United Electronics 311-CT / 211-C Vintage Vacuum Tube
Historic American Power Triode. Rare Vintage Electronics. A Distinctive Collectors’ Opportunity.
The United Electronics 311-CT is a vintage American power triode belonging to the historic family of high-power vacuum tubes associated with the 211 series.
Manufactured by United Electronics of Newark, New Jersey, the 311-CT represents an important chapter in the development of professional transmitting and industrial vacuum tube technology.
Today, surviving examples appeal to collectors of vintage electronic components, experienced valve amplifier enthusiasts and specialists restoring compatible historical equipment.
Chameleon Audio offers this vintage United Electronics tube listing for customers who appreciate the engineering and heritage of classic American vacuum tube manufacturing.
United Electronics: American Vacuum Tube Heritage
United Electronics was an established American manufacturer of transmitting tubes, power triodes and specialist electronic valves.
Its products served a variety of professional applications during the vacuum tube era, including radio-frequency amplification, transmitting equipment and industrial electronic systems.
The company’s historical catalogues document a wide range of specialised designs, including the 311 family of power triodes.
These original components are now of particular interest to collectors and experienced enthusiasts seeking historically significant valves.
The Historical 311-CT Design
The United Electronics 311-CT is a directly heated vacuum power triode.
Historical technical references identify the tube as a specialised RF triode used in transmitting and medical diathermy applications.
The tube features a substantial glass envelope and a four-pin jumbo bayonet base characteristic of many historic high-power valve designs.
Its construction reflects the requirements of professional high-voltage electronic equipment rather than the operating conditions of ordinary small-signal audio circuits.
311-CT and the 211-C Connection
The original United Electronics Electronic Power Tubes catalogue associates the 311-CT with the 211-C designation.
Other historical documentation links the 311 series to related 211-family triodes.
These relationships make the 311-CT particularly interesting to collectors researching the development of early high-power electronic valves.
However, a historical cross-reference does not necessarily establish direct electrical interchangeability in a modern high-end audio amplifier.
The original tube ratings and the intended amplifier circuit must always be considered.
Understanding the Difference Between 311-CT and 311-T
United Electronics manufactured several 311-series tube types, including 311-CT, 311-T and 311-CH.
Although these tubes share a historical connection, their designations are not interchangeable labels.
In the 1945 United Electronics catalogue:
311-CT is cross-referenced to 211-C.
311-T is cross-referenced to 211-D.
311-CH is cross-referenced to 211-CH.
These distinctions are important when identifying original tubes and assessing their possible applications.
Buyers should verify the type markings and the exact electrical requirements rather than relying solely on the wider 211-family designation.
Directly Heated Triode Construction
The 311-CT employs a directly heated filament structure.
In this type of vacuum tube, the heated filament itself performs the electron-emitting function.
Directly heated triodes are an important part of early electronic history and remain highly regarded among enthusiasts of traditional valve circuit design.
The 311-CT was designed for specialist applications, and any prospective audio use requires careful technical evaluation.
Filament Requirements
Published historical data lists the following filament specifications for the 311-CT:
Filament voltage: 10V
Filament current: 3.25A
Filament type: Directly heated
These figures describe the published characteristics of the tube type, not the measured performance of an individual vintage specimen.
The filament supply must be appropriate for the exact valve and intended application.
Jumbo Four-Pin Base
The 311-CT uses a jumbo four-pin bayonet base.
This substantial base construction was developed for high-power vacuum tube applications.
The physical similarity of different historical transmitting tubes does not guarantee that their pin assignments, operating ratings or electrical characteristics are identical.
Compatibility must therefore be checked carefully before any installation.
Why Original Vintage Tubes Attract Collectors
Original American power triodes represent a period when large-scale valve manufacturing supported professional communication systems and other specialist equipment.
Collectors may value the distinctive internal electrode structures, manufacturer markings, historical designations and surviving production examples.
For a rare tube such as the United Electronics 311-CT, accurate identification and documentation can be especially important.
Photographs of the glass envelope, internal construction and original markings should be examined as part of any purchasing decision.
Potential Audio Applications and Compatibility
The 311-CT is historically related to the 211 family, which includes several types of direct-heated power triodes of interest to high-end audio enthusiasts.
