What are you buying? I have a large quantity of New Old Stock testing 12BA6 (HF93) vacuum tubes available for an excellent price! Mostly from US manufacturers in the 1950’s and 1960’s, with some Japanese manufacture. Discounts are available for purchasing multiple tubes! Testing standards These 12BA6 are primarily tested for transconductance (gm) and plate current, and in order to meet the criteria for the NOS (New Old Stock) category, they must be within 20% of their nominal values for both measurements. This means that these are the equivalent of a brand new tube, and can be relied upon to perform as such, as well as have a full, long life ahead of them. Take advantage of this excellent deal on one of the most popular tubes of yesteryear, performing just like it’s fresh off the shelf! Notes on this model The 12BA6 is one of the most widely used miniature tubes in history. It is a remote-cutoff, variable mu pentode intended for use as a high gain radio frequency or intermediate frequency amplifier in standard broadcast or FM receivers, and features low grid to plate capacitance for minimal regenerative effects, and high transconductance for a high signal to noise ratio. Combined with suitable shielding and short leads in your equipment, it can be relied upon for excellent performance in wide-band, high frequency applications. This is an essential tube for most All American Five (AA5) radios, made en masse in the late 40’s through 60’s! Requests for specific types or features of this model type (manufacturer, year, label condition, build characteristics etc) will always be honored upon request at no extra charge, if I have the appropriate stock available. Pictures are a general representation of the appearance, vintage and manufacture of these tubes, and do not represent the exact tubes you will receive. Quick reference notes on policy, testing procedure and more… Please reach out with any questions, issues or concerns!Tubes are tested on the Essues Etracer curve tracer, the most accurate modern machine for matching tubes, and one of the most accurate for measurement of a wide range of parameters.A physical printout or email pdf of test results and parameters will be included with any purchase upon request. Custom testing parameters may also be provided upon request.Tubes marked NOS are measured within 20% tolerances on all critical valuesTriodes are measured for μ (amplification factor), rp (plate resistance), plate current, and gm (transconductance), in order of importance. Matched or balanced triodes measure within 5% of each other on the first 3 values, and checked across their entire operating range.Pentodes/beam tetrodes are measured for gm (transconductance), plate current, screen current, and rp (plate resistance), in order of importance. Matched pentodes/beam tetrodes measure within 5% of each other on the first 2 values, and checked across their entire operating range.Contact pins are de-oxidized, cleaned and polished! (gold pins not polished, of course)Best efforts have been made to clean tubes, preserve their labels, and provide original boxes, but vintage tubes commonly have variable amounts of dust on them, labels are commonly variably eroded, and boxes will commonly be substitutes.Refunds may be given for broken tubes only, not for variations in testing/performance, as they will commonly perform differently in different environments and equipment. Replacements for broken tubes will be issued as available. Exceptions at my discretion. Why purchase your tubes from The Tube Fairy? Integrity in pricing, testing and advertisement – many Ebay tube sellers use dishonest tactics, such as: writing incorrect model number equivalents in the title to make it seem as if the tube is higher grade; inflating prices far beyond the market value of the tube and using misleading language in the description to manipulate the customer into believing the absurd pricing somehow equates to better performance; advertising tubes as ‘matched’ (which should mean matched electrical performance) when they are only matched for date codes (no guarantee of electrical performance); advertising untested or poor testing tubes as NOS simply because they may be in the original box or in good cosmetic condition; and posting misleading testing results without references, to sell weak or dangerously over-performing tubes at NOS prices. The Tube Fairy skips all that nonsense, giving you hard data from professional performance tests, accurate information on manufacture, vintage and build characteristics, and fair pricing directly related to the test results and the modern market average. I have a lot of respect for my buyers, and it’s my mission to make sure they get exactly what they pay for. Tube refurbishing – vacuum tubes produced back in their heyday are likely 50 years old at least, if not 100 years old or even more! Even if they were stored well in their original boxes, the connection pins have often oxidized or may be covered in other substances, which can dramatically affect conductivity and quality of connection. In addition, deposits may have built up on the electrodes internally, which can potentially cause shorts or decreased emissions. The Tube Fairy addresses all of these ills by de-oxidizing, cleaning and polishing the pins back to perfect conductivity (gold pins are not polished as this would remove the gold coating), and using the Etracer curve tracer to provide pulsed DC to different electrodes, using the highest safe voltages to help remove impurities and prevent shorts. The most accurate professional grade testing and