Charles MacDonald's Electronic tube page

[A Picture of Me]

Years after they were declared dead, there is still interest in electronic tubes.

In reading the web, I have found several sites that have some strange ideas about what is good and bad about tubes, and more than a few folks who have said things that cause me to roll my eyes.

I do like to play with tubes, and I can relate to the fellow who signs his mail postings with the line:

Sure it's 1937 Technology, but it's Good 1937 Technology

These are a few of my opinions on tubes. I also have a page here that has a listing of some of the details about the more popular power tubes. I have also added a some details about Capacitors Here

More is to come, please let me know what you would like to know about.

Why on earth would anyone still be interested in Tubes?

There are many reasons.

WARNING!
Tube Equipment uses voltages that can KILL Please be sure you know what you are doing before you open the cover on any tube powered electronics.

What do you mean by asking Who made that tube?

The brand name on a tube is seldom any guide to the factory that originally made it.  When I was young, I often bought tubes from the local branch of Canadian Admiral Corporation.  The common tubes came in boxes that said Admiral, but some types that were slow movers came in Westinghouse Canada boxes. When I asked about this, I was told point blank that all the tubes actually were purchased from Westinghouse, but Westinghouse would only stamp "Admiral" on them if Admiral ordered a certain quantity, the rest just came in Westinghouse packages.
Two Admiral Tubes Two Tube Boxes
Canadian Admiral sold two lines of tubes, the Tubes in the red Boxes had red lettering, normally were Canadian Made and were sometimes marked PREMIUM, the Tubes in yellow boxes had yellow lettering Normally were imported and were generally marked SUPERTRON
This Photo shows two Boxes, one Admiral, one Canadian Westinghouse probaly made about 6 months apart. Note the similarities in the stamping on the boxs.
Very old Westinghouse Canada Box
Canadian Westing Radio Tube Box
Relaiatron was only in the USA 
This Early Canadian Westinghouse box is Probably from the 1930s
 Come 1950 the word Radiotron was replaced by "Radio Tube"
 Next Radio was replaced by Electronic, Tubes in the USA used the term RELIATRON, which was not used in Canada
end flap of a Fleetwood box
Doing the Continental
Fleetwood of Montreal was a maker of inexpensive radios and TV sets.  They sold tubes mostly to their own dealers. often the tubes they provided as replacements for defective ones in their sets had hand written type numbers.
Canadian Westinghouse used the "Continental" brand for their ecconomy line of Tubes.

One of my High School shop teachers had previously worked at CGE.  There he often got a chuckle out of seeing new tubes being stamped with the message "Replace only with Genuine (Brand X) tube" when they were being labeled side by side with the GE brand product.

Even GE or Westinghouse brand tubes were not always made in totaly in house.  I have a copy of a 1937 Sylvania Tube manual where they brag that they sold both finished tubes and compenent parts to other makers.  Often the company that first developed a given tube would sell it to the other makers, and when a factory had a requirment to restock a given type, they would evaluate if they should make it or just buy it.  If they had had a run on a particular part, it is likely that they would purchase some from outside to ensure that they could keep their dealers happy.  Units that were required to build radios and TV sets may also have received priority to be built in house, if for no other reason than to keep competitors in the dark about Set production.  Types that were only required for replacement sales may have had insufficent volume to justify the manufacture of tooling.  Factories may have also gone outside for product when they were having busy periods so that they would not have to add and then release staff.
The photo on the right shows a Admiral USA tube which indicates that It was made by CBS-Hytron - This sort of labeling would be the exception rather than the rule
 Made for Admiral by CBS-Hytron

This happened world wide, I have recently found a page as part of Andy's Radio and Valve page that links to a listing of source codes that Philips used to indicate where tubes sold under the various Philips brands were actually made.  Philips sold tubes in various countries under the Philips, Miniwatt, Rogers, Amperex, Mullard and Valvo names.  The codes did not indicate that Philips sold any given quantity of tubes from any of these factories, just that they purchased and resold some tubes from each at various times.

