Re: Ping Tester/ Complementary emitter-follower

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
 >
 > Original poster: "Jolyon Vater Cox by way of Terry Fritz 
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
 >
 > Antonio,
 > Are these steps you refer to like crossover distortion on a linear amplifier
 > or the dead-time (ie. the pause between positive and negative excursions
 > when the voltage is zero) on a Pulse Width Modulated half- or full-bridge
 > converter-might it not find application in such a role?
 > Do you have any oscilloscope pictures available of the waveforms?

Crossover distortion. I took some pictures while testing my magnifier:
This is an acceptable output while the pinger is exciting the circuit:
http://www.coe.ufrj.br/~acmq/tesla/vpinger.jpg
This is the voltage over L1 with the system correctly tuned:
http://www.coe.ufrj.br/~acmq/tesla/vl1right.jpg
This is what appears with a simple complementary emitter follower:
Pinger output (1V/div):
http://www.coe.ufrj.br/~acmq/tesla/vcross.jpg
Voltage over L1:
http://www.coe.ufrj.br/~acmq/tesla/vl1cross.jpg

 > How large do the step voltages need to be with regard to the +/-1.2
 > base-emitter voltage drop -would a 9volt battery be OK or does the voltage
 > need to be higher than this?

The tests above were made with 9V. Clearly unacceptable.

 > If single-ended emitter follower is used is it OK to substitute BC337/BFY50
 > for the BC307 you suggested for the output stage?

Probably yes. Nothing particularly critical there.

 > If complementary emitter-follower were to be employed after Pin 3, what
 > would be the best transistor types to use?

I used a BC337 just because I have a lot of them...

 > I am a bit concerned about having an "unlimited" current output on Pin 3 or
 > subsequent BC337 emitter follower stage because of the risk to the the
 > tester in the event that it is is accidentally connected to to
 > short-circuit. To prevent this, would it be possible to replace the real
 > tank capacitor with a low-voltage capacitor of the same
 > capacitance -permanently wired in series with the output stage of the
 > tester- during low voltage tests? Or do you just have to be careful not to
 > short-circuit the test prods.

Be careful, specially with the connection between the pinger and the
capacitor.

 > Finally, would it be be to use a milliameter -connected between the battery
 > and the output stage- to give an indication of the rise in current
 > associated with the commencement of resonance?

I tried this. Nothing significant is observed. The oscilloscope tells
everything.

I prepared a schematic of the pinger that I am using. I added a
complementary emitter follower, but added too an RC load to impede the
switching from one transistor to the other while the transients last.
http://www.coe.ufrj.br/~acmq/tesla/tuner.gif
This worked well with my 5 nF MMC and oscillations around 300 kHz.

Antonio Carlos M. de Queiroz