PW Sandbanks pulse generator question

Hi,

I've recently resurrected my Sandbanks build which had progressed as far as etching a new circuit board and collecting all the parts together (again . . . ) I've decided to do away with the CMOS ring oscillator and Toko coil power supply section (even though I still have an unused coil - quite a rare beast) and use a second battery as documented in these pages.

I started by loading the pulse generator section; IC1, C1,2 and 3 and R1 and R2 and then tested it as directed by connecting the battery (no switch at this stage)

Straight away I hit a problem in that while the output on Pin 3 should have been around 90 mV (since I was using a 9V PP3 battery and Pin 3 should have been 10% of battery voltage) I was seeing 147mV . . . I re-checked that all the components were correct and in the right place, no shorts between tracks etc and all seemed correct. I don't have an oscilloscope (at least one that works) so I connected a speaker to Pin 3 and sure enough it was oscillating. Since the IC is in a socket I changed it for a different one, which gave me 137mV instead . . .

OK, my question is - WHY? The components I installed only affect the timing of the pulses and nothing I can do will affect the amplitude (as far as I know the amplitude of a 555 is designed to be [supply voltage - ~1.7V]) Since the output isn't a sine wave my voltmeter wouldn't have read an RMS value if I set it to read AC instead of DC so it *shouldn't* have been that I was trying to read the wrong range. Could it be that back in 1979 more people were using moving coil meters which would average the pulses into a lower DC reading than my DMM displays and my circuit is all normal?

I'm guessing that if I put 50% higher voltage into the next stage it might just fry the BC214 transistor, and even if it doesn't the output from that might fry the TIP31A.

What to do?



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Do you have the Documents?

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http://www.thunting.com/smf/index.php/topic,56676.msg275098.html#msg275098

As the Article says, build it by stages.  Move to the next stage and see if it corrects.   Back in the 80's I bought two kits and did build one that worked good for what it was.  I was in the UK at said time.  I sold one kit and never heard from the guy again,.   I have all the Parts here for another but the Surf Pi Is a better less part count machine that can do the same or better.

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His kits Kick Butt for the Price.   I could not find the parts never mind make a board for the Cost.   Yep.  Good Deal.

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Most of his kits are developed around the Geotech Forum .  Just do the same as the sandbanks and build in sections.  One at a time.   That way you have each section working and if things go wonky you only have so much to deal with. 

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