However, the 311-CT was originally intended for specialist high-power electronic applications.
It should not automatically be considered a plug-and-play replacement for a modern 211, 211/VT-4C or other power triode.
Before use, a qualified technician or the amplifier manufacturer should verify:
Exact tube designation and pin configuration
Filament supply voltage and current
Permitted plate and grid operating conditions
Maximum dissipation and voltage ratings
Required bias and driver-stage characteristics
Physical dimensions and safe operating clearance
Do not install a vintage 311-CT solely because an amplifier is designed for a 211 tube.
Evaluating the Condition of Vintage Vacuum Tubes
Vintage valves should be evaluated according to their individual condition rather than appearance alone.
Useful information may include filament continuity, electrical measurements, signs of previous use and the condition of the original markings.
Where the tubes are intended for stereo amplification, the electrical performance of each tube may also need to be compared.
Chameleon Audio recommends requesting any available test results and photographs before purchasing.
Unless specifically confirmed for the actual items, the words NOS, unused, tested and matched should not be assumed to apply.
Historical Technical Documentation
Two valuable sources for researching the United Electronics 311-CT are the original United Electronics catalogue and the American military tube identification handbook.
These documents provide historical identification and technical context. They do not establish the present electrical condition of any individual vintage tube.
Explore Vintage Vacuum Tubes at Chameleon Audio
Chameleon Audio offers a selection of high-end audio components, specialist analogue equipment and vintage electronic valves.
Originally developed for specialist RF and industrial applications
Documented in historical American vacuum tube references
Collector interest in original United Electronics valves
Exact amplifier compatibility must be verified
Available through Chameleon Audio, Greece
Technical Specifications
Manufacturer
United Electronics
Tube Type
311-CT / 311CT
Historical Cross-Reference
211-C
Component Classification
Vacuum Power Triode
Filament Type
Directly Heated
Filament Voltage
10V
Filament Current
3.25A
Tube Base
Jumbo 4-Pin Bayonet
Historical Applications
RF Equipment / Transmitting / Medical Diathermy
Manufacturer Location
Newark, New Jersey, USA
Amplifier Compatibility
Must be confirmed for the exact equipment
Product Identification
Confirm against the actual tube markings
Historical specifications apply to the United Electronics 311-CT tube type. No individual test measurements or matching claims are implied.
Frequently Asked Questions
What is the United Electronics 311-CT?
The 311-CT is a historical American vacuum power triode associated with the 211-C tube designation.
Is the 311-CT the same as the 311-T?
No. The original United Electronics catalogue identifies the 311-CT with 211-C and the 311-T with 211-D.
Is the 311-CT a directly heated triode?
Yes. Historical technical data identifies it as a directly heated power triode.
What filament supply does it require?
Published historical specifications list a 10V filament drawing 3.25A.
Does the 311-CT use a four-pin base?
Yes. It uses a jumbo four-pin bayonet base.
Can it replace a 211 tube in my amplifier?
Not without careful verification. Historical cross-reference information does not guarantee safe compatibility with every modern 211 amplifier.
Is this tube suitable for collectors?
Original examples may be of interest to collectors of American transmitting valves and historical electronic components.
Are NOS status and electrical measurements guaranteed?
Only if explicitly confirmed in the description or supporting documentation for the actual items. Please contact Chameleon Audio for the available condition and testing information.
Can I request additional photographs?
Contact Chameleon Audio to enquire about detailed images of the actual tube markings, glass envelopes and bases.
Is international shipping possible?
Contact Chameleon Audio for destination-specific shipping, packaging and insurance information.
A Distinctive Piece of American Vacuum Tube History
The United Electronics 311-CT / 211-C is a fascinating example of historical power triode engineering.
For collectors, restorers and experienced tube audio enthusiasts, it offers an opportunity to explore an uncommon valve from an important American manufacturer.
Original Vacuum Tube Heritage. Historic American Engineering. A Collectors’ Opportunity.
Availability and Enquiries
Contact Chameleon Audio in Greece for exact item identification, quantity, condition information, test measurements where available, pricing and international shipping options.
