Benjamin's DRSSTC1

[Benjamin Lockhart]

Hey guys I thought I'd share my new coil!

Specs are
fga60n65smd half bridge, older Onetesla driver board, 210khz ish, 2.875"x7.75" 36AWG, 1.9"x8" aluminum toroid, I'm using an older Onetesla interrupter.
100nF tank cap, 100us max on time, roughly 280A peak primary current, breakout point is 18.5" off the ground. The whole coil stands about 15.5" tall.
Primary coil is 1/8" copper tubing spaced 1/8" apart, 7 turns. Inner diameter 3.9", outer diameter is about 7". Primary inner turn to secondary clearance is 1/2".
The primary is about level with the bottom turn of the secondary. 1/2" copper tube strike rail.
0.19 coupling coefficient
Primary is only detuned slightly here maybe 5-8% Tapped at turn 5.75
Max spark so far is 18.5", 470mm!

Longer than about 70us on time creates a 2nd beat (big notch and then current rise again) in the primary current envelope, and spark length does not increase further. I suspect that it could use more detuning and a slightly larger toroid for better sparks, but I'm happy with this!

This new short secondary and flat primary has solved all the tuning and flashover problems that I had with the original Onetesla kit and it performs better too!

[davekni]

Longer than about 70us on time creates a 2nd beat (big notch and then current rise again) in the primary current envelope, and spark length does not increase further. I suspect that it could use more detuning and a slightly larger toroid for better sparks, but I'm happy with this!

That sounds accurate.  As you say, looks like a great coil, so not much incentive to tweak.  Also, although more detuning will likely increase arc length a bit, music may sound better with tuning as is.

[Mads Barnkob]

Longer than about 70us on time creates a 2nd beat (big notch and then current rise again) in the primary current envelope, and spark length does not increase further. I suspect that it could use more detuning and a slightly larger toroid for better sparks, but I'm happy with this!

That sounds accurate.  As you say, looks like a great coil, so not much incentive to tweak.  Also, although more detuning will likely increase arc length a bit, music may sound better with tuning as is.

Correct, some notes wont play well, when you have detuned and need a large current buildup for breakout to appear, the note might be played half way through, before breakout occurs and only result in a "glimpses" like sound.

[Benjamin Lockhart]

My small coil is 100% done now!
I have had some troubles with adding an OCD circuit to the Onetesla board using Alex Yuan's board design, but it's working now, I just had to replace a few ICs.
I upgraded the MMC from a single 100nF cap to four in series-parallel because it was getting hot.
The OCD is set at 290A and only triggers on ground strikes. It has hit 19.5 inch sparks to a ground plate now, not too bad for a small half bridge.

The bus caps and 1/8 inch tube primary actually get hotter than anything else on high duty cycle songs.

Here are some tunes!

Pretty good bass using the midistick!

4 note polyphony

[Benjamin Lockhart]

Here's the javatc file if anyone is interested.