FAQ  Frequently asked questions


Q: What does the extra lettering like WA, or GTB mean?

A: This list is incomplete, but it may help.

GTA: when found in 6SN7 it has a higher plate dissipation
GTB: quick heating version of GTA.  For Hifi  GTA and GTB are the same.
WGT, W, WA, WB: were sold to the military.
B:  Cylinder glass.  5U4GB is the cylinder glass version of the 5U4G
JAN: Check under "Test processes"
S: Can be found on many tubes, indicates a special version. Can be anything, but for one tube number is it normally the same.
SQ: Special Quality. These have "SQ" data sheets What is special, is in the data sheet.



Q: What does JAN in front of the part number mean?
A: JAN = Joint Army Navy.  The word JAN is a protected, like a trade mark.  The tube factory must do a stress test (above 100% plate dissipation) on samples of standard tubes. When they survived, the whole lot is approved, and can be marked JAN-6SN7. The samples that are  actually used for the stress tests must be destroyed.  Auditors can show up unexpectedly to inspect the process.  JAN Specs are still in use for electronics today and can apply on any electronic part. For some reason people pay no extra for JAN tested tubes, probably because they know JAN has something to do with the military, but that's all they know.  Since the Army has no reputation for making better music, these tubes are not considered better.  But... they are! So take the opportunity to get a JAN tube for the same price as standard tubes.


Q: What are "VT"  tubes?
A: Just normal tubes. Only the VT numbering system was made by the military, to have their own, unique part numbers. This makes the ordering of those safer from an administrative view.  No extra tests or anything.  For some reason, people pay twice the price for tubes like this.  For instance, with VT231 this tube is usually the very nice older construction tube. But not always. So IF its the older type you get, this VT231 is a very good tube.  However, many standard 6SN7 are around, with just VT231 stamped on it.  This may not be what you were looking for.


Beware for internet getters specialists that are none.  These are the same people that replace mathematics by astrology. 

Q: Can I recognize good vacuum by judging the getter?
A: Not always.  Some gasses are not absorbed, the getter looks fine, and the tube can be gassy still.

Q: Can I recognize bad vacuum by judging the getter?
A: Often, but not always.

Q: When the getter shows signs of use, is the tube bad?
A: Perhaps, but not always.

Q: When the getter is bad, is the tube bad?
A: Yes.

Q: So, when is a getter bad?
A: A white getter is bad.  Dark spots inside the getter are not relevant. Getters can be dark, or metal shiny. Both is ok. Any rings or blue colored rings inside the getter is no problem.  The getter is near (but but at) the end-of-lifetime  when the edges are "digital".  With a good getter, the part where you can see through it is gradually starting, and can use something like 5mm. So there is the part where the getter is saturated,  then part where it is transparent, and finally clean glass comes. So, good getters have NO sharp edges. Exceptions can be with some of the long life tubes, like RCA 5692, and some of the TESLA ECC801, ECC802, ECC803 Series.  These have getters with sharper edges than normal.
Questionable Getter

Good getter


A: This is a version with older type of getter. So called "hot" getters. These getters do not work any more once the tube is finished.  They only worked during that short moment, when the getter was evaporated during the production process. Modern "cold" getters are active when the tube is in use, and have even limited function during storage.  If you would break the glass of a chrome top,  the getter will stay shiny, and gets white only after weeks.  This demonstrates it's very low ability to absorb gas, when cold.  By the way,  chrome tops are not made with chrome, it is just shiny color.  Some of the early "tall glass"  tubes have this getter too, but it is flashed from the side. It is an older  technology and 6SN7 like this is probably from around the 1940's.  Often found in the VT231, or sometimes in 6SNTWGT.

Q: Why are CHROME TOPS better, when the getter is not working any more?
A: The modern (cold) getters were not invented yet. Since the "hot" getter has no function once the tube is stored or used, the manufactures were forced to use much more clean materials. The tube needed to be clean by itself, for ever. Apparently this was the much better process, and I have never yet seen a defective chrome top tube. Unfortunately, the "hot" getter process got out of use, when modern cold getters were invented.  Beware: Not all tubes sold as chrome tops are actually the highly sought after "chrome" tops.  Most are later technology, with a darker getter color. These are no chrome tops, but look pretty much the same.  Be careful what you buy.