Philips Source codes exist for:

The end result is that even if you find a sealed carton of fresh tubes that has positive documentation that it came from a major brand name, there is almost no sure way to be sure that that company actually made the tubes, and did not simply buy them in bulk and have their name put on.
12ax7 RTT Made in India
This Rogers 12AX7 has a
typical Philips type code		 RTT 15CW5 Made in
India also
shows a code 

Some dealers will go by the actual type number makings to make a reasonable guess at the REAL factory.  RCA for example is known to place the type number in a rectangle with the corners cut at 45 degrees, GE USA often used a style that looks like a stencil, with a pattern of dots beside it for an internal code.  Sylvania was known to use a marking that has a goldish tone. Some factories put the type number on the end of the tube, others close to the base.  In the USA, it is illegal to sell goods with an incorrect country of origin indicated, so that can be a clue, but as you can see from the Philips Source list, a tube can have original markings that say "Mullard, Made in Great Britain" and still be actually built by EMI, Ferannti or Thorn.

Someone buying tubes who wishes to obtain units produced by a given factory will have to do a fair deal of research if they do not want to be confused.  I have not attempted to reproduce the actual symbols from the Philips list. They consist of Letters and Numbers, some are reversed and some are other symbols that look like a child's first attempt at writing.  Now years later, some folks may try to disguise a run of the mill tube as something that has aquired a reputaion as being something special.  If you are determined to play in that league, you will have to do some very detailed research if you want to get what you are thinking of paying for.

The Type Number marking on a tube can be a clue to the original maker
Made In 5U4GB 5AS4 Canada Made In 35Z5 GT Canada Made In 12AU7A Canada typical GE USA typical RCA USA
I believe that this Canadian Admiral 5U4GB was made by Canadian Westinghouse in the 1970's
 This JAN-CK-35Z5GT was made about 1956 by Canadian Westinghouse. This 12AU7 is also a Jan-CK Westinghouse made tube This RCA 6CE5 appears to be made by GE-USA This GE 5763 appears to be made by RCA-USA

The nice folks at Triode Electronics have put up Chart that shows some of the internal codes that Philips used, which could come in handy if you ever get a Philips made tube that has had the type number rubbed away, but still has the internal codes.

So what do the suffix letters on Tubes mean?

Suffix Letters Meaning
A More advanced Version of Tube
A May also mean a different Filament voltage, For example a 58A is a 6.3V version of the 2.5 Volt 58
A In connection with a W may indicate more advanced testing, or burn-in, or other Quality Controls beyond the normal for a Military Tube.
B More advanced Version of Tube than A
C More advanced Version of Tube than B
E Export Version
G Glass (as opposed to metal) often implies a ST style envelope.
GT Glass Tubular - Not an ST style - often a T9 envelope. May have slightly lower ratings than a G
GT/G Glass Tubular with the same ratings at the G version
LM Loctal-Metal a metal equivalent of a Loctal tube. These were mainly made during the time when Sylvania and Philco were attempting to gain acceptance for the Loctal design at the same time as GE and RCA were promoting the metal design.
M Rogers tube with an Octal Base, and a spray shield - Characteristics otherwise simalar, for example a 6A7M is an Octal version of a 6A7, with a Conductive spray coating
M-R Maintenance and Repair - Tubes produced for civilian use during the Second World War. Almost all tube production was restricted to military needs, but some civilian production was approved strictly to keep civilian sets running. The MR marking on these tubes was to ensure that they were not used for new radio production.
S Spray Shield - often a Rogers or Majestic Brand tube, with a coating on the envelope to eliminate the need for an external tube shield
X Ceramic base. Early tube bases made of Bakelite sometimes cased electrical losses in high frequency, high power or airborne applications. Ceramic has a better dielectric constant and so ceramic was used for some tubes. This may also be a Mica Filled Plastic base in some cases
Y Low Loss Base. This is often Mica filed bakelite or some other sort of plastic. Ceramic does not work well for Octal tubes as the keyway can be damaged easily. The base on a Y tube is often a mottled brown or red in appearance.
W War? Tubes made to Military Requirements. May be more rugged, higher ratings, have a low loss base, or other variations. Civilian version may be a numbered industrial type. For example, a 6AQ5W is also sometimes known outside the Military as a 6005. Some W types draw slightly more heater power than the related civilan version


