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Author Topic: VF14 ground  (Read 5522 times)

Offline Martin Kantola

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VF14 ground
« on: December 25, 2006, 03:47:21 pm »
Oliver,

I know you've dissected these tubes. How is the ground connection from the round pin to the metal shield done? Is it possible that this connection could fail somehow? I have a tube here that I suspect has that problem...

Martin

Offline Oliver Archut

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Re: VF14 ground
« Reply #1 on: December 25, 2006, 04:12:59 pm »
Merry Christmas Martin,

some of the biggest problems with "Stahlroehren" like EF12 and VF14 is that the Dumet wire used for the connection Fernico seal-socket is only copperplated steel that corrodes over the years and flunks off, mostly cracking and braking. Most likely for VF14 is the filament short when the plate voltage jumps 35-38V to 90V and back. Sometimes those tubes can live for quite some time, but most likely they will go bad fast.

Similar problems have the early AC701, when the Dumet wire was only tinned, after revision 2 (Index/serial number ends with 3) a three piece lead was incorporated, that replaced the dumet part outside of the tube with NI-steel wire.

There is no way to fix them, I saw people smearing nickel or silverpaint to get conductivity, but it won't really work that well.

Hope that helps,
Oliver Archut
www.tab-funkenwerk.com

We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.

Offline Martin Kantola

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Re: VF14 ground
« Reply #2 on: December 25, 2006, 05:57:41 pm »
Merry Christmas to you too!

Thank you so much for the info. The whole microphone has a lot of oxide, so corrosion sounds very likely. Think I even heard the broken wire rattle in there.

In this case it's good to know that other connections than ground might give up any time. Managed to make an improvised connection to the steel tube casing so the tube works now, but who knows for how long?

Another VF 14 bites the dust...

Martin  


Offline maxdimario

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Re: VF14 ground
« Reply #3 on: December 25, 2006, 07:45:41 pm »
did you try and heat up the tips of the pins with a soldering iron and re-fluxing/soldering?

that is an easy non-destructive thing to try..


Offline Oliver Archut

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Re: VF14 ground
« Reply #4 on: December 26, 2006, 12:08:52 am »
Hello Martin,

attached is a pic of the two different VF14 versions, the left one is the last production run and the ground is just spot welded to the housing, other than the earlier ones that had the connection done at the inside of the tube.
It is quite possible to solder to the housing and reattach the connection, but careful, removing the socket means probably breaking an additional lead.

By the way how is your mic project going?

Best regards,

index.php/fa/3929/0/
Oliver Archut
www.tab-funkenwerk.com

We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.

Offline Martin Kantola

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Re: VF14 ground
« Reply #5 on: December 26, 2006, 03:02:23 pm »
Thanks again,

that picture was very helpful in understanding how it's constructed! Since the only pin making trouble (so far) was the ground pin, I managed to fix it by making a new ground connection outside the tube. Not pretty, but it works.

Interesting how the socket was free to move around enough to make and break the connection inside. Is the socket attached any other way apart from the soldered pins? Considering how that tube socket holds the tube in a very firm grip I can understand those poor leads are under some serious stress if one doesn't remove the tube the right way.

My microphone project is much alive and well, thanks. As always, things progress much slower than expected, but I'm learning to enjoy taking it a bit easier. Some recent developments have really been most encouraging. We should talk in the near future...

Martin




 

Offline Oliver Archut

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Re: VF14 ground
« Reply #6 on: December 28, 2006, 10:15:44 pm »
Hello Martin,

all three versions of the VF14 used the same hookup style, the wafer is only held to the tube via the leads. As I pointed out those ones crack easily after 53 years...

Attached is a pick of all "stahlroehren" version by the different manufactures, the RFT VF14 uses the wire hook up for the wafer too, but the wide wafer sleeve helps to reduce the stress on the lead, but this VF14 version won't fit in a U47 due to the wide sleeve.

top VF14
2nd row left Telefunken EF14 pre war crimp style connection.
2nd row right RFT VF14 (glass)(post war)
3rd row left Valvo EF14 crimp style...(pre war)
3rd row middle Tesla EF14 (glass) crimp style...(post war)
3rd row right Tungsram EF14 crimp style....(pre war)

Best regards,


index.php/fa/3945/0/
Oliver Archut
www.tab-funkenwerk.com

We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.