Microphonic NOS GE JAN 12AX7

[minim]

Hi folks,

I have in my possession one of the above. I was curious as to what all the fuss was about re NOS tubes, so I bought one of these fellas. And indeed it does have a superior musical quality - to my ears - than the current production stuff I have. Enough for me to persist with it. However, as stated in the title, it exhibits noticeable mechanical noises through the speakers when I remove its tube shield and/or tap it gently with a fingernail. I also hear the familiar ringing/rattle when sustaining selected notes, mostly bass-oriented. This is the second one like this - i returned the first one because it was worse.

I paid AUS $65 for the tube. What bothers me is, is this what i should expect from these tubes, from your experience? Is this a "death rattle", or alternatively something I should just live with? For reference, I have a friend with a Rivera R30 that has a non-original PT providing 520+ volts to the Sovtek EL34s in it, and those Sovteks have been ringing for years but keep bending over and taking it like trojans.

I know you are not Soothsayers. However, your thoughts? The vendor is very obliging and willing to exchange without a fuss.

Mitch

[Mick Bailey]

There are too many charlatans peddling stuff through e-bay for my liking. Unless you're dealing with reputable suppliers it's a lottery best avoided.

I've come across;

1. Cleaned up 'pulls' from tired old equipment., Especially Mullard EL84s with their gravy-brown internal staining. A glass fibre brush in the pins, straighten them out and polish the glass, and you're away.

2. Returned-as-faulty stock that's come from old radio shops.

3. New tubes re-branded as NOS Telefunken or Mullard. Even to the point of using a glass etch kit to apply the Mullard Blackburn factory code or the RCA markings.

4. Freshly printed 'original' boxes.

For the price of a single NOS tube you can buy a range of new-production tubes and audition them. When you discover something you like there's a good chance of getting the same tube again. With NOS you spin the wheel every time. The exception perhaps are the old Russian tubes that were made in vast quantities and superb quality. They don't have the sex-appeal of a bathtub full of soapy Kylies like some tubes, but they're good value and can sound excellent.

[soundguruman]

Hi folks,

I have in my possession one of the above. I was curious as to what all the fuss was about re NOS tubes, so I bought one of these fellas. And indeed it does have a superior musical quality - to my ears - than the current production stuff I have. Enough for me to persist with it. However, as stated in the title, it exhibits noticeable mechanical noises through the speakers when I remove its tube shield and/or tap it gently with a fingernail. I also hear the familiar ringing/rattle when sustaining selected notes, mostly bass-oriented. This is the second one like this - i returned the first one because it was worse.

I paid AUS $65 for the tube. What bothers me is, is this what i should expect from these tubes, from your experience? Is this a "death rattle", or alternatively something I should just live with? For reference, I have a friend with a Rivera R30 that has a non-original PT providing 520+ volts to the Sovtek EL34s in it, and those Sovteks have been ringing for years but keep bending over and taking it like trojans.

I know you are not Soothsayers. However, your thoughts? The vendor is very obliging and willing to exchange without a fuss.

Mitch

As a rule, NOS tubes are not worth buying. There are too many possible problems compared to
just buying new tubes.
You never really know what you are buying, and you are taking a chance with NOS tubes.

Just because a tube "tests" good, does not mean it's low microphonic, or low noise!
The tester does not detect those problems.

But some people have lots of money...

Yes the old USA / UK tubes do sound pretty good.
But from age, they develop rattles and noises. As you said, some of these have microphonic ring.
This indicates that the tubes were rejects, or very used...and you paid too much.

But many tubes do ring. Even new ones.

Some people try to find "selected" non microphonic tubes.
But you may find that 2 out of 100 are low noise, low microphonic and good gain...
it takes quite a bit of searching to find one that won't have noises.

We used to buy New Bugle Boy GE, and those were really good. about $$30 each
but we bought all of them.

The most consistent ones have been JJ ECC83 (12AX7)
Which have good gain, low noise overall, very few defects.
I have very few problems with JJ tubes.

However there are several excepted methods to stop the ringing.
And these methods are used in many high performance amps.

I like a capacitor between plate and grid, this capacitor is about 6-7 pico Farads.
The capacitor should be rated 1000 volts,
or use two capacitors in series, 12 pico Farads 500 volts each in series, for 6 pf 1000 volt rating.

The capacitor is installed between pin 2 and 1
or between pin 7 and 6, on the 12AX7 preamp tube.
Whichever side of the tube is V1A. The capacitor is installed between plate and grid of the first preamp stage.

This method is used by Fender and Marshall on certain amps, to stop the microphonic ringing.
And it works pretty good.

There are also several other methods, which I don't like as much,
because I don't like the way that they affect the tone of the preamp.

