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Re: [TCML] 810 tube coil

Chris/All - I've tried minor changes to grid resistor +/- 30 % but no major changes to grid R or C yet, working on it. I did a hi pot test on my mica caps and they seem to hold 3kv ok, I think they might be just fine. I had bought two .001uf, 10kv G2's of ebay for $20 a piece just like that one up for auction, for this project. What I'm doing now is, I've connected my O' scope to the grid circuit at the tube (using a fluke HV probe) to monitor the voltage to the grid and the overall wave form envelope and I'm seeing way to much voltage on the grid. I'm in the middle of unwinding grid turns to get the voltage to the tubs specs.
I'll be back -

On 12/17/2017 2:22 AM, Chris Reeland wrote:
Hi Dave,

Have you tried to change any of the grid leak values? I think you said you
are reaching 300ma at about 50% on variac. Wow, seems to me conducting
heavily soon. Maybe try adding more resistance to bring down ma, then it
should give more room to raise the voltage which is better anyway.  I could
be wrong, but worth a try. Also you may try changing the feedback winding
ratio. And yes could be possible, like I originally said, cap. on high
voltage, not working properly, which others also mentioned too.
Your tank cap looks to be a G2 Series. (BTW, nice looking coil I saw in
video.) I have several of the G1,2,3,&4 series caps.While they look "bullet
proof" they can be hurt even though a basic capacitance check, checks ok.
It is also a good ideal to give fairly good taps with a brass hammer on the
cast aluminum caps while measuring, I have had a couple that change when
doing this which is not good...I tried to take apart one to fix bad
connection, but couldn't. It is potted with what seemed to be identical to
the "black tar like" potting used in neon sign transformers. Out of
curiosity I immersed in some gasoline to dissolve this away, to see what
the mica stack looks like, but it just all fell apart the mica sheets and

Keep trying, and post any progress...

Also try for that eBay cap., I have seen it been passed on a few times
now...even with the low starting bid. I was almost tempted, but I have
enough of the small ones currently. Could maybe get great deal, still
taking a chance though...but could be good, whether you need it or not. Who
knows, but your tank cap may be ok, and you will have a spare. Or maybe you
will be adding this in parallel. You never know...


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