R/E/P Community
R/E/P => Klaus Heyne's Mic Lab => Topic started by: DanDan on May 29, 2020, 02:50:44 PM
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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
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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 90º, to pry the tube up and free it. A click can be heard.
Then do the same on the opposite side of the socket.
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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?
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In my experience, pins of octagonal tubes have not been a cause of contact deterioration or malfunction.
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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,
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Now it gets confusing: are we still talking about U47 or now U67 tube sockets? The latter have had zero problems with contact issues.
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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...
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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?
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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.
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Correct. Though gold is the best in terms of corrosion resistance, it's not as good a conductor as silver.
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The good thing about silver is that silver oxide is also a conductor!
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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.
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Interesting!
Oxide, I can imagine, because oxygen is in the air. But where does the sulfur come from?
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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
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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.
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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.
The term is called "metal migration". It's the effect of dissimilar alloys reacting and separating. It's best to mate similar metals whether gold, silver or tin/lead. Otherwise, wiggle the tube in the socket to scape off the corrosion every few months.
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The term is called "metal migration". It's the effect of dissimilar alloys reacting and separating. It's best to mate similar metals whether gold, silver or tin/lead. Otherwise, wiggle the tube in the socket to scape off the corrosion every few months.
Wiggling, as mentioned, isn't a permanent solution.
Thoroughly cleaning, or if contacts are too worn out, replacing the socket is.
You don't want the microphone to start crackling in the middle of a session.
I have a easy time getting as many of these sockets from eBay as I like for cheap. They turn up quite often, at least here in Germany.
Usually they have to be cleaned.
I spray the contacts with Kontact 60 after removing them, after an hour a tiny brush or Q-tips to remove anything non metallic.
Then spray the socket and contacts with brake cleaner, followed by a good scrub with isopropy alcohol + water to regain good isolation and hundred percent removal of the Kontact 60, because it will eat the coating if left alone.
The quality of contacting metal to metal has a lot to do with enough contact force.
Sometimes the contacts have to be slightly bent to do that.
Tube contacts are dry wiped, very carefully.
I never had metal bottle tubes with contacts that looked oxidized, even on rusty tubes!
Better materials, obviously, German military grade for marines.
I don't know of anything that can be applied to the contacts that does not vaporize under the heat conditions, leaving residue that is making things worse.,
So I leave it alone, never have any problems again usually.
Under no circumstances anything may be applied to the tube itself, it can creep between the contacts and housing and kill the tube.
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Wow, I had nearly forgotten what a good forum can do...
Thank you for those helpful thoughts.
Kai, do you buy actual Preh Sockets? Next time you see one, could you please post a link here. I will be notified. I will also reach out to some German friends at Vertigo and Mr. Grosser.
I think a new socket, carefully cleaned has to be the ideal solution.
I have Kontakt Gold 2000, a bit old. OK to use?
Jim, I will resolder using silver solder. If I wait until I can get the mic to Andreas, I will bring that up for his consideration.
All, please don't be confused by my wandering style. This U47 is new to me. I have two 67's for years.
They both crackle now and then. I clean the valve pins and the sockets to some extent with Isopropyl and Kontakt.
I have left the Kontakt on there it seems mistakenly. I thought it best to let it continue doing it's thing, and work as a lubricant.
This cleaning tends to work, for a while, but perhaps it has as much to do with the physical wiggling the tube out and then in again.
If the noise starts up at an actual session, I shut down the mic, use the other one perhaps, or let it cool and give it a little wiggle.
This work, for now, but I am really considering a Gold Plated Teflon Socket.
I know Silver is more conductive, but surely in context that is a minuscule difference. Gold seems much less prone to tarnish.
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I repeat: I see no need to replace an original Neumann U67 tube socket. They have ever failed for me in 35 years of regular. servicing. I have not found a single tube crackle in a U67 that was caused by a deficient tube socket.
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I noted that well Klaus. But the observed behaviour over time is factual too. I am trying to find solutions here, so all facts are welcome.
Ultimately whatever is going on has to fit all the facts. I have enough tubes to be pretty sure they are not all faulty. And wiggling the tube as Jim also finds, can and does stop the noise. That suggests to me socket or pins.
When cleaning the EF pins and sockets to some extent, perhaps I should not have left Kontakt to soak on there.
DD
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I was talking U47.
U67 is a completely different story.
The small pins of these type of glass tubes get oxidized or sulfurized all the time.
They even get much hotter.
