diff --git a/build/pdp10-ka/start b/build/pdp10-ka/start
index 6e2c3379..cffb53c0 100755
--- a/build/pdp10-ka/start
+++ b/build/pdp10-ka/start
@@ -1,6 +1,10 @@
 #!/bin/sh
 
-TVCON=${TVCON:--2}
+#Defaults.
+TVCON=${TVCON:--2BS}
+VT52=${VT52:--B -b 9600}
+DATAPOINT=${DATAPOINT:--a -B -b 4800}
+TEK=${TEK:--b9600}
 
 EXIT=:
 trap "" QUIT INT TERM
@@ -44,17 +48,17 @@ type340() {
 }
 
 datapoint() {
-    (sleep 2; tools/vt05/dp3300 -a -B -b 4800 telnet localhost 10020 >datapoint.log 2>&1) &
+    (sleep 2; tools/vt05/dp3300 $DATAPOINT telnet localhost 10020 >datapoint.log 2>&1) &
     started "Datapoint" "$!"
 }
 
 vt52() {
-    (sleep 2; tools/vt05/vt52 -B -b 9600 telnet localhost 10018 >vt52.log 2>&1) &
+    (sleep 2; tools/vt05/vt52 $VT52 telnet localhost 10018 >vt52.log 2>&1) &
     started "VT52" "$!"
 }
 
 tek() {
-    (sleep 2; tools/tek4010/tek4010 -b9600 telnet localhost 10017 >tek.log 2>&1) &
+    (sleep 2; tools/tek4010/tek4010 $TEK telnet localhost 10017 >tek.log 2>&1) &
     started "Tektronix" "$!"
 }