Mounting tubes horizontally. - Page 1
Forum section: electronics / projects

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: July 29, 2022, 05:53:44 pm
content: I want to mount tubes in an amplifier (preamp tubes like 12AX7's and EL84 or 6L6GC output tubes depending on the circuit) for layout and cooling layout benefits, but is it safe to do this? the top and bottom of the envelope would get much hotter than the sides which would have large convection currents cooling them.I would try to design the cooling vents so they wrap around as much of the tube as possible, but still...reliability is a big deal to me, don't want the tube going gassy or having the filament short to the cathode over time.

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 29, 2022, 05:56:58 pm
content: Read the data sheets eg on Duncan Amps.They often show allowable mounting orientations. Sometimes it is necessary to search more than one manufacturer's data.

author: coppercone2
author_rank: Super Contributor
timestamp: July 29, 2022, 05:59:30 pm
content: I have seen horizontal tubes before. They have metal strap around a bracket to fix them in placeI don't think you will have problems unless its impacted hard like turbulance

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 29, 2022, 06:05:46 pm
content: Usually stated for the beam power tubes, the small ones should be OK

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: July 29, 2022, 06:46:22 pm
content: There are beam power tubes that are made for horizontal mounting.There are some that cannot be mounted this way because they fail.This has been an issue in HAM Linear AMPS where a brand of tube will be prone to fail in horizontal position.I do not know specifically about the 6L6, But I will ask someone who should know probably next week.Quote from: mag_therm on July 29, 2022, 06:05:46 pmI think mag therm is correct. Some power amp tubes were rated for horizontal application, some were not.Quote from: ELS122 on July 29, 2022, 05:53:44 pmI do not think getting gassy is associated with being horizontal. And I think the short is not with the heater but with some of the grid components. When they get hot they sag and can contact another part of the tube.

author: Benta
author_rank: Super Contributor
timestamp: July 29, 2022, 06:47:17 pm
content: 50s/60s TV sets all had the tubes mounted horizontally (the chassis was vertical). Never saw a problem except a bit of dust buildup.The Höfner bass power amps had the EL84s mounted horizontally (relatively flat enclosure).The Ampeg power amp I used in my rock guitarist days in the early 80s had the tubes upside-down. Man, did those have a cool blue glow from the anodes!Don't see an issue.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 29, 2022, 06:56:41 pm
content: Good enough for Tektronix, that's the swing-out chassis for a time base.

author: wraper
author_rank: Unknown
timestamp: July 29, 2022, 07:00:29 pm
content: Tubes mounted horizontally was how every Soviet tube based TVs were made.

author: jonpaul
author_rank: Super Contributor
timestamp: July 29, 2022, 07:27:32 pm
content: Power tubes (valves, ampoules) with direct heated filaments may have a restriction in op pos.Most small vacuum tubes are indirectly heated cathodes, no issues.See the OLD RCA and other tube manuals, the complete spec include allowed operating positions.Jonm

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: July 29, 2022, 07:42:34 pm
content: 6L6GC can be mounted any positionIt is on the first pagehttps://pdf1.alldatasheet.com/datasheet-pdf/view/229316/GEC/6L6-GC.htmlThe first in the line, the 6L6, can also be mounted in any position. I think they were metal tubes.The EL84 is a real pentode, the 6L6 are beam power tubes, a bit different, not much though.

author: TimFox
author_rank: Super Contributor
timestamp: July 29, 2022, 08:32:49 pm
content: All (at least all American) tube data sheets gave allowable mounting positions.For tubes that have restrictions on mounting orientation, some data sheets specified which two pins must be in a horizontal or vertical plane.For example, the Tung-Sol datasheet for a 2A3 power triode specifies (in rather small print) that pins 1 & 4 shall be in a horizontal plane when the tube is mounted horizontally.https://frank.pocnet.net/sheets/127/2/2A3.pdf

author: Gyro
author_rank: Super Contributor
timestamp: July 29, 2022, 08:34:19 pm
content: The same with European power tubes such as the KT66 and KT88.The normal orientation is grid support rods vertically in line (one above the other) to prevent grid sag.