[km6xz]

What are you using the tube in? Is it a combo or head. Of a head, you have the option of isolating the amp from the vibration of the cabinet. A pad of dense foam under the amp can do wonders for micro-phonics. Combos are usually really hard on tubes, the vibration can be intense and both power tubes and small tubes eventually will be vibrated into unusability. Well designed amps use shock mounted sockets and damping material surrounding the first preamp tube. Shock mount sockets were very common in the heyday of tube test instruments and communications.

Are NOS worth the price that are asked for them now? I do not think so, it makes more sense to optimize your amp to get the best out of the tubes available now. An amp that is modified to reflect the actual parameters of a current model production tube will be cheaper to own and give just as good sound. The old tubes will have different characteristics from the tubes for 40 years ago so the circuit designed years ago have will probably work just fine with tubes characteristics of the same era since that is what the designer had access to. Modern amps, if designed well around current era tubes, it will probably get the best results from modern tubes.
Tubes do not have an intrinsic sound, but whatever parameters it actually has will interact with the rest of the circuit to as a whole that has a characteristic sound style. Changing anything can have as much or little impact on sound as tubes or any other component component

[minim]

I'm using the tube in a JCM900 combo from which I have removed the preamp board and hand wired a standard 2204 preamp circuit, plus changed some values in the PI to standard. I'll try the tube in one of my heads and see if I can live with it.

I have to say, the NOS tube does sound more complete. But as you imply, they won't be around forever so maybe I should break off the engagement before I form an addiction.

[Mick Bailey]

No amount of snubber cap will stop a mechanically defective tube from ringing. Just like putting bananas in noisy transmission won't fix that, either.

[dai h.]

maybe if you have gear that tends to show the tube's character more (non-distortion reducing, cancelling type topologies), is more of an instrument (like many gtr. amps where a big part of the purpose is to "impart" a sound rather than simply reproduce and amplify accurately--depends on what "gtr. sound" you are going for though, I'm sure), and the gear happens to have been developed (maybe lots of empirical experimentation) using older production, it could make sense to source and consume old stock tubes, but OTOH the gear is already designed to work well with newer production (adjustments in operating conditions, load, whatever have been carefully made), maybe it doesn't.

(Unless you have deep pockets and money to burn) dealing with old stock is full of pitfalls and caveats. Unless you're buying from a totally honest and knowledgeable seller, it could be difficult to determine what you are buying, since there are out and out fakes, legitimately re-branded tubes (alternate supply from another manf. or maybe to get around export controls), people passing off used (or worse) tubes as new and so on and so forth.

I think old stock (new or good used) can be really good value (and really be worth the money), but (like lots of other situations) it helps to have specifics of what the needs, goals are.

[guitician]

Even to the point of using a glass etch kit to apply the Mullard Blackburn factory code or the RCA markings.

I don't think Mullard etched codes into the glass, at least not on any of the original ones I've owned.

[guitician]

If your tube is used in a sensitive section of the amp, it needs to be tested for microphonics. That tube may work fine in the phase inverter section of the amp. I agree the old tubes are well worth the price as long as you get real NOS and they are tested well first.

[guitician]

Are NOS worth the price that are asked for them now? I do not think so, it makes more sense to optimize your amp to get the best out of the tubes available now.

If it's and old amp, then stick with old tubes, for the pre-amp ones anyway. And the "Reissue" power tubes should be direct replacements, so what's with "Optimizing" the amp to use them?

[Mick Bailey]

I don't think Mullard etched codes into the glass, at least not on any of the original ones I've owned.

I've had originals with etched, printed grey, printed white and printed silver codes.

[dai h.]

I've had originals with etched, printed grey, printed white and printed silver codes.

yeah Mullard (and other Philips family tubes) have various (internal) factory and date codes (presumably for quality control). You can find documentation explaining the symbols on the web.

[guitician]

I've had originals with etched, printed grey, printed white and printed silver codes.

I've only seen etched codes on US tubes, but I've also had people refer to printed codes as being etched, those people shouldn't be selling tubes.

[Mick Bailey]

I've only seen etched codes on US tubes, but I've also had people refer to printed codes as being etched, those people shouldn't be selling tubes.

If you get a 50s tube with the Blackburn code printed in dark grey and scrape away the surface paint with a scalpel, you'll find that the glass is etched underneath and no amount of scraping will remove that. I've done just that with an EL84.

It appears as though this is intentional - possibly a self-etch paint was used to ensure the code would remain even if the surface got rubbed. Usually the the rest of the printing can be rubbed off easily with your thumb (which is also an indicator of an original tube - the fakes I've seen have bright, firmly attached printing).

But, they aren't all like this. Some of them have paint that can be removed easily. Maybe there's a particular date range for etched tubes.

[guitician]

OK, your right I just looked at my I61-BOJ coded 12ax7's and they are etched under the paint. Thanks, I learn something new here almost every day.

Opps, on closer inspection under a microscope, what first appeared to be etching was just the under film of the paint.