matching available – there are many types of tube testing equipment, from those that test all possible performance parameters, to those that more or less only determine if the thing turns on! Even most competent testers only evaluate a tube at a single operating point, or measure a single value, which may not be relevant to your equipment or application. In addition, many sellers list incomplete information about their testing results, usually something like “testing at 94 where 45 is the minimum value”. This says nothing about what the testing parameter is or what it relates to, and makes tubes that are testing far beyond their nominal values seem acceptable, which could potentially be bad news for your equipment if the parameter happens to be something like plate current on a power tube! These sorts of results do nothing to evaluate the tube across the high voltage operating range that it may experience in your gear, do nothing to evaluate tube longevity, and have very limited matching accuracy. My testing device is the Essues Etracer, capable of measuring all relevant performance indicators across the tube’s entire operating range, including: filament current, plate current, transconductance, amplification factor, plate resistance, and screen current. The results can be evaluated to accurately determine the quality of regular performance, and also how much life a tube has left, the quality of its linearity, and how it performs at, and even beyond, the limits of its operating range. This device is able to represent measured information graphically, and this is the most accurate possible way to ‘match’ tubes for performance, meaning that their electrical characteristics will be identical within a certain tolerance across their entire operating range. This is crucial for push-pull power amplifiers and phase inverters, as well as many other applications. Friendly, honest service – I sell these wonderful little buggers because I love them, I love the world of audio and audio enthusiasts, and I dearly want to bring excellent sound and performance to your system, whether it be a hifi amp, a mic pre, an effects unit, a studio compressor, or a roaring guitar amp! Each tube is packaged lovingly with extra insulation material and a strong, fresh mailing box to ensure they get to you safely. If a tube ever arrives broken, I will gladly and swiftly issue you a refund, or a replacement at my shipping cost if requested and available, no muss no fuss. Our high-tech world has brought us a lot of wonderful things, but I firmly believe it benefits everyone when the knowledge of how your devices work is close at hand. I hope to do my small part in making that information, and tube technology in general, accessible to everyone, but especially low-income and underserved communities that have been priced or gatekept out of being able to take advantage of this technology. That’s why I am ALWAYS happy to disseminate information and answer questions! I am still learning, myself, but I am careful not to speak on anything I am not certain about and researched on, and I’m happy to relate my answers to whatever your level of experience and knowledge may be, so don’t be afraid to come to me as a casual consumer or beginner! DISCLAIMERS Performance differences – tubes are temperamental and sensitive little things. Their measured performance may change up to 5% or sometimes more based on factors like temperature, altitude, amount of warm-up time, time of day at which they are tested, and wall voltage. I do my very best to test all parameters thoroughly and redundantly before selling a tube, and post my testing parameters and results on each listing, as well as including a printout of the test results with the tube purchased, and/or custom testing parameters, if requested. However, the golden rule of vintage audio is: Your Mileage May Vary. The Tube Fairy is not responsible for how tubes may perform in your gear, or test in any other tester, or any differences between those testing results and the ones I’ve listed. Tubes perform differently in different circuits, and there is no way for me to ensure one will perform perfectly in every single one. These tubes are tested as amplifiers and, for diodes, rectifiers; this will not ensure ideal performance for a tube used as an oscillator, for example. This has NEVER been an issue with any tube I’ve sold, however, as tube circuits will allow for a wide tolerance of performance parameters from a tube (at least 20% is common) and small fluctuations will make little to no difference. In addition, testing a tube’s full range performance as an amplifier will give the best estimation of performance for all applications. Refunds and replacements – there is only one condition under which a refund or replacement will be issued – if there is physical damage to the tube. This does NOT include damage to the fragile and disintegrating screen printed label on the tubes, the tube boxes, or slightly bent or discolored pins. This DOES include: broken contact pins or guide pin, cracked or broken glass, and white getter flash. The getter flash is the chrome/grey/silver coating on the inside of the tube, usually on the top, and it’s an indicator of the integrity of the vacuum seal of the tube. If the getter flash is powder white, the vacuum seal is broken, the tube will not function, and should absolutely not be plugged into any gear. I will be happy to issue a refund for such tubes, or a replacement if one is available, with shipping at my cost. If no direct equivalents in all capacities are available, the customer will have