The codes may be used in combination. For example the latest 6L6 variant is the 6L6GC, there is also a 5U4GB, a 6SN7GTB, a 6SN7WGT, a 6SA7YGT, 12AX7WA and so on.

Two 25L6 tubes
ST style 25L6G (left) and T9 Style 25L6GT show the difference in sizes between G and GT tubes
Three WW2 era Tube boxes
Sylvania Loctal and GE metal Tube
These three Boxes are from the Second World War era.  The MR stamping (circled in Blue on the Sylvania Box) indicates that the tubes were sold as replacement parts during the time when tubes were rationed for the war effort.
 The battle of the 30's - One the left is a Loctal tube, and the right is a metal tube.  The metal tubes ended up being more popular.

It is necessary to consult the manufacturer manuals to determine the actual differences between a regular or an A version of a tube. In many cases a modifed version has a heater which is designed to warm up in exactly 11 seconds, so that all the tubes in a series string will warm up (and so start to drop less heater current) at the same time. In other cases, the difference may be higher ratings, or a specification that is subject to tighter control. Normally one can use a higher revision tube in place of an earlier version. A 6SN7GTB, which has the controlled warm-up time will replace a 6SN7GTA for example. A 6L6GC with its 35 watt rating will be quite happy in place of a 19 Watt 6L6GB

What's with these JAN Tubes?

Many folks seem to be confused about JAN tubes. JAN stands for "Joint Army Navy" and is the designation that the US military uses to describe tubes made to military specifications. The Canadian Military also uses JAN to indicate tubes made to Military specs.

The military specs are compatible with commercial production in many ways, with more testing, and tighter control of tolerances. Each type has a thick book of specifications, based on industry best practice, that tube factories are expected to follow.

Since military requirements call for keeping enough spares to ensure that all equipment can be kept in good repair, even at times when there is a group (called "The Enemy") trying very hard to knock things out of repair, the military often would stock more than one spare tube for each tube in service in military gear. Some gear was also tube based for long after most civilian equipment had changed to solid state, often because of the long design and implemetation cycles for updating military equipment, or perhaps because of fears that solid state equipment might be disabled by electromagnetic pulse interference from atomic weapons.

The result is that tubes were being made for the Military long after most civilian production had stopped.

According to the .PDF File on revoked standards that is avalible at the US Defense Logistics Agency under Commodity code 5960, the 6SN7WGTA was only removed from the books 1996/04/26, which is not bad for any technology that first saw the light of day in 1939/1940.

The Second World War is another reason for there being a large supply of JAN tubes. When the Second World War was in progress, production of tubes was raised to an unprecedented level. Every factory was working flat out to create as many tubes as possible for all the new electronic equipment that was invented during the course of the war. Canadian Production ramped up at the start of the war, and once the US finally joined in the war effort in 1941 or so, (having previously been only involved as a supplier of materials under the lend lease program), almost all tube production was JAN units for the war effort.

In late 1945, the war ended rather suddenly with the surrender of Japan, while large quantities of tubes were still on order. The two Governments maintained many of these orders, so that the factories could gradually switch to civilian production in an orderly way, Much of this inventory was stored, and sold as surplus over the next several years, as there were concerns that a large quantify of ANYTHING coming onto the market would delay the switch to civil production. HAM radio operators benefited by being able to buy all sorts of tubes to go along with military radios that happened to be easy to convert for HAM operation. Much equipment was broken up, as having no civilian purpose. (Radar transmitters are not really of much use to most folks.) The spares for these were added to the stockpile of JAN tubes. (6SN7s were found in many radar sets from what I have heard.) Over 50 years later, some stockpiles of these 1941-45 tubes are still to be found, factory sealed and unused.