The socket holes are too small to do anything mechanical for cleaning the contacts, except maybe you can try with ultrasonics or 24h in strong desoxy (Kontakt 60, Caramba,.. ) and special cleaner afterwards:
brake cleaner and washing with isopropyl alcohol/destilled water, then pure alcohol to remove the water, long dry.
Kontakt Gold does nothing good in cleaning oxidized contacts, it's meant to be protection for Chinch connectors by greasing them.
I'd start with cleaning the tube pins.
Glass tubes don't need to be handled extremly carefully, in the unlikely case the EF86 (or whatever made it's way into the mic over time) is damaged, it's replacable.
Leave no residue of cleaner, or the pins will oxidize again soon.
If you already contaminated the socket contacts there's no way round removing and either clean (see above) or replace it.
Hopefully you did not really spray into the mic, else everything inside is contaminated and needs checking and washing.
For soldering I'd stay with standard 60/40m tin/lead electronic solder.
If you feel better use silver, anyway so called "silver" solder contains few % of silver only, rest is tin usually.
If you go that route I'd use the stuff that is manufactured at full moon (or was it new moon?) by blond virgins :) - sorry, I couldn't hesitate.
The flux with some silver solders is a bit suspicious, needs cleaning after soldering - hard to do inside the mic and unneccessary hassle IMO.
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Regarding the 67's:
I will get some Kontakt 60. I doubt if the Kontakt Gold 2000 has done any harm. The spec does say it is particularly suitable for lubrication and protection of soft metal plated contacts e.g. Silver. It's been a while, but there is no way I sprayed it willy nilly around the Mic. For the sockets I would have used a drop on a cotton bud or just left some on the valve pins when reinserting. Do you really think they need to be removed and cleaned at all? I have access to an Ultrasonic bath. But I have no idea what desoxy is, or special cleaner? Also from earlier, brake cleaner?
The valves I have are mostly NOS Telefunken EF806S. One is a National which came in the 90's 67 reissue.
Back to 47:
I think lead solder is illegal in the EU these days, but I have both in any case, and it seems to make sense to mate silver with the remaining thin silver on the sockets.
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The Kontakt Gold probably has converted to a nice tar coating on the socket contacts.
Strong desoxy e.g. is Kontakt 60 or the stuff you find with car repair, e.g. Caramba, but NOT WD40.
I'd go with Kontakt 60, it eats everything, included it's own can (over 10 years or so).
Brake cleaner is the best and cheapest solvent to degrease something after desoxy, again easily obtainable.
There's expensive stuff for electronic board cleaning too, over the top IMO.
For repair of pre-lead-free equipment lead solder still is allowed in EU, for a good reason: don't mix solders, joints may break over time by termal stress.
The U67 is constructed for 60/39/1 Sn/Pb/Cu solder and collophonium flux.
Anyway the U67 contains lead, so it becomes "hazardous waste" at the end of it's lifetime, in 200 year :)
Or will end up in a museum.
Or will be restored for someone recording music.
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67-
LOL, so optimistic! I took a look just now. There is no contaminant visible anywhere on the Teflon on on the PC board. But interestingly, as you said, the EF806S Pins are not at all shiny. I gave them a little Isopropy on a bud. No visible contaminant came off but they did become visibly cleaner when I persisted. That sounds like your 'tar' no? Now they are a cleaner looking, a little shiny but just have that slight rainbow colouring which valve pins get from heat I presume. I can't see anything inside the gold sockets but I am thinking it would probably be best to replace them if Neumann will supply new ones. Seems we have an answer, idiot used wrong Kontakt!
I will order Kontakt 60 now for the valve pins. Also brake degreaser. I won't mix solders on your advice.
47- Just got a very speedy answer from Tele USA. Although not advertised they do indeed sell their Teflon and Gold y8A. Also the soft sponge tube support.
Klaus, should we change the thread title? 47/67 Tube Socket issues. Or blond bimbo buys wrong cleaning product.... Perhaps the thread will serve as a cautionary but ultimately advisory tale that asking first is wise and gets very real valuable answers for all you kind folks here.
All good, DD
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I have had good results with DeOxit, though I use the red version that comes in a bottle, sparingly. If I apply more to areas, to help break up corrosion more, I clean it up before running the gear. I might put the tube in and out of the socket a couple times, gently.
I usually find myself doing this with sockets, but I have done it with tube pins as well. Again, sparingly as I can, and with cleanup.
I think sometimes very light oxidation seems to just burn off with a little time if you’re lucky.
