Re: Stereo amplifier

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi Sue,

At 06:00 PM 3/7/2003 -0500, you wrote:
>Hi Terry,
>
>I was just curious- Have you ever tried modulating the supply voltage of the
>SSTC with those amps. I was entertaining the notion of trying it when I
>build that mosfet coil sometime in the future.

No.  I just feed them with sine waves from a generator.  I never had them 
last long enough to try anything fancy.


>I figured that all one would need to do is obtain a high powered
>matching(modulation) transformer to match the low impedance output to the
>impedance of the SSTC. One winding is connected to the amp output, and the
>other winding is placed in series with the SSTC power supply the same way I
>did it with my tube coil. You could use an RF choke in series with that, and
>then an RF bypass cap to ground to keep the coil's garbage out of the
>modulation transformer. The transformer itself would further isolate the amp
>from the coil anyway (audio transformers don't transfer RF too good).

Why not just ride an audio signal on top of the sine wave and feed it into 
the line input.  Tear out the HF traps first...  The trick is to make a 
coil with a real low Fo.  The GMHEICSLR TC ran at only 10kHz.


>I think the problem would arise in finding a beefy enough transformer with
>the correct impedance match. With my tube coil it was easy because there are
>quite a few modulation transformers kicking around from old Amateur radio
>gear, but solid state stuff has a different set of impedances. Perhaps
>something could be custom wound?

I played with those 70V PA multi-taped transformers a lot.  I think Radio 
Shack still sells them.


>Also, an older tube type high powered tube type amp, or modulator is more
>impervious to RF garbage than solid state amps, but even those things are
>worth a lot of money to Audiophools these days!

I only had solid state.  But toob amps may do much better.

Cheers,

         Terry


>Sue
>
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Friday, March 07, 2003 12:21 AM
>Subject: Re: Stereo amplifier
>
>
> > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
> >
> > Hi,
> >
> > I guess I should point out I used to design fancy power audio amplifiers
> > (very wide DC to 100's of kHz bandwidth) and all that countless moons
> > ago...  Almost all of the prototypes and such I had, ended up getting
> > destroyed running Tesla coils :o)))  The "load" of a Tesla coil will
> > probably tear the guts out of most normal ampli"fires" let alone if you
> > also remove the usual 20kHz filters an all.  Unless the amp is worthless
> > and you are looking for a way to blow it up, I would not try running a
> > Tesla coil with it.  So I guess the answer to the original question is
>"no"...
> >
> > IC's like the LM12CLK are probably a better choice since they are tough
>and
> > easy to replace.  You should probably look at toob or SSTC designs long
> > before blowing up your stereo amp...
> >
> > I was somewhat humbled this week in finding I had no more "un-fried" amps
> > left in the house and had to buy a new one from Dr. Moog this Tuesday
> > ;-))  I have zero intentions of hooking it to a Tesla coil ;-))
> >
> > Cheers,
> >
> >          Terry
> >
> >
> > At 10:49 PM 3/6/2003 -0600, you wrote:
> > >Matt,
> > >
> > >To my knowledge almost all solid state audio amplifiers have a low-pass
> > >filter on the output limiting the output above 20kHz.  The -3dB point is
> > >generally higher, perhaps around 50kHz.  Also, even in "decent"
> > >amplifiers, the gain of the amplifier is fairly low at RF
> > >frequencies.  Add in some cheap output transistors that have a bandwidth
> > >of only a few 100 kHz to a MHz, and you have a recipe for blown fuses or
> > >worse - magic smoke.
> > >
> > >I suppose you could remove the low-pass filter (parallel RL) and the
>Zobel
> > >Network (shunt RC) on the speaker terminals, but the amplifier would
> > >probably start oscillating, leading to increased operating temperature
>and
> > >premature failure.  Some amplifiers also have a low-pass filter on the
> > >input which would likely need defeating as well.
> > >
> > >As Terry suggested, I wouldn't subject my Denon to the torture.  However,
> > >HarmonKardon amplifiers have a "Wide Bandwidth" up to about 100kHz
> > >(according to their published specs), and would probably be more tolerant
> > >than some other amplifiers.
> > >
> > >Good luck!
> > >
> > >Mark Broker
> > >Chief Engineer, The Geek Group
> > >
> > >On Thu, 06 Mar 2003 19:51:04 -0700, Tesla list <tesla-at-pupman-dot-com> wrote:
> > >
> > >>Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>"
> > >><Fucian-at-aol-dot-com>
> > >>
> > >>Hey...I was wonderign if the amps for stereo systems could be modefied
>to
> > >>drive a sstc?
> > >>
> > >>Matt
> > >>
> > >
> > >
> > >
> >