Some argue that the last of the tubes produced for the military in the 1980s may not be the best. By then, about the only plant in the US that was still capable of bidding on military contracts was either the old Ken-Rad/GE plant in KY that by that time had converted to almost strictly specalty tubes by its new owners MPD Components, Inc, or one of the old Sylvania tube plants that by that time had been transferred to Philips as part of the sale of the Sylvania ECG replacement semiconductor group.

If you find any JAN tubes with 1980s packaging dates you will often find they look like Sylvania parts, but are labeled "Philips ECG". It is somewhat ironic that the JAN tubes are often a bit cheaper than civilian tubes, because for some types there are more of them out there. I have old catalogs that show that JAN spec tubes commanded a the time because of the extra testing they were subjected to to earn the JAN designation.

If you are interested in what a tube needs to meet Mil Spec, the specifications are in Spec PRF-1 the test procedures are spelled out in a 2 meg .PDF file that can be downloaded here there is also a 1.5meg .PDF that tells how one is supposed to package tubes for Shipment

I suppose that the history of 6SN7s in combat is no more ironic than folks saying a 6SN7 is an audio tube, when perhaps most of them spent their entire life as part of the vertical defection circuits of a TV set.


Advertisment from 1967 Offering Cheep Tubes

The advertisment above was found in a 1967 Electronics magazine. You will note that the company was offering "new used or Factory second" tube or JAN surplus tubes at what today seem like very low prices. Too bad we can't all get in our time machine and buy a load of suplus 2A3 triodes

Tubes from these sort of companies would normaly have the original marking replaced by the vendors name, and often came in boxes saying that they were "Standard Brand" Tubes.

Some All- American five tube sets

Household radios were one of the first products that used tubes. It did not take long for the factories to standardize on a set of tubes that allowed for mass production. (the fact that everyone had to buy licences from RCA for many of the basic radio patents, also probaly had a standardising effect.)

By the late 1930's a typical Radio could be built with 5 tubes, including a Penatgrid Converter, a IF amplifier, a detector, and and audio Output tube. Power was provided by a rectifier tube, and gradualy the power transformer was phased out in favor of wiring the heaters of the various tubes in series like christmass tree lights of the period. This style of Radio is called an "All American Five" in the USA.

Function

2.5V

(1927)

6.3V

(1934)

 300 ma Metal Double end (1935) 150 ma Metal Single end
(1940)		 Loctal 7 Pin for Battery Radio 150 ma 7 pin Minature (1946) 100ma 7 pin Minature 12v plates for car radio use
Pentagrid Converter 2A7 6A7 6A8 or 12A8 or 6K8 12SA7 7B8 or 14B8 1R5 12BE6 18FX6 12GA6 12AD6 12AG6 12FA6
IF amp 58 6D6 6K7 or 12K7 or 6S7 12SK7 7A7 or 14A7 1T4 12BA6 18FW6 12EA6 12AC6 12AF6 12BL6
Detector and first audio 55 6B7 6Q7 or 12Q7 12SQ7 7B6 or 14B6  1U5 12AV6 or 12AT6 18FY6 12FM6 12AJ6 12FK6 12AE6 12FT6
Audio Output 53 or 2A3 41 or 43 or 25L6 6K6 or 6L6 or 6V6 or 25L6 or 35L6 or 50L6 25L6 or 35L6 or 50L6 50A5 3S4 or 3V4 or 1T4 50B5 or 50C5 32ET5 or 34GD5 Transistor
Rectifier 80 or 6Z4 80 or 25Z5 5Y3  35Z5 35Y4 Selenium or 117Z3 for AC versions 35W4 36AM3 N/A
NOTES: 4,5 and 6 pin tubes with grid caps
Octal with Grid caps Octal Philco and Sylvania pushed Loctal as an alternative to metal tubes. Popular for Car Radios AC versions fast warmup

Car radios require RF performance that was not avaliable from early Transistors

In the immediate Post WWII period, as production was getting back to speed, some makers produced five tube radios with a mixture of the Octal and seven pin 150ma tubes, depending on what supplies they could get.

