Tube Advertising

Vintage Vacuum Tube Advertising

One of my favorite glimpses into the golden-age of vacuum tube electronics is the advertising for the tubes themselves. Even though only a few factories actually manufactured ‘receiving’ tubes, various ‘brand names’ all tried to lure you over to their quality and reliability. However, by reading ‘between the lines’ of sample advertising, we can derive at a few interesting observations. Let’s begin, shall we?


Here is a classic example of the ‘My tube is better than your tube’ advertising that went on in the early years of vacuum tube manufacturing. This RCA ad promises that no tube even dreams about leaving their factory (wait a minute, didn’t GE make RCA tubes?) until it passes a myriad of ‘tough tube’ contests. No mention is made of drug testing after though. Other RCA ad slogans of the late 1940’s/early 1950’s include… “9999/100% pure… yet we threw it away!” “Take a look at quality being born.” (With a few factory pictures showing the ‘RCA’ tube plant) and “Quality control by feedback… the secret of RCA tube performance.” (Supposedly RCA engineers listened to service technicians and audiophiles about how to make tube ‘improvements’.) A very interesting website has the history of many tube companies, including RCA. This website also has a factory tour, showing how an RCA tube is manufactured. Check it out HERE.

CBS bravado claimed that their tubes were ‘more dependable’ and would ‘cut callbacks’.

At the same time, CBS claimed they alone put their tubes through rigorous cycled tests, at low (105VAC) and high (140VAC) line voltage conditions, to ‘weed out’ problematic tubes. They also tested for ‘gradual deterioration of electrical characteristics’, in order to cut ‘callbacks’ (there’s that phrase again). Later on these ‘super-tubes’ somehow became ‘super-duper tubes’ when matched. There were many CBS tube advertisements, and they usually told you more in their advertising than most other ‘manufacturers’. To check out a very informative advertisement explaining why a CBS rectifier tube is ‘better’ than the competition, HERE.  The ads will absolutely give you something to consider when shopping for a rectifier tube.

 Mullard7025     AmperexECC83     Sonotone_7025


When Philips caught on that the original 12AX7 (developed in 1948) wasn’t a very good audio tube, they introduced the much better ECC83. Of course Philips manufactured tubes under many other brand names, including Amperex and Mullard. The advertisement for the Amperex ECC83 can be seen above left. It had all of the features that Sonotone tried to lure you with over to their 12AX7 replacement, the 7025. The Sontone advertisement for their 7025 can be seen above center. The Mullard ECC83/7025 advertisement can be seen above right. Strange that a tube originally ‘conceived’ as a high gain audio voltage amplifier should be ‘born’ with so many ‘birth defects’. Stranger yet is the blatant omission that anybody’s 7025 sounds better than the ‘old’ 12AX7, or has better linearity and less distortion. They are simply advertised as being more reliable, have less noise, be less microphonic and have less filament hum. Any tube labeled 12AX7 after the mid 1950’s is probably a 7025 anyway, with the improved construction. This includes the many tubes labeled 12AX7/7025, done in hopes of striking a familiar ‘name’ with old-timers out tube shopping.


Another RCA ad campaign started out with this header. Most capacitor ads as well mentioned that the ‘callbacks’ could have been avoided if only the technician had used ‘Brand X’ tube/capacitor. Later on, ‘tube matching’ was a shtick dreamed up to dissuade customers from buying surplus tubes from electronic ‘discount shops’ that had proliferated after WWII.

Take THAT, you dirty ol’ UNMATCHED tube!

Most tube manufacturers, who earned a small fortune selling overpriced tubes to the government and military sectors during the war years, now had to deal with their ‘full price’ retailers that were feeling the pinch of the surplus tube market after the war was over. To make matters worse, every corner drug store and hardware store had a tube tester, and the frugal customer could test his own tubes, and then purchase a surplus replacement, saving twice (no service call charges, and a cheaper tube). To see a vintage Canadian tube price list from RAD-TEL tubes, HERE. But was all this ‘competition’ really healthy for the retail tube industry? Consider that even the business of testing tubes was gaining momentum! Many outfits sold/rented tube testing equipment, targeting the usual outlets; anywhere Mom and Pop may have wandered when they hit the big city on a Saturday afternoon. An article appeared in the December 1957 issue of Electronic Technician telling the ‘legitimate’ TV repair shop that they should also look into renting a tube tester to place in the corner Drug Store! Below is a scan of the first page to the article.