Click this image to see the details


Q: Some tubes have "powdered" gray plates, some have shiny gray plates, others have black plates. Some have even white plates. What is the difference?

A: Powdered gray plates is the latest technology. The plates are sprayed with a special graphite paint. This only works with the later type (so called "cold") getters.  Used since the 1950's, until today.  (Our standard process at Emission Labs)

Non shiny dark black plates have a carbonized surface.  With this technology nothing can go wrong.  Only, it produces big fat clouds of DIOXENE during production, and this process is ABSOLUTELY forbidden since decades in any country that respects human life.  For those who know, for this process the poisonous "benzene" fluid is burned in a chimney , but without giving enough oxygen to it.  So inside the chimney a stinking fat cloud occurs.  You just hang the plate in this smoke for some minutes, and it is covered with a fat layer of black dirt. During production, when the plates are heated,  the dioxin gas is set free, and pumped out of the tube. What is left is a pure carbon layer. DIOXENE and PLUTONIUM are the most poisonous materials that exist.  Both will cause genetic defects, no matter how small portion you were exposed to, no matter how short.  In larger doses it will cause cancer. So even if you don't get cancer from it, your children can get inherited genetic defects.  In the USA and West Europe, Philips and GE stopped with it first, RCA was the last. In East Europe was still used until some years ago. The Chinese still use the process today. It works cheap, and needs no expertise. To get rid of the poisonous gas, they just open the windows of the factory. (bon apetit...)

Shiny black-grey plates.  A few methods can be used to produce this coating.  By treating carbonized nickel, the shiny gray Nickel-Carbide surface results from it as well.  Difficult process, requiring expertise.  Perfectly under control by Sylvania.  Very rare with ECC81....88 types.  Keep those if you find them.

White plates.  These have no treatment at all.  Can be shiny or opaque.  Results in lower dissipation, and larger size plates, but less production steps, so less risk on contamination.

Mesh plates. Originally used because this gives higher dissipation, and uses less (expensive) tube grade nickel. The higher dissipation comes from the fact that one plate can partially radiate heat THROUGH the other one. Also the filament heat can be radiated directly through the holes. Today, this process is very difficult to repeat. Will result in fully resonance free plates. Today only made by Emission Labs.  Good made mesh tubes have LONGER lifetime than standard tubes.

Semi mesh plates.  Used by TJ/Fullmusic, just from nickel plate with holes in it. Process is taken from CRT mask (Color TV Tubes). Doesn't seem to give the sound advantage of real mesh, but sure looks nice. This material seems to be not ideally suited for making anodes from it, and the tubes can become gassy.

Titanium plates.  No titanium, but titanium coating.  A way to make the plates light gray Very interesting and very reliable coating process.


Q: How can I repair that?

A1: Not with 10-seconds glue. It will come off again, dissatisfaction guaranteed.  At Ebay, it seems this is what everybody is doing here.  mmm ;(

A2: Perhaps two components glue, but the temperature coefficient is not the same as glass.  You can not use it with ceramic or metal sockets.  This will break the glass later, but also with normal sockets this can cause glass breakage.  Risky repair, not recommended.

A3: Original tube glue, as used by manufacturers can also be used, but not when the glass is older than 20 years.  Otherwise the glass will break. Either during the baking of the glue, or later on stock it can crack also. Risky repair, not possible when the glass is older.

A4:  Use the special tube repair glue from Emission Labs. This glue is magic, and can repair any tube that has some remains of the old glue inside.  It partially solves the old glue, and will give no visible signs of the repair.


Q: Is the tube bad?
A: Mostly not.  Check here


Q: How do I burn in a new tube, and why?
A: Check here


As complete as can be. 10 pages at the moment. Check here


Q: How can I recognize if a Valvo or Philips tube was made by Mullard?
A: "Made in England"  is a good sign. There is some small coding at the glass, close to the tube base.  A list of these markings will be added later.