Tubes test OK, but noisy?

muncybob

I still have barely gotten my feet wet in the tube swimming pool, but today I had my 1st rolling adventure. Have a pair of 12AX7 that I put in the phono stage. Numbers on the box are 2100/2100 min 950 and 2200/2300 min 950.....these mean nothing to me except I was told that they tested good?

Anyhow, I like the way they sound but man are they noisy in silent passages. My Tung Sol pair can be in the preamp and I can turn the volume WAY up and not a peep unless you press your ear right up to the speaker. The above tubes were hissy even from 8' away. I am a bit disappointed.

megasat16

They are noisy tubes. Try cleaning the pins gently and clean the tube sockets with DeoxIT stuff. It may not help if the tubes are really microphonics / noisy in nature.

About 80% of all vintage tubes out there are microphonics to some extent. The newer tubes may be less noisy since they are plenty and the factory rejected the noisy ones. Unfortunately, previously rejected 50-60 years old tubes got recycled repeatedly by tube sellers these days because they fetch good $$ in the market.

Having said that, most AX7 tubes are noiser than AU7 or AT7 tubes from the same family tree.

pitdogg2

They can also get that way by being banged around in shopping if they were not packed well. Life is too short for noisy tubes mark it use it as a substitute if need be, but trying different items to quite it takes away from the ability to buy some newer tubes. As said try cleaning if it don't work then let it be. I have never been a fanboy of the dampers as the few I treid on some 6sn7 tubes just made the church Bells less noisy.

mhardy6647

Sometimes vacuum tubes just are noisy. 12AX7s are (dual) triodes of rather high "mu" or amplification factor (compared, e.g., to a 12AU7), and, especially when used in high-gain applications (microphone, tape head or phono preamps) they're just noisy.

12AX7 http://www.tubebooks.org/tubedata/HB-3/Receiving-Type_Industrial_Tubes/6681_12AX7.PDF (amplification factor = 100)

Try another tube/pair/set/whatever of 12AX7s.

Not a big 12AX7 fan, FWIW (or the 6922, for that matter) -- I like the big ol' octal dual triodes better (6SN7, amplification factor = 20) -- even the higher amplification factor tubes (6SL7, amplification factor = 70). They tend to better behaved compared to their miniature 9 pin counterparts, and they tend to sound better, too.

Westies closeup by Mark Hardy, on Flickr

heiney9

In almost every case cleaning the PINS with Deoxit rendered good testing, noisy tube silent.

mhardy6647

Cleaning pins (and cleaning/retensioning sockets) absolutely is a great panacea for old tubes; I've rescued many an FM tuner by cleaning tube pins.

It's worth a try with new tube sas well, I suppose (especially NOS) -- but if the tube itself is noisy (thermionic noise, which plagues high mu tubes/high gain vacuum tube circuits or microphonics).

Thus was whole class of military/industrial tubes developed with incredibly robust internals to minimize the latter. The former sort of comes with the territory.

It is, upon reflection (heh, a good night's sleep) well worth a try before writing off a tube. Cheap and and easy enough to try. It might help, it might not.

muncybob

They did seem to be fairly well packed but who knows what they went through in shipping.
I'll try cleaning them again with Deoxit then, did use Kontak on them before trying them out. The Tung Sols tubes sound good but the Telefunken were suggested and a pair came up.

muncybob

So from what I have just read(thanks to the mu info above) it's as much about total bandwidth as it is about amplification? If that's true, then in these types of tubes I would be better off looking at 12AV7?

Those Westies are sweet looking though!

mhardy6647

Some of the modern 12AX7s do a pretty good job of minimizing noise (the "12AX7LPS" with spiral filament comes to mind); Telefunkens were/are among the best 12AX7s (ECC83s) extant, and prices are commensurate.

Nothing that a tube tester tests (emission, grid leakage, shorts, even transconductance in a "real" tube tester) will give any insight into noise, or "tone" of a tube... thus I always like to say the best test of a tube is a use test! :- )

A transconductance type tube tester, properly calibrated, is very useful, though, for selecting and matching power amplifier tubes to ensure that they'll hold bias in a given amplifier. Even a cheap emissions-type tester (disclosure: which is all I have, at present!) can identify a "tired" output tube that might not be able to achieve/hold the proper bias to allow safe (in spec) operation of an amplifier.

mhardy6647

Realizing full well that much time has passed since these were written, I would still suggest the following as a one-stop primer for some basic info and interesting opinions about the 12AX7 (ECC83) and its kin (in case you're not familiar with it):
http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html

Might also be worth mentioning that the vitage 7025 tube was a 12AX7 variant selected for lower noise and hum (since these were issues even way back when for high-gain preamp applications -- mag phono, tape head, and microphone):

http://www.mif.pg.gda.pl/homepages/frank/sheets/168/7/7025.pdf

The other interesting 12AX7 "variant" -- if the OP doesn't need the extra gain -- was the 5751. These are AFAIK essentially interchangeable with the 12AX7 but with a bit lower mu (85):

http://www.tubebooks.org/tubedata/HB-3/Receiving-Type_Industrial_Tubes/5751.PDF

"Intended for applications where dependable performance under shock and vibration is paramount"

Now, that, of course, means the guts of the tube are ruggedized compared to a plain vanilla 12AX7 -- microphonic resistance should be better but there's no guarantee that electronic noise levels would be any lower for a 5751. The lower mu means that 5751s are not always great choices for MM phono preamps.

heiney9

It is possible it took a good jarring that is causing the noisy tube. When you say noisy, do you mean hissing, crackling and popping? Or are you having microphonic type issues?