By simply placing your ‘Self-Serve’ tube tester in a busy locale, you too can profit from tube sales!

The article mentions that since the ‘business’ of testing tubes is booming, so why shouldn’t the ‘legitimate’ TV shop get in on the action? Apparently, a conservative estimate has it that there are between 20,000 and 25,000 ‘Self-Serve’ tube testers in the US alone in 1955. A further estimate has it that this is worth between $20,000,000 and $30,000,000 in tube sales yearly. To test the tubes was always a ‘freebie’, and if needed, the replacement tubes were purchased right on the spot. The ‘owner’ of the machine typically split the profit of the tube sales 50-50 with the Drug Store or Hardware store that allowed the tester to be placed in their establishment. So of course it is no surprise that ‘Self-Serve’ tube tester advertising picked up quite nicely during the 1950’s. Below are a few sample ads from various magazines of this era.

Equipment_Leasing     Shell     U_Check_Em
If there’s a Dollar to be made, you can be sure there will be competition.

These advertisements all point out that the machines can either be purchased outright or rented. Also mentioned are some ‘facts’ about how much money can be made simply by leaving such a machine in your local Convenience Store. As an example, it is claimed that $50 worth of tube sales per week is not unreasonable. Even in ‘poor’ locations, tube sales of $20 to $25 per week is ‘normal’. So how do the tube manufacturers and retail sector fight back? Placards were sent to all retailers, offering ‘Free, Professional Tube Testing, On the Latest Equipment’ (big deal; ‘Self-Serve’ testers are also free to use), but the service shops were encouraged to take as much time as necessary to make the customer feel like his problems were being handled with sympathy and a technical understanding that the corner druggist simply didn’t have. Then a definite ‘bright idea’ of the decade came along; those tubes at the drug store weren’t ‘matched’ (Gasp)!

CBS_matched_ad1    Philco_tube_ad    CBS_matched_ad2

Although these same tubes only left the factory after meeting… ‘exacting quality standards’ and being… ‘thoroughly tested and inspected’ on Monday, they somehow sounded ‘better’ and offered fidelity that was a little higher when… ‘Their critical audio characteristics are matched’… into pairs on Tuesday. Of course, those millions of government surplus tubes made last Sunday weren’t ‘matched’, and shouldn’t be purchased from your local surplus electronics retailer. Always buy the freshest batch and only from the manufacturer or licensed full price retailer, OK? To be fair, today’s tubes have a poorer quality control standard, which makes matching (or more like weeding out the really bad ones) a necessary evil. The CBS ad above throws in the statement that their matched tubes allow for… ‘reduced distortion even below that attainable by controls for balancing plate currents.’ In other words, pay more for two tubes that already have similar current draw characteristics than waste time fiddling around with controls and two ‘unmatched’ tubes. In a stereo amplifier this may be warranted, but in a guitar amplifier it may not be desirable to have perfectly matched output tubes. This of course assumes that the phase inverter and output transformer are perfectly balanced as well.

I don’t believe Fisher made their own tubes, but Damn, those EL37’s look cool!

Fisher promised to select their tubes individually, and chose only those tubes that exhibited… ‘maximum gain, low noise, exact tolerances, long life and… absolutely identical performance characteristics.’ Yet they were available as single units or in matched pairs. So, again, how are they ‘better’ when ‘matched’? Shouldn’t two ‘singles’ be the best possible tubes? Fisher also states that ‘Only The Best Goes Into Every Box!’, yet somehow their ‘best’ got ‘better’ when shipped in pairs. Perhaps Fisher felt it was really only better for their cash register.

How would “Tube to Tube Uniformity” improve with matched pairs?

Even Mullard was known to exhibit a bit of bravado about the quality of their tubes. This 1962 Electronics World advertisement mentions….. ‘Tube-to-Tube Uniformity and Section-to-Section Uniformity’ and that ‘Each tube (is) Individually Laboratory-Tested’. Surely this could foreshadow an embarrassing case of hoof-in-mouth disease if they jumped on the matched tube shtick.


