Discussion in '"Boat Anchor" & Classic Equipment' started by W5INC, May 27, 2019.
Steve, are you saying that this is getter flash? If not, what is the purpose of this stuff?
Nope. Getter flash is silver.
From 2003....still relevant today:
6146s in High End Audio
The 6146 family of tubes can be used in many high-end audio designs with good results, replacing tubes such as the EL-34 and 6550 with some circuit value changes.
However, the 6146 family of tubes were designed as RF transmitting tubes. This means their internal structure and construction were optimized for radio-frequency signals, not audio. As they come from the factory, or when found in NOS condition, 6146s are not sonically balanced for audio, regardless of tube-tester indications.
In Class C RF service, which the 6146 was originally designed for, the ideal tube would have very "square" characteristics, with "sharp corners" to the various characteristic curves. The popularity of 6146s in RF applications is testimony to this "squareness".
If used in audio amplifiers without the proper pre-conditioning, 6146s will have muddy, poorly defined, "small-mouthed" bass, a confused, indiscriminate midrange and excessively bright, "genius-level" highs. They will also tend to annoy dogs, disrupt the echolocation of bats, confuse any nearby dolphins, reroute bird migrations and destroy supertweeters if played at high level.
Fortunately, 6146s can be made useful to the audiophile be being pre-conditioned for audio. All that is required is for them to spend a considerable number of hours in RF service, which will "round off the corners" of their characteristics and render them most ideal for high-end audio.
The correct amount of preconditioning of a 6146 is reached when the RF output drops significantly enough to warrant their replacement in the RF application. At this point, they are ready for the audiophile. Zero RF output is the ideal, however, most preconditioned 6146s will produce at least some RF.
Today, the most common RF use of 6146s is in amateur radio transmitters. This fact offers the audiophile with the perfect opportunity for a symbiotic relationship with the radio amateur.
Most amateur radio transmitters using 6146s use them in pairs, which will cause them to be optimally balanced both sonically and electronically by the end of the preconditioning time.
All the audiophile needs to do is to obtain some new, unpreconditioned 6146s and offer to trade with local radio amateurs for preconditioned ones. Since radio amateurs are obsessed with RF and "communications quality" sound, it is preferable to employ the term "used" rather than "preconditioned" when talking with them.
The bonus value of preconditioned tubes will vary with several factors, such as brand, age, amount of preconditioning, type of transmitter, color of box the tube came in, phase of the moon, number of times per minute the radio amateur says "by golly", "QSL?", "balum", "diapole", "strapping" or "microphonium" while on the air, etc., but in no case should it be less than about three times the value of a "new" 6146.
In bargaining with the radio amateur, an initial offer of two new major-brand unused boxed 6146s for one "used" 6146 is recommended, so you can work upwards from there. A cash premium of $5 to $15 per tube, in addition to the 2-for-1 swap, is recommended as part of the initial offer.
A successful deal with one radio amateur may lead to others, as they will search their "junk boxes" for "used" 6146s. The promise of "new" tubes and a cash bonus will be irresistible to them.
It may take some convincing to get radio amateurs to part with their preconditioned (aka "used") tubes, as they may feel such tubes are almost useless ("worn out" or "soft" in their parlance), since they do not function well for RF. One method of convincing them is to present a notarized release form relieving the radio amateur of all responsibility for the condition and remaining useful life of said tubes, and transferring the responsibility to the audiophile. Besides convincing the radio amateur, this will help alleviate any guilt the audiophile may feel over getting preconditioned audio tubes at such low prices.
73 de Jim, N2EY
Different Steve here ...
That coating is not getter flash. It is aquadag. It is a graphite coating sprayed inside the tube envelope.
Aquadag was a vital component in CRTs. In audio tubes, it's use might have been snake oil.
There is not much literature that I can find on it. In reading posts on various audio hobby forums many years ago, I learned (but can't prove with citations) that aquadag was supposed to provide shielding, much the same way metal tube envelopes did. But shielded from what? Power tubes (pentodes and beam tetrodes) are pretty immune to picking up noise like high-gain small signal tubes can. That's why small signal tubes often have steel or aluminum shields fitted.
I've seen a lot of old power tubes with aquadag. I'm pretty sure the aquadag used in power tubes was all about the visual effect. Marketing. Perhaps the Chinese manufacturers have picked up that baton.
..that is a curse.
What is your problem ?!
I had the chinese language course, while in the U.S. Army.
It was supposed to be for a “good will tour.
"Despite being so common in English as to be known as the "Chinese curse", the saying is apocryphal, and no actual Chinese source has ever been produced. The most likely connection to Chinese culture may be deduced from analysis of the late-19th-century speeches of Joseph Chamberlain, probably erroneously transmitted and revised through his son Austen Chamberlain."
Very interesting about the aquadag as I have 12 or so 6SN7s that are coated on the inside just like the picture NW2K posted. I will fire off a Email to the China tube folks and see what kind of a answer they send back concerning their HPCC coating and what it's use is. Snake oil with Soy sauce? Must have been a reason the 6SN7s and a few other tubes have the coating in them, could be the marketing aspect also. Nice post there N2EY on the 6146s.
From chapter 1, part 2, section iv, Bulbs, of Langford-Smith's Radiotron Designer's Handbook, 4th edition (available from tubebooks.org):
The inside surfaces of glass bulbs are frequently blackened. This has the effects of making them more or less conductive, thereby reducing the tendency to develop static charges, and reducing the tendency towards secondary emission from the bulb.
I appreciate this mention, as although I vaguely knew what an aquadag coating is, I hadn't yet determined its derivation. This time a quick search found https://en.wikipedia.org/wiki/Aquadag. Have you hugged your Aqueous Deflocculated Acheson Graphite today?
Somewhere, I have a World War II era magazine that had a formula, and application notes, on making / using a mixture made from, primarily, coal, that was painted on the outside of vacuum tubes to replace the metal tube shields that were very common in receivers manufactured during the 1930s. Because of a shortage of metal in the civilian arena during the war, various schemes were devised to replace metal wherever possible.
This mixture reportedly did do the job. Since coal was the major fuel used for heating houses in those days, there was always plenty of small pieces of coal, as well as coal dust, around for such purposes.