I have only had 3 noisy tubes that supposedly tested well. Two of the tubes had the getters on posts that were broken off and wedged or sitting on the top mica. A broken getter in and of itself doesn't necessarily mean the tube won't function properly, but in these two cases they are noisy and muffled. The third case was a 1949 Tung Sol 12AU7 black glass, black plate, it's just a noisy tube...........not huge noise, but noisy nonetheless.

TKF's are impeccable as regards to build and quality control, but I don't think they are the "best" sounding tube ever made. But we have to remember (and this is fascinating to me) that these glass bottles w/delicate innards are 30-60 years old!! It amazes me how many (as a percentage of those produced) still have a lot of life left and function as they did long, long ago.

H9

mhardy6647

Vacuum tubes were -- and are -- very tough.
Especially "small signal" tubes like the titular 12AX7s. Service life of a good 12AX7 can - and probably should - be tens of thousands of hours.

By, say, 1960, the vacuum tube was a very mature technology -- perfected, even.

There was a lot of "anti vacuum tube" marketing in the early days of soiled state consumer components. The basic tenor of marketing "new and improved" hasn't really changed since -- well, those "new and improved" elephants were brought out to replace the mastodons.

The irony was that the early consumer soiled state hardware (with germanium semiconductors) was actually pretty darned fragile... but that's another story entirely.

1950s missile technology depended on vacuum tubes... and missiles were a pretty tough environment for electronic components (especially that bit right at the very end of a successful flight).

In total fairness, very demanding applications (high frequency radio/television and the very sophisticated and "close tolerance" circuitry for compatible NTSC analog color television) put high demands on vacuum tube performance, and probably added to the perception that "tubes need to be replaced all the time".

Audio amplifiers require much less performance (so to speak) from vacuum tubes -- other than sheer brute force power handling in the case of output power amplifier tubes.


TransistorPower1964_ by Mark Hardy, on Flickr

Pure "transistor sound"

:- )

mikeyb128

I'm still blown away by the fact you can buy tubes from the 60's that still test strong after 50-60 years, and who knows how many hours they were used in military equipment.

I use some Russian military tubes in my shanling, I believe the mig 25 used vacuum tubes for EMP reasons. Needless to say I accidentally dropped one on the hardwood floor in my basement and still works fine lol

mhardy6647

mikeyb128 wrote: »

I'm still blown away by the fact you can buy tubes from the 60's that still test strong after 50-60 years, and who knows how many hours they were used in military equipment.

I use some Russian military tubes in my shanling, I believe the mig 25 used vacuum tubes for EMP reasons. Needless to say I accidentally dropped one on the hardwood floor
in my basement and still works fine lol

Arguably the most robust vacuum tubes made for routine (for lack of a better word) service were the 175HQ. These were used in the repeater amplifiers in transoceanic cables -- they were designed to work for the service life of the cable.

When cost is literally no object, it's pretty amazing what could be done.

http://www.ase-museoedelpro.org/Museo_Edelpro/Catalogo/tubes/records_nw/175HQ/175HQ_rec.pdf
http://lampes-et-tubes.info/sp/sp056.php?l=e



http://www.radiomuseum.org/tubes/tube_175hq.html

mikeyb128

Very cool... Not one tube failure in 22 years, and the life of the tubes in service was equal to 57 centuries.. My mind is officially blown. Very cool read, thanks for the link.

mhardy6647

Think about the vacuum tubes (krytrons) that are AFAIK still integral parts of at least the United States' hydrogen bombs ;- )

https://en.wikipedia.org/wiki/Krytron

-- because, when you need to switch 3000 amps at 5000 V with a 1 nsec pulse, you just can't use transistors.

mhardy6647

Oh, and them there 175HQs are pentodes, so they probably be kinda mediocre hifi amp tubes ;-)

Nightfall

Are you talking about hiss that gets louder as you turn the volume up? I get that too, I thought it was just the nature of tubes?

muncybob

Nightfall wrote: »

Are you talking about hiss that gets louder as you turn the volume up? I get that too, I thought it was just the nature of tubes?

Yes, that's exactly what I am referring to. No crackle or pop, just hiss. As I mentioned, the Tung Sol have no audible hiss until well past 12 o'clock on the pre and even then you have to be right up to the speaker to hear it. The Tele's have audible hiss at 8' away well before 12 o'clock. These tubes are in the phono stage...if that makes any difference?

