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Author Topic: REGLUING AND RESOLDERING PLATE CAPS IN OLD TUBES (811A TYPE)?  (Read 2028 times)
G3RZP
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Posts: 1319




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« Reply #15 on: September 15, 2018, 09:33:53 AM »

Another getter material used back in the early 1920s was phosphorous. Stained the inside of the envelope a browny-yellow colour.


Quote
but some tubes can be rebuilt.

Some big TX tubes were repairable on site. Known as 'demountable valves', they were continuously pumped, and the tx station techs would rebuild them as required. But if one of the techs had sweaty hands , they sometimes could never the vacuum high enough until they stripped the thing down and washed all the parts in carbon tetrachloride - no worries in those days about carcinogens! My wife's father was working on those in an HF station in the early 1950s...

They had spare filament and grid assemblies in stock....
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N2EY
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Posts: 5095




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« Reply #16 on: October 01, 2018, 01:34:42 PM »

BTW:  K5JXH also mentions the importance of restoring the mercury to the base of a mercury-vapor rectifier tube after being moved.  Put the tube in a sturdy sock with the pins facing the toe.  Swing the sock in a circle like an impromptu centrifuge for a few moments.  Mission Accomplished.

Please don't do this. IMHO it's dangerous and ineffective - and completely unnecessary.

All that's needed to restore the mercury to the bottom of the bottle is to fire up the MV rectifier filaments with no high voltage applied for 20 to 30 minutes. This will boil all the mercury off the tube innards and allow it to condense at the bottom.

In practice, what I do when I need to work on a power supply with MV tubes in it is to remove the tubes and keep them vertical . An empty tin can or jar of suitable size does the job for 866As.

I've been using MV rectifiers for my rigs for almost 40 years now, with no real problems. I think I've had 4 failures in all that time, all of which were end-of-life wearouts. (None of the tubes was new when put in service here.)

You can also get away from the mercury issue without using silicon by using 3B28 xenon rectifiers, which are direct plug-in replacements for 866s. The 3B25 xenon rectifier is also a direct plug-in replacement BUT has lower PIV - it will work in some but not all applications.

73 de Jim, N2EY
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KOP
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Posts: 346




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« Reply #17 on: October 12, 2018, 10:44:13 AM »

Apply HV (and load) to a MV tube without proper warm up at your own (and the tube's) risk. Ask me how I know .
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I considered a microwave oven magnetron and a 4' dish as a drone-killer. The ERP would be on the order of a hundred thousand watts or so. ~anon

November 28, 2018, 09:16:04 AM
KM1H
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Posts: 5533




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« Reply #18 on: October 12, 2018, 11:31:37 AM »

Ive replaced all of my 866A's with 3B28's or the plug in 1N2637 which was very popular in broadcast and other commercial HV supplies. If you cant see them why take a chance of using them as they dont give a warning before arcing over.
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N2EY
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Posts: 5095




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« Reply #19 on: October 13, 2018, 10:25:16 AM »

Apply HV (and load) to a MV tube without proper warm up at your own (and the tube's) risk. Ask me how I know .

They do give you quite the fireworks show, though.

I've been using 866As in my power supplies for almost 40 years now. Never lost any to premature electrification, because all the supplies included a simple time-delay circuit using an Amperite thermal time delay relay and a power control relay. (See H&K in QST for May, 1995, page 84).

Between the 2 866As and the six VR tubes in the various supplies, it's quite a light show. Even more impressive when I took the setup on Field Day.

There are xenon, vacuum and SS replacements for the 866A - but there's nothing like the real thing. What's REALLY cool is a true 866 (no A) - but they are rather hard to find, since they stopped production in the 1930s.

73 de Jim, N2EY
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