the option of receiving a lower testing or less valuable equivalent model, along with a partial refund to make up the difference in cost. Refunds or replacements will not be granted for differences in tube performance. However, I ask all customers to please reach out if you have any issues at all, and I will always do my best to make it right. Exceptions to the refund/replacement policy should not be expected, but may be granted at my discretion. If you experience failure or poor performance from the tube, the reason can often be determined from the details of the failure. I am always happy to give preliminary advice or guidance in diagnosing such issues, whether the tube is at fault or not. Noise/hum/microphonics – tubes sold by The Tube Fairy are not tested for noise, hum, or microphonics. Some model numbers, such as US military 4-digit numbers, may already be screened for these factors at time of manufacture; if this is the case it will be listed in the description, but even this is no guarantee. I am developing a device for testing for these factors, but there is no possible way to completely guarantee a lack of noise, hum or microphonics, as these factors can be caused by many things and are very dependent upon the other factors of the system the tube is being used in. If you experience any of these issues, please reach out and I will do what I can to help you determine the source of the issue! Cosmetic condition – tube boxes never have their condition guaranteed. Whenever possible I will send the tubes in their original boxes, or a period and brand appropriate original box, but these have often decayed beyond the point of use, and in those cases, the tube will be contained in a brand new blank white box with the model number written on it. I am happy to meet customer requests for boxing as I am able, at no additional charge. Tubes themselves will be cleaned to whatever extent possible, without compromising whatever labeling remains, but no guarantees are made to perfect cleanliness or condition of the labels. Often, cleaning the surface of the glass completely would remove what remains of the delicate silkscreen, and often the silkscreen may be removed even more when the tube is taken out of, or placed into, a box. Pictures taken will represent the level of cleanliness the tubes have been restored to, but any labels pictured may be more eroded by the time they reach the customer. All attempts to prevent this will be made. If customers prefer I prioritize cleanliness over label preservation, or vice versa, I am happy to oblige as able. Testing procedures, result analysis, and testing category standards New Old Stock (NOS) tubes are tubes that have tested within the standards for a brand new tube, which usually means all critical values measure within 20% of nominal. These tubes are regarded as brand new, as they can be relied upon to perform as such, but there is no way to 100% guarantee that these tubes have never been used. There are completely unused tubes that will test poorly, and there are some very hardy tubes that still test as NOS even though they have been used for a while. New In Box (NIB) simply means that the tube has been found in a box that matches the model, brand and vintage on the silkscreen label on the tube itself, and that both the tube and box are in somewhat decent condition. This is an estimation at best of whether the tube is brand new, and says nothing about testing standards. A used tube is a tube that meets one or more of two qualities: the tube tests as usable, but outside of NOS standards; the tube demonstrates typical signs of age for that tube type, such as high rp and μ, combined with low gm and plate current, for a triode. This is also an estimation of the tube having been used, and is no guarantee. There are three major types of tubes I am selling and can fully test – diodes, triodes, and pentodes/beam tetrodes. Other types either will be tested as one of these types (pentagrid tubes tested as pentodes), or have a method of testing that is self-explanatory, non-numeric, and/or fairly uniform across all testers (magic eye tubes tested for strength of neon glow, and width of aperture opening at two different voltages). Some tubes contain multiple sections, which will be tested individually, and individual categories given for each section if they test differently. Diodes have two electrodes (electrical elements), triodes have three, and pentodes/beam tetrodes have five. There is an additional element in nearly all tubes called the filament, and its purpose is simply to get hot to cause the cathode to emit electrons. In some tubes (primarily old ones from the 1910’s and 20’s) the filament and the cathode are the same thing, but usually they are separate. As the filament serves no purpose beyond this, it is not included in electrode counts and testing procedures. The only relevant testing parameter for the filament is how much current it draws, and this is a pass/fail condition. All tubes being sold will only have very minor, if any, filament current deviations from the nominal value. Tubes that test within a certain percentage of their rated nominal values, usually 20%, are considered ‘NOS’, which means New Old Stock, indicating that the tube will essentially function as if it were brand new, and is regarded and priced as such. All critical measurements must be within the appropriate tolerance range, or I will not consider them NOS. NOS testing tubes may have been used in the past, it is impossible to determine with certainty, but can be relied upon to provide the performance