Success with Audio modulation of a VTTC

Hello all,

Well I have finally attempted to modulate the grid of my tube coil with a
audio signal, and have found that it is not as difficult as I originally
thought. I am using my 12 mH 3 inch coil driven by two 833A's with filtered
DC to the plates, it will put out about 4+ inches of flame-like discharge.
I am modulating the grid by using a small, 115V pri, 2.5V -at- 10 Amp sec,
transformer as the "audio" transformer. I placed the 2.5V secondary in
series with the grid leak coil and the grid, then fed the 115V primary with
the output of a old tuner amp. The tuner/amp had one channel still good, it
put out about 40 watts, I think (uses the STK0039 IC). When first I tried
this it didn't seem to work, i.e., I just herd the buzz of the discharge,
no audio. I then tried lower power and drew a arc to a grounded object,
that is when the audio came through the discharge, way cool! I am assuming
that with more audio power I could actually produce a corona that pulses to
the beat of Pink Floyd! I was just using the tuner, tuned to a local radio
station for my input. I am hooked, but after some time trying to get best
bang for the buck, the RF must have finally destroyed the amp. So I have a
couple questions for those that have done this before:

Is there a good circuit I could use for protecting the amp from RF? 
I know that the so called "audio" transformer I used is not ideal (just
grabbed it off my shelf)  is there something I need to look for in a audio
"coupling" transformer, regarding this project?

Thanks for any replies,

David Trimmell