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Re: bombarding trouble ***see video
Posted By: Tom U. In Response To: Re: bombarding trouble ***see video (George Vidas)
Date: Thursday, 19 June 2014, at 6:08 p.m.
Ditto on George's second point. In your video, you are clearly flashing back. It looks like you do have a grounding electrode, but to open/close the stopcock while this is happening seems risky.
In my opinion, this also indicates that you have a lower vacuum in your manifold than in your units, that's why the current is traveling "backward" toward your manifold. Like others, I'd also suggest letting the units pump down longer before initial bombardment. This will allow the units to outgas more under vacuum.
Do you do a preheat stage? If you let the units pump down again after you reach 150C, I predict you'll have much better results. This will eliminate a huge percentage of the moisture in the units.
You compare your two systems, but unless they are identical in manifold, vacuum pumps, etc, there are a heck of a lot of variables that may cause different results.
What prompted the diagnosis of a "weak bombarding transformer"?
Tom U.
> A few scattered thoughts:
> -- I'd guess that two different bombarders,
> especially one paired with a slide choke and
> one with a saturable core choke, will dial
> down and up differently. Are you doing
> anything to measure output current while
> you're bombarding?> -- In my shop, touching the manifold while
> the bombarder is on and opening the main
> vacuum valve while the bombarder is on are
> two things that I avoid doing at all costs.
> You are, of course, free to do whatever you
> want. But it strikes me as an unnecessarily
> risk, especially while you're putting power
> through a tube that is not holding a steady
> arc.> -- I'll second (third? fourth?) what
> everyone else has said about long/wet/dirty
> tubes being fiddly.> -- What are you using to measure vacuum? It
> seems possible that the "better"
> pumping set-up is pulling much deeper
> vacuum, meaning the water/etc is offgassing
> out noticably faster.
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