Can't believe I'm asking this - let's talk about vacuum tubes. - Page 1
Forum section: electronics / repair

author: cvanc
author_rank: Frequent Contributor
timestamp: August 20, 2018, 02:58:51 am
content: Hi all-I find myself working on some tube gear and I need to buy a couple replacements. If any of you have thoughts on brands that are good (or awful) I'd be most appreciative.Last time I had tubes at home was a long, long time ago and I do not really know any of the current vendors.Right now I'm looking for both KT88 and 12AU7... thank you!

author: coromonadalix
author_rank: Super Contributor
timestamp: August 20, 2018, 10:30:27 am
content: My friend is still repairing tube radios, i have my deceased father 56 years old Phillips Multiband radio who's been rebuild by him, it works great, still manage to catch foreign languages with an very good antenna. I love tube amplifiers, i had few of them in the past.For your tubes: you still have them on Ebay, you can try amateur radio web sites, there's some trading and selling there, i'll try to get a link.Do you have an tube tester ??

author: VK5RC
author_rank: Unknown
timestamp: August 20, 2018, 10:52:08 am
content: A rule of thumb I was told was to stick with the manufacturer used in the original design as often they allow for that manufacturers inter- electrode capacitance - ie no extra neutralisation required.I restored a "chicken shed find" Tek 545 oscilloscope with lots of tubes - I bought and built a tester around the uTracer tube tester- I found it very goodhttp://www.dos4ever.com/uTracer3/uTracer3_pag0.htmlhttps://www.eevblog.com/forum/repair/restoration-repair-of-tektronix-545/msg1018767/#msg1018767

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 20, 2018, 03:19:38 pm
content: Those are common tubes available either brand new or NOS pretty much everywhere. Prices vary greatly though, shop wisely.https://www.google.com/search?q=kt88+tubes&prmd=sivn&source=lnms&tbm=shop&sa=X&ved=0ahUKEwiig-vj9fvcAhWvwFkKHZtUAo4Q_AUIESgB&biw=962&bih=601https://www.google.com/search?q=12au7+tubes&prmd=sivn&source=lnms&tbm=shop&sa=X&ved=0ahUKEwjckIvB9vvcAhVRtlkKHSJ5DOUQ_AUIESgB&biw=962&bih=601

author: MaxFrister
author_rank: Regular Contributor
timestamp: August 20, 2018, 06:21:35 pm
content: I repair old tube equipment from time to time (see my recent Oscilloscope repair). For tubes, I try to get NOS on ebay but it is an adventure.Many people are selling their (or someone else's) junk box tubes. They probably don't work well.Many times the original tube is not available and then you have to try a substitution. Lots of tubes are similar and there is often a close match under a different number.Finally be aware that tubes can test fine on a tester and still not work right in the unit (and vice versa).I don't worry much about the brand for the old tubes. New (Chinese and Russian) tubes are another matter.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 20, 2018, 06:34:57 pm
content: 12AU7 are plentiful enough you shouldn't have trouble finding good ones. Avoid the fetish brands (Mullard etc.) with jacked up prices, and avoid the Chinese brands (they'll burn out in 2000 hours despite being a small-signal tube). Any generic NOS will do.KT88 you may have a harder time finding. It's a fetishized type already, and I doubt there will be any middle-ground NOS you can find. I forget if there's new production (Russian or Chinese), probably is. That'll be your best deal, but expect them to be badly made, underrated and short lived (e.g., red plate running at what's supposed to be nominal rating, lifetime under 1000 hours?).Tim

author: Gyro
author_rank: Super Contributor
timestamp: August 20, 2018, 07:18:52 pm
content: Despite the slightly lower datasheet maximum Va and Pa ratings, I've yet to find an application where a 6550 couldn't be directly substituted for a KT88. Old RCA 6550As are particularly tough if you can get them and are probably easier to source in the US than Europe.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 20, 2018, 07:23:45 pm
content: I don't buy a lot of tubes butwww.vivatubes.comhas a large stock and prices have been ok.

author: Johnny10
author_rank: Frequent Contributor
timestamp: August 21, 2018, 12:07:48 am
content: Elpaso tube ampon Youtube buys and tests tubes for his amp builds and tube amp repairs.So does BlueglowWatch the videos and ask in the comments these guys are great!

author: KungFuJosh
author_rank: Super Contributor
timestamp: September 02, 2018, 12:24:41 am
content: There are plenty of sources for tubes. 12AU7 and KT88 are not at all uncommon, both are used for music/guitar applications. If you search for guitar tube supply stores, you can compare prices.For new production tubes, I like Tung-Sol, and Mullard. JJ is okay for most tubes, but never get a JJ EL84.I wouldn't recommend going anywhere near any NOS tubes unless you have a tube tester + tracer and absolutely know what you're doing. NOS tubes are usually more mojo and BS than anything else, and almost everybody selling them lies about the quality and/or doesn't know how to properly test them.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 02, 2018, 02:35:39 am
content: Even back in the twilight of the tube era, Soviet "receiving " tubes had a poor reputation, so I would shy away from NOS tubes from the ex USSR.The Soviet/ex-Soviet/Russian RF output tubes do seem to be good, though.When I used to work with a lot of tubes, the best were, in about this order:-Australian made AWVRCASiemensSylvaniaPhilipsMarconiMullardGECBrimarReal crap was:-Zaerix, who used tubes sourced from whoever was cheapest--- usually the USSR.The problem I see with buying "NOS" these days is that some may be factory "seconds" which didn't reach specs, & were probably meant to be destroyed, but in the last days of the business were "acquired"by someone.Others may prettied up "pulls" from old equipment, which may have been removed because they tested "bad".The most common fault with "receiving" tubes is heater to cathode leakage, which, judging from all thecircuits with DC heaters on the Internet is rampant with those tubes currently available.A good indirectly heated tube can be used with ac heaters on all but the most sensitive instrumentationcircuitry.

author: Old Printer
author_rank: Frequent Contributor
timestamp: September 02, 2018, 03:32:06 pm
content: Surprised no one has asked you what the "gear" is. As has been said the 12AU7 is common as dirt, the KT88 not so much. Do you know that it is what should be there from the factory? Only that someone might have subbed it for a different original during its life. I look forward to your progress, I have a couple old Fender silver face amps I am restoring. With all of the counterfeiting of electronic parts going on I would wary of that if paying for a brand name.