By using Sylvania tubes, you are guaranteed that these tubes met ‘exacting standards’, and all were pre-tested to ensure that each and every tube delivered ‘exceptional performance’ (doesn’t everybody make this claim?). Could they be even better if they were sold in selected, matched pairs? Apparently not, as Sylvania didn’t jump on the matching bandwagon. Perhaps the military (pictured above as the primary recipient of this outstanding performance and dependability) didn’t need matched 5881’s in their B52’s.


Not to sound like a broken record, but these late 30’s/early 40’s ads from RCA state that their precision construction techniques will guarantee a very consistent performance from quality tube to quality tube. Most other tube manufacturers(?) had similar claims, with catchy slogans like… “Only Our Very Best Goes Into EVERY Box!” To their benefit, RCA never really jumped on the tube matching shtick that started in the late 1950’s, although the above ad implies that every RCA tube is ‘matched’ right from the beginning (I’ve highlighted the point #1, which should be a dandy conversation starter). FYI; The 2A5 shown above is a 2.5-volt filament pentode, and is electrically identical to the 6.3-volt heater 6F6 (Very similar to the 6V6. The lesson here is that just as Chrysler built many models on a ‘K-Car’ chassis, Many tube types are built on only a few different structures). It was possible to achieve 19 watts output with a pair of push/pull 2A5’s.


Why not let even the tube testers get in on the act? This is the ‘My tube tester can pick out bad tubes your tube tester says are good’ type of advertising common when ‘mutual conductance testers’ became the buzzword. This is an ‘oddball’ though, as the Sencore Mighty Mite is an emission tester! It does have the advantage over simpler emission testers in that it tests tubes at ‘rated load’, which is a fancy way of saying higher test currents. Cheaper emission testers used cheaper power transformers, which cannot handle high current demands (the tubes emission could ‘sag’ under heavier load). Testing at lower currents may miss problematic tubes, as the above advertisement mentions. Emission testers as a whole are inferior, as they connect all tubes as virtual diodes, by shorting any grids to the plate. The plate current is measured as an AC voltage is applied. The ‘upgraded’ emission testers used beefier power transformers and higher voltages to try and weed out the borderline weak tubes. Nonetheless, emission testers lost favor with the service technician besieged with callbacks because they only indicated the condition of the cathode coating. Since most tubes other than diodes rely on the ability of the control grid to regulate the flow of electrons, the actual number of electrons flowing seems less important. Having said that, I still do own and operate a number of vintage/later model service-type tube testers, both emission and mutual conductance types. I just let my ears and eyes do the final ‘testing’. For a complete idiot’s guide to understanding the basics of tube tester function, see HERE.

The only honest tube advertisement I have ever found.

And, finally, this Amperex advertisement. It is the only ‘honest’ tube advertisement I have found to date. Every statement made is factually correct. However, what is omitted is the proviso that these statements are only true compared to a 5U4 and similar rectifiers. Other rectifier tubes (like the 83-v, or the 84/6Z4) available before the 5AR4/GZ34, or the 5V4, available during the same time would offer equal ‘improvements’. With a tube manual or a tube theory book in your hands, read about the differences between a directly heated cathode and an indirectly heated cathode. What differences do each type yield in our amplifiers? Which has more ‘sag’? Which type actually helps our output tubes last longer?

Basic Hickok Troubleshooting

Hickok Troubleshooting Guide

I have assembled a very basic ‘guide’ to assist you in repairing your Hickok tube tester. You may be hesitant about buying that ‘Handyman’s Special’ for $50 because the thought of repairing a tube tester frightens you. I would be more afraid of someone who would pay $50 for a non-working Hickok, but that’s me. I’ve done it myself in the past, but only because it was something like an otherwise pristine 752A. You might not be that lucky, but you just never know. Unless one of the power transformers has a short or open winding, most any can be repaired; it just takes a little patience and a lot of luck. If your soldering iron is plugged in, let’s tackle that Hickok! Let’s assume you have one of the ‘basic’ Hickok tube testers; the 533 say. If you have the manual, great. If not, download it (or any similar tester), and study it. What you should see from the schematic is as follows.

