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Author Topic: U47/VF14 problem.  (Read 6875 times)

NVS

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  • Real Full Name: Narve Vik-Strandli
Re: U47/VF14 problem.
« Reply #15 on: January 15, 2013, 11:51:53 am »

Update.

Oliver Archut suggested that I resolder the pins on the tube. This has worked so far. At least enough to use it. By this I mean that it’s still kinda microphonic, but only if I knock the mic. It doesn’t ring like it used to. Sound does not trigger the ringing any more. I only have this amount of experience with this one U47, so I don’t know if they in fact all are microphonic when knocked a little bit…? I am thinking that it could be it still has a “bad” filament, but that the soldering somehow changed the way the filament behaves? Maybe the heat from soldering altered it? Anyway, it’s usable now, and because of the fear of killing it, I still have not tried to really knock it.

By the way, this tube now lives in a copy that I built. The copy has an original K47 and an Oliver Archut BV8 with NOS lamination built in the Archut 47Kit. It has got “that” sound. The original 47 has now got the Andreas Grosser VF14EF, which is in my opinion a great substitute. The original VF14 does sound slightly more “exiting”, but so far I’ve decided to just keep the VF14EF in the 47. I’ve only really missed the “exiting” sound of the original when I’ve recorded soft singing vocals, but for that I can now use the one I built. As soon as you sing or play a little louder, there’s not really much difference between the two.

While it may sound strange to some, I don’t know if I’ll ever put the original tube back because now the 47 is a reliable and great sounding tool, “just as it was” with the original and besides, I don’t have to worry about a VF14 failure. Maybe a “new” original tube one day, I don't know, but for now I’m really happy with the way it is.
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klaus

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Re: U47/VF14 problem.
« Reply #16 on: January 15, 2013, 02:44:26 pm »

I am glad that you were lucky enough that your radical approach to killing microphonics worked without killing the tube.
But I don't want anyone else reading this to think that resoldering the tube pins of a steel tube is a preferable solution to microphonics or anything else: The danger is this: if the vacuum of the tube becomes leaky, through the heated, liquefied solder, the tube is forever finished.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

mwurfl

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Re: U47/VF14 problem.
« Reply #17 on: January 16, 2013, 02:19:06 pm »

So Klaus, are you saying that the vacuum seal in these tubes is entirely dependent upon the integrity of the solder in the pins?  All the based glass tubes I've ever seen that have their leads soldered to the pins in the base have the actual leads vacuum sealed as they pass through the glass in the tube's base, such that one can un-solder and re-solder the leads to the base pins without risk to the seal (if one is reasonably skilled at prompt soldering).  So it's interesting to me to hear that these metal tubes may not be built this way...

Thanks & best regards,

Mark
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klaus

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Re: U47/VF14 problem.
« Reply #18 on: January 16, 2013, 05:38:00 pm »

The picture below shows how tube filaments are attached to, and sealed off from, the tube pins in octagonal tubes like the VF14:

After the filament is soldered to the (hollow) tube pin, a liquefied glass drop forms the seal at the top of each pin.
In addition to the welded-on metal cap which seals the whole tube construction against leakage, these glass plugs form the vacuum seal between pins and filaments.

It is easy to understand that when applying a solder gun to the pin, 1. the solder will melt and potentially allow air into the pin channel, setting the stage for a vacuum leak: 2. the metal cylinder (pin) surrounding the glass plug will expand quickly when heated, forming a leak between plug and pin, or, worse (and I have had a few cases) the plug cracks.

Bottom line: direct application of solder iron to VF14 tube pin is a bad idea, akin to playing Russian Roulette
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com
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