The following is taken from a posting by Joe Sousa in the thread "Ageing in Tubes" so that it is immediately apparent on the tube page.
I got permission from the seller David Navone (ebay id: carsounddave) to post his photos here, along with some of his description.
The 175HQ tube may be the rarest vacuum tube in the world. This vintage vacuum tube was used exclusively for the first Key West, FL to Havana, Cuba undersea telephone cable of 1950. This cable run was so successful that the Bell Labs 175HQ repeater tube was exclusively used in the first TransAtlantic Telephone Cable (TAT-1) laid undersea in 1956 and successfully operated until it was retired in 1978. The quality of this Bell Laboratory 175HQ pentode tube is so high, that none of them failed in the 22 years of operation! (The “H" denotes a pentode design and the “Q” describes an indirectly heated, cathode-type, vacuum tube.)
The TAT-1 system required the British 'HMS Monarch's' undersea cable laying equipment to be highly modified in order to accommodate the “bubbles” in the cable. Each “bubble” contained three of the Bell Labs 175 HQ pentode tubes. There was one cable for the Tx (transmit audio) and one cable for the Rx (receive audio) Quoting from, “A History of Engineering and Science in the Bell System – Electronics Technology 1925 to 1975”, ‘The TAT-1 for its time, ranked in engineering difficulty with the later feat of putting an earth satellite in orbit.’
This Bell Labs 175HQ tube is the heart of the repeating system of the TAT-1 – the first successful trans-Atlantic telephone cable. There were a total of 390 of the Bell Labs 175HQ tubes buried in the two TAT-1 cables which ran from Newfoundland to Scotland. The tube for sale in this auction was manufactured as a replacement in the event of a catastrophic failure in the TAT-1 or Key West Florida to Havana Cuba cable. This vintage tube has never been used and has been successfully burned in for at least 5000 hours.
Work on the 175HQ repeater tube was started at Bell Laboratories in 1933 and continued until the outbreak of World War II. During the war, the burn-in trials continued, but the R&D was deferred to the war effort. At the end of WWII in 1945, serious development on the 175HQ tube was commenced and by 1950; a working proto-type tube was ready for field trials in the Key West, Florida to Havana, Cuba undersea run. In this initial run, six undersea repeaters – containing 18 of the 175HQ tubes – went into operation in June 1950.
The manufacture of the 175 HQ tube was exclusively handled by Bell Labs and only one in seven tubes was accepted – after a minimum of 5000 hours of burn-in. Data from the burn-in tests of these tubes was entered into IBM punch cards for early computer evaluation. This resulted in over .5 million bits of data which was a huge number for analysis during the mid 1950s.
In a total of 4800 of the 175HQ type tubes were manufactured, only four failures were reported and all four failures were prior to the 5000 hour burn-in period. In a 1957 Bell Labs technical report on this tube, it was projected that “no failures will occur in 20 years” (page 26). Remember, six out of seven tubes were unacceptable. These undersea tubes lasted 22 years without a problem until the TAT-1 was retired. This means that none of the 390 175HQ tubes were ever replaced due to failure; however, fishing nets from trawlers, and boat anchors sometimes required exceedingly expensive cable repairs. This explains the need for this spare NOS 175HQ.
The Bell Labs 175HQ was designed under three basic assumptions: 1) Operation at the lowest cathode temperature, 2) Operation at the lowest anode and screen grid Voltages, and 3) A minimal cathode current density. The money and time spent on developing the 175HQ tube is comparable to landing a man on the moon. The results were identical.
The cathode temperature of the final design of the175HQ tube is 670 degrees Centigrade (true), the anode and screen Voltages are specified at 32 to 51 Volts respectively, and the cathode current density is 0.7mA/cm x cm. Life tests on this 175HQ tube were run for a minimum of 5000 hours of burn-in. During this burn-in, only one in seven tubes were accepted. After 8 years of operation, no significant difference in performance was noted from anode and screen grid voltages from 40 Volts to 60 Volts. After 14 years, there was no difference noticed over a 12-1 range of densities such as from 2.5 mA/cm x cm and 0.2 mA/ cm x cm. The result was that the 175HQ was operated at a current density of 50 mA / cm x cm.
