Re: 3-1000z coil, more questions

[FutureT-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 7/31/00 11:22:58 AM Pacific Daylight Time, 
tesla-at-pupman-dot-com writes:

> 2.  I don't really understand what the grid-leak network is all about.  I
>  have a good understanding of disruptive coils but this triode stuff is
>  making me feel dumb.  It would really help me out if someone could give me 
a
>  general overview of what is happening in the typical triode TC circuit.

Ross,

The grid leak network just builds up a negative voltage to keep the
tube cut off when it's not on, the tube has to conduct for just a small
part of the RF cycle to give good class C operation.  The tube coil is
just a an amplifier with feedback, in other words a power oscillator...
coupled to the secondary.  

When power is first applied to the circuit, the grid cap has no charge
so the bias voltage is zero.  Without bias, the tube conducts and
plate current flows which induces a positive voltage in the grid coil.
this voltage makes the grid positive with respect to the cathode
which results in the flow of grid current and the charging of the grid
cap, as a result of the voltage drop across the grid resistor.  The
cap plate nearest the grid becomes negative.  During negative half
cycles (of RF) the cap tries to discharge through the grid resistor, but
the time constant allows the negative voltage to build up from cycle
to cycle until teh full bias voltage is created.  This design makes the
oscillator self starting and self-regulating.  

Each time the tube conducts, energy from the power supply is added
to the tuned tank circuit.  The resonant energy is then transfered to
the secondary.

The tube runs only during the positive half cycles of the 60 Hz AC,
so it's really half-wave rectified.

>  
>  3.  Anyone see anything terribly wrong with the schematic (other than wrong
>  values in the tank circuit and lack of chokes)?

Are you running raw ac on the plates?  I never use any chokes.
>  
>  4.  I know that the leads from the filament transformer to the tube should
>  be short.  Is 2.5ft with 10ga wire too long?  I can mount it under the top
>  deck right near the tube if I need to.

That's probably OK,  as long as the voltage is there.... it's OK.
>  
>  If I ever figure this !-at-#$ thing out I'll be sure to thoroughly document it
>  on my page so others can come up to speed more quickly.

I hope this helps some, cheers,
John Freau

>  
>  Thanks,
>  Ross-O