Some AA5 sets used a 35L6 and a small resistor so that they could be designed to work on a 110V line, that was the design standard in some parts of North America. a AA5 using a 50L6 would require 121 volts. Note that the difference is well within the normal voltage variation. Modern guidleines now call for a design to use 120 Volts.

For more information on AA5 radios see WA2ISE's AA5 History page

What is a NOS Tube?, A NIB Tube?

NOS for "New Old Stock" is a term that is used in the old car hobby. It refers to a part that was made for a given car, around the time that car was new, and that has not been used.

When applied to tubes, it would imply a tube that was made and has been in storage as a spare part. The normal expectaion is a item that is brand new, with perhaps some shelf wear from being in a stock room. It might no longer be in the original box, because of deterioration of the cardboard. Tubes that were originaly packaged in bulk for use in Equipment Manufacture may also be NOS.

NIB means "New In Box" - Still in the original box.

Both terms are normaly interpreted to mean unused, although some will accept items removed from unused equipment as being still NOS.

In almost all casees, A NOS tube will be stamped with the SAME brand name as the box it came in. Many TV technicians would return the old tube that they had removed from a set in the box that the new tube came in. Anytime you find a tube in a different brand box, you should assume it is likely used. In a few cases, the technician may have later decided that the old tube was good, but did not retrive the new tube. Thus a good used tube was added to the technicians stock.

On rare occasions a tube will have two brand names. This is generaly a case where the the selling company did not buy enough to have the tube custom labled, but they still wanted to sell it in their own brand box.

Rare exception, Westinghouse bought this 1LH4 from RCA

It is of course posible for a NOS NIB tube to still be defective, because of a slow leak, or mechanical damage. Thus some dealers will offer NOS Tested tubes, which have been checked for function before being shipped.

How can you tell if a tube is NEW?

Actually, since tubes are run for a while in the factory prior to shipment, it is almost imposible to be sure that a tube is really new, but their are signs that may indicate that it is used.

For example, the ink used to put the brand on a minature tube can be wiped off by handling - of course the handling may just be testing to ensure that the tube is still good. When a tube has run for a while, there is often a shiny deposit directly above the heater, this is not to be confused with the getter. There may be a darkening of the envelope near openings in the plate. This is not to be confused with a dark coating that may be found in some tubes as a internal shield, or a means of improving heat or static electric dissapation.

Heater deposits tube from a Standard Brand Box white top tubes
The 35Z5 on the left is new, the one on the right shows darkening from the heater. This Tube is marked to indicate that it is a retested used tube. Even though these two tubes were NOS, the white getter deposit shows that they had leaked enough to be useless.

Are Black Getters better than Rainbow Getters?

Tubes normaly have a metalic appearing deposit on the inside of the envelope, or on the glass stem. This is the result of the firing of a getter during tube manufacture.

Creating the high-vacuum needed for the funtioning of a tube is a difficult process. While air will flow from an area of higher presure, to an area of lower presure, once the tube reaches a partial vacuum, the random motion of the air molecules reduces the ability to completly remove all the air from the tube. Tube makers use various techniques to assist in the removal of the air. Tubes are heated and connected up and run - sometimes beyond their normal ratings for an extended period of time to allow as many molecules as possible to leave the tube. This step is called "Processing" in tube industry lingo, and preceeds the sealing of the exhast tip.

Some chemical reactions, like activating the cathode, also occur during processing.

