[SteveFord]

Whenever you get a NOS tube, please test it before using.
I just had smoke start coming out of my preamp but luckily I was two feet in front of the off switch and all appears well except for the hunka junk tube, of course.
PLEASE don't be stupid like I was, test the tube before inserting.

[Maritan]

Yikes! So, just the tube went up in smoke? The UV3 is perfectly functional? Which tube was this? Something was watching over your preamp. 

Off topic - What tube tester do you have?

[Bob in St. Louis]

HHmmm.....not cool. Who's going to pay for that?

[FullRangeMan]

How the custumer would test a cold tube??
Would be useful any tip about how test a tube(cold, outside of the amp) with a digital multimeter??
Most audiophiles had only a DMM or nothing.

[Ericus Rex]

I have a Sencore Mighty Mite tester that's good for general testing including shorts.  No gm though.  For a true test of gm you'd have to buy an Amplitrex.  The Sencores can be had on ebay for not a lot of dough.  I think I got mine for $75.  I also see testers on craigslist all the time.  If buying a tester would save your amp or pre then it's money well spent.

[Bob in St. Louis]

If buying a tester would save your amp or pre then it's money well spent.

True, but with that way of thinking, you'd have to have a tester for every piece of equipment you want to put in the chain.
What if a brand new driver is shorted internally and you blow your amp. Should you now be expected to own the equipment, and be required to test the specs of a driver?
How many here have ohm tested their drivers before they wired them up?

Nah...I'm not buying it. WHen you sell something, it is with the understanding that it works to it's rated specifications.
If it doesn't then you're selling paper weights and need to advertise them as nothing more, and charge accordingly.

But then again, I've come to expect to receive things I've bought as they've been sold to me.
Bob

[FullRangeMan]

I have a Sencore Mighty Mite tester that's good for general testing including shorts.  No gm though.  For a true test of gm you'd have to buy an Amplitrex.  The Sencores can be had on ebay for not a lot of dough.  I think I got mine for $75.  I also see testers on craigslist all the time.  If buying a tester would save your amp or pre then it's money well spent.

I agree, it can save the amp and even avoid a fire.
A tube tester worth own if it is inexpensive. In a brevis search I could only found this expensive amplitrex:
http://www.amplitrex.com/about.html
Some one had any link to a tube tester under $500 in new condition??

[medium jim]

Steve:

I had a new production 6550EH pop and poof and I also was very fortunate that I was able to turn off the amp before any damage resulted.  I have an Eico 667 tube checker that I was to lazy to pull off the shelf.  My friend has a TV/7 tester that what I should have to test my tubes.

Jim

[SET Man]

Hey!
   
   This is one of the thing tube user fear every time putting in new tubes.

    Because of that a few years back I decided to pick up a Hickok 6000 tester. I test all tubes new and NOS before I put them in my system. Unfortunately there are two tube types in my system that I can't test on this tester... 845 and KR Audio 842VHD, don't know setting for that later one.

    Anyway, not everyone have tube tester or want one... so keep your finger crossed.

Take care,
Buddy

[SteveFord]

It was a Philco 5AW4 rectifier tube which I was going to send out an a tour - glad I didn't!
No damage to the preamp that I can see but some grey hairs have sprouted on my head.
My local repair shop has a tube tester so until I pick one up for myself I know what I'll run over there. 

[underdawg]

my 2 cents:
I think everyone who has tube equipment should have some kind of tube tester.
A digital multimeter would only be good for testing opens and shorts if you know the pinouts.
Again this is just my personal opinions.

[Ericus Rex]

True, but with that way of thinking, you'd have to have a tester for every piece of equipment you want to put in the chain.
What if a brand new driver is shorted internally and you blow your amp. Should you now be expected to own the equipment, and be required to test the specs of a driver?
How many here have ohm tested their drivers before they wired them up?

Nah...I'm not buying it. WHen you sell something, it is with the understanding that it works to it's rated specifications.
If it doesn't then you're selling paper weights and need to advertise them as nothing more, and charge accordingly.

But then again, I've come to expect to receive things I've bought as they've been sold to me.
Bob

NOS/UOS tubes are a special circumstance.  I would imagine Steve got them from ebay and not a reputable tube dealer; what reputable dealer wouldn't test them and notice the short?  These tubes are old and have likely been sitting in a basement for decades, and then they are shipped perhaps a couple of times before arriving on your doorstep.  I wouldn't trust them in my amp until I had tested them, for the exact reason Steve described.  Hell, I wouldn't trust any electronic device made in the 50's or 60's before completely checked over.  New equipment and speakers?  I'd just plug that stuff in.  1960's speaker?  I'd probably plug it in to a cheap receiver first.  Even if the tubes were tested prior to the sale who knows how rough shipping was on them and what could have loosened up in transit.  I have found a few shorted tubes in my collection since buying the tester.  I think it was money well spent.

