555 timer Astable Mode output Voltage

Good Day,

I have made 7 number of 555 timer astable multivibrators on 7 different perfboards with the following circuit to each give output of 0.1, 7, 14, 28, 35 and 42 Hz Frequencies.Here are the values of resistance and capacitance I used for these frequencies.

0.1 Hz:Ra = 5.5 kOhmRb = 719 kOhmC = 10 uF

7 Hz:Ra = 5.5 kOhmRb = 1021000 OhmC = 0.1 uF

14 Hz:Ra = 5.5 kOhmRb = 510 kOhmC = 0.1 uF

21 Hz:Ra = 5.5 kOhmRb = 340 kOhmC = 0.1 uF

28 Hz:Ra = 5.5 kOhmRb = 254.5 kOhmC = 0.1 uF

35 Hz:Ra = 5.5 kOhmRb = 203 kOhmC = 0.1 uF

42 Hz:Ra = 5.5 kOhmRb = 169 kOhmC = 0.1 uF

I made it all and I was finally testing the output voltages on no load. When I tested the 0.1 Hz circuit, initially at Vcc of 12 Volts DC, the voltage between output pin and ground was 11.9 Volts. The voltage was going up and down between 0 and 11.9 Volts every 5 seconds.

Now I tested the 14 Hz circuit. Initially the voltage between output and ground was 5.3 Volts. Then after a few minutes I saw that this voltage go to 11.9 Volts and it stayed there. Whenever I measure it shows 11.9 volts.

Then I tested the 42 Hz frequency circuit. Same as the 14 Hz, initially it showed 5.3 V between output and ground and suddenly after a few minutes it shows 11.9 Volts output and it stays there even if I power off and on multiple times.

Now I have three circuits - 0.1 Hz, 14 Hz and 42 Hz giving an output pulsating Voltage of 11.9 Volts.

Then I tested all the other four circuits with 7 Hz, 21 Hz, 28 Hz and 35 Hz. Initially they showed 5.3 Volts output but they never went up to 11.9 Volts as in the above cases. Two of them went up to 6.9 Volts and stayed there.

So I need some help I am confused and I cannot figure out why this happens. I thought it was the discharging capacitor, I tried discharging it but still I couldnt get it all to give more or less equal voltage output. When I try measuring voltages between the pins for very long, it fries up the 555 timer IC and I lost 3 of them.

Thanks.