Tube-number record
ER 21 A
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BrandElesta
ClassCold Cathode Triode
BaseMiniature 7-pin (B7G)
Construction
Primary TypeTriode
EnvelopeGlass
SectionsSingle
Filament / Heater
Absolute Maximum Ratings
Plate Voltage240 V
Cathode Current25 mA
Audio Performance
Key Features
- Cold cathode
- All-glass miniature design
- No heater power required
- High control sensitivity
- Sägezahnschwingung starter control
Typical Operation
| Mode | Plate V | Gm (µmhos) | Rp (Ω) | µ | Plate mA |
|---|---|---|---|---|---|
| Relay Operation | 220 V | — | — | — | 22.5 mA |
Application Notes
Used in relay amplifiers, photo-contacts, light barriers, and electronic timers. Requires an RC snubber or short-circuit winding for relay drop-out delay to prevent chattering.
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