  • Most Hickok tube testers use a 5Y3 and an 83 rectifier tubes.
  • The 83 is there solely to provide B+ to the Plate of the tube under test.
  • The 5Y3 is there to provide Screen Grid voltage and Bias voltage to the tube under test.

Of course, we will check the ‘fuse’, which is often an 81 bulb. If the ‘fuse’ checks OK, we continue on. Set up the tester for a 6V6 (but do not insert a tube), and check the following. Keep in mind that the ‘negative’ lead of your VOM should be in pin #8 of the octal socket for any voltage measurement other than the filament. These initial tests are done without lifting the panel! Are all filament voltages present? Are they ‘correct’?

  • By pressing the ‘P4’ button, do you get a signal voltage on pin #5? (Typically 5VAC)
  • By pressing the ‘P4’ button, do you get a Screen Grid voltage? (Typically <130VDC)
  • By pressing the ‘P4’ button, do you get a Plate voltage? (Typically <150VDC)
  • Set the bias control fully clockwise. Measure the DC voltage at pin #5; it should be -40VDC. Now adjust the bias control to ’22’ (the setting for a 6V6), and check the voltage. It should be -3VDC.

We have now checked the tubes under the panel (without removing the panel screws) and confirmed the bias potentiometer is working. That last part is important, because the bias potentiometer isn’t available from Radio Shack today. If one or more voltages are ‘missing’, we will have to open up the panel, and look around inside. Usually, the rectifier tubes are mounted to a small bracket on the power transformer. Below is a view of the interior to a Hickok 600A, showing how the rectifier tubes are situated.

Interior view of Hickok 600A, showing rectifier tube bracket.

Some models will make you remove the bracket bolts, and position the bracket in such a manner that voltage checks are possible. By carefully having the bracket positioned so you can do some voltage measurements (use clip leads!), press the ‘P4’ button, and check the following.

  • Do you have <320VACbetween pin #4 and pin #6 of the 5Y3?
  • Do you have <340VACbetween pin #4 and pin #1 of the 83?

If all checks turn out OK thus far, you are actually in trouble! This is because you now enter the realm of the esoteric fault. I once had a Western Electric KS-5727-L1 that had multiple faults. Aside from leaky capacitors, the plate voltage was very low. A new 83 didn’t cure the symptoms, nor did using 1N4007 diodes instead of an 83 (just to be sure I didn’t swap one bad 83 with another bad 83). The plate voltage is fed from the 83 through a small tag board (I had cold solder joints here, so be advised), over to the ‘P4’ switch, as well as through to the micromho/grid signal range switch! Either switch is a pain to get at well enough to service, and chances are this is where the trouble is if everything else checks OK. There are 47-ohm resistors on three switches (buried very cleverly) that also can act as a fuses. When these ‘blow’ from trying to test a shorted tube, few people know to look for them. Even if you do know what to look for, you go cross-eyed trying to find them. Other odd-ball faults are as follows.

  • I had a 750 that would not light up the tube but the filament voltages checked OK! It turned out to be a high-resistance cold solder joint on the filament transformer. The high impedance of my VOM showed full filament voltage, but with a tube inserted the voltage dropped too low to light the tube up.
  • I had a 533 that ‘partially’ blew the 47-ohm resistor on a switch. The resistor was barely touching its two ‘halves’ together, and sometimes the resistor halves would not touch, and I would not get a reading. Some days I would get the reading just fine, and those days drove me to drink. Just the act of physically moving the tester back and forth could cause the tester not to work some days, as the two resistor halves became jarred loose.
  • If the ‘Bias’ potentiometer or the ‘English’ control prove to be faulty, you can always use that tube tester as a door stop. I have had a 1% success rate rebuilding either control, and refuse to even attempt such a ‘repair’ anymore. These potentiometers are simply not available, except through organ donations from deceased Hickok tube testers.

