Directly Heated Power Triode Ca and Its Comparison with AD1 Vacuum Tube Ca (Valvo)
Vakuum Tube Ca (Valvo)
Production Period
The Ca tube is one of the rarest early German (Valvo) power triodes, produced around the late 1920s to early 1930s. It was intended for both radio receivers and amplifiers at a time when vacuum tube technology was still in its developmental phase and each manufacturer was experimenting with different solutions.
Specifications:
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Type: Directly heated power triode
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Anode voltage: ~200–250 V
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Anode current: ~20–35 mA
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Load resistance: ~4–6 kΩ
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Power dissipation: ~5 W
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Amplification factor: ~4–5 µ
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Filament voltage/current: ~4 V / 1 A
(Note: Parameters may vary, since early tube specifications were often updated or changed between production batches.)
Applications
The Ca tube was mainly used as:-
An audio power output triode in radio receivers,
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The final amplification stage in early tube amplifiers,
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Occasionally in experimental audio and telecommunication devices.
It was considered a transitional design between small-signal triodes and the later, more popular European power triodes such as AD1 and RE604.
Mono amplifier Latvija by VS-Audio using the Ca power triode
Sound Characteristics
Among audio enthusiasts, the Valvo Ca is described as a tube with:-
A very warm and natural tone,
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Soft high frequencies, well-suited for classical, vocal, and acoustic music,
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Gentle bass, not as strong as later power triodes,
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A romantic, musical character emphasizing listening pleasure rather than technical accuracy.
Its sonic signature is often compared to early Telefunken RE tubes – offering a true vintage character with historical charm.
Comparison of Power Triodes Ca (Valvo) and AD1 (Telefunken)
Production Period
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Ca (Valvo): Late 1920s – early 1930s. An early directly heated power triode, suitable for lower power applications.
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AD1 (Telefunken): 1935. Designed as a high-end audio power triode, which became a benchmark in the European tube industry.
Specifications
| Characteristic | Ca (Valvo) | AD1 (Telefunken) |
|---|---|---|
| Type | Directly heated power triode | Directly heated power triode |
| Anode voltage | ~200–250 V | ~400 V |
| Anode current | ~20–35 mA | ~60–80 mA |
| Power dissipation | ~5 W | 15 W |
| Amplification factor | ~4–5 µ | ~5–6 µ |
| Load resistance | ~4–6 kΩ | ~5–7 kΩ |
| Filament | 4 V / 1 A | 4 V / 1.2 A |
Applications
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Ca (Valvo): Used in early radios and amplifiers, suitable for low-power output stages.
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AD1 (Telefunken): A high-end hi-fi amplifier triode; widely used in professional audio and studio equipment; still regarded as one of the most musical and prestigious European tubes ever made.
Sound Characteristics
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Ca (Valvo):
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Warm, natural, and soft tone
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Romantic and musical character
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Relatively weak bass, more suited for acoustic music and vocals
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Typical “vintage” sound
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AD1 (Telefunken):
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Very musical and well-balanced sound
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Strong but controlled bass
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Transparent, yet non-harsh high frequencies
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Excellent dynamics and accuracy
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Versatile – suitable for classical, jazz, and rock
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It shows that Ca emphasizes warmth and romantic character, while AD1 provides broader dynamics, stronger bass, and more transparent sound.
Summary
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Ca (Valvo): An early, low-power triode with historical value and very warm, vintage sonic qualities.
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AD1 (Telefunken): A more technologically advanced and powerful triode with outstanding sound quality, which became a legend in the hi-fi world.
One could say that Ca is a beautiful forerunner, while AD1 represents the fully matured masterpiece of audio history.
Practical Use in Music Reproduction
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Ca (Valvo):
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Classical chamber music (strings, cello, violin)
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Vocal and choral works
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Acoustic music, jazz with piano or double bass
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Enjoyment of vintage recordings – adds warmth and romantic mood
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AD1 (Telefunken):
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Symphonic music and opera (wide dynamic range)
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Jazz with brass instruments – clear and transparent tones
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Rock and electronic music – strong and controlled bass
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Hi-fi recordings and studio audio – accuracy and balance across the spectrum
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