author: TimFox
author_rank: Super Contributor
timestamp: July 29, 2022, 08:53:38 pm
content: Quote from: Wallace Gasiewicz on July 29, 2022, 07:42:34 pmThe "6L6" (ancestor of RCA beam power tubes with 0.9 A heaters) is a metal octal tube.All other 6L6 types (6L6G, 6L6GA, 6L6GB, 5881, and 6L6GC) are glass octal tubes, with differing plate power ratings.

author: Benta
author_rank: Super Contributor
timestamp: July 29, 2022, 09:53:33 pm
content: You're overthinking this.

author: eugene
author_rank: Frequent Contributor
timestamp: July 29, 2022, 11:05:40 pm
content: It's in the datasheets.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: July 30, 2022, 12:23:30 pm
content: I am working on an old Blaupunkt car radio its tubes varyverticle, horizontal and upside down of corase space is at a premium.Jeff

author: vk6zgo
author_rank: Super Contributor
timestamp: July 30, 2022, 01:13:40 pm
content: Much rack mounted equipment in the tube era had them mounted horizontally, as the real estate available for circuitry is limited in normal racks if using horizontal oriented chassis, especially for complex devices like Synch Pulse Generators, necessitating connecting cables etc between different stages, which are not necessary with horizontally mounted tubes on a larger vertically mounted chassis.

author: N2IXK
author_rank: Frequent Contributor
timestamp: October 10, 2022, 05:57:36 pm
content: Generally, most tubes can be operated in any position.The issues come with filamentary cathodes, (like the 2A3, 5U4, 300B, etc.) where the filament must be oriented so that if it sags under gravity when hot, it will not come into contact with the grid or plate. The internal elements are situated with a specific orientation with respect to the base pins, and the tube datasheet will often specify something like "horizontal operation permissible if base pins 1 and 4 are in a vertical plane". This needs to be checked CAREFULLY for modern production tubes, because there was at least one Chinese manufacturer of 811A tubes which didn't orient things the correct way, causing a high failure rate in Collins 30L-1 linear amplifiers, which run 4 811As in a horizontal position. The filaments would sag into contact with the grid, destroying the tube rather spectacularly.The other time there will be a required orientation will be with mercury vapor rectifiers. The tube must generally be operated vertical, base down, so that any condensed mercury will remain at the bottom of the tube, and not short anything out. Obviously, ignitrons, with a pool of liquid mercury in them needed proper orientation as well.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 17, 2022, 02:54:19 pm
content: small fry

author: TimFox
author_rank: Super Contributor
timestamp: October 17, 2022, 03:57:45 pm
content: Vacuum-tube installations like that typically used redundant assemblies, so that one could be serviced while another operated.Since service involved pulling tubes, it would have been very difficult with vertical tube mounting.

author: TimFox
author_rank: Super Contributor
timestamp: October 17, 2022, 03:59:45 pm
content: Quote from: ELS122 on October 11, 2022, 04:48:25 amThe Collins 30L-1 is a linear amplifier for RF applications, specifically the amateur bands between 3.4 and 30 MHz.It would not be happy driving an 8 ohm load.

author: strawberry
author_rank: Super Contributor
timestamp: October 17, 2022, 04:57:28 pm
content: vacuum is good heat insulatoranode radiated IR heats up glass envelope

author: TimFox
author_rank: Super Contributor
timestamp: October 17, 2022, 05:07:59 pm
content: That's why modern high-power RF tubes often have an "external anode", where the metal envelope (usually cooled by forced-air) forms the anode and contains the vacuum.That's not necessary for low-power tubes, such as 12AX7 preamp tubes.

author: james_s
author_rank: Super Contributor
timestamp: October 18, 2022, 06:23:22 am
content: Quote from: ELS122 on October 18, 2022, 05:55:01 amNot really. The anode cap on those tubes isn't connected to a wire, it's a massive block of metal, usually copper that is part of the anode structure. It would be way less efficient to use the pins out the base, and why would they do it that way when they can just extend the anode out the top?

