audio tubes and how to buy and test  - Page 1
Forum section: electronics / repair

author: Planobilly
author_rank: Regular Contributor
timestamp: December 10, 2015, 07:33:24 pm
content: Hi guys,The more I read and study about vacuum tubes the more uncertain I become about the issues. The prices I see on the internet can range from 5 bucks to over a thousand for a 12AX7 for example. Here is one...lol...Telefunken ECC803S, diamond mark, Ultra-low noise premium 12AX7, gold pins. EXTREMELY RARE MATCHED PAIR for $1600.00 Anyone who is willing to pay the big money for even a NOS RCA Black Plate is not dealing with me in general to begin with...lolIt appears that even the best of the tube testers really don't tell you what you need to know and in general are as much misleading as they are useful.Is there any way short of something like a Tektronix 576 curve tracer with outboard amps to get the the correct voltages that are of any real value?Is there anyone that can be trusted and actually has the proper test equipment to buy tubes from. The hype on the net seems endless...lolCheers,Billy

author: dave_k
author_rank: Frequent Contributor
timestamp: December 10, 2015, 09:08:18 pm
content: Quote from: Planobilly on December 10, 2015, 07:33:24 pmWhy yes, there is!

author: Seekonk
author_rank: Super Contributor
timestamp: December 10, 2015, 09:47:00 pm
content: They exist. I had saved one microprocessor based off somewhere but can't find it now. Here is a fairly simple one.http://www.valvewizard.co.uk/curvetracer.html

author: Gyro
author_rank: Super Contributor
timestamp: December 10, 2015, 10:25:40 pm
content: Well in terms of the buying part of your question, the only ones worth going for these days are the NOS Soviet military ones. The prices for European / US ones are just plain stupid, even the Chinese ones are costly these days. The soviet ones are mil spec construction for materials for relative peanuts. The output tubes that I use are £3-4 each versus £60-200 for European/US consumer ones. If you're going to get into tubes it's the only cost-effective way of doing so. At least it's a way of getting sensible quantities to experiment with.

author: kc8apf
author_rank: Regular Contributor
timestamp: December 12, 2015, 09:41:17 pm
content: If you're just looking for a reliable source that does reasonable testing, look athttp://www.ramlabs-musicreference.com/

author: vk6zgo
author_rank: Super Contributor
timestamp: December 13, 2015, 01:22:49 am
content: Quote from: Planobilly on December 10, 2015, 07:33:24 pmBasically,the people asking such huge prices are crooks!There were "matched pairs" of 12AX7s made in the old days,& they were a little bit more expensive,but not to that extent.Gold pins don't do a lot that standard pins don't.Back in the day,we used a lot of Receiving type.tubes in our Marconi TV Transmitters.Dear old "Macaroni" had a few spots which were a bit marginally designed,& needed tubes which were "at the top of their specs"(not just "in spec").We found that these worked best with Australian "AWV",Siemens,or RCA tubes----these,of all suppliers were the most consistently at the top of spec.Strangely,Marconi's own tubes were consistently "just in spec",Philips & Mullard were a mixed bag,other brands,such as Brimar & Zaerix were again,"just in spec"--with some of the latter not making spec.Some of the "prettiest" tubes---gold pins & all,were among the worst performers.My theory is that tube manufacturing was winding down in the UK & Europe,so some were "bought in" & re-labelled',without the former degree of quality control.Many of these tubes worked perfectly satisfactorily in our Fernseh PGM75 video & sync generator.Obviously it wasn't as fussy!

author: Brumby
author_rank: Unknown
timestamp: December 13, 2015, 01:52:36 am
content: When I see the prices of valves today, I sadly reflect on the day I cleaned out my junk box, ditching maybe 100 - 150 of those little glass hand warmers. Don't get excited, it was more than a decade ago.But reading this thread about testing valves brought back some memories....Does anyone remember one of these in their local Tandy store?.... (I think it's this model)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 13, 2015, 02:24:03 am
content: There are a few more-or-less mainstream suppliers for tubes. The reserves are either old stock (produced up until, oh, the 70s or so), or a select range of the most common audio types (12AX7, 6V6, etc.) in new production from Russia and China. The production quality is generally quite poor, but you get what you pay for.AES atwww.tubesandmore.comis the first that comes to mind. There are many others. Disclaimer: not affiliated, blah blah blah.If you don't know anything about buying tubes, then:The reason some are highly sought after by collectors, are due to certain features, associated with higher quality manufacturers and short supply. Like, say, stamp collectors, the features are basically aesthetic. Unlike stamps, tubes are functional as well as aesthetic, and are typically ascribed magical properties in terms of audio rendition (the broad reserve of adjectives used by the audiophile community boggles the mind..). Despite their mythical reputations, these sought-after parts are rarely measurably different from cheaper variants, and don't usually even match the quality of manufacturer-selected premium quality types (which are distinguished by physical and electrical characteristics: higher purity of materials, tighter manufacturing precision, and exhaustive burn-in, testing and selection).An extreme example of premium quality tubes being those used in undersea telephone cable repeater amplifiers: together, millions of tube-hours of successful, reliable operation have been logged. Those tubes were manufactured with significantly more effort (the scrap value of gold alone makes them valuable today..), but using all the same knowledge and practice as standard "PQ" tubes used, just much more of it.So, PQ vs. regular: not much electrical difference (usually noise being the most important), higher reliability. Usually defined by type, e.g., 12AX7(A) vs 7025; 6DJ8 vs. 6922 (and respective variants of European numbers, e.g., ECC88, E88CC, etc.).Regular vs. sought-after: little or no difference in electrical characteristics or reliability; mainly superficial.As for suppliers, eBay prices are eBay; if a $1 item is listed at $5, and sells, then that's that. The smart shopper will notice that the minimum price for that item is $1, or close to it, and avoid such sales.Retail prices are always high, because retail is retail. Old stock parts may have availability issues as well, as collections and supplies come and go over time. They have to account for stocking inventory, and volatile bulk prices. In return, you can expect prompt and reliable service -- you'll most likely get what you paid for, and it will be in good condition.Tim

