There are fake Bugle Boys out there already. Along with fake just about everything else. They are not that common though. As @audition__audio said if you have a lot of experience with tubes, more than I have, you can spot fakes by examining the structure. They don't make them like they used to.
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Assuming that this can be considered a high price for a dual triode (stereo) preamp tube relative to its NOS availability, when might someone attempt to perfectly clone this Amperex tube?
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Yes you are correct. Almost impossible to fake the acid etched codes. After a great deal of experience, you become aware of the internal structure of certain types from certain manufacturers. Even the thickness and shape of the glass become familiar. One of my greatest irritations currently is the contention that Sylvania Bad Boy 6SN7s extend beyond the true bad boy which is a very distinct tube.
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Some info about the original question. I think the 5AR4s were made in England in the Blackburn Mullard factory but were sometimes labelled Amperex. Phillips was a Dutch conglomerate that owned many tube brands, Mullard, Amperex, Siemens, Valvo, and on and on. Tubes made in one factory could be labelled with the brand of a different factory. The way to tell where and when a tube was made is to check the codes etched into the glass of the tube. here is a list of the codes and how to interpret them:
Phillips Factory Codes
Any tubes you come across today will be "New Code’ so just ignore the ’Old Code’ stuff. Also etched tube codes can be hard or impossible to read, but that doesn’t necessarily mean the tube is a fake.
For example look on page 11 of the linked document for a lower case f and 3, f3 and you’ll see that’s the code for a GZ34 (AKA 5AR4)
There were also many other tube makers who had their own way of identifying tubes, for example, Telefunken, RCA, GE, etc.
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Hook the Amplitrex to your laptop and it will trace the tube. I have never bothered to use mine in that mode. I like that it gives you real measurements, plus the expected values, and for ultra idiots like myself, it provides the "good," "weak," etc. evaluation.
The thing with estimating remaining life is that it really depends on how a tube is being operated. If operated gently, it may last a long time after beginning to test weak. Also, a weak tube may still be able to do its job extremely well depending on the circuit. I had a pair of 6sn7 tubes that tested quite weak on the Amplitrex, but the amp sounded good. I emailed Audio Note (the maker of the amplifier) about whether it was safe to continue using the "weak" tube and I was told to continue using it because, in their circuit, even a weak testing tube could sound just fine.
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Well the very best by far are the units which allow testing and tracing at numerous operating points.
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Even if the tester is properly calibrated, it is hard to estimate remaining life of any tube that tests strong--at or near the expected value. That is because of the way tubes perform with age. When brand new, a tube will typically test very strong--well in excess of expected value, but performance will quickly fall to near or slightly above the expected value. The vast majority of the tube's life will be at or near this plateau. and only near the end of its life will its performance begin to decline. The fall off from there can be quite rapid. When you get a tube that tests strong, you really don't know where along the broad plateau that the tube is at--is it at the beginning or is it close to where performance will drop dramatically? It is hard to tell. If the tube is testing weak or marginal, it probably is well into the end phase--that is about all you can tell from test results about remaining life.
If a tube is tested on a modern machine like an Amplitrex, the tube is being tested under stress conditions that are better at revealing the age of the tube. I've seen quite a few tubes that tested very strong on machines like a TV-7 that did not look quite so good on an Amplitrex. That tester is sort of the gold standard and most tube sellers who claim that they test their tubes will proudly claim use of that tester if they use it (some post screen shots of the readout). Amplitrex does not use a number scale, like xx/xx, so results given with such number mean that some other tester is being used.
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op is inquiring about a 5ar4 / gz34 rectifier, so gm (transconductance) is not a concern
gm levels matter for most tubes that are directly in the signal path (input, driver, buffer, follower, power tubes)... though most traditional testers have severe limitations testing real world performance of power tubes as well, other than most basic function (is it even working or not)
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Thank you to all for the informative replies--much appreciated.
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Getter flashes should be either silver or can be darker. What you dont want is translucent. A very good test for strength are life tests. If your tester doesnt have a life button simply lower the filament voltage 1 setting and compare these test results with the data from the normal or correct setting.
Tsushima is correct with the assertion that gm values from tester to tester are not universal or constant. Each tester can be idiosyncratic and test certain types higher or lower than the norm. To know the life left by testing you would need to know the test results when this tube was new as new tube values of the same type and manufacturer can vary by up to 25% sometimes more.
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Something more to add on @tsushima1 good comments.
We have to know the initial figures of a tube, when brand new.
Suppose initial readings were 130/130 so 98/96 represents approx 75% of that value, meaning that the tube is closer to end of life and not closer to new.
This is my understanding.
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OP, bare in mind that measured test results are only useful when one is aware of the make/model of vacuums tube tester that measured those results if they were tested on a mutual conductance tester, as a Hickock 6000A will produce a different set of test figures for a 100% Tube to those of an AVO 160, you need to know the scale for the valve in question on the tester in question.
Measured test results are generally a very good indicator of the useful life of a tube.
In a simplistic hypothetical scenario if your valve has a scale of 100/100 = NOS
and 60/60 as borderline usable then one can draw some conclusions about a valve that measures 98/96 against a second tube that measures 76/72.
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I used 4pcs of 6922 Ampe bugle boys in my pre, and the sound is very very good.
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amperex’s ’bugle boys’ was a marketing/sales branding by the amperex company, later bought out by the dutch electronics conglomerate philips, and the underlying tubes could be made in the uk or in holland... both are legit real deal amperex’s - the gz34 rectifiers in the ’60’s and ’70’s were made in blackburn, england and heerleen, netherlands
no you cannot rell the remaining lifespan fom the tested figures... best to look at the condition of the tubes themselves, especially how shiny and new the getter flash is at the top of the tube, and whether there are heat/burn marks elsewhere on the glass envelope
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