Enamel on secondary breaking down?

[nzoomed]

It sounds like a slightly larger MMC would fix the tuning range. What's your MMC value?

I think lower primary impedance would probably be beneficial to the spark length as well.

I think your coil is very similar to my DRSSTC3 and Loneoceans DRSSTC3 right?
Mine is 60kHz, 0.365uF MMC, the primary is tapped at 7-ish turns and it does 2.5 meter sparks, with 800A OCD setting.

Yes its very similar spec to loneoceans DRSSTC3, my MMC is on the smaller side, only rated at around 1000ApK from memory, I didnt have much money at the time to build a bigger unit and those doorknob caps are not easy to find, cost me like around $400 for the caps at the time, ive got 40 CDE series caps in the MMC,  (CDE942 series, 5 in series x 8 in parallel 0.24uf total)
Im still getting good streamers at least 2m long with this thing, have set the OCD to about 800A
Was considering upgrading the MMC to increase its power output, I could take advantage of this to alter the resonant frequency to suit at the same time.

[Benjamin Lockhart]

Your MMC caps don't all need to match each other.
I'd add more caps in parallel with your existing MMC to make something between 0.35uF and 0.44uF.
0.44uF is a bit on the high side but I know of one build that works well with it. I think 0.36uF is around the sweet spot for this design.

Aliexpress dawn caps are pretty cheap, and work well in mine and several other builds.
Here's a link to some that I bought. https://www.alibaba.com/product-detail/0-44UF-3000V-resonant-capacitor-for_1600736413239.html?

[nzoomed]

Your MMC caps don't all need to match each other.
I'd add more caps in parallel with your existing MMC to make something between 0.35uF and 0.44uF.
0.44uF is a bit on the high side but I know of one build that works well with it. I think 0.36uF is the sweet spot for this design.

Aliexpress dawn caps are pretty cheap, and work well in mine and several other builds.
Here's a link to some that I bought. https://www.alibaba.com/product-detail/0-44UF-3000V-resonant-capacitor-for_1600736413239.html?

Its pretty awesome what you can find out of China these days! 10 years ago there seemed to be much less options available on the market, plus international shipping can make things cost prohibitive at times. Those doorknobs that loneoceans used also sold out pretty fast, so just had to settle on the CDE series caps.
I see loneoceans MMC is about 0.37uf which would probably bring mine into that sweet spot should I raise its value.
I also was shown this source of surplus caps on ebay a little while back that appear a good option too, what are your thoughts?
https://www.ebay.com/itm/183875016042

[Benjamin Lockhart]

Those look like a good deal! 30 of them (10 series, 3 parallel) would add 0.14uF at 10kV putting you at 0.38uF total

High RMS current rating (which those have) is an important thing in DRSSTC tank caps.

[nzoomed]

Those look like a good deal! 30 of them (10 series, 3 parallel) would add 0.14uF at 10kV putting you at 0.38uF total

High RMS current rating (which those have) is an important thing in DRSSTC tank caps.

Yeah they look quite suitable, might be an option fir for a second build also.
So I could add a bank of these parallel to the CDE caps with no issues?
Not sure if the ESR would matter if it's not matched?

[Benjamin Lockhart]

I don't believe it world be an issue with slightly different ESR.