And you're not even completely safe with new production tubes.  I bought a quad of Black Treasure KT88s a couple of years ago that were shipped from China.  They were brand new and factory tested/matched.  I still tested all four upon arrival and one of them had an intermittent short.  I can only imagine the damage that tube could have caused if I hadn't tested it beforehand.

FRM, the Amplitrex is the only tested I know of currently in production.  It's great but it's pricey.  Bruce Rozenblit of Transcendent Sound had a kit for a while, and I heard he was designing a new and improved version to be released soon, but it's still $700 or $800.  As I said before, there are always lots of them on ebay.  Some may need calibrating by a professional but even then you could still have one for under $500 total.  And for the DMM, you could test for shorts with it but keep in mind that you're testing a cold tube and heat expansion could reveal a short that otherwise tested fine cold.  Tube testers test for shorts with the tube hot.

[Bob in St. Louis]

Yea...ok. I guess you sold me on the idea. You made some good points there Ericus.
I'm still worried about where the smoke came from. That's not good.

Bob

[Freo-1]

NOS/UOS tubes are a special circumstance.  I would imagine Steve got them from ebay and not a reputable tube dealer; what reputable dealer wouldn't test them and notice the short?  These tubes are old and have likely been sitting in a basement for decades, and then they are shipped perhaps a couple of times before arriving on your doorstep.  I wouldn't trust them in my amp until I had tested them, for the exact reason Steve described.  Hell, I wouldn't trust any electronic device made in the 50's or 60's before completely checked over.  New equipment and speakers?  I'd just plug that stuff in.  1960's speaker?  I'd probably plug it in to a cheap receiver first.  Even if the tubes were tested prior to the sale who knows how rough shipping was on them and what could have loosened up in transit.  I have found a few shorted tubes in my collection since buying the tester.  I think it was money well spent.

And you're not even completely safe with new production tubes.  I bought a quad of Black Treasure KT88s a couple of years ago that were shipped from China.  They were brand new and factory tested/matched.  I still tested all four upon arrival and one of them had an intermittent short.  I can only imagine the damage that tube could have caused if I hadn't tested it beforehand.

FRM, the Amplitrex is the only tested I know of currently in production.  It's great but it's pricey.  Bruce Rozenblit of Transcendent Sound had a kit for a while, and I heard he was designing a new and improved version to be released soon, but it's still $700 or $800.  As I said before, there are always lots of them on ebay.  Some may need calibrating by a professional but even then you could still have one for under $500 total.  And for the DMM, you could test for shorts with it but keep in mind that you're testing a cold tube and heat expansion could reveal a short that otherwise tested fine cold.  Tube testers test for shorts with the tube hot.

Sage advice indeed.

 If one is going to become a serious tube-head, then it is worth it (IMHO) to invest in a decent tube tester (preferably one that checks transconductance as well as emission).   I have learned (or in my case, relearned) a lot about tubes as result of testing each and every tube before throwing it in the circuit.  Wound up changing out several tubes that were "working", but did not measure all that well.  The difference in performance after that was noticeable.
 
The new production tubes (to me) are a crapshoot if you get them directly from China.  I've had similar tales of woe with KT88's going bad WELL before their time.  Getting them from a reputable dealer reduces, but does not entirely resolve the issue.  The Chinese Penta KT88SC (Straight Copy) is a pretty reliable tube if you get them tested from a reliable dealer (EG: Doug's Tubes).  The Russian KT88's sound OK, but reliability is always a question.  The winged "C" 6550 is not a bad tube provided the dealer tests them out ahead of time to weed out the squirrely ones.  To me, none of them are as good as the GE 6550A, but good luck finding those at any reasonable price. 
I got so fed up with the state of those tubes that I sold all my 6550/KT88 amps, and got out of tubes for awhile.  When I did decide to get back into tubes, went the DIY route instead.  This allows one to use NOS high quality tubes that are much more reasonably priced.  There are a lot of designs on the DIY circuit that use 6SN7 driver tubes and 807 output tubes.  The 807 is a outstanding tube (the tube that help win WWII), and was used extensively in audio in the late 40's/early 50's.  I call it a 6L6 on steroids. In order to increase tube availability, decided to use the 12V version of these tubes (12SN7/12SX7), and 1625 output tubes.  The only issue with using the 807/1625 is that the screen voltage needs to be no greater than 300V, so best to run it with a separate screen supply.  A pair of monoblocks with 12SN7/1625 tubes can yield 55 wpc, and can sound as good (and even better) than a Citation II.  Here is the best part: the replacement tubes are cheap and plentiful. 

[Freo-1]

Yea...ok. I guess you sold me on the idea. You made some good points there Ericus.
I'm still worried about where the smoke came from. That's not good.

Bob

My guess is one or more resistors.  Should check them with a meter.