The low tranconductance of the 175HQ tube (1000 mS), the low cathode temperature, and the large cathode area contributed to the longevity of this single “getter” vacuum tube. (A “getter” is a device used during the manufacture of a vacuum tube to burn out impurities.) Filament protection was provided by an ingenious gas-discharge tube wired in parallel with the tube, that instantly by-passed the 175HQ in the event of a failure. Every 38 miles of undersea cable resulted in a loss of around 65 dB. The 175HQ pentode tube “repeated” the signal by supplying 65 dB of gain (amplification).
The tube’s leads are extremely flexible and constructed of gold-plated stranded beryllium-copper. The aluminum oxide heater insulator is extruded with 7 holes. The heater insulator is held by a .025” molybdenum rod at each center hold. The heater (filament) is 36 inches of 0.003 inch tungsten that is wound into a helix with an OD of .013 inches. The heater filament was then dip coated and threaded through the six outer holes of the insulator. Next, an aluminum oxide suspension was injected into the holes of the insulator and the heater was fired. This task accomplished total embedment.
The Bell Labs 175HQ tube was designed to withstand a single 500G one-millisecond shock without incident. This is 500 times the force of gravity. Specifications for this tube include heater current = 220 mA, Cathode temperature = 670 Degrees Centigrade, Cathode current density = 0.7 mA / cm x cm, Heater Voltage 18.2 Volts, Heater power = 4 Watts, Control-Grid bias = -1.40 Volts, Screen Voltage 38 Volts, Plate Voltage 51 Volts, Screen current 0.30 mA, Plate current = 1.40 mA, and Transconductance = 1010 micromhos, Input capacitance = 9.20 uuf, Output capacitance – 15.6 uuf, and Plate to Control-grid capacitance = .030 uuf.
In the 22 years of operation of the 2000+ mile undersea TAT-1, the Bell Labs 175HQ tubes ran without a single failure. There were a total 306 of the 175HQ tubes that operated on the 1.7” diameter TAT-1 cables at the bottom of the ocean until November 1978. This yields an incredible 287,000,000 tube – hours without a failure. The next generation tube was the 455A-F and were designed by Bell Laboratories and manufactured by Western Electric. The 175HQ tubes were exclusively manufactured by Bell Labs under extremely tight quality control. This is due to the fact that the undersea cables were never designed to be repaired. Once “ploughed” under the ocean bed, they had to operate for 20+ years without a problem. Clean rooms, rubber gloves, masked workers, etc. were standard procedure for this project.
The gas discharge by-pass tubes were necessary to protect against transient surges in the event of a mechanical problem in the cable. Such problems included anchors from ships and fishing nets from trawlers. These by-pass tubes could handle up to 0.25 A of current and are responsible for maintaining continuous communications.
By paying close attention to refining the tungsten heaters and extremely tight control of the materials required for assembly, processing, aging, testing, and inspection of the 175HQ, Bell Labs created the highest quality vacuum tube ever produced. Clean rooms with rubber-gloved technicians, incredible quality control, vacuum ovens, etc. were required to produce the 175HQ. This technology is standard today, but in the late 1940s, these innovations were cutting-edge.
The initial capacity of the TAT-1 (the first Trans-Atlantic Telephone Cable) was only 36 channels with 4 kHz of bandwidth per channel. By dropping the bandwidth to 3 kHz, the TAT-1 was capable of handling 48 channels. There was one cable for each direction. The coaxial cable diameter is 5/8” with repeater spacing of 38 miles. The total number of repeaters in TAT-1 is 58 in each direction. The repeater gain per 175HQ tube is 60 to 65 dB. The reason that the 175HQ number is not printed on the tube is because these tubes were only produced to be inserted into the repeaters for the TAT-1 cables (and the Key West, FL to Havana, Cuba cables). Only Bell Laboratory engineers installed the 175HQ tubes into the TAT-1 cable repeater “bubbles” which could be rolled over the undersea cable pulleys, lowered miles deep into the ocean, and ploughed into the ocean bed in shallow areas.
