
12.6 volt tubes were obviously designed to be powered from a 12 volt lead acid battery, and the B+ was provided with a vibrator and step-up transformer. Series string radio & TV sets used a wide range of filament voltages. Different functions needed different heater power levels so they developed tubes based on filament current IE: 150 ma string. You added up the required voltage of all the tubes , and if needed, you added a series resistor to drop the voltage. Some radios used a "Resistor cord" AKA "Curtain burner" which had three wires, one of which was nichrome for the filament string.
If you have more questions about tubes, and tube history visit: news:rec.antiques.radio+phono where you'll find people who collect and restore old radios, as well as a number of retired engineers with a lot of knowledge about tubes and early electronics.
--
Former professional electron wrangler.

Michael A. Terrell
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