author: Len
author_rank: Frequent Contributor
timestamp: December 13, 2015, 02:28:18 am
content: Quote from: Brumby on December 13, 2015, 01:52:36 amWhere I come from, you'd find one of these in the local drugstore.

author: Brumby
author_rank: Unknown
timestamp: December 13, 2015, 03:09:49 am
content: In Australia, I only ever saw them in Tandy Electronics (our experience of the, now defunct, RadioShack) - but they disappeared more than 20 years ago.

author: nowlan
author_rank: Frequent Contributor
timestamp: December 13, 2015, 03:19:20 am
content: I was looking into valve/tubes recently. I like the look of nixies etc. Unfortunately would know where to start with regular valves, eg codes etc.I had hoped to find a single valve preamp. The kit prices seem to get expensive really fast.Most of the stuff on youtube is guitar related.

author: Gyro
author_rank: Super Contributor
timestamp: December 13, 2015, 11:15:06 am
content: Go former Soviet, and don't pick the mainstream ones.P.S. Before and After photo's!

author: garre
author_rank: Contributor
timestamp: December 16, 2015, 03:26:03 am
content: I recently retired and dug this old over the counter tube tester from a storage shed. It works. I don't expect it to give detail tube information, but it does indicate if the tube still has any gain. I still have a few tubes in a large box. i have recently repaired an old 41 Plymouth car radio for a friend. Most of the repair was capacitor replacement.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 16, 2015, 03:50:28 am
content: Most likely only emissions, and maybe shorts. Those are the most common faults, at least -- and, transconductance/gain doesn't drift independent of cathode current, and voltage offsets and gains are defined by the geometry, so it's more or less a good enough check.When checking transistors, likewise, the most common faults are leaky/shorted (really, a leak is a microscopic short) and open (or high resistance).Tim

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 16, 2015, 03:57:41 am
content: An excellent book for audio tubes ishttp://www.elektor.fr/audiotubeIt's really excellent. Oh, you'll have to learn French... O0

author: vk6zgo
author_rank: Super Contributor
timestamp: December 16, 2015, 04:00:42 am
content: Quote from: T3sl4co1l on December 16, 2015, 03:50:28 amAnother important one is heater to cathode leakage,especially if you are using ac heater supplies,as was all but universal..Apparently some modern tube circuits use regulated dc instead---no hum.but leakage could still upset your bias.The AVO Valve Testers,except for the most basic model,measuredgmas well as all the other stuff.

author: JimRemington
author_rank: Regular Contributor
timestamp: December 16, 2015, 04:39:47 am
content: People who would pay $1600 for a matched pair of 12AX7s are also likely to buy gold plated monster cables for interconnecting their audio components, because they think it will sound better.Total hype, but who knows, maybe the cost alone makes it "sound better".

author: Gyro
author_rank: Super Contributor
timestamp: December 16, 2015, 01:14:04 pm
content: The more or less definitive collection of tube books, covering tube theory, construction, testing and circuits can be downloaded from Peter Millett's excellent tubebooks.org website:http://www.tubebooks.org/technical_books_online.htm

author: gadget73
author_rank: Regular Contributor
timestamp: December 24, 2015, 09:22:29 pm
content: Here in the US, I tend to get my tubes from Jim McShane at mcshanedesign.net. He's a reasonable guy and he tests his tubes at full working voltages. Most of your common testers don't do that, especially on power tubes. My Eico for example will max out about 170-180 volts and most power tubes run easily 250 volts on the plate and some much higher. Better testers like the Hickok units run closer to proper voltages and will give a transconductance figure rather than a percentage of emission. Its still single-point testing though, not fully indicative of real-world operation.If you want really involved testing to match curves and such, a modern solution is something like a uTracer. Its not the cheapest bit of kit, but MUCH less than a vintage Tek tracer. Mostly for small signal tubes, you don't need to do all that. Testing for leakage is a good thing, and in-circuit testing will tell you if its noisy or microphonic. Basically plug the thing in and if it makes silly noises, its a dud. Power tubes benefit more from matching, but exactly how much depends more on the circuit. Some are more adjustable and therefore more forgiving than others. Some you can modify to make more forgiving.Tangent, I have a Fisher TA-600 receiver and part of the output bias circuit relies on the heaters of the two 12AX7's in the phono circuit to make it go. They're basically being used as resistors. One of those tubes developed a heater-cathode short which seriously changed the effective resistance on the stage. The tester will and would have found that, except that the tube was fine when I put it in. It developed that short after being used for a while. Its not a new tube either, its likely been in and out of service for 40 years before dying. Basically, just because its good the moment it comes out of the tester doesn't mean it will remain in that condition forever.