Re: GM HEI

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

Original poster: "Kevin Ottalini by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ottalini-at-mindspring-dot-com>

Terry:
    I just measured the resonant frequency of the "GM" coil I have here.

This particular one is a Niehoff GM replacement model PT226 for
a '76 Caddie 500 cid engine.

With the core, the primary inductance is ~2.8mH at 1kHz and
the secondary is 17.22H at 1kHz.

I drove the primary directly with a 1vpp sinewave.

The peak output is around 13.5kHz, but the response is quite
broad, from 3kHz to about 20kHz with only a small roll off.

I used a siggen that can drive low impedance coils, but it
didn't appear to be working very hard, so I measured the
primary resistance and it was a very nice 58ohms at 1kHz.

The secondary resistance was ~544Kohms at 1kHz.

Since I'm using only 1V for drive, I was able to use my Tek scope
directly to see the output waveform amplitude and envelope with
the sweep function.

I haven't removed the core yet, but if you need measurements
with the core off let me know.

Hope this helps.

Kevin

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, January 18, 2002 11:29 AM
Subject: Re: GM HEI


> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>
> Hi Rocky,
>
> I have a schematic of my GM coil setup at:
>
> http://hot-streamer-dot-com/TeslaCoils/Misc/GMHEI/sch.gif
>
> Bob also sent me some data that I will post in awhile.
>
> Measuring the frequency of GM coils is a bit tricky since you cannot
> separate the primary and secondary coils.  You pretty much have to connect
> up the secondary with terminal and all as you want it and then stimulate
> the primary to find the frequency.  A signal generator (perhaps with an
> audio amplifier) can drive the cored or uncored primary and then an
antenna
> probe to a scope should be able to find the resonance.  One can then put
in
> a primary capacitor, disconnect the secondary connections, and tune the
> primary to the frequency.  These coils are harder to tune since you only
> have one primary inductor tap.  You have to vary the primary capacitance
> for tuning.  I added or subtracted 0.1uF caps and ended up with 1.7uF.
>
> Cheers,
>
> Terry
>