Not so common sense

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Maritan

Re: Not so common sense
« Reply #20 on: 23 Mar 2013, 04:05 pm »
Yeah, I think we're all hoping for no damage, but to be safe, the pre needs to be opened up and checked out completely starting with the components around the rectifier tube.

Some good advice by Ericus Rex here. The interesting part is the apparent relative uselessness of the transconductance test. very interesting. If I find one of the tube textbooks for a reasonable price, I'll have to pick it up.

Good luck with the pre, Steve. Let us know what you find.

SteveFord

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Re: Not so common sense
« Reply #21 on: 23 Mar 2013, 04:07 pm »
Nothing charred, burnt smelling or refusing to measure, thank goodness, and it sounds the same as it did before.
I think it was the carrier agent in WD40 (which I put on the pins) smoking off the beat tube. 
That would really suck is this preamp was damaged as I just shipped my Sonic Frontiers off it's new owner and the I'd have two silent stereo systems.

kevin360

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Re: Not so common sense
« Reply #22 on: 23 Mar 2013, 04:22 pm »
That would really suck if this preamp was damaged as I just shipped my Sonic Frontiers off it's new owner and the I'd have two silent stereo systems.

:lol: Sorry, it's not funny, but I understand what you mean all too well. The occurrence I mentioned above happened about two weeks after I finally got around to selling my Pass X350. It would have been nice to have that amp while my valve amp was off for repair. The smaller X150 worked okay, but I didn't spend much time listening to that system in the absence of 'my precious' - just failed to involve me in the same way.

Freo-1

Re: Not so common sense
« Reply #23 on: 23 Mar 2013, 05:22 pm »
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 accommodate 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!!!

Thank you, Mr. Rex.  Since your visit, did a little tube rolling, and was able to get about 15 to 20% improvement from the setup.  Swapped out the 12AX7 preamp tubes for 7058's, which helped a lot.  Much quieter noise floor, and increased clarity that was noticeable.  The 7058's are so good, they are even better in some ways than the Telefunken 12AX7's (in this application).  Also rolled in RCA 12SX7 smoked glass driver tubes in the power amps, and they seem as good as the MIL SPEC Canadian 12SX7's.
 
Regarding the tube testers, I think there is some validity to the stated limitations.  Having said that, I still think they provide a good picture of the health of small signal tubes.  As I said earlier, I was able to improve the performance of my setup a fair bit by swappig out tubes I thought were OK, but measured low transconductance.  They do tell the truth to the best of their limitations.  Even for power tubes, they have saved my bacon on a few occasions by weeding out dodgy power tubes that otherwise tested OK on basic emission testers.  For you guys running high power tubes, buying them from a vendor that burns them in for 24/48 hours first helps a lot.  Even then, I would STILL test them before throwing them in the amp.
A couple of notes on testers:  As Ericus Rex pointed out, they need to be calibrated in order to provide an accurate reading.  I got mine from a olderr gent who works on these things for the love of it.  For many testers, there are manuals and extensions/adapters available for obsolete tubes.  My Hickok 600 came with a obsolete tube manual, so I can test my stash of 1625's (which is roughly seventy some odd in numbers).  Out of all those NOS tubes, I found only four that were squirrely.  The rest all tested pretty well.
 
One other note: If you can, stay away from Ebay tubes.  Better to deal with folks like Jim Cross at Vacuumtubes.inc, or the brother team at Radio Electric Supply.   They stand by their tubes, and their prices are actually better in a lot of cases than EBay.

Ericus Rex

Re: Not so common sense
« Reply #24 on: 23 Mar 2013, 05:27 pm »
WD-40 in the pins.  Hmmm.  Who recommended that?

SteveFord

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Re: Not so common sense
« Reply #25 on: 23 Mar 2013, 09:01 pm »
I guess I will send it back for a check up just to be on the safe side.
Very disheartening but at least I didn't send the tube out to someone else which is what I was getting ready to do.

medium jim

Re: Not so common sense
« Reply #26 on: 23 Mar 2013, 09:45 pm »
WD-40 in the pins.  Hmmm.  Who recommended that?

I was wondering the same thing...WD-40 will attract grime, best to use a contact cleaner like Deoxit which has lubricating properties, but without residue.

Jim

cheap-Jack

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Re: Not so common sense
« Reply #27 on: 23 Mar 2013, 10:29 pm »
Hi.
I was wondering the same thing...WD-40 will attract grime, best to use a contact cleaner like Deoxit which has lubricating properties, but without residue.

Jim

Yes, the last thing we want is greasy residue sticked around the pins.

