Difficulty programming sound via AppleSoft & machine language

[KP <kjpmail@gmail.com>]

I have a program listing that I've typed in from a (very) old issue of
3-2-1 Contact magazine (successor to the old Enter magazine) from the
mid-80s.  It is supposed to produce sound, but when it hits line 320
(the CALL to location 770), it just hangs.  I have tried everything
and can't seem to get it to work.

Does anyone have a suggestion?

Here's the program (only about 32 simple lines):

REM SPACE PHONE
REM 3-2-1 CONTACT MAGAZINE
REM BASIC TRAINING
REM PAGE 36

10 HOME
20 FOR AD = 770 TO 790
30 READ BYTE
40 POKE AD,BYTE
50 NEXT AD
60 DATA 173, 48, 192, 136, 208, 5, 20, 6, 1, 3, 240, 9, 202, 208, 245,
174, 0, 3, 76, 2, 3, 96
70 HOME : VTAB 12
80 PRINT "PREPARE TO RECEIVE ALIEN TRANSMISSION
90 K = 32
100 FOR J = 50 TO 17 STEP - 1
110 GOSUB 300
120 NEXT J
130 HOME
140 B = INT (RND(1) * 80 + 1)
150 GOSUB 230
160 VTAB 20 : HTAB 1
170 PRINT "WHAT IS YOUR REPLY?"
180 INPUT R$
190 IF R$ = "BYE" THEN 210
200 GOTO 130
210 B = 5: GOSUB 230
220 END
230 FOR A = 1 TO B
240 J = INT(RND(1) * 45 - 20)
250 K = INT(RND (1) * 45 - 20)
260 PRINT CHR$ (K);
270 GOSUB 300
280 NEXT A
290 RETURN
300 POKE 768,J
310 POKE 769,K
320 CALL 770: RETURN