1T4
1T4 is also designated DF91. Completed sales put the typical price at $9.75 per tube.
Description
The 1T4 is a variable-mu pentode intended for use as a radio-frequency or intermediate-frequency amplifier, particularly in battery receivers. It has direct heating with a filament voltage of 1.4 V and a filament current of 50 mA; the filament may be supplied in series or in parallel. The tube uses an A 19-2 envelope and a 7 C 10 base, and may be mounted in any position.
Construction
The 1T4 has a miniature base. Its input capacitance is 3.6 pF, output capacitance is 7.5 pF, and grid No. 1 to anode capacitance is 0.01 pF.
Ratings
The maximum anode voltage is 90 V, the maximum grid No. 2 voltage is 67.5 V, and the maximum grid No. 2 supply voltage is 90 V. The maximum grid No. 1 voltage is 0 V, and the maximum cathode current is 5.5 mA. Maximum anode dissipation is 0.35 W, and maximum grid No. 2 dissipation is 0.11 W.
Operating characteristics
The Philips datasheet, dated 25.1.1949, gives operating characteristics for the 1T4 when used as an RF or IF amplifier.
| Designation | Evidence | Confidence |
|---|---|---|
| DF91 | 67 independent documents | strong |
Equivalence is asserted only where the archive's own literature states it directly, in at least 40 separate documents. Tubes that merely substitute in some circuits are not listed here.
| Measure | Per tube |
|---|---|
| Median | $9.75 |
| Typical range (25th–75th) | $7.24 – $15.66 |
| Most sales (10th–90th) | $4.62 – $31.77 |
| Extremes incl. outliers | $3.95 – $35.22 |
| Completed sales | 21 |
| Brand | Median | Range | Sales |
|---|---|---|---|
| Sylvania | $10.00 | $6.24 – $10.40 | 3 |
| Mullard | $26.99 | $21.68 – $35.22 | 3 |
| Condition | Median | Sales |
|---|---|---|
| NOS | $8.97 | 14 |
| used | $9.38 | 6 |
Per-tube prices from completed sales, 2026-04-01 to 2026-09-03. Matched pairs and quads are divided out. See the price index for how these move over time.
Original manufacturer datasheets for 1T4, hosted by Frank Philipse's Electron Tube Data sheets.
| Manufacturer | Designation | Datasheet |
|---|---|---|
| Mazda-Belvu | 1T4 | PDF (311 KB) |
| General Electric | 1T4 | PDF (269 KB) |
| Tung-Sol | 1T4 | PDF (147 KB) |
| Brimar | 1T4 | PDF (96 KB) |
| Philips | DF91 | PDF (458 KB) |
| Philips | DF91 | PDF (322 KB) |
| Mullard | DF91 | PDF (91 KB) |
| Mullard | DF91 | PDF (77 KB) |
Documents held here and used to write this page.
- DF 91 "Miniwatt" (filed under DF91)
- 1 T 4
2 further designations appear alongside 1T4 in the literature but below the evidence threshold used here, so they are not listed as equivalent.