And to be clear, I am just talking about “in general”, NOT the Neumann sockets. I post this because mainly because I would be extremely reticent to use some of the heavy duty treatments mentioned here on ANY tube socket. So I mention this as something I have seen to not have detriment over long term (seemingly), and where I know another few people who have done similarly.
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As Klaus has said, the sockets in a U67 dont go faulty. I have had occasion to increase the tension on them. By very carefully with a small screwdriver, poking it down the side of the socket in the holder. This also works on Tuchels. Also, you can very slightly bend the pins on the valves so they impart tension. Sticking liquid cleaner in things is always risky.
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47- Just got a very speedy answer from Tele USA. Although not advertised they do indeed sell their Teflon and Gold y8A. Also the soft sponge tube support.
Please read what I wrote about aftermarket octagonal sockets.
Klaus, should we change the thread title? 47/67 Tube Socket issues. Or blond bimbo buys wrong cleaning product.... Perhaps the thread will serve as a cautionary but ultimately advisory tale that asking first is wise and gets very real valuable answers for all you kind folks here.
The problem (intermittent, oxidized U67 tube sockets) and its solution (applying all kinds of goo to the contact surfaces) don't compute with my experience, which, for the third time, is that the tube sockets Neumann has used throughout the life of U67 do not corrode.
So this opinion will not be part of any advisory I agree with or approve, and therefore warranting a title change. But I'll leave it up, for now, as opinions to air on the subject.
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Klaus please trust that I really do hear you, loud and clear, and greatly appreciate your generosity in sharing. If I invest in a Tele USA socket it will be to give me time to deal with the existing socket or send it to an expert, and or find a NOS Preh.
67s
Kontakt 60 is available by mail within Ireland, Caig no.
Klaus assurance that those 67 Teflon Gold sockets do not cause trouble, conflated with Kai's suggestion that the erroneous Kontakt Gold 2000 has probably dried and turned into something unwelcome strongly suggests that I have done some harm. i.e. Contaminated both the gold contacts AND tube pins. I will see if I can get new sockets from Neumann. If not thorough cleaning and degreasing as per Kai.
FYI I did look at one of my unused EF806S Tele's. The pins do appear to be a little bit dull so definitely some deox and cleaning before deploying in the future. Can't do any harm right?
The 47. Luckily I asked here and have not touched it. Hopefully it will be possible to bring it to Andreas soon.
Tx to all, warm regards, DD
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Curious to hear a little more about Kai’s vf14 socket re-tensioning success. Do you just go by feel? Your emphasis of the word “slightly” makes me wonder if there’s anything in particular to watch for? What’s your implement of choice for bending the contact pins?
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Tensioning tube socket contacts:
• If you don't have problems - don't do it.
• With contacts easily visible, compare and equalize the open space for the tube pins to match the one with the smallest opening - not more.
• Too much bending back and forth weekens the spring effect.
If you want too much you get less.
Inserting the tube bends back a contact spring if its material is stressed outside the "elastic-" into the "plastic range".
• If bent, carefully straighten the pins on glass tubes WITHOUT APPLYING MUCH FORCE TO THE GLASS.
Straight pins give equal contact force within the socket.
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Thank you, Kai. Here’s a photo of one I’ve got here right now. Aside from the tarnish and potential absence of silver plating and cracks in the Bakelite.... Does the spacing look right? Images of other sockets seem to have less gap for the pins (tighter fit), but it’s hard to tell... Any thoughts on the amount of open space here?
Also, I've never removed a contact, so I don't know what the complete shape of a contact looks like? Does anyone care to draw the shape of a contact, or post a photo of a removed one?
(Lame attempt at a diagram of a side profile view below...)
A.)
/l\
/ l \
l or.....
l
_/\_
B.)
/l\
/ l \
\_l_/
l
_/\_
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Huh, this thing is about to retire.
The plating is gone completely, or is this the tar leftover from dried kontact fluid?
The upper two in the picture look a bit loose, else the bent looks OK.
But that doesn't help, copper or copper plated steel(?) isn't suited as contact material, heated it oxidizes faster than you can say f...
A crack (I don't see it), BTW, could be fixed with epoxy glue (Uhu Plus 300, heat cured) if no other socket is handy.
Get a bunch of sockets from Ebay (they usually go in bigger lots) and select a good one, clean it - mount it - done, forget it.
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No Prehs on eBay. The cheap ones that are available have sub-standard plating from the get-go. So you might as well have yours re-plated, as I had mentioned earlier.
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I had a look through my stock:
8 out of 10 sockets don't look much better than the one pictured.
2 look quite OK.
