i dropped one of these on the garage floor and it just bounced off like it enjoyed it,
these tubes were used to fire afterburners in F-14 fighter jets, and ICBM's,
God Bless Charlie Kittleson for his awesome magazines,
here is Eric's article instead of the link:
Excerpts from original article in VTV #5
RED BANK: The ultimate tube
1. Intro
The fact is this: many NOS tubes have developed cult followings, because of the efforts of gurus to hype these tubes into godhood. Usually the tubes in question deserve the good reputation, especially given the poor quality of current Chinese tubes. So, consumers are exhorted to search out Tung-Sol 6550s, and Western Electric 300Bs, and Telefunken smooth-plate ECC83s, and a few other things. This has driven the prices of the things to outrageous levels.
There is a brand of tube that you have not heard of. It was introduced in the early 1950s, and was bought by virtually only one customer: the U.S. military. A few of the tube types this company made were commonly used in the electronics in early ICBM warheads. These tubes were used in missiles because they were the most rugged, overdesigned and extravagant tubes available. Their primary reason for existing was because the U.S. Air Force wanted super-tough tubes for use in missiles and avionics, in a steady supply. To win the Cold War, of course.
The identity of this mystery tube maker is so unexpected that tube "experts" will probably joke about it. But the fact is: these super-tubes were made by an obscure division of Bendix Aviation Corporation. The plant in which they were made was called Bendix Red Bank Division, Eatontown, New Jersey. Thus, they are called Red Bank tubes. Even though they were second-sourced by Tung-Sol and, later, Cetron, the "Red Bank" name sticks to all the special types in this series. You guitarists know what else was made in the Red Bank/Eatontown area.....yes, Danelectro guitars and amps. No doubt the Danelectro engineer knew about the Bendixes, but didn't dare specify such expensive tubes for guitar amps.
You have to look a bit askance at "tube experts" who try to tell you what the "best" tubes are. They are biased in favor of something, often something they themselves have a few hundred of, hidden in a closet. All bets are off when you bring up Red Bank tubes, because they ARE the best ever made- from the standpoint of reliability, consistency and physical toughness. And as far as I know, NOBODY is hoarding Red Bank tubes, certainly not like 300Bs or Tung-Sol 5881s. And please don't wave those cute RCA "Special Red" things at me. Good they may be, but next to Bendix Red Banks they seem like pale imitations.
Red Banks were NEVER used in audio equipment. All of them were originally versions of some commercial prototype, but usually used a nonstandard base pinout. In the advertisement shown here, most of the types available in 1955 are shown. Note the many versions of the 6X5 rectifer, but the few signal or power types. So, no equipment known is wired for them, except possibly some scrapped ballistic-missile assemblies rusting in a junkyard somewhere.
Those few types usable for audio-the 5992 beam tube, 6094 beam tube, 6384 beam tube, 6385 and 6900 dual medium-mu triodes-can be retrofitted to guitar amps and high-end equipment, by rewiring the sockets. I was able to borrow some from John Atwood for the tests below (many thanks, John).
2. 6094
This type seems more common than the others. Examine the photo carefully, and you will see nothing but wretched excess. This is a 12.5 watt beam tetrode, a small tube similar to a 6BQ5. Mica spacers would be more than adequate, yet all the spacers are made of ceramic. Note the numerous structural supports, just the ticket for 500g mechanical shocks in a missile. The glass envelope isn't regular glass at all, but Nonex, a type of silicon-boron "hard" glass only used for transmitting tubes and lamps which get very, very hot.
It's more difficult to see the cathode construction deep inside, but the heater isn't just coated with alumina, folded and inserted into the cathode sleeve. Instead, Red Bank engineers went back to 1928 for a vulgar, extravagant touch; the heater is threaded into tiny holes in a machined ceramic block, which is then inserted into the cathode. The only other place you'll see this is in very early indirectly-heated tubes like the UX-227. It was very costly, so as soon as the alumina coating was perfected, the ceramic block disappeared. Its use here is mute testimony to the purity of design practiced by Red Bank. It gives the 6094 a heater-cathode voltage rating of +-450 volts, and since the plate rating is 275 volts, you have to think that this tube is rated in a grossly conservative fashion. This also gives a very long warm-up time.
