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Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
A few days ago i started to build a real vttc using a 813, yersterday night i had first light, today i rewound the primary and feedback windings, primary is 26 turns of regular stranded 1.5mm2 mains cable used in house installations and 23 turns of 0.5mm wire for feedback, roughly 1.25 inches above the primary.
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
Yeah nice start
But, did you run the coil on full power? I got same discharges with my first vttc using a pl509 pentode with 20watts or so. For a mot system and a power tube that cannot be all. somethings wrong with your settings, wrong primary frequency or so
Registered Member #290
Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673
Good day,
One thing I found to work well on a VTTC is to have the grid feedback coil able to slide up and down on the primary form @ . This allows fine tuning of the grid and really makes a difference. 23 to 25 turns seems to be the magic number. Rgs, Christopher
Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
Mr Miles, yup i thought on this as i have some mylast strips thjat would make the feedback winding sliding easily on the pvc tube, but i went with a stationary feedback because all tape i had was what i previously had on the feedback. Btw do you even dare to touch thr feedback winding on a running vttc with 2-4kV in the tank cir??
That was a MOT ran with around 80-90VAC in on the 230V winding, i had a go at full blast 230V but there was no difference in streamer output, but the 1M bleeder resistor on the MOC smoked. The 813 get real hot after a while (no plate redding tho) which suggest there could be some power flowing, since i have a safety xmfr in the power supply, the power limits to around 500 watts, which is the specced max 813 can handle.
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
No- I wouldn't touch it, but you can get vastly different results just by moving it a quarter inch in the VTTC- move it up maybe 1/8 inch at a time, and eventually you will find just the right spot. Its a matter of moving, backing away, and turning it on...repeat...
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My vttc build