author: TimFox
author_rank: Super Contributor
timestamp: October 18, 2022, 01:03:29 pm
content: Bringing the anode wire up to a "plate cap" on the top of a glass envelope (e.g., 807 or 6146, and a host of horizontal-deflection tubes for old TVs) avoids high voltage on the base pins, but doesn't conduct much heat away from the anode.Thicker wires, such as on an 829B to thick pins can use a ribbed connector to help conduct some heat away, but not as much as with a genuine external anode.An example of a true external-anode RF power tube, with ceramic-metal construction:https://frank.pocnet.net/sheets/140/7/7203.pdfNote how the anode is surrounded by a metal-to-air heat exchanger, with vanes between the inner diameter (anode and tube envelope) and outer diameter sleeve.It is designed to have forced air through the vanes to remove heat efficiently in a small volume.A glass-envelope tube of similar power, with internal anode:https://frank.pocnet.net/sheets/140/4/4-250A.pdfAgain, it should be operated with forced-air cooling past the base and envelope, and is physically larger than the 4CX250B.Chapter 6 of the classichttps://w5rkl.com/wp-content/uploads/2014/04/Eimac-care-and-feeding-of-power-grid-tubes.pdfincludes forced-air and other cooling methods, including water and steam.An example of a "regular" glass-envelope tube with a plate cap:https://en.wikipedia.org/wiki/807_(vacuum_tube)Note the resemblance in the photograph between the 807s and an early 6L6G (no plate cap) on the right; the electrical characteristics are similar.

author: coppice
author_rank: Super Contributor
timestamp: October 18, 2022, 09:11:00 pm
content: Quote from: Benta on July 29, 2022, 06:47:17 pmSome 60s TVs had tubes pointing in every direction, as they worked the electronics into a ring around the CRT.

author: TimFox
author_rank: Super Contributor
timestamp: October 18, 2022, 09:16:34 pm
content: The ceramic-metal 4CX250 tubes (note the "C") evolved from the 4X150 glass-metal tube.Ceramic-metal construction has a higher temperature rating than glass-metal, but lacks the aesthetic appeal of the filament glow through the glass.According to the Eimac data sheets, the ceramic-metal seal is rated up to +250oC, the glass-metal seal up to +175oC, and the anode itself up to +250oC.Since the thermal expansion co-efficients of the metal and insulator (ceramic or glass) differ, the glass-insulator seal is the weak point in the envelope as the tube heats up.The 807 is merely a 6L6 with a plate cap. Just about all power tubes with a 6.3 V, 0.9 A heater have the same electrical characteristics within their power and voltage ratings.RCA continued to print the same set of 6L6 plate curves from their introduction of the 6L6 (with metal envelope) in 1936 until they ceased tube manufacture in the 1980s.Either their production was very reproducible over all that time, and introduction of different envelopes and power ratings, or they never bothered to re-measure the device.Early RCA monochrome TV sets used an 807 for horizontal deflection, but purpose-built sweep tubes (e.g. the 6BG6 re-packaged 6L6 with octal base and plate cap) were built as application-specific devices.The 6BG6G entered the MIL-STD-200B list of preferred standard electron tubes for military use by 1955, along with the 6L6GWGB NATO standard tube.

author: TimFox
author_rank: Super Contributor
timestamp: October 19, 2022, 02:11:14 pm
content: Probably the 829/829B/3E29?https://frank.pocnet.net/sheets/049/8/829B.pdfHeater power is somewhat larger than two 6L6s.The 832 is a lower-power version of the 829.There is also an octal dual tube, the 815: similar to the 829 but not as good RF construction for VHF, heater power slightly lower than two 6L6s.https://bms.isjtr.ro/sheets/049/8/815.pdf

author: TimFox
author_rank: Super Contributor
timestamp: October 19, 2022, 07:01:25 pm
content: The tubes I cited above are all designed for push-pull amplification (at VHF), with common cathode and common screen terminals and an internal screen bypass capacitor to the cathode.The actual active devices in the 829 and 815 are somewhat similar to a 6L6, typical for RCA.