No Preh in sight here too.
I polished one contact insert to see what it's made from: some kind of bronze.
Then I looked over my tubes: about ~60% of the pins are either nickel plated, very shiny (no silver).
The other 40% are brass, uncorroded with one exception.
I couldn't see any correlation of materials with the embossed or stamped markings.
One is stamped "Wehrmacht" (= pre 1945) and has nickeled pins.
Conclusion:
• Buying old sockets from Ebay or other sources likely won't bring you any further unless you catch a bigger batch.
NOS - (NEW Old Stock) - mostly is a lie anyway on Ebay.
The plating on this at least 65 year old stuff is not made to last that long.
• I have no trust in the Chinese brands. These guys, by my experience, don't have the slightest clue of what materials to use, it just has to be cheap, thin and usually is unsuited for the purpose.
• Option #1 is to follow Klaus' proposal of getting the contacts re-plated - or replate DIY, can't be too hard, the ancient Babylonians 3000 BC already did it.
• Option #2 dismount and polish the contacts with a Dremel/felt disk until the contacting area is perfectly mirror-shiny and smooth.
Needs to be done anyway before replating.
If the tube pins are clean and shiny too, this might work for a long time without the silver, if contact force is strong enough.
Bronze does not easily corrode if kept perfectly clean and dry.
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Thank you gentlemen.
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Indeed, +1
DD
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A friend of my wife is a goldsmith.
She said, galvanic plating these little contacts with any metal - she suggested gold - is common in her job, no problem, and not expensive.
I indeed would vote for gold (or platinum), as the tube contacts seem to be either nickel or brass, the combination works well and does not suffer from contact-corrosion.
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Hi Kai, more good info tx. Funnily I was just now logging in to PM you a question to clarify something, but I guess it is probably of public interest.
You mentioned not to mix solders. What happens if one does?
Also, I have been using Sennheiser HD 480s for decades. They cause great happiness in Recording Studios. The continuity fails so I have been buying new drivers, new cables, new pads when the foam starts to crumble.
I have three sets left and I was about to butcher them, try to solder directly to the drivers...... But another comment here came to mind, contact pressure. Optivisor on, I discovered that the tiny contacts were transverse springs rather than similar to valve sockets. A little precision bending has rebirthed them.
Everyone:-
I am getting in some cleaning fluids for the workbench. Caig Deoxit vs Kontakt 60?
67s-
No response from Sennheiser UK (Neumann) so I plan to investigate if there is any Kontakt 2000 residue in the U67 sockets.
Any thoughts on Interdentals for this job? Socket upside down to drain the fluid of course.
Rather than brake cleaner of unknown brand and composition, is there a truly great proprietary electronic cleaner?
DD
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Solders:
Stay with 60/40 tin/lead ELECTRONICS solder with collophonium flux, the whole mic is built that way.
The 98/2% tin/silver (euphemistically so called "silver solder") is mechanically less reliable, harder to work with, and the flux of some needs to be washed away after - impossible to do in the mic.
The contact springs in some Sennheiser headphones' series are known to fail.
Sennheiser offers (offered?) improved replacements.
Soldering the cable is not a real option.
Beware not to break the very thin driver leads, very hard to fix.
For cleaning the tube socket it has to be removed, and the contacs have to be taken out.
Quite straight-forward to do.
Poking in the contacts with whatever leaves the job half undone at best.
Most deoxi works on sole metal contacts.
A bit of rub is needed anyway.
Kontakt 60 is proven.
There are various expensive "washers" available, like Kontakt Chemie "Tuner Spray".
For me brake cleaner always did the job, I use this one:
https://smile.amazon.de/Brake-Cleaner-Aerosol-500ml-08901087/dp/B07NJ9SNLS/ref=sr_1_5?__mk_de_DE=ÅMÅŽÕÑ&dchild=1&keywords=Würth%2BBremsenreiniger&qid=1591860657&sr=8-5&th=1 (https://smile.amazon.de/Brake-Cleaner-Aerosol-500ml-08901087/dp/B07NJ9SNLS/ref=sr_1_5?__mk_de_DE=ÅMÅŽÕÑ&dchild=1&keywords=Würth%2BBremsenreiniger&qid=1591860657&sr=8-5&th=1)
It's cheap, no need to use it sparse, so it really "washes".
It's pure Naphtha as far as I know.
Washers have to fit to what is to be removed.
In this case Kontakt 60 to desoxy and dissolve, then brake cleaner to degrease/remove the Kontakt 60 is what is needed.