The Getter is a small amount of a highly reactive substance, often Barium, that is set off by a Radio Frequency Heater near the time that the tube is sealed off. The exact colour of the deposit left by the getter on the walls of the tube depends on the exact substance that is used, the temperature that it is fired at, the amount of Air still in the tube at the time the Getter is fired, and probaly the phase of the moon. Getter deposits range from a Mirror like silver to a dark black. If the coating is very thin, a rainbow like effect - similar to an Oil spill on water - may develop.

If the Getter is exposed to any residual gas in the tube, the gas will react and be trapped by reaction with the Getter material. The Getter in a leaky tube will be quickly used up and only a Milky stain will remain. If a tube has a whitish edge to its getter it can mean that it was sealed before the processing was complete, or that it has had gas induced by a slow leak, or from some contamination that was left on internal parts during assembly.

The Glass to Metal seals that are needed for tube leads to exit are very hard to make, and so it is possible for them to be imperfect. Leakage may be assisted by extremes in temperature. (like the vendor that claims to improve sound by dumping tubes in a refrigerant)

For a more technical overview of what a getter does, you may be interested in the web site of SAES Getters who make Getters for the CRT industry.

An British collector named Jonathan Evans has posted a copy of an article that was orginaly published in October 1950 that talks about the advantages and disadvantages of various Getter materials on his web page.

What is a "Frame Grid"

A conventional grid is a self suporting coil, that is spot welded to two upright supports. The wires must be stiff enough to stay in place while the tube is assembled, and also not droop with time.

A frame grid is instead wound around a stamped metal support. There is a notch for each grid wire, and the only part of the grid that is not supported is held in a stright line. The precison of the stucture allows the designers to use thiner wire, spaced closer together, and the element spacing can also be reduced. The result is a tube that can have higher gain, and fewer microphonics. The frame grid family was started by the 6AK5 developed during the second world war by Western electric.  Later there was a broad range popularised by the Philips group, and includes 6EH7, 6EJ7, 6ER5, 6ES8, 6FY5, 6GK5, 6HG8 and the series string variants.

Why were they packed in groups of five

These days many users of tubes are looking for matched pairs to use in various audio gear, and are surprised that tubes were normaly shipped in packges of five in bigger cartons of a hundred.  The major customers for boxed tubes were the TV repair industry and they would normaly order tubes every week from the local distributor.  A repair shop would probaly oder anywhere from 1 to 10 of a given type, and the five packs made it easy for the distributior to count out the order.
Typical quick order card.


Each package would come with a punch card, that the distributor could save and send to the supplier.  A sylvania Order-Matic card is shown although I also have seen the same system used by RCA and GE.  Sending the card back would get the distributor another pack of 5 tubes.

Where are they now?

When RCA finaly switched all Colour TV production over to solid state around 1975 the handwriting was on the all for most receiving tubes. Gradually most production was discontinued, often replaced in the short term by imports.

I have tried to trace some of the old brands.

  1. Allan B. Dumont: Their CRT division is know known as Lexel Imaging Systems Along the way, that have aquired lines of tubes from Raytheon, Litton, IST, Hughes and other mostly moilitary suppliers. They make mostly CRTs for the Military.
  2. GE-USA: see Ken-Rad
  3. ITT: ITTs ITT Electron Technology Division in Easton, Pennsylvania is now owned by Triton Electron Technology Division of Triton Industries. Main Products are Military, Industrial and Transmiter tubes.
  4. Ken-Rad: (AKA Kentucky Radio formerly Kentucky Lamp Company) Founded in 1902, company started making Tubes in 1925. The Tube business was bought out by GE-USA in 1945. (the lamp business went to Westinghouse at that time) GE had to divest the plant in Owensboro KY in 1987 as a result of merging with RCA. It is curently owned by an employee investor group, and makes microwave components and ceramic parts. Their web site Caution has java script that crashes my browser says that they no longer produce receiving tubes, but that it is the product that they get the most inquiries about. The military Qualified products list still seems to list them as a source for type 12SN7WGTA but that may be a stock that they are holding for the military.
  5. RCA Lancaster PA:The Lancaster facility was opened in 1942 as a US Navy plant operated by RCA for the manufacture of radio and microwave tubes.

