3B28
3B28 has no equivalent designation confirmed by the archive. Completed sales put the typical price at $28.66 per tube.
The 3B28 is a xenon-filled half-wave rectifier for use in high voltage circuits, incorporating a hard glass envelope, a well-supported mount, and an efficient, fast-heating oxide-coated filament.
Construction
The tube has a T-16 bulb and a medium 4-pin bayonet base, type A4-10. It can be mounted in any position. Its maximum overall length is 5.87 to 6.15 inches, seated length is 5.25 to 5.53 inches, and maximum diameter is 2.07 inches. Net weight is 4 ounces.
Ratings
The filament is rated at 2.5 volts ±5% and 5.0 amperes, AC or DC. Minimum cathode heating time is 5 seconds. The tube is designed to operate over a wide temperature range without heating or cooling devices, with ambient temperature limits of -55 to +75 degrees Celsius.
Maximum ratings depend on operating conditions. The maximum peak inverse voltage is 5000 volts at a maximum supply frequency of 500 CPS, or 10000 volts at a maximum supply frequency of 150 CPS. Maximum peak cathode current is 2.0 amperes or 1.0 ampere depending on conditions, and maximum average cathode current is 0.5 ampere or 0.25 ampere depending on conditions. Maximum surge cathode current is 20 amperes for a maximum duration of 0.1 seconds. Maximum averaging time is 30 seconds.
Typical voltage drops include an average anode voltage drop of 10 volts, a peak anode voltage drop of 14 volts, and a critical anode voltage of 50 volts.
Operation
The 3B28 is particularly suited for military and industrial use. Quadrature excitation of the filament is recommended for obtaining the longest tube life, though the tube carries full ratings for in-phase operation of the filament. The Tung-Sol datasheet provides operating characteristics for various rectifier circuits, listing DC output values supplied to a choke input filter with a pure sine wave supply.
| Measure | Per tube |
|---|---|
| Median | $28.66 |
| Typical range (25th–75th) | $20.00 – $43.96 |
| Most sales (10th–90th) | $16.11 – $54.10 |
| Extremes incl. outliers | $15.44 – $54.10 |
| Completed sales | 10 |
| Brand | Median | Range | Sales |
|---|---|---|---|
| RCA | $27.90 | $24.00 – $29.43 | 3 |
| Condition | Median | Sales |
|---|---|---|
| NOS | $29.43 | 7 |
Per-tube prices from completed sales, 2026-06-25 to 2026-09-02. Matched pairs and quads are divided out. See the price index for how these move over time.
Original manufacturer datasheets for 3B28, hosted by Frank Philipse's Electron Tube Data sheets.
| Manufacturer | Designation | Datasheet |
|---|---|---|
| Tung-Sol | 3B28 | PDF (175 KB) |
| RCA (HB3) | 3B28 | PDF (117 KB) |
| EEV | 3B28 | PDF (81 KB) |
Documents held here and used to write this page.
- TUNG-SOL -
6 further designations appear alongside 3B28 in the literature but below the evidence threshold used here, so they are not listed as equivalent.