author: N2IXK
author_rank: Frequent Contributor
timestamp: October 31, 2022, 04:56:52 pm
content: Never saw a pair of 6L6s in a single tube, although there were some types that were close (mentioned above). Unfortunately, the 829/3E29/815 all have a common screen grid connection for both sections, so they can't be used in an ultralinear PP circuit. The individual sections are somewhere between a 6V6 and a 6L6 in terms of power handling.Some Sylvania military 6L6WGB types I have seen were constructed as a dual section tube, strapped in parallel. Each section looked similar to a 6V6.There is a somewhat obscure type, the 6DZ7, which is a pair of 6BQ5s/EL84s in a single bulb, again with common screen grid and cathode connections.

author: TimFox
author_rank: Super Contributor
timestamp: October 31, 2022, 05:35:16 pm
content: Another small-envelope tube with two beam-power tube sections (again with common screen and cathode connections, only nine pins in the base, no plate caps) is the 6360.These tubes were common in VHF applications with the sections in push-pull, often driving their larger relatives (829, 5894, etc.).https://frank.pocnet.net/sheets/077/6/6360.pdfAs audio amplifiers (not "ultra-linear") they were capable of 12 W (in class AB1) and 17.5 W (in class AB2) output in push-pull.

author: N2IXK
author_rank: Frequent Contributor
timestamp: October 31, 2022, 06:02:08 pm
content: The coolest example of the push-pull VHF beam tetrode design has to be the RCA 8D21. Designed for the first generation of VHF TV transmitters, it provided 5 kW output on channels 2-13, and looked like an 829B on steroids. Used a thoriated tantalum filament drawing 125A at around 3 volts, and had 14 separate water cooling connections, with every element internally water-cooled.http://lampes-et-tubes.info/tt/tt299.php?l=e

author: TimFox
author_rank: Super Contributor
timestamp: October 31, 2022, 08:03:07 pm
content: In that series of tube numbers (e.g., 8D21), the initial number refers to the filament/heater power. "8" means 500 to 1000 W.The 9C21 triode required 19.5 V at 415 A, or 8 kW, with 40 kW plate dissipation rating.(That filament power seems high for a measly 40 kW; RCA also demands that the heater current never exceed 750 A, "even momentarily". The cold resistance of the filament is only 4.2 m\$\Omega\$)

author: mag_therm
author_rank: Frequent Contributor
timestamp: October 31, 2022, 08:19:29 pm
content: Query about 829B horizontal mounting:RCA Data sheet for 829B says "Horizontal, plane of each plate vertical".Does that mean the two anode pins are in the vertical plane?Looking at the Septar socket Jedec 7-2, where would the fat pin (Pin 4) be oriented?Thanks

author: N2IXK
author_rank: Frequent Contributor
timestamp: October 31, 2022, 09:02:13 pm
content: The 9C21 used a pure tungsten filament, which was considerably less efficient than thoriated tungsten. Like many of the older designs, the water-cooled 9C21 was "re-spun" post-war into a thoriated version, the 5770:https://www.radiomuseum.org/tubes/tube_5770.htmlThe air-cooled version (9C22) became the 5671, which saw service in a LOT of 50 kW AM stations.Broadcast stations could save appreciable power costs by swapping out the filament transformer and converting their transmitters to use the newer types as they were released.When mounting an 829B horizontally, the 2 anode pins should be in a horizontal plane. This puts the longer axis of the plate structures vertical, to minimize the risk of sag-induced interelement shorts. The fat base pin can be on either top or bottom, as dictated by circuit layout.

author: mag_therm
author_rank: Frequent Contributor
timestamp: October 31, 2022, 09:07:30 pm
content: N2IXK,Thanks!