As a final check; let’s assume you have a Hickok that appears to test the 6V6, but does not register a reading on the meter. Check the ‘Fuse’ bulb as you hold the ‘P4’ switch down. Does the bulb glow very faintly, and increase slightly as you hold the P4 switch down? If so, the trouble is between the P4 switch and the meter movement. Check all wiring between the P4 switch, the micromho range switch, and the meter movement. There isn’t much to go wrong; some wiring, and a few precision resistors. The remaining possibility is the meter movement itself. That about wraps up all that I can share with you regarding Hickok tube tester trouble shooting. Most testers I have come across have given no trouble over their 50+ years of service, but there is always that one ‘dog’ to contend with. If I am looking over a prospective purchase, I check to see that all of the panel screws are in place. Missing screws almost always points to the fact someone else took time to ‘fiddle’ with the innards of that Hickok, and only Jehovah knows what they have ‘screwed up’. For $20, I have taken the gamble, if only to have a cadaver to donate organs so that another Hickok may live again. But, thanks to the magic of eBay, even beat-to-crap, non-functioning Hickok tube testers can now fetch $125 or more, and some neurotic tube jockey still feels he is getting a bargain. I recently witnessed a Hickok tube tester with no meter movement, no bias potentiometer, and a case that looked like it had been dragged behind a team of wild horses offered for auction. Don’t bother asking what the final selling price was; anyone offering over $1 should have their head examined.

Hickok Tube Testers

Hickok Tube Testers

The number one name in vintage tube testers is Hickok, without any doubt. Their name is held in the highest esteem, and Hickok tube testers are very much sought after today. Although they manufactured quite a large number of tube tester models (beginning in 1928!), today’s audio ‘experts’ seem to only covet the later models. A very early model (though certainly not the earliest model I’ve seen) is the 510X, which also doubles up as a VOM. An example can be seen below.

Hickok510XHickok 510X is not as coveted as many other Hickok tube testers.

Not quite what you thought it would be, is it? This model was manufactured up until approximately 1935, during which time most every model of tube tester was superseded by an ‘upgraded’ version, complete with a new model number. The 510X had the ‘drawback’ of having no room for a roll chart, thanks to the VOM function. This model was replaced after the war years with the 530B, which thankfully had the roll chart, as well as sockets to test the ‘new’ miniature tubes. Hickok really had quite a colorful history, and here we have but a very small sampling of the advertising/catalog inserts I could find. Most Hickok advertising states that a tube is ‘tested under simulated operating conditions’, although I have never owned a Hickok that could put 500VDC on the plates of an EL34. To be fair, most tube testers that claim ‘operating conditions’ actually do have voltages similar to television and radio equipment of that era; guitar amplifiers are a horse of quite a different color. Let’s check out some of the vintage advertising below.

Hickok tube testers were quite expensive in their day.

The ad above is from the January 1953 issue of Radio-Electronics. The prices seem quite extraordinary for the 1950’s, and even today I can’t imagine how long it took a repairman to save that kind of money. The Model 539c, listed below, is the most sought after Hickok tube tester, and commands incredible prices on the open market (i.e. eBay). Their popularity may be explained in part by the observation that Hickok manufactured the ‘539’ model (including the 539a, 539b, and 539c) from about 1948 right up until approximately 1975, and there appears to be an extraordinary amount of these testers available.

Later day Hickok catalog shows the 539c very expensive.

Here along side a CRT tester/rejuvenator we have some later day advertising for Hickok tube tester models 6000A and the guru-approved 539c. Damn, but they are expensive. What made them so expensive? Mr. Hickok himself manufactured meter movements before entering into the test equipment business. Most Hickok testers feature real glass for their meters, and pretty elaborate D’Arsonal-style movements. These are important, but don’t affect the accuracy or validity of the reading. These are still two popular testers to find on eBay, and the prices haven’t changed much.

Hickok_Ad2    Hickok800    Hickok_121
Hickok Model 121 above looked expensive for the serviceman of 1959.

