Quote:
Originally Posted by Peter Lindemann
When I spoke to John, he told me that getting the circuit to work is a real pain. The circuit controller must be able to produce a perfect 50%-50% flip-flop. The "cigar box" unit used Ni-Cad batteries, which is why they are labeled as 5 volts (4 x 1.25 volts each). The final working model used the 2N5885 transistor instead of the 2N3055H as listed. The control chip was the SG 3524 instead of the SG 3984 as listed. The system switched slowly, at no more that 20 CPS.
|
Sorry for the late post to this thread, but I just found out about this forum...
A couple of observations:
1. The 2N3055 would probably work just fine. The 2n5885 is just a slightly beefed-up version of the same thing. In many electronics stores you can find the NTE181, which is considered a "replacement" for either. It is even beefier than the 2N5885. (Regardless, it can be a real pain dealing with the standard TO-3 or similar package when doing these types of circuits)
2. Pollaehn's timer circuit on pg 28 of the Mueller report gives a variable rate of ~6-10 CPS. I can understand why John would remember it as "slow, not more than 20 CPS", if that is the actual setup used.
3. Also, Pollaehn's timer circuit on pg 28 of the Mueller report does a good job of giving the 50-50 pulses.
4. The SG3524 is a lot more common and available than the SG3984, which is hard to get and even considered obsolete by some places. Using the SG3524 circuit in figure T-1 on pg 10 of the Mueller report would definitely require some "tweaking" in my opinion... Also, be careful, that figure shows a connection to pin 3, which is relabeled in the figure as pin 9. The feedback should come from pin 9, not pin 3. Pin 3 is an output that doesn't need to be used for this to work... at least in my dealings with the 3524 chip. Part of my reason for feeling that it would need "tweaking" is that based on the RC constant (including switched in/out components and the variable resistor) being used and the way the frequency is generated in the 3524, that circuit will give anywhere from just under 11 Hz all the way upto 1.3 kHz. Quite a range to find a "sweet spot" in. Though using the PWM helps to create that desired 50-50 pulse mentioned.
Keep learning,
ITF