The photo shows some of the variations of the 6094. The original Bendix Red Bank was the 1950s original, while Tung-Sol made a version from the late 1950s until its purchase by Webster Electric in 1970, and up until it closed its doors in the late 70s. The Cetron starts in the 70s and looks suspiciously like the Tung-Sol; the same tooling may have been used. Cetron 6094s apparently were made until the late 1980s.
I made two adapters to allow plugging 6094s into EL84/6BQ5 sockets. Although the EL84 has much more gain, the 6094 is similar enough to work well in a variety of EL84 amps. (It is actually more similar in characteristics to the 6CW5/EL86 p; tech. ed.) But the pinout is different, as it is on most Red Banks. First a single-ended listening test was done, using the VTV test amp with no feedback and comparing with some EL84s.
We agreed in general on the EL84s; all had quite distorted and bloated bass, and highs that varied quite a bit. The Sylvania 6BQ5, from the 1970s, had modest detail and was very warm. The Sovtek EL84M was somewhat better balanced in sound, while the Yugoslavian EI EL84 had a glassy effect in the midrange and accentuated highs. All the 6094s were lower in voltage gain, but used virtually the same bias point at 300 volts. They were much clearer than any EL84, with clean bass, very nice highs and a slight nasal quality in the mids. There were some small differences between the versions, the Bendix was a little softer-sounding while the Cetron and Tung-Sol showed a bit more treble detail and the Tung-Sol gave a "forward" effect to the drums.
Then a matched pair of 6094s was plugged into one channel of an Eico HF-86 amp. This is one of the finest-sounding EL84 stereo amplifiers ever made. The example was in near-new condition and was provided by our publisher. Upon comparison with a pair of fresh Mullard EL84s from the 1960s, the 6094s gave slightly cleaner bass and a less congested midrange. Imaging was excellent with both tube types. The difference was not as dramatic as in the SE test, and the difference in tube gain was less noticeable, due to the considerable negative feedback in the Eico amp. Yet a small improvement was apparent.
Even though they sounded cleaner than EL84s, the 6094s gave considerably higher distortion readings on the test amplifier than typical EL84s. The distortion at 300v 40 mA, 1 watt into 3200 ohms, was on the order of 0.9% to 1.2%, while EL84s average around 0.9%. This load is rather severe for the 6094s and probably favors the EL84s. Peak power from the 6094s was about the same as from EL84s.
And for toughness, even the old 7189A is a toy. I put 500 volts at 40 milliamps on a 6094's plate, with 300 volts on the screen. It didn't even blink. No red spots on the plate or the screen, no creaking. Try that with any other 12-watt tube, and you'd better stand well back.
3. 6384
The debate often taken up in various magazines, about which 6L6 type is "best", seems a bit silly if the 6384 is compared to the available 6L6 types. Even the Tung-Sol 5881, Mullard EL37 and Genalex KT66 look like fragile and lightweight toys next to the Red Bank tube.
So it's safe to say: you won't see the likes of this tube again. The base is some kind of ceramic material, and is one of the few ceramic octal bases I have ever seen. The construction is the same luxurious style as the 6094, with all-ceramic spacers and a heater block. The pinout is the same as the obscure Tung-Sol 6AR6, a very similar tube to the 5881 physically but not quite the same electrically. Still, the 6AR6 or 6384 can be easily substituted into a 6L6 socket with rewiring or an adapter, and are rated closely enough to work well, though the 6384 makes the 6AR6 look pathetic. Extreme scarcity means we had only one 6384 to test, a new-in-the-box original Red Bank. The plate rating is 750 volts at 30 watts, which is outrageous for a 6L6 type and more typical of the infamous Mullard EL37. Yet EL37s bring $200 or more on the current NOS market, while 6384s are scarce but have nearly no value. It shows how narrow-minded the gurus can be. Simply rewire your amp's sockets, and you can use this "Beastatron".