The ‘Cardmatic’ tube tester series we saw previously had more than model(!), as seen above left is the advertising for the Model 121. Here the Model 121 is advertised as being the low-cost alternative to the more expensive(!) Model 123A. I’m not sure how it can ‘pay for itself’, but I can’t imagine the retailer letting me take one home claiming the tester will indeed ‘pay for itself’. In 1959, I believe $249.50 would easily exceed many a technician’s weekly paycheck. To remind you that Hickok made much more than just tube testers, above center is the ad insert from the October, 1967 issue of Radio-Electronics. To understand just how expensive it was to own a Hickok anything, note that a ‘general purpose 4mHz oscilloscope’ for your bench costs $635! That would take the average repairman about an entire month to make that much money, even in 1967. The ‘portable’ oscilloscope, aimed at the TV repairman, is still $219.95. I’ve seen tube testers after they’ve been bouncing around in the service van for many years; I can only imagine what a $219.95 oscilloscope looked like after the same treatment. The thing to keep in mind is that the Model 800 (above right) was definitely not their top-of-the-line unit, yet it was still priced quite a bit higher than the Superior TV-12 or the Eico 666 tube tester, as examples. It is priced comparably to the B&K 650, all of which also test transistors. Advertisements invariably show Hickok tube testers originally priced much higher than many other brands, which partially accounts for their high resale value today.

Hickok6000a       Hickok800_ad
1962 advertisement proclaims Model 800 as ‘Lowest Priced Hickok’, and 1964 advertisement proves it.

Above left is an ‘alternate’ advertisement for the Hickok 800. Again, the ad proclaims this as the ‘lowest priced’ Hickok available. By my math, if you were earning approximately $2.25 an hour in 1962, you could devote an entire two-week paycheck towards the purchase of this tube tester. According to The American Institute For Economic Research, $179.50 in 1962 is the equivalent to $1,284.44 in 2008. Compare the retail price of a Hickok 800 to the retail price of a Hickok 539c, which would require you to earn approximately $9.35 an hour in 1962, and earmark your entire paycheck for the luxury of owning this most highly regarded tube tester. According to The American Institute For Economic Research, $750 in 1962 is the equivalent to $5,366.72 in 2008. Above right is an ad pulled from the November, 1964 issue of PF Reporter for the Model 6000A. This ‘new’ tester no longer has provisions for checking 4/5/6-pin tubes, but can test all the latest tubes, including Nuvistors and Compactrons.

An unusually rare Hickok tester was developed in 1965, perhaps in answer to the ‘average’ TV technician complaining how expensive Hickok test equipment was! Below is a sample advertisement for the Hickok 799 tube tester, dubbed the ‘Mustang’.

Even Hickok was known to sling a little BS in their advertisements.

Taken from the July, 1965 issue of PF Reporter, the advertisement above is ‘proof’ even Hickok could resort to hype and misleading advertising. At first it would appear that the Mustang would be an ideal tube tester; manufactured by the most famous name in tube testing, this unit should be a ‘no compromise’ unit, as promised. But is it? ‘

  • 100% Gm Tests… No Emission Tests, No Compromise!’ Well, how do you measure the ‘Gm’ of a GZ34? The ad further compares itself to other tube testers, and mentions ‘… at best, no more than 10% of their tests were actually mutual conductance.’ The truth is no tube tester measures actual mutual conductance; they are measuring the AC gain capabilities of the tube, and at one (usually lower than ‘real world’) plate voltage. Lastly, the Mustang connects all tubes as triodes, which could easily be construed as a compromise.
  • ‘A solid-state power supply gives increased accuracy and dependability.’ So, my 539c doesn’t have this ‘accuracy’ and ‘dependability’? I have a hunch then even though the 799 is pretty rare, they will not command as much respect from the modern tube ‘guru’, nor will they garner as much hype or cash on eBay as a 539c.
  • ‘An all-transistorized gas and leakage test circuit sets a new standard or reliability for spotting ‘tricky’ tube defects that can ‘chew up’ your profits.’ This ‘new standard’ was used by B&K (albeit with a tube) for a few years before the Mustang was thought of.

The Mustang ‘borrowed’ a few layout ideas from B&K as well. Common tube settings were printed right on the panel, trying to speed up the process. I have only seen a very few Hickok 799 tube testers, and I own one of them. They are a nice tester; they calibrate very easily, and seem to operate smoothly. Would I use it as my ‘go to’ tester? Probably not. From the same era, most other B&K tube testers are cheaper, set up as fast, and test a 6L6 as a 6L6, and not as a triode. It’s no wonder more TV shops used B&K test equipment than any other brand, including Hickok.

