Minimum Specifications and Spots
L3Harris | Minimum Specifications and Spots
Spots
L3Harris Tubes ending with UM or UA (ex. 18UM vs. 24UA) have differing tolerances for dark spots.
- UM (military) tubes permit spots greater than .003" (diameter) in Zone 2 and 3. Spots greater than .003" are not permitted in Zone 1.
- UA (aviation) tubes limit spots greater than .003" to Zone 3 only. This is L3's strictest spot spec.
- Dark spots less than or equal to .003" don't meet the threshold as a countable spot and are commonly referred to as "peppering".
To reference the Zone regions, you can refer to the image above which shows a tube photographed on a Hoffman Engineering 126A test set.
Military Spot Spec:
| Spot Size | Zone 1 | Zone 2 | Zone 3 |
| (Inches) | Limit | Limit | Limit |
| >.012 | 0 | 0 | 0 |
| >.009 | 0 | 0 | 0 |
| >.006-.009 | 0 | 1 | 1 |
| >.003-.006 | 0 | 2 | 2 |
| Bright Spots | 0 | 0 | 0 |
| Dark spots </= .003” are acceptable |
Despite adding up to 6 total (above), L3 tubes are limited to 4 spots max
Aviation Spot Spec:
| Spot Size | Zone 1 | Zone 2 | Zone 3 |
| (Inches) | Limit | Limit | Limit |
| >.012 | 0 | 0 | 0 |
| >.009 | 0 | 0 | 0 |
| >.006-.009 | 0 | 0 | 1 |
| >.003-.006 | 0 | 0 | 2 |
| Bright Spots | 0 | 0 | 0 |
| Dark spots </= .003” are acceptable |
Performance
L3Harris unfilmed tubes are available with various minimum performance levels (18, 20, 22, 24).
The higher the performance series number (i.e. 20 vs. 18), the higher the minimum performance.
This performance series is then combined with a spot spec to identify the tube. For example, the 18 performance series, with unlimited FOM ("U"), and Military ("M") spot spec would be 18UM.
Tube Model Performance summary:
18 Series (UM or UA):- SNR: 24.1 minimum
- Center Resolution: 64 lp/mm minimum
- FOM: 1540 minimum
- Halo: 1.0 maximum
- EBI: 2.5 maximum
- SNR: 28 minimum
- Center Resolution: 64 lp/mm minimum
- FOM: 1792 minimum
- Halo: 1.0 maximum
- EBI: 2.5 maximum
- SNR: 30 minimum
- Center Resolution: 64 lp/mm minimum
- FOM: 1920 minimum
- Halo: 1.0 maximum
- EBI: 2.5 maximum
- SNR: 33.75 minimum
- Center Resolution: 64 lp/mm minimum
- FOM: 2160 minimum
- Halo: 1.0 maximum
- EBI: 2.5 maximum
- SNR: 36 minimum
- Center Resolution: 64 lp/mm minimum
- FOM: 2304 minimum (implied)
- Halo: 1.0 maximum
- EBI: 2.5 maximum
- Aviation Spot Spec (Spots limited to Zone 3 only)
Other:
1610 Tubes / 2376+ FOM models of PVS-31A, BNVD 1531:- SNR: 33 minimum
- FOM: 2376 minimum
- Center Resolution: 72 lp/mm minimum
- Halo: 0.85 maximum
- EBI: 2.5 maximum
- Military Spot Spec (Spots permitted in Zone 2 and Zone 3)