Vacuum tubes and Valves - Page 1
Forum section: electronics / beginners

author: edy
author_rank: Super Contributor
timestamp: August 16, 2014, 02:46:50 am
content: Hi, I found an old TV being discarded that was too heavy to carry, but I managed to scavenge the tubes (see photos) figuring I could use them one day in a project. The TV looked like the one shown, a 1963 RCA set as far as I could read the label. Has anyone played around with these types of tubes before? Are they easy to test with modern equipment? I was hoping to make some simple devices. Has anyone made or seen any simple projects or is this beyond beginner level? My other option is to sell them but I have no way to know if they are good or in spec so probably wouldn't get much for them and I would not know if there is even a market for TV tubes from 1960's. They are Westinghouse, Philips, GE, Admiral mostly.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 16, 2014, 03:27:47 am
content: All the tubes/valves/firebottles will have numbers etched on the glass. You can look up those numbers on the internet and see what kind of tubes they are.Many of them will be rather specialized for old TV receiver circuits, and some or many of them may be weak or gassy and past their prime.There may be a market for some of the types if you can prove that they are still OK. But otherwise, they may just be a novelty.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 16, 2014, 03:29:20 am
content: You could consider purchasing a Hickok or other tube tester. Without knowing their operating condition it might be hard to price and sell them. If you know the condition (based on testing) you can check market values on eBay and other sites, including some audio enthusiast and radio enthusiast sites.This is a 539B, a highly regarded model (the C might have been a tad better). Hickok and others made lots of models - they can range from roughly $100 - $1000, so unless you are really into testing a lot of tubes it might not be the first choice in test equipment. DMMs probably outsell tube testers by a good marginBut if you are into knobs, sockets, and meters - not to mention vacuum tubes - it's hard to beat a tube tester for sheer vintage cool factor.http://www.ebay.com/itm/Hickok-539B-539-B-Tube-Tester-/231275972332?pt=LH_DefaultDomain_0&hash=item35d91f46ec&nma=true&si=Zcpc%252F83LGKmmxAywEwOn5MRmkUo%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

author: edavid
author_rank: Super Contributor
timestamp: August 16, 2014, 04:18:58 am
content: Well, if anything you should have kept that great TV cabinet and thrown away the tubesTV tubes are very common and cheap, usually not worth selling unless you have hundreds of them.They are not so great for beginner projects because of the dangerous plate voltages that are normally used.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 16, 2014, 04:31:48 am
content: You basic 'getting started' play around / testing setup needs heater power (the first digit or two of the tube number, AC or DC at a few amps will be more than enough) and high voltage (100-400V is common in most applications, though they'll still work as low as 10-50V, just not very well).Best way to get both: assuming your tubes are all 6.3V, a 120:6.3V transformer is all you need for that (or whatever line voltage is), good for a couple amps, say 2-5A. Then use another, back-to-back, to step 6.3V back up to 120V (or get a 240V primary if you're okay with extra voltage). Rectify and filter that, to get about 150VDC (or 300V), good for up to maybe 100mA.It's a shame you couldn't scavenge the rest of the TV, because the second hardest thing you'll need is output transformers. You can't drive speakers directly from tubes, not easily that is. You need a transformer there, too, and not just any will do (a common power transformer will saturate if you run DC through it). So it might be worth buying some more parts to cover that. Small SE OPTs (single ended output transformers, which are made to tolerate DC -- assuming you want to play with single ended audio amplifiers and that sort of thing) start around $10 for average quality, and go up from there (sometimes ridiculously so..).Tim

author: edy
author_rank: Super Contributor
timestamp: August 16, 2014, 01:51:31 pm
content: Thanks for the advice. There was no way I could grab the whole TV, it was looking quite beat up and I had no room in the car. I was heading to work so it was either the tubes or nothing. It was also dirty and had the back off, and had been sitting outside. Plus I had no room to put it at home. I didn't have the tools to start pulling out transformers either, and it would have been some work taking it apart on the side of the road.So for what it's worth, I never had vacuum tubes before, so the find prompted me to read up on them and watch some old Westinghouse videos on Youtube. I don't want to work with high voltages if I can avoid it. I was hoping to heat up the tubes with 6v DC or ac and try out the pins to see if they can do basic rectification, switching or amplification without electrocuting myself. I will look for the tube ID etched on the glass and let you know what I find.

