R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1] 2 3  All   Go Down

Author Topic: U47 Tube Socket Restoration or Replacement?  (Read 1425 times)

DanDan

  • Newbie
  • *
  • Online Online
  • Posts: 43
  • Real Full Name: Dan FitzGerald
U47 Tube Socket Restoration or Replacement?
« on: May 29, 2020, 02:50:44 pm »

Title says it all I guess. Ideally I would like to simply replace the valve base in my U47. Is there a replacement available?
If not I would greatly appreciate any advice on cleaning and deoxing the pin sockets. Ditto the valve pins?
DD
Logged
Dan FitzGerald  MIOA MAES
www.irishacoustics.com
www.soundsound.ie

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1824
Re: U47 Valve Base Refurb/Replace
« Reply #1 on: May 29, 2020, 03:18:53 pm »

Hello Dan,
I assume with "Valve Base" you mean the tube socket? (Anticipating your approval, I changed the title)

What is wrong with your (hopefully original 'Preh'-made) socket? The plating on its eight contacts has been notoriously deficient: the silver wears down with time and through oxidization, causing discharge noise that's often misinterpreted as tube noise.

If I am correct with my diagnosis, first order of business when addressing the tube socket contacts: unsolder all wires (after removing the tube***, otherwise you may destroy its vacuum), then remove each contact by bending its two solder trails straight up, sliding the contact out of the socket. Inspect the silver plating with a magnifying glass. If there is enough silver left on the contacting surface, clean with a chemical, not abrasive, silver polish.

If the plating on any of the contacts is worn through, to where you can see copper color, take all eight of them to a silver-plater. Cost for stripping and re-plating them in a silver bath is usually a fixed charge per order, around $100 or so. Installation is in reverse. Add a drop of Caig Pro Gold to each contact surface before re-installing the tube.

If the plastic of your Preh tube socket is cracked to the point of unsuitability, you can still get octagonal sockets on German eBay, but they often will be of sub-quality in regards to the contact material and plating, compared to the Preh brand. (See above for re-plating  of the contacts).

I advise against buying currently-made copies of U47 octagonal sockets: the surface resistance of the plastic they use is often too low, and compromises the super-high impedance at the grid connection.

*** Please note that removing the VF14 tube from the socket can be difficult and can break the tube's plastic center key if not done right. There are two "tube removal" slots cut out of the bottom of the socket: insert a flat blade screwdriver (4-6mm) into the first slot, turn the screwdriver 90║, to pry the tube up and free it.  A click can be heard.
Then do the same on the opposite side of the socket.
Logged
Klaus Heyne
German Masterworks«
www.GermanMasterworks.com

afterlifestudios

  • Full Member
  • ***
  • Offline Offline
  • Posts: 150
  • Real Full Name: John Raham
Re: U47 Tube Socket Refurb/Replace
« Reply #2 on: May 29, 2020, 05:50:19 pm »

Great info.  Any recommendations about the tube's pins?  Are those plated too? (thicker?)  Are the tube pins often a source of problems in the connection between tube and socket, or is it usually with the socket contacts?
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1824
Re: U47 Tube Socket Refurb/Replace
« Reply #3 on: May 29, 2020, 06:06:47 pm »

In my experience, pins of octagonal tubes have not been a cause of contact deterioration or malfunction.
Logged
Klaus Heyne
German Masterworks«
www.GermanMasterworks.com

DanDan

  • Newbie
  • *
  • Online Online
  • Posts: 43
  • Real Full Name: Dan FitzGerald
Re: U47 Tube Socket Refurb/Replace
« Reply #4 on: May 29, 2020, 06:12:15 pm »

Colonial heathens! I will speak with HRH about such corruptions of the language. Fleming's Thermionic Valve of course being an invention within the empire.
I will avoid referring to the London Metro or Paula Yates long running TV series.....