There are many models of Hickok tube testers, and I have only touched on a select few. There are also many websites devoted to these testers, and below is another ‘select few examples’. Some will have manuals you can download, as well as calibration procedures. Also keep in mind that many discussion groups regularly bring up the subject of Hickok tube testers. If you are lucky enough to own a Hickok tube tester, you owe it to yourself to visit these sites. You should also buy at least a handful of spare 83 tubes, as well as #49 bulbs and #81 bulbs. Those who have ‘been there, done that’ know what I am talking about. Hickok would be just a faint memory today, were it not for the military sector. Due to their high retail prices, not many ‘civilian’ radio or television service technicians could afford a Hickok tube tester (or any other piece of Hickok test gear). But the military, known for paying $385 for a ‘mil spec’ hammer, seemingly bought a tube tester for every enlisted man. These testers now show up like Jehovah’s Witnesses all over eBay. The most popular, the TV7, is a very good tester. Read up on the various models, and decide if you’d rather make a mortgage payment or own a twenty-five pound boat anchor that cannot test ‘modern’ tubes. Remember, Hickok played up their ‘Dynamic Mutual Conductance’ circuit to death, so it is exactly the same tester under the panel of a 533A as it is in a TV7. The military paid as much as $1130US for that TV7 tester between 1960 and 1982(!), meaning they are very plentiful today. 

Hickok752    Hickok752A
 Can you see a difference? Is that difference worth $34?

I am always amazed that people will pay for photocopies of tube tester manuals on eBay, when most of them can be downloaded for free. Original manuals might be worth buying (if your tube tester is immaculate, and an immaculate manual would complete ‘the picture’), but recently an original Hickok 752 manual fetched $36US via eBay. I downloaded the manual for my very same tube tester, and for a total cost of less than $2 had it bound into a spiral ‘book’. Buying photocopies makes sense only if you cannot find a ‘free’ version, and/or you are too lazy to download and print your own manual.

Emission Tube Testers

Emission Testers

Here are but a few samples of ’emission’ testers. You will see these testers frequently on eBay, and the prices are not that much lower than B&K ‘transconductance’ testers, as one example. This is a prime example of sellers only understanding that there is money to be made on eBay, and not how the very tester they are selling works, or if it works at all! You’ll see many auctions claiming ‘I don’t know anything about these things, so it is being sold “AS IS”.’ Or else something along the lines of ‘Untested, and being sold “AS IS”.’, or I have no tubes to test this thing out with, so it is being sold “AS IS”.’ To be fair, I’ve acquired many tube testers from the original owners, who insisted that the tester was fully functioning, only to get it home and discover it was anything but. Unless you walk around carrying a tube in your pocket should the opportunity arise, it is always a gamble.

Sencore_MightyMite  Lafayette_TE50
Simpson_555  emc
Emission testers are always compact, with few controls to adjust.

You can often spot an emission tester by the absence of fancy switching arrangements. Typically, there will be a filament voltage selector, and perhaps two other controls; one could labeled ‘Load’, and the other ‘Circuit’. Some testers simply labeled these controls ‘A’, ‘B’, and ‘C’. Also look out for faceplate labeling along the lines of ‘Qwik-Check’ or ‘Dyna-Test’, or ‘Rapid-Test’, or something similar. You may also notice emission testers usually have a simple ‘GOOD’/’BAD’ scale, and a percentage rating designation. Mutual conductance testers usually have the scale marked in ‘micromhos’. There is also usually a range selector switch, seeing as all tubes can’t read accurately on just one 0-15,000 micromho scale.