author: N2IXK
author_rank: Frequent Contributor
timestamp: August 16, 2014, 03:02:12 pm
content: The 2 types I can make out are 12BH7 and 12AU7/ECC82. The larger octal based Westinghouse one looks like a 6SN7 or similar dual triode. All 3 of these have potential applications in audio amps.The 12BY7 and 12AU7 have dual voltage heaters that can run from 6.3 or 12.6V. You should be able to play around and get some kind of useful operation with only 30-40V on the plates, but linearity and gain won't meet datasheet specs.

author: edy
author_rank: Super Contributor
timestamp: August 16, 2014, 08:07:22 pm
content: I read off the numbers on the tubes and here is what I found:1. 6BX7 GT Westinghouse (largest tube)2. 6CB6A (5CF6? QK) Philips (I have 2 of them)3. 6CB6 GE4. 6CB6A (388) Admiral5. 6AQ5A QN Admiral6. 6AU6A Admiral7. 6T8A (unknown maker, can't make out writing faded)8. 12AX7 (A4QX) GE9. 12AU7A Philips10. 12AU7 (32) Admiral11. 12AT7 GE12. 12BH7A GE13. 12BH7 GEI also found this site that may help me learn to build something simple:http://diyaudioprojects.com/Tubes/tubes.htmI am hoping the simplicity and easier to see and understand what is happening in a tube will be a good learning opportunity.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 16, 2014, 10:43:43 pm
content: The tube type numbers are standard across brands. So the brand name is not significant when looking up the tube specifications.The TV receiver likely had all "Admiral" tubes as it was probably an "Admiral" brand receiver.But the presence of other brands indicates that over its life-cycle, the TV likely had several tubes go bad and replaced by the owner.Retail shops (grocery stores, drug stores, department stores, etc.) had public DIY tube testers where you could test the basic functionality.Then there was a locked compartment underneath where they had a stock of the more common types, and you could purchase replacements.

author: edy
author_rank: Super Contributor
timestamp: August 17, 2014, 01:37:14 pm
content: I found this nice manual regarding vacuum tubes which is an excellent primer:http://www.hnsa.org/doc/neets/mod06.pdfHow would one go about knowing which tube needed replacement? Would you take all the tubes out of your TV or radio over to the tube tester/vending machine and test them all out? Imagine figuring how to put them all back. Would failed tubes make a noise when shaken, did they often have physical signs of damage or just drift out of spec?

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 17, 2014, 02:22:30 pm
content: More intelligent TV owners might analyze what went wrong and pull the relevant tubes to test. But most people would probably take ALL the tubes in a shoe-box down to the public tube tester. TV receivers would have a printed "tube map" glued inside the cabinet so you would know where each tube plugs in.Physical failure (especially where you can see/hear something loose and rattling inside the envelope) was pretty rare IME. More often a tube would become "weak" and loose gain (or "transconductance" as the tube people call it) and/or "gassy" from a slow leak of the vacuum seal. It was rare to be able to diagnose a tube visually. Typically a bad tube looked exactly like a good one. That is the the reason for the tube testers. They typically only connected the tube (of whatever configuration) as a triode and measured the basic gain/transconductance. The more professional testers would perform additional tests for shorting between elements, etc.Here is a typical tube "map" This is an early-model RCA "reference design" called "CT-100"