    After the war, RCA bought the plant and it specialized in Televison and other imaging applications. Whn GE bought RCA, The plant was sold in a management buyout and was renamed Burle Industries major focus these days is Phototubes and other detectors for scientific applications including solid-state electro-optics.

  6. Rogers: Ted Rogers Sr invented a radio tube that could work on AC, thus removing a rack of lead-acid batterys from the radio. His company made tubes in Toronto, and also started Radio Station CFRB (Canada's First Rogers Batteryless). He merged with Majestic of Chicago, to form "Rogers Majestic". There are many unique tubes that the company developed, such as tubes with a spray on shield, rather than the external metal shield used by most of the industry.

    The company was sold when Ted Rogers senior died. The tube business was run as Phillips Canadian plant, (The Philips plant code is a small letter r).

    Ted Rogers Jr. has built up a major media and comunications business, (Video stores, Cable, Cell-Phones, Radio Stations) but is not really connected to the classic Rogers Tubes.

    Rogers was a major supplier of tubes in Canada.
    Rogers Boxes
    Early Rogers 2X3 base
    		Rogers 6CG7 Box
    Rogers used the Rogers and also Rogers-Majestic names
    This Early Rogers 2X3 Octal Tube has the brand name molded into the base
    		One feature of some Rogers Tube boxes was a diagram that gave the pin-out of the tube.
  7. Tung-Sol Lamp: After tracing a half dozen corporate history sites in the the search for Tung-Sol, I came to the conclusion that what is left is now the Wagner Lighting Divison of Cooper Industries. Main products these days are light bulbs and mechanical flashers for turn signals.

The 6CA4 rectifer in my Amp is dead, can I just use a Silicon Diode?

Perhaps. One of the first places that solid state devices worked their way into home electronics was to replace rectifer tubes. Many TV repair folks used to carry a supply of Silicon diodes to solder across the pins of Rectifier tube sockets or failed Selenium rectifiers. A company named Sarkes Tarzian even used to make a solid state rectifier that would plug right in the tube socket in in place of a Rectifier tube. (Sarkes Tarzian, Inc. is in the TV broadcasting business rather than a parts supplier these days) A pair of 1500V, 1 amp silicon Diodes could be wired in place of your 6CA4, and save about 7 watts of heater power. You should know that as the silicon diode has a lower voltage drop, you may end up suppling too high a voltage to the rest of your amp. Also since the Silicon has instant warm-up, the power supply will be on before the rest of the set has had a chance to warm up, this may mean an even greater voltage in the first couple of seconds after you switch on. This may be hard on the filter caps. This is particularly the case where the power transformer is slightly on the small side, and may now be puting out a higher voltage with one less heater to supply.

Another problem sometmes encountered is that as the silcon diodes switch on, they may emit an electrical noise pulse that may appear as a buzz in the sound.

Some techs will use Diodes called FREDs which make less switching noise, install limiting resistors to make up the voltage drop, insert noise filters and upgrade other components to compensate.

If you are talking about a Musical Instrument amp, you should be aware that the drop in voltage across the rectifer that occurs when you play a note, called SAG is part of what makes a tube amp sound like a tube amp. The higher curent drain while a note is playing causes the Power supply filters to partly discharge, they charge up again between notes. This effect will not occur with silicon diodes in the power supply unless the power transformer is way too small for the output of the amplifier.

I want to experiment, but tubes are expensive - any hints?

Popular tubes found in Sound and Audio equipment are becoming hard to find, and so they are also becoming somewhat expensive. Some ideas for experimenters.

Are there any Really useless tubes?

