Filament voltage standards for tubes (valves)

Gosh, it's great to learn there are other survivors who remember tubes!

I saw a sample of undersea cable and a repeater at Murray Hill in 1965. I think the loss between repeaters was 60 dB. Is that correct?

Roby

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).

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Not much of an advantage, particularly when compared with all of the disadvantages and the ease of installing a separate shield if needed.

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.

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.

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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!

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

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

Most filaments were 6.3volts. Even 12 Volt tubes like the 12AU7, 12AT7, etc. had center taped filaments and were usually powerd by 6.3 Volts. Higher voltages were popular for line operated radios where the filiments were all in series adding up to 121 volts, no transformer needed. Five tube sets had

50, 35 and 3, 12 volt filaments in series. Other voltages were available for battery operated and specialty equipment as somebody mentioned. The five volt rectifier was a special case requiring five volts at high current isolated from the other voltages, 6.3V etc. Isolation was required because these were directly heated cathodes where the filament was often several hundred volts above ground on the rectifier cathode. This could not be connected to other filament circuits which were near ground potential. They always had their own insulated transformer winding. The voltage was low, five volts because the filaments were thick and had low resistance, but the current was high. Smaller, receiving tube filaments used thin tungsten wire in a metal sleeve that formed the cathode. The thin wires were higher resistance and also lower power than the rectifiers. These usually ran at near ground potential to keep the filament to cathode voltage a low as possible. Bob

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

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".

And by that time you probably had to order your tubes from Russia! :)

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

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.

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.

>

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

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.

may provide insight.

Matt Roberds

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.)

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.