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On Sunday, July 9, 2017 at 2:43:31 PM UTC-4, Foxs Mercantile wrote:
On 7/9/2017 1:13 PM, Ian Field wrote:
The DSE one has a comparator rigged to generate spike pulses -
the ringing pulses clock a logic 1 along a shift register and
basically counts how many times the inductor rings.

The schematic is floating about the web, and there's nothing
hard to find in the parts list.

https://www.flippers.com/fbt-main.html



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Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

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i swapped the D360 diode with another from the board, no difference. i
dont really understand from the schematic what the pump up circuit is. it
has 24V thru a electrolytic cap in series to pin7 . is that an input or an
output? the same circuit( before the cap) goes to pin 3. there is only
about 1/2 volt on pin 7. is it supposed to pulse, pin 7 pulling down the
24 v?

There's sometimes an electro with ambiguous purpose (also on audio amps). It
bootstraps the output to the bias network for the output transistor bases.
Its almost positive feedback that reduces drive current requirement for the
output pair and improves linearity.