Nightfall

I'm using a RCA 6V6GT and 5U4G, Holland made Amperex 12AX7's and 12AT7. I can also hear it from 7' away before 12'oclock on the dial. I have tried GE 12AT7WC, Sylvania 12AT7WC, Mullard 12AT7, a clear glass RCA 6V6GT, and nearly brand new Chinese tubes in all of the mentioned slots - all of them had the same amount of hiss.

How do the Tung Sol's sound?

muncybob

Both tubes sound good. The noise is not apparent until a silent passage or between songs. I think I would prefer the Tele's if not for the hiss...maybe I should make them my rocking out tubes

voltz

So far I've only been able to hear noisy tubes in my Headphone amps.

mhardy6647

Nightfall wrote: »

I'm using a RCA 6V6GT and 5U4G, Holland made Amperex 12AX7's and 12AT7. I can also hear it from 7' away before 12'oclock on the dial. I have tried GE 12AT7WC, Sylvania 12AT7WC, Mullard 12AT7, a clear glass RCA 6V6GT, and nearly brand new Chinese tubes in all of the mentioned slots - all of them had the same amount of hiss...

So, yes, hiss is inevitable in tubes (or transistors) at very high gain. In tubes, it's mostly thermal noise; in transistors it is "shot noise" (essentially a statistical effect of "things" moving randomly). But some tubes are noisier than others, depending on -- all the usual suspects (materials of construction, geometry of design, physical construction quality).

It can be -- in fact, it is -- the operating points for the tubes that will influence how much noise you hear from them "in situ" in the circuit. I'm guessing the 12AX7 (highest mu tube in your amp) is just being run 'hot' enough (in terms of gain, not bias) to be noisy, more or lesee independent of the usual suspects.

I am further guessing you're not using the same amplifier model (circuit design) as the OP -- but I am too lazy to look back through the thread, so I could be dead wrong about that! :-p

Nightfall

My amp is SS, it's a tube preamp I am talking about.

Curiously my 12AT7 gets hotter than any of the four 12AX7's and also glows slightly brighter. I have read that I can try 5751's in place of the 12AX7's to experiment with less gain? Perhaps that would lessen the hiss? It would seem that choices between 5751's are less than 12AX7's though - they're mostly GE, RCA, Philips and Sylvania's. There is a single Amperex 5751 on eBay right now. One. Doesn't appear to be any Tele's.

mhardy6647

The point of operating points for the tube would apply to preamp tubes or power amp tubes.
That said...

wait, your preamp has a 6V6 in it? What is it doing there?

Brighter is most likely a characteristic of the heater in the particular tube (or tube type). Generally means nothing -- the electron emission from the (indirectly heated)

Hotter may mean that the tube is being operated with more plate dissipation (relatively speaking) in one case than in others -- or it may just be the difference in tube types.

Yes a 5751 will have less gain, may have less hiss -- although the signal to noise ratio may not change at all.

So what if there are less choices? If you find one you like, you're finished. If you don't, you're finished too.

:- )

I am always a little amused by the focus on tube rolling on this forum.
It's just not something I get too worked up about. I guess folks who are really into it really enjoy it, though.

Nightfall

mhardy6647 wrote: »

wait, your preamp has a 6V6 in it? What is it doing there?

You're asking me? I have no clue, is a 6V6 an unusual tube for a preamp?



This was the clear top RCA 6V6GT, I now have a smoked glass RCA in there.

Amused? I take that as you don't hear differences in sound between tubes? I distinctly heard in your face midrange frequencies with Mullard that I do not hear with the Amperex's. I say all of this in the most non combative way, hard to tell with text.

mhardy6647

I can hear differences -- I just focus on different things. I use tubes I like and/or that have a good reputation, and focus more on the choice on the circuit design (and application of tube types specified in the design) and iron.

E.g., rather than fiddle with 12AX7s, I'd prefer to go with a design using 6SL7s - all things being equal. Plenty of 6SL7s to play with, or go with a tried and true variant.

I cannot think of what a beam power amplifier tube like s 6V6 is doing in a preamplifier circuit. It is a bog-standard power amplifier tube (and not a bad one) good for about 10 to 12 watts push-pull or maybe 4 or so single-ended. I am baffled.

Maybe it is being used as a power supply voltage regulator in your preamp? You don't have a headphone amp in it or anything?

I'm assuming that the schematic's not available for it?

6V6 specs: http://www.tubebooks.org/tubedata/HB-3/Receiving_Tubes_Part_2/6V6-GTA.PDF

BlueMDPicker

mhardy6647 wrote: »

It is a bog-standard power amplifier tube (and not a bad one) good for about 10 to 12 watts push-pull or maybe 4 or so single-ended. I am baffled.
6V6 specs: http://www.tubebooks.org/tubedata/HB-3/Receiving_Tubes_Part_2/6V6-GTA.PDF

They were commonly used in car radios. Ooops! Showing my age........

Nightfall

No headphone output. I'll see if I can do this with just my tablet, my laptop is busy upgrading the Windows side of my dual boot to 10 from 7.

Nightfall

Not sure if this camera will be good enough for you to see this or not.

Nightfall

Bunch of gibberish if you ask me.