Even when mutual conductance testers became vogue, the emission testers fought back by advertising how fast you could test a tube on an emission tester! As a piece of useless trivia; Radios did the same thing, as the very first sets had multiple tuning knobs that had to be adjusted at the same time! Later, when multi-ganged tuning capacitors became available, ads popped up stating how fast and accurate a certain radio could be tuned. Tube testers followed suit with those cute nicknames and ads stating how much time the service technician can save by using that tube tester. “No more wasting valuable time setting multiple switches! No more cumbersome roll charts to fight with! Just two simple controls to set and any tube is fully tested in under 10 seconds!”. The latest emission testers sometimes advertised that they tested all tubes ‘under full load’, meaning they simply applied higher voltages to the virtual diode when called for by setting the selector switches. Sometimes this control is even labeled ‘LOAD’. While this is ‘better’, as the tube’s emission can ‘sag’ under heavy current demands, it’s still an emission tester. A final problem with cheap emission testers (and cheap transconductance testers, as well) is with the ‘Shorts’ test. This necessary test is made with an AC voltage that is applied between each tube element, where leakage will pass enough current to activate an indicator in series with the circuit. It is important not to further test any tube which fails a ‘Shorts’ test. Doing so usually results in damage to the meter movement. In the ‘Shorts’ test circuit, a series resistance must be used to keep the lamp from burning out when there is a ‘direct’ short between two tube elements. This series resistance places a limitation on the maximum resistive short that can be indicated to about 1 Meg. There are TV and radio circuits where 1 Meg of leakage resistance will have absolutely no adverse effects, and there are others where this would disable the circuit and cause confusing symptoms. This leads to many TV technicians deciding after the second or third time he was led astray by his tube tester to put it away, and use tube substitution as a repair technique. A crude idea of how this particular test circuit works is shown below.

Typical ‘shorts’ test circuit seen in lower-priced tube testers.

Fancier emission and even transconductance testers (like my Hickok 752A) sometimes have an ohm-meter scale on the meter movement; utilizing the ‘Shorts’ tests converts the meter to the ohms scale, and a leakage reading is done. This is much more sensitive, and is usually only found on more elaborate (and more expensive) testers. A crude representation of how this might be implemented is shown below.

Improved ‘Shorts’ test is really a ‘Leakage’ test. 

In conclusion; emission testers are suitable for testing diodes and rectifiers only (as these tubes have no ‘gain factor’ to measure, and can only be tested for cathode emission). A ‘good’ emission tester will still find 75% of your bad tubes; providing the tester uses a heavy-duty transformer, and your tube is ‘suffering’ from low emission. If you want an emission tester for having an emergency ‘backup’ unit, that’s perfectly fine. Beware of their limitations (don’t ever try and ‘match’ output tubes on one), and don’t pay hundreds of dollars for any emission tester.

CBS Tube Advertising

Tube Advertising

Here we see a classic advertisement from CBS, in which they explain why their tubes were superior to the competition. There are a plethora of examples similar to this copy for the CBS 5U4, and they each struck me personally as cute, clever, and well thought out.

CBS tube advertisement can teach us a lot, if we ‘read between the lines’.

If you cannot quite make out the copy, here is the main highlight. The plates are made from a ‘non-emissive’ material, which takes some explaining. Essentially, the plate heats up enough (from electron bombardment) that electrons are emitted from the plate itself, and attracted back to the filaments! This is not good, so the design of the plate material is such that this phenomenon is all but eliminated. Of course, CBS claims they test their tubes very strenuously, and won’t market a tube that does not meet stringent quality control. This is probably true, as the few CBS tubes I have used always seemed well-made, and performed flawlessly.

We can also see an advertisement below for the GE 5U4GB, which will tell us why their 5U4 lasts a little longer than the competition’s 5U4.

GE 5U4GB utilizes smooth plates in order to protect the filaments.


p style=”text-align: left;”>What we are told is that the ‘ribbed’ plates can collect ‘contaminants’ along the ridges, which will build up into sources of back-emission. This causes ‘hot spots’, and the back emission can eventually melt the filament! GE had other advertisements explaining all the developments used in producing their vacuum tubes, each making a GE tube a little better than the competition. I’ll give you a few more examples for a later ‘update’.

Where this is all interesting pieces of esoteric knowledge is as follows. I have seen many Chinese 5U4’s ‘blow up’ in a high-voltage Boogie, or Russian 5U4’s bite the biscuit even in a Matchless. I had originally though no one makes a decent 5U4 anymore; I may be right. I questioned how it could be possible to make a ‘bad’ rectifier, and these advertisements explained it to me. By using cheaper materials, Russian and Chinese tubes may not last as long (this applies to more than just rectifier tubes). Now, that is a pretty broad paintbrush to use; there are good Russian and Chinese tube out there today. But now you have food for thought if you should ‘go through’ 5U4’s a little quicker than you’d like. Lastly, keep in mind 5U4’s have their own evolution. A good tube manual will explain that to you better than I can, so compare the rating for a 5U4 from RC-16 up to anything in the neighborhood of RC-29.