and longevity of a brand new tube. These are the testing categories a tube may be listed in, and the percentage deviations from nominal values that typically award it placement in that category:Low – 65%-69%Good – 70%-79%NOS – 80%-120%Strong – 121%-135%Tubes with critical values measured at less than 65% or greater than 135% are typically unusable and not listed. Exceptions are detailed below. A small amount of flexibility (5% or less) on a single less critical value may be allowed for when placing a tube into a testing category. For example, a triode that is well within a 20% tolerance on μ, rp and gm, but where plate current is low or high out to a 25% tolerance, may still be categorized as NOS even though the plate current is not technically within that range. This is because μ and rp are by far the most crucial values for a triode, and if those values are close to nominal, a tube with 75% or 125% of nominal plate current will still perform as new. This is not the case for tubes that show signs of aging, however. The electrodes involved in these tubes and their basic functions are as follows:Cathode – emits electrons when heated by the filament, to be collected by the plate, and regulated by the grids.Plate (anode) – receives positive DC voltage to attract and collect electrons emitted by the cathode, usually high voltage.Control Grid (grid, grid 1) – between cathode and plate, receives various static or fluctuating voltages to control the flow of electrons through the tube. Screen Grid (grid 2) – between control grid and plate in pentodes/beam tetrodes. In an amplifier, it receives positive DC voltage to accelerate electrons towards the plate, collecting a small amount of them itself. Usage varies widely across applications.Suppressor Grid (grid 3) – between Screen Grid and plate in pentodes/beam tetrodes. Usually grounded at 0V to reflect electrons that bounce off the plate, back at the plate. Sometimes connected to the cathode internally. The tube types and testing methods, as well as an analysis of results, and categorizations of different results, are as follows: Diodes – these are extremely simple. A positive voltage is applied to the plate, and the resulting plate current is the only relevant measurement to make. As diodes are usually meant to have AC applied to the plate and not DC, and the Etracer provides DC, which draws much higher current, they are only tested in a fairly low voltage range, but this is sufficient to extrapolate high voltage performance. As an added measure, graphical representation of plate DC voltage vs. plate current is provided up to the current limits of the tube, and gives an even better estimation of performance at close to the tube’s maximum rated values. The graph should show a smooth curve all the way to the current maximum, with an even slope. Triodes – these have a cathode and a plate like diodes, but with a control grid superimposed in between to regulate the current flow. Various positive voltages are applied to the plate, usually up to several hundred volts, while various smaller negative ‘bias’ voltages are applied to the control grid to reduce the current to specific amounts. Various measurements are taken, listed here from what is typically most important to least:μ (pronounced ‘mu’, also called amplification factor)Rp (plate resistance)plate currentGm (transconductance) (not very important factor for triodes, may be usable as low as 50% or high as 150%) Triodes are matched by a combination of μ, rp, and plate current. In addition, the graphs of the plate voltage vs. plate current must show matching curves within 5% across the entire operating range. I will not call a tube matched unless all 3 of these parameters are matched within 5%, and the curves are as described. The only exception is that I will allow a match of perhaps 7% or 8% on plate current, if the μ and rp are matched well under 5%, and the curves are identical in shape and difference across their entire range. ‘Balanced’ triodes are single tubes with multiple triodes in the same glass envelope, where the triodes are matched. The same standards apply. Multiple tubes may be balanced and matched, meaning all sections of all tubes are matched, or matched and unbalanced, meaning the different tubes’ multiple sections are unbalanced identically. Triodes show age and use by demonstrating very high plate resistance, along with somewhat high μ, low plate current and transconductance. Tubes that display these characteristics, even if they meet the tolerances to be rated as NOS, will be listed as ‘used’ as this is likely the case. Conversely, tubes with low plate resistance, high plate current and transconductance, and nominal μ, with all values within the NOS range, can be relied upon for extra long life. Pentodes/beam tetrodes – these two tube types only differ in the physical construction of the suppressor grid; their electrical function is identical. The function as an amplifier is similar to the triode, but with the addition of a Screen Grid to accelerate electrons towards the plate, and a Suppressor Grid to reflect electrons that bounce off the plate, back at the plate. Various measurements are taken, listed here from most to least important:Gm (transconductance)plate currentRp (very inaccurate for most pentodes)Screen current (importance depends greatly on application) Pentodes and beam tetrodes are matched for transconductance and plate current, with the same 5% tolerance and graphical matching standards as triodes applying. Aging is determined similarly, though plate resistance is less of a reliable factor.