Tube of the Week
Opcom:
Updating the previous 866Jr post:
https://amfone.net/Amforum/index.php?topic=46518.msg337822#msg337822
Found a couple of the Taylor units today and here's a good picture of them. Different year of manufacture looks like.
Sorry that can't be ON and glowing!
Opcom:
Today, I present the 0G3, also known as the 85A2.
This 85-Volt gas regulator tube is not as common as other 7-pin regulators, but it's a more precise tube than the usual higher-current 0A2-sized tubes, and used in various test gear as a reference. Advantages are a more stable and constant voltage over the life of the tube, which helps gear stay calibrated. The usual operating current in the 0G3 is 1 to 6mA.
The H/P 400D/H/L series of VTVMs use the 5651 regulator, but I have one with an 0G3 in it and it seems no less accurate for the substitution.
The image is of 21 of them placed in series in a phenolic? box. (cover present but removed) Anyone recognize this assembly?
Opcom:
This week, lets look at the 6012 Shield Grid Xenon Thyratron. It's a big brother of the 2D21 and 2050. It's about the shape of a 6146 sans cap, maybe a bit taller than the 6146.
Looking at it, you can tell it's not the average tube. The large rectangular anode fills the glass from side to side, beckoning to megalomaniacs.
Some data:
Heater 6.3V +/-10% @ 2.6A
Forward Plate voltage: 650 (non-conducting)
Reverse plate voltage: 1000 (1300 peak on AC)
Peak plate current: 5A
Average plate current 500mA
One application is as a motor drive, very nice indeed. Otherwise, used as a relay and grid-controlled regulator.
Opcom:
How about the 4B31 ?
The 4B31 (RK-4B31) is not a typical 'cheaply had' tube, nor one that is seen frequently. Nonetheless, I got one for free in the W5FRS estate and it's interesting to consider for at least one analog AM application, so it's worth a place here.
They are at first glance costly to buy at $12 to $60, but it's a high-value tube when comparing ratings per dollar, so it's really dirt cheap plentiful because the audio folks don't like them for some unknown reason!
4B31 is the same tube as:
RK-4B31
CV3510
QK98
The Raytheon 4B31 is designated as a clipper diode and rectifier. It's ruggedized, exhausted at high temperature to a higher vacuum than many rectifiers, and has a 'hard glass' Nonex envelope. The plate is Gold plated and Zirconium Molybedenum coated. The cathode is heliarc-welded. The spacers are ceramic. Looking closely, it appears to have two cathode structures acting in parallel.
Considering it as a clipper for purposes of negative peak limiting/keep-alive or 'ultramodulation', it could be compared to the 8020 vacuum rectifier, both easily handling the usual ham radio plate modulation voltages and currents. There is no mention of the 4B31's plate dissipation but it's a big plate there.
(There have been many neg peak limiter/keep alive/supermodulation setups with Mercury rectifiers (as famously shown in a video with Ashtabula Bill), and also many with semiconductor devices, but I want to split hairs here and highlight the smooth vacuum rectifier characteristic)
4B31 basics:
Absolute Maximum as Clipper Diode:
Filament voltage: 5V@5A
Heating time: 2 minutes
Cathode: indirectly heated
Peak inverse voltage: 16KV
Peak plate current: 12A
Average plate current: 60mA
Absolute Maximum as Rectifier:
Peak plate current: 470mA
Average plate current: 150mA
Characteristics /Typical Operation:
Plate current @130VDC: 300mA
Peak emission @2500V: 18A
The average resistance of the tube is 400-300 Ohms over a forward voltage of 40 to 150V (The 8020 has a resistance of about 1000 Ohms).
I don't know what to make of "The plate is Gold plated and Zirconium Molybedenum coated.". There is a gold appearing area on the plate but I can't tell if it extends to the inside of the plate, and don't understand the use of 'zirconium-molybdenum'. There are plenty of pictures of this type on the internet to examine.
https://www.google.com/search?q=4B31+tube&tbm=isch
Datasheet: https://frank.pocnet.net/sheets/138/4/4B31.pdf
KA3EKH:
Enough of these Thryratrons! veterans’ day is coming up so what about a good military only tube? The PL-177WA, that was the final amplifier in the AN/PRC-47 and think as far as I know wan never used in anything else. The PRC-47 was somehow considered a field radio although it required a crew of at least two to three people, usually Marines being the Army had better radios like the PRC-70 or PRC-74 so they did not have to lug that mess around.
The PL177WA provided 100 watts of USB from 2 to 12 MHz with 1,500 volts on the plate in high power and 650 volts in low power, although every PRC-47 I have ever owned would do maybe half that.
Another good contender would be the 4CX350F that’s the military version of the 4CX350 except it has a 24-volt filament and is used in radios like the AN/GRC-106 and the Collins 618T transceivers. May be mistaken but think they were stuffed up the AN/URC-32 also.