author: N2IXK
author_rank: Frequent Contributor
timestamp: August 17, 2014, 03:55:06 pm
content: Quote from: Richard Crowley on August 17, 2014, 02:22:30 pmYes, the good old days where more people actually had enough "hands-on" ability to handle minor repairs for themselves. Of course, more people used to change their own oil and do tuneups and brake jobs in their driveways, as well.QuoteAbout the only visual tipoff of a bad tube was a white getter deposit in the case of a tube that had cracked and gone completely to air. The getter is a silvery metallic deposit of barium on the inside surface of the glass envelope. It is intended to react with any residual gas molecules, and keep the vacuum "hard" for the life of the tube. If the tube envelope leaks, the getter quickly oxidizes away, leaving a white barium oxide crust.QuoteMost of the "drugstore" testers were even worse than that. They tested emission only, by strapping all elements except the cathode together, and testing all tubes as simple diodes. No gain or transconductance test at all. The drugstore testers were often rigged to show anything but a brand new tube as "weak", to boost replacement tube sales.Transconductance testers were more sophisticated, but generally only used by service techs or other professionals. They didn't lend themselves well to the unskilled DIYer, with multiple switches and pots that needed to be properly set for each tube type, and a "line balance" control that needed adjustment to compensate for varying line voltage and filament current draw. True transconductance testers are still in great demand by hobbyists who play around with tubes, and prices on vintage Hickok or B&K units are well into the ridiculous range nowadays.QuoteThat's more than a "reference design". That thing is historic as RCA's first mass-marketed color set, released in 1954.http://www.antiqueradio.org/RCACT-100Television.htmThere are a few surviving units, but they are fairly rare because the picture tubes were prone to vacuum leaks because of the many glass/metal seals used. Back when CRT rebuilding services were available, several folks attempted to rebuild the 15GP22 tubes, with no luck.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 17, 2014, 04:22:06 pm
content: Quote from: N2IXK on August 17, 2014, 03:55:06 pmWow. It would be pretty easy to make a microcontroller-based (or PC-controlled) tube tester along the lines of the $20 LCR/transistor/diode/SCR tester. You could do all sorts of detailed, automated measurements, including curve-tracer, etc. I would be surprised if someone wasn't doing that already. I have little interest in firebottles or I would play around with making one myself.

author: N2IXK
author_rank: Frequent Contributor
timestamp: August 17, 2014, 05:55:46 pm
content: I have a couple tube testers in my shop at the moment. First one is an early 60's US military surplus unit model TV10-D/U. Originally a Hickok design (using their clever, patented circuit.) Tests essentially all tubes from the 1920s 4 pin UX base, up through subminiatures, with socket adaptors for some oddball transmitting types (3E29, 829, 832, 2C39). No nuvistors or compactrons, but I don't usually work on stuff that "new".Other one is a real neat piece. A Hickok "Cardmatic" tester, built for Western Electric. Intended for use primarily in central offices where LOTS of tubes were being tested/replaced on a daily basis, this guy has regulated bias and plate supplies, and gives a real precise set of tests that otherwise would otherwise need a dedicated tube testing bridge that tube manufacturers used.Pic of similar unit here, toward bottom of page:http://padgett.performanceresearch.us/tester/branded.htmRather than manually setting dozens of switches and pots, you insert a PUNCHCARD for the tube type into a clunking mechanical cardreader, and it sets all the voltages and pinout automatically.Unfortunately, I got mine from somebody who took the cardreader apart to attempt repair/cleaning, and didn't reassemble properly/lost some parts. Would really like to get this beast running, and am looking into replacing the pin switch matrix with a USB addressable bank of relays and tube sockets, like these guys did:http://tubesontheweb.com/matic.htmUnfortunately, they don't sell schematics/kits/software separately. They want you to ship them the tester, and they install it, at a pretty stiff price ($2k to install, $3K if they provide the tester, as well).If I completely removed the mangled cardreader assembly from mine, most/all of the new electronics could fit inside the tester housing, rather than the ugly external box and umbilical they used.