While some would say that usefulness is in the eye of the beholder, the tubes that were created to act as shunt regulators in tube type colour TV sets have got to be the least useful of all tubes.  (outside of retoring an old Colour TV of course.) These are high power triodes, that act as a variable load on the high-voltage section of a TV set.  Failure would result in excessive high-voltage, and many were recalled because they were a prolific source of X-rays. Long before the end of the tube era, Colour TV designers switched to other regulator circuts.  Because they were intended to work at a very high voltage, they are not useful at normal voltages. I am amazed the number of times that I see someone listing one of these on a auction site as a rare high-power triode audio tube.  Some typical numbers:
6BK4 6BD4 6BU4 6EF4
6LC6 6BK4 6EH4 6EJ4
6EL4 6EN4 6LH6 6LJ6
6MA6 6EA4

Finaly here are some tube Boxes


 Boxes from Japan
 Can Marconi Tube boxes
Marconi Citation Boxes
Many Canadian Tube Caddys included a least a few Marconi Tubes.  The box style on the left was unchanged from the 30's until the 50's when they switched to the "CMC" style.
 These are the boxes that were used when supplies started to come from Japan.  Some were called "Citation Radiotrons while others were just Radiotrons.
 Canadian GE box from early 1950's
  		 This is a box used by CGE in the 1940s and 50s, before the blue boxes.
Orange box tubes compared
 While the Orange and Grey box version used by GE is very common, their is a slight difference between the version used in the USA and Canada.
Canadian Boxes have the type number UNDER the Logo.
Late CGE tube Box
Towards the end of the Tube era, Canadian General Electric started to use these unique CGE boxes. For a while they were making their tubes in a clean room, later they sold imported tubes marked "made to CGE specifications"


GE communication Service part box.
 Like Motorola - GE USA also sold special tubes to be used in repairs to two way radios.
Older Motorola box from the 50's

Two types of Mot boxes
Vital Comms
Motorola had Both a consumer line and a communications line of Tubes, the First box above is a consumer line box from the 1950 era. The next box is from the consumer line (Circa 1960's), The Motorola consumer TV line was eventualy renamed Quasar and subsequently sold to Matsushita (Panasonic), the Tube box at the bottom is a Two-Way radio tube.
I am not sure if the Character with the box is a SCUBA diver or a rocket man, but he seems in a hurry to get new tubes into a radio somewhere. This is from a communications Tube

Perhaps the most common brand of tubes was RCA
Typical of the front of an RCA tube box, this one states that the fountainhead of modern tube development is RCA This box front refers to the worlds best known tubes The side of a USA market box, giving the Harison NJ address A Canadian RCA tube box side, note the His Masters Voice logo, and RCA Victor Company Ltd. Montreal. The front of the box would have the RCA logo.
This RCA Victor design, (two sides of the box shown) was used in the USA Cunningham was a Brand that RCA primarly used in the Western United States.
Arcturus was an Early brand, that was later common for re-branded tube.This view shows 2 sides of the box. The Hytron Company was probaly the first to make a T9 size GT tube, which they called a "Bantam", the firm was later taken over by CBS. Note the Canada Ocean map of the USA used as a logo.
The Blue GE boxes used before the Orange ones. This one is for the American market. Another "bargain Brand" box, (Western Electronics) this one seems intended to look like a CBS box.
Off brand Box made to look like Tungsol
 Simalar to Standard brand
 another bargin brand
The guardian Tube was apperently a "Bargin" brand. Notice how much the box is designed to look like one from Tung-Sol at first Glance.
 This box from a  distributor out west is designed to look like a generic Standard Brand Box.
 Zaltron was a ecconomy brand in the USA


Please let me know what questions you have, some of them I may even be able to answer.

The naviagtion button for this page is based on one of the scans of tube boxes placed on the web by a tube dealer called PaxCom

Electronic Tube related link page

HAM radio

Historical Electronics

General Electronic surplus

Parts for Tube equipment

Parts in general

Electronic Information

If you can suggest a site that should be added to this list, I would appreciate if you would e-mail me at cmacd@achilles.net

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