1R5
1R5 is also designated DK91. Completed sales put the typical price at $7.50 per tube.
Description
The 1R5 is a miniature pentagrid-converter designed for use as a combined mixer and oscillator in superheterodyne circuits. It is especially adapted for compact, battery-operated equipment and has a coated filament cathode.
Construction and Base
The 1R5 uses an RTMA 7AT base. It has a direct interelectrode capacitance with an external shield (RTMA 316) connected to pin 1. Pin assignments are as follows: pin 1 is negative filament and grid number 5; pin 2 is the plate; pin 3 is grids number 2 and 4 (screen); pin 4 is grid number 1 (oscillator grid); pin 5 is negative filament and grid number 5; pin 6 is grid number 3 (mixer grid); and pin 7 is positive filament.
Characteristics
Oscillator characteristics (not oscillating) include an amplification factor of 6.5 and a transconductance of 1400 micromhos. The amplification factor is between grid number 1 and grids number 2 and 4 connected to plate. Capacitance values are as follows: grid number 3 to all is 7.0 μμf with shield and 7.0 μμf without shield; plate to all is 12 μμf with shield and 7.5 μμf without shield; grid number 1 to all is 3.8 μμf with shield and 3.8 μμf without shield. Maximum interelectrode capacitances are: grid number 3 to plate, 0.3 μμf with shield and 0.4 μμf without shield; grid number 3 to grid number 1, 0.2 μμf with shield and 0.2 μμf without shield; grid number 1 to plate, 0.1 μμf with shield and 0.1 μμf without shield.
Operating Notes
The datasheet notes that all voltages are referred to the negative terminal of the filament. Characteristics shown are obtained in the standard RTMA conversion conductance test set which uses separate excitation. These characteristics under separate excitation correspond very closely with those obtained in a self-excited oscillatory circuit operating with zero bias.
| Designation | Evidence | Confidence |
|---|---|---|
| DK91 | 65 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 | $7.50 |
| Typical range (25th–75th) | $4.95 – $11.55 |
| Most sales (10th–90th) | $3.87 – $14.99 |
| Extremes incl. outliers | $2.13 – $44.86 |
| Completed sales | 33 |
| Brand | Median | Range | Sales |
|---|---|---|---|
| RCA | $5.95 | $4.97 – $7.81 | 13 |
| Tung-Sol | $11.55 | $5.00 – $24.99 | 3 |
| Condition | Median | Sales |
|---|---|---|
| NOS | $7.50 | 15 |
| used | $4.79 | 13 |
Per-tube prices from completed sales, 2026-06-14 to 2026-09-10. Matched pairs and quads are divided out. See the price index for how these move over time.
Original manufacturer datasheets for 1R5, hosted by Frank Philipse's Electron Tube Data sheets.
| Manufacturer | Designation | Datasheet |
|---|---|---|
| General Electric | 1R5 | PDF (276 KB) |
| Mazda-Belvu | 1R5 | PDF (237 KB) |
| Tung-Sol | 1R5 | PDF (208 KB) |
| Brimar | 1R5 | PDF (96 KB) |
| Philips | DK91 | PDF (783 KB) |
| Philips | DK91 | PDF (476 KB) |
| Mullard | DK91 | PDF (224 KB) |
| Mullard | DK91 | PDF (146 KB) |
Documents held here and used to write this page.
- DK 91 Battery-operated frequency changer (filed under DK91)
- 1R5
2 further designations appear alongside 1R5 in the literature but below the evidence threshold used here, so they are not listed as equivalent.