6688
6688 is also designated E180F. Completed sales put the typical price at $13.02 per tube.
General
The 6688 is a vacuum tube tested under MIL-E-1 specification. It operates with a heater voltage of 6.3 V and a heater current between 285 and 315 mA.
Electrical Characteristics
Under the stated test conditions (Ebb = 180 Vdc, Ec1 = Ec3 = 0, Ec2 = 150 Vdc, Rk = 78 ohms), the plate current (Ib) is between 8 and 18 mAdc, and the grid #2 current (Ic2) is between 2.9 and 3.7 mAdc. The transconductance (Sm) is between 14,200 and 18,800 µmhos, and the plate resistance (rp) is approximately 0.09 Megohm. Typical operating conditions include a plate voltage (Eb) of 190 Vdc, a grid #1 voltage (Ec1) of +9 Vdc, a grid #2 voltage (Ec2) of 160 V, a grid #3 voltage (Ec3) of 0 Vdc, and a cathode resistor (Rk) of 630 ohms.
Capacitances
The grid-to-plate capacitance (Cgp) is a maximum of 0.03 pf. The input capacitance (Cin) is between 6.7 and 8.5 pf, and the output capacitance (Cout) is between 2.5 and 3.5 pf.
Pinout
Pin 3 is the cathode, and pin 4 is the heater. Pin 6 is left floating when an external shield is used.
| Designation | Evidence | Confidence |
|---|---|---|
| E180F | 62 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 | $13.02 |
| Typical range (25th–75th) | $9.08 – $22.45 |
| Most sales (10th–90th) | $3.85 – $26.38 |
| Extremes incl. outliers | $3.85 – $33.00 |
| Completed sales | 19 |
| Brand | Median | Range | Sales |
|---|---|---|---|
| Amperex | $10.67 | $9.36 – $17.29 | 4 |
| Condition | Median | Sales |
|---|---|---|
| NOS | $17.38 | 13 |
| used | $10.90 | 4 |
Per-tube prices from completed sales, 2026-06-25 to 2026-09-15. Matched pairs and quads are divided out. See the price index for how these move over time.
Original manufacturer datasheets for 6688, hosted by Frank Philipse's Electron Tube Data sheets.
| Manufacturer | Designation | Datasheet |
|---|---|---|
| Tesla | E180F | PDF (1045 KB) |
| Philips | E180F | PDF (819 KB) |
| AEG | E180F | PDF (280 KB) |
| Philips | E180F | PDF (280 KB) |
| Siemens | E180F | PDF (207 KB) |
Documents held here and used to write this page.
- STRMÁ VF PENTODA (filed under E180F)
- Technical Information