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Re: VTTC first sound :-)
Original poster: "David Trimmell by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davidt-at-pond-dot-net>
I am asuming you placed the 230V side of the "Audio coupling" transformer
in series with the grid to grid coil, and ran audio input into the 12V
side? I have found that using transformers with a low voltage/low
inductance (impedance) side as audio input you do get some nasty
distortion. I have had best results with a 115V to 1000V Plate
transformer, audio into the 115V side. Unfortunately, it is too large for
a portable demo coil I am currently working on, about 20 to 25lbs. The
sugestion by Jim Lux on using audio output transformers from a tube amp
does sound appealing, but on some preliminary tests I have conducted with
a small one from a 15 watt amp, they appear to suffer the same issues as
other low impedance transformers... But really do need do some more
testing. One thing I have done in the past is to place a large (>1000
uF) cap in series with the hot audio lead into the audio coupling
transformer, this assisted with matching, but does waste audio power.
Keep up the great work!
On Thu, 22 Feb 2001, Tesla list wrote:
> Original poster: "Herwig Roscher by way of Terry Fritz
> Hi fellow VTTC builders,
> Today I audiomodulated of my system for the first time. I used a 20
> W car amplifier/equalizer driven by a signal generator. A 12/230 V
> mains transformer was connected between grid coil and grid leak
> combination. No other modifications were necessary.
> Connecting the scope across a 4-turn-pickup coil wound 3.5" below
> the primary, I easily could adjust the amplitude of the signal
> generator to a point, where the amplitude modulation was just 100
> %. Deafening noise forced me to use ear protection. Sweeping the
> modulation frequency I had to state, that the frequency response of
> the mains xformer (like suspected) was dissapointing. So I'm
> looking for an output tranny of a tube amplifier now.
> Still a lot of work to do, but a lot of fun as well.