I've been using paint thinner liquid to clean my old VCR heads - effective without any residue. I think same liquid can be used to clean tube pins though I have not tried it yet.

c-J

Ericus Rex

Re: Not so common sense
« Reply #28 on: 24 Mar 2013, 12:26 am »
I just did a quick test and WD-40 is non-conductive.  I wonder if coating the pins in it could have messed with the contact between pin and socket?  So many dud tubes in one batch is a little suspicious.

SteveFord

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Re: Not so common sense
« Reply #29 on: 24 Mar 2013, 02:29 am »
Did you ever have a shop repair something and then they put the beat tube back into the box that the new one came in and they give it all back to you?  Two of the "brand new" tubes have brown silver on the top.
I still haven't heard back from the seller.

medium jim

Re: Not so common sense
« Reply #30 on: 24 Mar 2013, 02:44 am »
Steve, it is clear that the tubes were bad if they had brown tops.

Jim


Freo-1

Re: Not so common sense
« Reply #31 on: 24 Mar 2013, 03:06 am »
Steve, it is clear that the tubes were bad if they had brown tops.

Jim
Not necessarily.  Many of the older NOS tubes were "burned in" before they left the factory.  So, some tubes may show some burn marks.  Some of the older tube types I have owned over the years were "brand new", but had some burn in markings. 
 
This has been documented in some articles.
 
 

medium jim

Re: Not so common sense
« Reply #32 on: 24 Mar 2013, 03:18 am »
It takes more than a normal burn in to turn the silver tops brown.  Sure, it normal to have burn marks in the sides of NOS tubes, not in the tops. I would love to see a documented example of a NOS 5AW4 with burns in the top....

Jim

kevin360

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Re: Not so common sense
« Reply #33 on: 24 Mar 2013, 04:07 am »
Doesn't the color (finish) of the getter depend upon the speed at which it flashes the gases in the envelope? Yes, a getter that changed from a mirror finish to brown is a clear indication of being past its prime, but a getter can start out that way.

medium jim

Re: Not so common sense
« Reply #34 on: 24 Mar 2013, 04:31 am »
Doesn't the color (finish) of the getter depend upon the speed at which it flashes the gasses in the envelope? Yes, a getter that changed from a mirror finish to brown is a clear indication of being past its prime, but a getter can start out that way.

Kevin:

I just don't ever recall seeing a rectifier that was new with a factory brown top.  The getter could be on the sides, close to the glass and cause burn marks.  However, there typically is greater distance between the getter(s) and the top of the tube when the getter(s) are on top.  Typically the top will turn black, then brown.

Lest we forget that Steve bought 4 tubes all branded the same, it would be irregular to have two with different  physical appearances if truly NOS.

Jim

kevin360

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Re: Not so common sense
« Reply #35 on: 24 Mar 2013, 04:46 am »
:dunno: I was just thinking about the physics and the chemistry of flashing. I really don't know what all rectifier tubes look like in this respect. I just don't think one can always tell the condition of a tube from the getter color.

medium jim

Re: Not so common sense
« Reply #36 on: 24 Mar 2013, 04:55 am »
Kevin:

You are correct that during the gases forming inside of the envelope that the getter flashing can be silver, brown or black.  I stand corrected, however, this would be where the flashing has no loss.  A well used tube will start to lose its flashing and turn brown. I hope this clarifies what I am trying to say. 

I guess what gets me is that the two tubes with the brown flashings were the tubes that were bad.  More than a mere state of chance.

Jim

medium jim

Re: Not so common sense
« Reply #37 on: 24 Mar 2013, 05:14 am »
To support what Freo is saying:

http://www.audiotubes.com/nos.htm

It's all good.   

Jim

kevin360

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Re: Not so common sense
« Reply #38 on: 24 Mar 2013, 05:20 am »
I was unaware that both of the brown top tubes were bad. I only saw the reference to one of them producing smoke and another reference to the fact that both of the new tubes have brown/silver tops. As I mentioned earlier, I'm not questioning what getters which have turned brown indicate. I merely wished to point out that getters can start that color. I have far too little information to form an opinion about this, but I would be inclined to agree with you if both tubes have indeed proven bad. Steve?

SteveFord

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Re: Not so common sense
« Reply #39 on: 24 Mar 2013, 08:58 am »
1 tube was bad which had brown flashing - (it is now brown, blue and gold)
2 tubes have brown flashing
2 tubes have silver flashing

I see where the confusion lies - I said 2 had shorts in another thread - that was an assumption based on the brown flashing.  I only know, from empirical data, that one has a short, the wretched piece uh crap. 

The seller purchased some bulk lot of kits which had Philco tubes in them.  Where they came from, I do not know.  It could have been items which were to be returned to the factory for all I know.

The only point I was trying to make was to test the tubes before you insert them.

Kara at deHavilland says don't use the pre as it needs surgery so that really throws a stick in my spokes.