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Subject: Re: Home Made Spot Welder
Date: Jun 21, 1:16 pm
Poster: Richard Hull
On Jun 21, 1:16 pm, Richard Hull wrote:
>Thanks for the comments Richard. I was just wondering, do you know how the commercial welders
>handle the pulse switching.
Beefy thyratrons are the norm in small welders although SCRs are preferred and demand a whole lot of extra circuitry to protect them. My welder uses a National 670 thyratron as its main switch, but that is 1956 technology. I note that Newark electronics has it in stock for $817.00 I bought mine new, NOS, at a hamfest in Manassas three weeks ago from a grizzled old tube dealer for $6.00.
The internet and E-bay are killing the old prices by driving them upwards. Those old dealers are wising up quick. Why should the dealer have drive 200 miles, pay to sell at a hamfest and then have to dicker with some drawlly yahoo in a field at a rural North Carolina fairground over a $10.00 tube being forced to accept $8.00 or lose a sale, when some well heeled, over paid, techno nerd from sillycon-valley will gleefully mail $50.00 to him and pay postage for the same item!
More and more of the old dealers are not "doing" hamfests anymore.....They are staying home in the air conditioned trailer and selling on line. The trash they can't sell outright, they put on E-bay with an overblown, but accurate description laced with words like "classic", "vintage", and "antique". These often bring in more than the good stuff they sold via the normal offering channel on their website!
Times, they are a changing!........For better and worse.
The ignitron is the switch of choice in really large spot welder capacitive discharge systems.
I have one medium sized and one giant water cooled ignitron in my collection. They are probably one of the most robust switches in the 0-5000volt @ 200-10,000 amp range around, though they are hard to locate, and outrageously priced at Newark....$1,000 plus! Most of the good old surplus ignitrons were smashed up years ago for the nearly half pound of mercury found in them.