Sct controller reported a loss of separation and a MVA violation.

Attributes
ACN	1661543
Time
Date	201907
Local Time Of Day	1801-2400
Place
Locale Reference	SCT.TRACON
State Reference	CA
Environment
Light	Daylight
Aircraft 1
Make Model Name	Small Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 135
Flight Phase	Final Approach
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Route In Use	Other Instrument Approach
Flight Plan	IFR
Person 1
Function	Approach Instructor
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 5
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Procedural Published Material / Policy Inflight Event / Encounter CFTT / CFIT

Narrative:

This was my first ojti session on the arrival sector. The developmental issued aircraft X a heading toward the final; but did not instruct the aircraft to join (vector angle too large). The aircraft began slowing as aircraft Y was coming up behind. The developmental recognized the blow through of the final and issued a la (low altitude) alert and a turn back west. We were focusing on aircraft X and getting him out of the MVA that we didn't notice right away aircraft Y overtaking; but still with vertical separation. I eventually had aircraft Y maintain visual separation with aircraft X; but I don't know exactly at what point that occurred. There were other IFR conflicts that we were focusing on and traffic was getting busier. I failed to listen actively and assumed aircraft X was going to join the final. I should have stopped aircraft Y at 4;000; but was too concerned about aircraft X and the MVA. I realize that in this sector; control from the ojti must be maintained constantly or things get out of hand quickly - not like other sectors where there's room to correct actions.

Original NASA ASRS Text

Title: SCT Controller reported a loss of separation and a MVA violation.

Narrative: This was my first OJTI session on the arrival sector. The developmental issued Aircraft X a heading toward the final; but did not instruct the aircraft to join (vector angle too large). The aircraft began slowing as Aircraft Y was coming up behind. The developmental recognized the blow through of the final and issued a LA (low altitude) alert and a turn back west. We were focusing on Aircraft X and getting him out of the MVA that we didn't notice right away Aircraft Y overtaking; but still with vertical separation. I eventually had Aircraft Y maintain Visual Separation with Aircraft X; but I don't know exactly at what point that occurred. There were other IFR conflicts that we were focusing on and traffic was getting busier. I failed to listen actively and assumed Aircraft X was going to join the final. I should have stopped Aircraft Y at 4;000; but was too concerned about Aircraft X and the MVA. I realize that in this sector; control from the OJTI must be maintained constantly or things get out of hand quickly - not like other sectors where there's room to correct actions.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.