LOL,  Klaus, thank you so much for sharing your  specialised and frankly valuable skill and experience. Wow.
Ideally I will bring this mic by hand to Andreas Grosser. He was recommended by my friends at hestudioteknik.  They refurbished and racked my V76 and V78 and used to work with these old  mics too.
Now they are Vertigo.
Long story, but there is absolutely no way I would ship from or to Ireland. Seen too much damage, costs are x4 what you might imagine and insurance is not available.
So until I can get a flight to Berlin, not easy at the best of times from Cork.....

So, while pretty idle here, I am gathering information.
I have two U67s
Their issue is the usual crackling and spitting noises,  which I used to think was caused by tube detioration in my U67's  Luckily I have not thrown away any of the tubes I replaced.
Perhaps I should replace the tube sockets in them with a modern teflon and gold? One is original the other a 90s reissue.

The U47
This mic was sold to Radio Tehran in 1960. A singer songwriter friend Jimmy McCarthy subsequently owned it for a decade or two. Now retired, he 'forced' me to buy it from him.
On test over a day or two it crackled pretty much continuously. Eventually I gave it a minor internal cleaning. No Iso, just dry Johnson's cotton buds. Just the easy surfaces around the capsule but never touching it or it's wires. I was rewarded with a visible amount of fine black dust on the buds. So I kept going until there was no more.
This stopped the continuous crackling, but I think there was still an occasional burst. On my own voice on reference headphones, it didn't sound as good as I remember another 47 I used to hire for special albums. Who knows if such a time shifted guess means anything. But I do know this singer would refuse to use a pop shield..... 
I had hoped to source a brand new, teflon and gold, octal, or is it 10Pin?  socket. If it is standard Octal I would have thought the HiFi tube amp crowd....... Or an original part from Neumann?  I used to be in good communication with them before Sennheiser took over. Dr. Peus repaired my KM84!  Perhaps replace the multi meg resistors. Do something about the 235 +  AC voltage we have here.
That cleaning process is a bit scary sounding, so maybe I wait. At least the capsule but  more likely the whole mic is bound to end up with Andreas sometime in the future.
Or maybe you fancy a little Holiday in Cork Ireland Klaus?

Warm Regards,









Logged
Dan FitzGerald  MIOA MAES
www.irishacoustics.com
www.soundsound.ie

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1824
Re: U47 Tube Socket Refurb/Replace
« Reply #5 on: May 29, 2020, 06:39:04 pm »

Now it gets confusing: are we still talking about U47 or now U67 tube sockets? The latter have had zero problems with contact issues.
Logged
Klaus Heyne
German Masterworks«
www.GermanMasterworks.com

afterlifestudios

  • Full Member
  • ***
  • Offline Offline
  • Posts: 150
  • Real Full Name: John Raham
Re: U47 Tube Socket Refurb/Replace
« Reply #6 on: May 29, 2020, 06:44:26 pm »

I had hoped to source a brand new, teflon and gold, octal, or is it 10Pin?  socket. If it is standard Octal I would have thought the HiFi tube amp crowd....... Or an original part from Neumann?
I'm sure Klaus will chime in on this, but it's my understanding that using dissimilar metals on these contacts (gold socket/silver pins) can contribute to the "leaching" or "migrating" of the plating material.  Even the standard lead/tin solder will do this leaching from the silver plating, and solder with some silver content should be used.   This mismatch could possibly put you back in the same position you are currently in with less than ideal pin/socket connection...
Logged

DanDan

  • Newbie
  • *
  • Online Online
  • Posts: 43
  • Real Full Name: Dan FitzGerald
Re: U47 Tube Socket Refurb/Replace
« Reply #7 on: May 29, 2020, 06:57:42 pm »

Sorry, my post covers too much. My two U67's crackle occasionally. If it doesn't go away naturally, I remove the tube, clean the pins and apply a touch of Contact 2000 Gold. No Caig here. I have replaced the tubes with NOS Telefunken EF806S, but it doesn't seem to make much of a difference, the crackling still occurs now and then. Everything on both mics is spotlessly clean, dry, they have never experienced smoke, never been without pop shield. 


