how to add if statement for this specific example in pandas [duplicate]

I have six variables (they are a column in my dataset), for example

 A   B  value_old 
aaa  x   0
aaa  y   0
aaa  z   0
bbb  x   0.4
bbb  y   0.2
bbb  z  -0.01

I want to get a new set of values based on the signs of value_old (only compare the values if they have the same value in column 'A')

for 'aaa':

if value_old = 0, the new set value is 0.2
if value_old >0, the new set value is 10
if value_old <0, the new set value is 5

Expected output:

A   B  value_old  value_new
aaa  x   0          0.2
aaa  y   0          0.2
aaa  z   0          0.2
bbb  x   0.4        10
bbb  y   0.2        10
bbb  z  -0.01       5