The TAT-1 transatlantic telephone cable ran from Oban Scotland to Clarenville, Newfoundland. When either the Tx or Rx channel (undersea cable) failed, the consequence was to quickly bring up as many radio channels as possible. This process was handled by British Telecom or Bell Laboratories / Western Electric on opposite sides of the Atlantic. The next step was to locate the problem with the cable and replace the damaged section. The cable depths ran below 2.5 miles undersea. The 175HQ tube in this auction is a repeater replacement tube in the event of catastrophic failure of the Tx or Rx cable. The original TAT-1 cables were completed three months ahead of schedule and went into formal operation at 4:00 PM on September 25, 1956.
The TAT-1 was the marriage between the Canadian Overseas Telecommunications Corporation, the British Post Office Engineering Department, the Long Lines Department of The American Telegraph and Telephone Company, and Bell Telephone Laboratories. The project was divided into 40% for the UK, 50% for the US, and 10% for Canada. The cost of this cable in 1956 dollars was $42 Million US; however, the cost for the first three minutes of conversation was $12.00. This was a huge amount of money in the 1950s. The TAT-1 cable was officially opened on September 25, 1956 and was retired in 1978. In the first 24 hours in service, the TAT-1 handled 588 UK to US calls and 119 UK to Canada calls. The original Trans-Atlantic Telephone cable service began in 1927 with radio transmitters / receivers. All investors made a huge amount of money and Trans-Atlantic Cables were here to stay. This super rare vintage 175HQ tube is a piece of history.
The plate and grids of this 175HQ Bell Labs pentode are at opposing ends of the tube. The filaments are wired in series and supplied with high Voltage DC from the opposite ends of the cable. This means that the plate Voltage is the Voltage drop across the filaments per “bubble” repeater section – between 50 and 60 Volts.
In the winter of 1982, an attempt to retrieve the retired TAT-1 cable and repeaters was made by AT&T. After two months of frustration, and only minimal results, this project was abandoned. The only other 175HQ tube that we have been able to find is at the American Museum of Radio and Electricity in Bellingham, WA. I personally talked with one of the AT&T engineers on this project and he has a one foot section of the TAT-1 cable as a souvenir. This Bell Laboratories 175HQ tube is probably the world’s most expensive tube ever produced. Since the price per minute of use in 1956 was $4.00, and the only alternative was telegraph or radio, the TAT-1 Trans-Atlantic Telephone Cable was a guaranteed good investment --- provided the 175HQ tube did not fail. Due to the incredible fortunes that were made in the trans-ocean communications industry, no amount of money was too much to spend on developing the 175HQ. It’s quite possible that each 175HQ tube cost $10,000 or more to develop and produce in 1940 dollars. (This is an even larger number in 2005 currency.)
Western Electric was not trusted to assemble the undersea telephone repeaters for the first trans-Atlantic telephone cable (TAT-1). Only Bell Labs technicians, working in the World’s first clean rooms, were trusted to assemble the 175HQ tubes and the undersea repeaters that lasted trouble-free for 22 years until retirement in 1978. This tube was first envisioned in 1933 and working proto-types were being tested from 1934 until this tube was produced in the early 1950s. Since only one is seven tubes was accepted (after 5000 hours of successful burn-in), this pentode has to be the most incredible tube ever produced. We can only find one museum with a 175HQ tube (Bellingham, WA), and every serious tube collector needs this Bell Labs tube in his / her collection. This 175HQ comes with the rubber insulating shock mounts - end caps that were used exclusively in the TAT-1 repeaters (and the Key West, Fl to Havana, Cuba test cable.). If you collect vintage vacuum tubes, this NOS tube is the world’s most expensive, and rarest, tube ever made.
The 175HQ tube for sale in this auction was purchased on June 24, 2004 by my partner, Richard Clark, in a government auction of the super secret Western Electric facility in Burlington, NC. This facility was a defense contractor specializing in missile technology from the mid 1950s until 1999. Until June 24, 2004, this 175HQ tube was guarded by the US Government.