But my current issue is a U47.
While researching I noticed a few 'recipes' for removing silver tarnish by immersion in a solution of baking soda and hot water, with aluminium foil in the pot.

Thanks afterlife, I strongly suspect this mic has not been touched since manufacture, so probably not silver solder back then I am guessing.
Lead is discouraged here in the EU, but I have both types on the workbench. I guess if I do remove and clean I may as well resolder with the silver.
I am wondering though, if I go all the way to plating is gold  possible and better?
Logged
Dan FitzGerald  MIOA MAES
www.irishacoustics.com
www.soundsound.ie

afterlifestudios

  • Full Member
  • ***
  • Offline Offline
  • Posts: 150
  • Real Full Name: John Raham
Re: U47 Tube Socket Refurb/Replace
« Reply #8 on: May 29, 2020, 08:12:10 pm »

I am wondering though, if I go all the way to plating is gold  possible and better?
AS far as I know, it's the mismatch o metals that causes the leaching problems.  So unless you are going to re-plate your vf14 pins gold ( :-[), then I'd stick with silver.  There are other reasons why silver was chosen as well... maybe because of its lower resistance.
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1824
Re: U47 Tube Socket Refurb/Replace
« Reply #9 on: May 29, 2020, 11:52:30 pm »

Correct. Though gold is the best in terms of corrosion resistance, it's not as good a conductor as silver.
Logged
Klaus Heyne
German Masterworks«
www.GermanMasterworks.com

RuudNL

  • Jr. Member
  • **
  • Online Online
  • Posts: 56
  • Real Full Name: Ruud van Steenis
Re: U47 Tube Socket Refurb/Replace
« Reply #10 on: May 30, 2020, 03:29:58 am »

The good thing about silver is that silver oxide is also a conductor!
Logged

afterlifestudios

  • Full Member
  • ***
  • Offline Offline
  • Posts: 150
  • Real Full Name: John Raham
Re: U47 Tube Socket Refurb/Replace
« Reply #11 on: May 30, 2020, 01:09:51 pm »

The good thing about silver is that silver oxide is also a conductor!

I've read that most of the "tarnish' we see is silver sulfide not silver oxide.  And that silver sulfide decreases electrical conductivity causing potential problems, especially with low voltages present.  I'll try to dig up the article.
Logged

RuudNL

  • Jr. Member
  • **
  • Online Online
  • Posts: 56
  • Real Full Name: Ruud van Steenis
Re: U47 Tube Socket Refurb/Replace
« Reply #12 on: May 30, 2020, 02:15:15 pm »

Interesting!
Oxide, I can imagine, because oxygen is in the air. But where does the sulfur come from?
Logged

afterlifestudios

  • Full Member
  • ***
  • Offline Offline
  • Posts: 150
  • Real Full Name: John Raham
Re: U47 Tube Socket Refurb/Replace
« Reply #13 on: May 30, 2020, 02:57:48 pm »

Here's an article about a study on why tarnish is more silver sulfide than silver dioxide...  Even just trace amounts of sulfur in the air (in the parts per billion range) will cause silver sulfide to form. Likely just from pullution and volcanic activity I'm guessing?

https://www.chemistryworld.com/news/simulations-solve-mystery-of-why-silver-tarnishes/3010299.article
Logged

DanDan

  • Newbie
  • *
  • Online Online
  • Posts: 43
  • Real Full Name: Dan FitzGerald
Re: U47 Tube Socket Refurb/Replace
« Reply #14 on: May 31, 2020, 09:14:28 am »

If you Google cleaning silver, that technique using Hot Water, Baking Soda, Aluminium Foil, will pop up.
In one, they describe black and yellow flakes of tarnish and sulphur.
If I do dive in, I am considering this as one of the cleaning options. Some warn against Silver polish, particularly with plating.
So I am also thinking about Ultrasonic cleaning.
It would be great not to have to bend and extract those connectors.
Logged
Dan FitzGerald  MIOA MAES
www.irishacoustics.com
www.soundsound.ie
Pages: [1] 2 3  All   Go Up