[Ericus Rex]

There's an open debate about the usefulness of transconductance (gm) meters.  Some say since they don't apply real-world voltages on the plate of the tube their readings are worthless.  I'm not sure how I feel about that.  The first person I heard this from was a tube vendor who happened to have designed his own tester that did use real-world voltages on the plate.  Vested interest, surely.  But then I heard the same thing from other sources (Building Valve Amplifiers book, Bruce Rozenblit's new book and the Audiocycolpedia).  These sources have no stock in selling tubes so I have to accept their findings.  I'm guessing that you can actually get a ballpark gm figure from these testers but actual readings at running voltages may differ.  Freo, as you're an avid tube lover I'd be interested to hear what you think of this criticism.

Steve, since you did see/smell smoke I'd have that pre looked at right away.  Sounds like a resistor may have been compromised.

The caveats of older tube testers are that they usually don't accomodate tubes considered obsolete when it was manufactured.  For instance, my Sencore won't test early DHTs like the 45 or 300b.  Also, not a single one (with the exception of the Amplitrex when you buy the adaptor) will test the 6C33.  The older ones run on tubes which means these have to be carefully calibrated and monitored as a bad tube running the tester can give a false tube reading.

I've had the great pleasure of hearing Freo's 807 tube amps, albeit too briefly due to my travel companions.  They sound absolutely mahvelous!  Wow!  A quick ebay search shows those output tubes sell for under $10 each!!!

[medium jim]

Hey!
   
   This is one of the thing tube user fear every time putting in new tubes.

    Because of that a few years back I decided to pick up a Hickok 6000 tester. I test all tubes new and NOS before I put them in my system. Unfortunately there are two tube types in my system that I can't test on this tester... 845 and KR Audio 842VHD, don't know setting for that later one.

    Anyway, not everyone have tube tester or want one... so keep your finger crossed.

Take care,
Buddy

I concur!   I sure was worried about retubing and because of that, stood right there and glad I did.  In my case, I don't think it would have mattered if I had tested the tubes as the old ones were at the end of their life and while they were still holding a bias of 65, the bias pots were nearly all the way opened and the new tubes were showing 117-119ma before I adjusted them down to the proper 65....which I did within 5mi and checked again at 20 and 1hr. 

Again, glad that my amp was well built and handled the heat so to speak.   I guess the lesson I learned this time around was to turn the bias pots down to around 1/3rd open when inserting new tubes....again, common sense.  But in my defense, this was the first home audio amp that I retubed where the old tubes were that used up.   On my Eico the old tubes tested good, on leaks, shorts and were in the good range (around 94 with 80 as bad).   The new tubes came in at around 130 with 140 the high reference point.  Most NOS or New tubes test at around 120-130 for Mutual Conductance. 

BTW, while I too smelled smoke, a careful examination revealed no damage and I was able to use one of the old tubes  (it biased) until a new replacement tube arrived and it also biased in according to Hoyle. 

Jim

[SteveFord]

Yeah, I guess I'll have to pop the bottom and have a look see.
The silver cap on that tube went blue and gold in spots.

[medium jim]

Yeah, I guess I'll have to pop the bottom and have a look see.
The silver cap on that tube went blue and gold in spots.

If it sounds okay, I would think no damage, let's hope anyway....In my case, if there were damage to the amp, the tube wouldn't bias or hold bias as the first thing that goes is the bias resistor.  I know this is apples and oranges as in Steve's instance it is a Pre and mine a power amp.  Again, hoping for no damage.   

Jim

[kevin360]

Oh, the agony and the ecstasy of owning tube gear! I had a KT88-98 go weird on a power up, inducing a screen resistor to arc and go up in flames (flame proof – no such thing). Fortunately, the amp's manufacturer not only put it right, but added a sentry to, hopefully, prevent such an occurrence in the future (all of those resistors are also sleeved in Teflon now). The funny thing is that every one of those KT88-98s tests fine – so, the warm and fuzzy feeling obtained from testing these things may be unfounded.

Not wanting to risk a repeat experience, I ordered a new set of output tubes – KT88-SCs. My first night with the newly repaired amp and a new set of tubes was interesting. After a couple hours and a few bias tweaks, I thought all was settled and turned up the wick. Within a half hour, the amp went quiet and one of the new LEDs lit up (brighter than the fire that prompted the upgrade). The tubes were fully tested before being shipped to me (by the manufacturer of the amp – VAC), yet one of them drifted wildly. At least I learned that the watchdog is effective – shuts the amp down faster than I ever could when it detects danger. Since weeding out the miscreant, all has been perfectly stable and absolutely wonderful.

The danger posed by a misbehaving valve is just one of those things we accept as the price of admission into tubeland. Although a tester may decrease the likelihood of encountering the dark side of tubes, it won't eliminate it. Some of us are crazy enough to face the agony in exchange for the ecstasy. It's worth it.

---

Yeah, Steve, I think you ought to take a look inside.