Tests showed that it is indeed a beast. At 300v 50 mA, distortion was 0.77%, lower than that of a typical Tung-Sol 5881. Peak output was 9.8 volts, far more than most 6L6 types and even better than a KT66. It's a shame that so few modern hi-f amps use 6L6s, as the 6384 is a hot little number. Oddly enough, the single sample made a chorus of tinkling sounds while heating up and cooling down. It didn't appear to affect electrical behavior. I briefly put 500v 75 mA into the tube, and it continued to work without showing red spots on the plate.
4. 5992
I believe this to be the frst-ever Red Bank electron tube. When it was introduced in May 1952, Bendix called it the "Eclipse-Pioneer" tube. This was because Red Bank Division started out as Eclipse Instrument Company, a maker of aircraft electrical generators in the 1930s. It's hard to find out why Bendix started making tubes there, knowledge was lost over the years and Red Bank Division itself is believed to be defunct.
The 5992 is a 6V6GT with balls. Although rated for 10 watts and 300 volts, its construction is the same kind of wretched excess. So it's probably safe to assume that this tube can take far more than the rated voltage. The pinout is identical to 6V6, so it can be used in 6V6 guitar amps with no changes. Unfortunately, some gurus have found the type in their GE tube manuals, so samples are very hard to find even by Red Bank standards.
5. 6900 and 6385
The 6900 is a version of the 5687 medium-mu triode. Like the power types above, its construction is massive, though it does feature a mica spacer. It plugs right into a 5687 socket and works. Its transconductance is about twice that of a 5687, making the 6900 a very intriguing item for high-end audio equipment. I've seen a few in surplus, so some fairly common military radio gear must have had sockets for it.
The 6385 is a dual triode which can replace the 2C51/5670 VHF triode. Since the 2C51 is a good-sounding signal tube, the 6385 may make an excellent line amplifier. We did not have any to test, again due to its scarcity.
6. FINAL NOTE
Red Bank tubes may be the ideal devices for the guitarist who loves music enough to buy only the very best. They were created to help destroy the "Red Menace", and represent Pentagon spending excess reminiscent of those $700 toilet seats, in 1950s electronic form. At that time, one could buy a very good 6L6GC for $3, while a 6384 (assuming you were permitted to buy one) was $50 or more. Imagine someone today paying $1000 for a 6L6, and you will get the idea. It does seem more appropriate to use these expensive "Commie smashers" for making and listening to music instead. In a world drowning with advertising hype and ego, it's nice to know of something that is unquestionably "the best".
As a postscript, it does seem that Richardson/Cetron has made these tubes up until recently. So they may still have the special tooling, stowed away in the warehouse. If enough demand for Red Banks reappeared, Richardson might be interested in restarting production.
Table 1: Rewiring amp sockets to accept 6094s and 6384s
6BQ5/EL84/7189A to 6094:
a) be sure pins 1 and 8 are open.
b) lift wiring on pin 2 (grid), move to pin 1.
c) lift wiring on pin 7 (plate), lift wiring on pin 9 (screen).
move screen to pin 7, plate to 9.
d) lift wiring on pin 3 (cathode), move to pin 8.
e) lift wiring on pin 4 (one side of heater), move to pin 3. Bias adjustment not needed but voltage gain of amp will be less.
6L6 to 6384:
a) lift and relocate any wiring on pin 1 and 6.
b) lift wiring on pin 8 (cathode) and move to pin 1.
c) lift wire on pin 7 (one side of heater) and move to pin 6.
d) lift wire on pin 2 (other side of heater) and move to pin 8.
e) lift wiring on pin 5 (grid) and move to pin 7.
f) lift wiring on pin 4 (screen) and move to pin 5.
g) a small adjustment may have to be made to biasing. Note that 6384's heater draws 1.2 amps, so the power transformer must be capable of supplying the extra current.
Excerpts from original article in Fall 1996 Vacuum Tube Valley Magazine. This back issue is available - see home page.
should get a scanner, camera no good, grab your bi-focals>
