Re: CW coil top terminals?

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

Original poster: "David Trimmell by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davidt-at-pond-dot-net>

Hi Jim, Yes, I have been thinking about the loss at Audio frequency in the
Iron core power transformers I have used for Audio coupling. I had not
thought of Audio output transformers from a Tube Amp, though. Great
Idea! Thanks! The Plate Mod Transformers are quite pricy, and I have not
run across any on the surplus market. I have a old Kenwood Tube amp that I
may "borrow" a output Transformer from, I think it is rated for 600-700V
with taps for 4,8, and 16 Ohm. I found that I needed about 200 to 250V
(point to point, as measured with a o-scope) on the grid side to get good
modulation with 40 to 50K in the grid leak. Well maybe I'll have too get
this setup again. If only I had more spare time!

Regards,

David Trimmell
www.ChaoticUniverse-dot-com

On Tue, 30 Jan 2001, Tesla list wrote:

> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<jimlux-at-earthlink-dot-net>
> 
> 
> 
> Tesla list wrote:
> > 
> > Original poster: "David Trimmell by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <davidt-at-pond-dot-net>
> > 
> > Hello Dunckx,
> > 
> > Actually I was serious, as Audio Modulation has been one of my favorite
> > effects that I have created with CW VTTC's. See:
> > http://www.chaoticuniverse-dot-com/webdoc2.htg/Tubez.htm for details of my
> > designs. They need a great deal of work, but I can get decent Audio Output
> > from the spark. The weak link is the Audio coupling transformer... One day
> > I will perfect this, as it does make a very "ear/eye" catching demo.
> > 
> 
> What you need is a "plate modulation transformer" for an AM transmitter,
> which was designed just for what you are doing. They typically are
> insulated for several kV (whatever the plate voltage is in the
> transmitter), and have a suitable turns ratio to get the P-P output voltage
> swing equal to the plate voltage (assuming 100% modulation).  You probably
> don't need the voltage, since you are grid modulating, but what you DO need
> is the audio bandwidth.  Typical transformers would be used up to 5-10 kHz,
> making them quite different from a power transformer optimized for 60 Hz
> would be.
> 
> Another possibility is the output transformer from a Tube audio amp.  They
> run at several hundred volts at several K ohms on the high impedance side,
> and 8 or 16 ohms and a few tens of volts on the speaker side.
> 
> Finally, you could always string together a bunch of 70.7 V line
> transformers, although, I'll bet that would be an expensive way to go.
> 
> One source for this sort of thing is Peter W. Dahl Company
> http://www.pwdahl-dot-com/... Don't tell them it is for a tesla coil, though,
> because they've had problems with coilers in the past.
> 
> They have a variety.. For instance, a DX-100 modulation transformer has
> primary Z = 8K, 845VCT, secondary 500/2800 ohms -at- 250 mA
> 
> 
> 
>