To make it clear: nothing senseful can be done with the socket inplace, it has to be taken out of the mic.
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Thanks for the specific name of brake cleaner, I will invest in some K60 also.
Again sorry my bad, there is a bit of 'bleed' between topics. I am doing nothing about the 47 for the moment. Until Andreas gets to revitalise the Valve and assess the capsule there seems to be no point in treating unidentified symptoms. I have cured most of the noise for now with simple dry cotton bud cleaning. I have a German friend looking for a Preh.
There is a spread of opinion about the absolute necessity for that brand, but I am sticking with Klaus's advice. I intend replacing the U67 sockets, on the basis that they definitely got several small doses of Kontakt 2000 from valve pins deliberately, mistakenly, left wet.
Neumann/Sennheiser are not responding, so I will try an upside down cleaning using Interdentals and Isopropyl. No fluid will get up into the mic.
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RE: Naphta:
I just quoted the manufacturer of the brake cleaner.
In EU manufacturers are forced to tell what is used in their products.
Naphtha is a mix of lighter hydrocarbons, mainly C5 and C6, distilled from crude oil.
If something is used for cleaning you want to make sure that it does not do any damage.
Despite alcohols and other solvents, pure Benzin does leave most materials alone.
In my experience it never did any harm to anything I used it on, for degrease.
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I went with the Kontakt cleaner recommended by them.
As well as grease it claims to remove oxides and sulphide etc.
https://ie.rs-online.com/web/p/contact-cleaners/0405165/
Kai, I sent you a Private Message.
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Well I set about the cleaning the two 67 sockets and valve pins last night. The instructions on the Kontakt 60 are minimal. How long should one leave a Deox on Glass Valve Pins?
I noticed my 90's re-issue U67 has what looks like a ceramic base and silver plated, or silver, pins. The other, an original West Germany one, has gold plated pins and what looks like a Teflon? base.
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So, finally back to the Original Topic proper. I have carefully extracted the Tele VF14 which looks to be honest, new. While unsoldering the Preh two of the wires popped off cold. I have cleaned the Preh with 60 and WL and Iso. I haven't done a long Deox soak because I am thinking of getting them silver plated.
I am a little nervous of straightening those bronze parts and then bending them again. Encouraging words please! Also any tips on removal and reinstall. The VF pins look very shiny, silvery. When I go to my plater, I would chose gold or silver I presume. Which do ye recommend?
Warm thanks.
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Cold solder joints are not uncommon on VF14 tube socket connections. Push and press each contact hard with a small screwdriver, or, to be safe, resolder all socket connections.
I would only replate the socket contacts if, after thorough wiping with Caig Pro Gold, you experience discharge sounds.
Try that first.
There is no harm in straightening the bent-over ends of each contact, so that they pass through the plastic slot in the plastic socket. Re-bending them after they have been plated is harmless. I've done it hundreds of times with not a single break.
I caution against gold plating, for two reasons:
1. While corrosion resistant, gold is a worse conductor than silver
2. Dissimilar metals (silver/nickel plated tube pins and gold socket contacts) accelerate corrosion.
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You are very generous Klaus. Thank you.
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Well, with respect to all the generous help here, a progress report. A couple of hours with Kontakt 60. An interdental brush. Good wash with Kontakt WL and finally Isopropyl.
The light temp makes this a little off, it is quite silvery in reality.
The valve looks as new. Amazing really.
I think I will pursue a bit more cleaning by taking off the little circuits etc. Good to check the wire soldering, given that two came away from the Preh when I was gently removing it.
A last question please. The Head basket and body tube are off obviously. Good time for some sort of Wash, or Bath? Washing up Liquid? Isopropyl?
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Every of your cleaning steps is fine, except the last one: I would not leave the contacts bone dry and unprotected, but coat the contacts with an anti-oxidization fluid. I use Caig Pro Gold for that.
As to cleaning metal parts of a mic, I wrote a sticky on that: https://repforums.prosoundweb.com/index.php/topic,37300.0.html
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Hmm, US products can be difficult here. I have Kontakt Gold. To be honest I am pretty convinced my worst problems were appalling soldering and a build up of black superfine dust like you would see around an ioniser.
I am clearing the workshop of another restore (1176) so the great rebuild is imminent. Wish me luck. I remember that sticky well, but it is the head basket I am focussed on. To be honest, it doesn't appear dirty at all. But as it is apart, I am inclined to give it a soak in water and washing up liquid. Unless there is any danger of staining or things I don't know.
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How's it working out DanDan? Did your restoration of the socket clear up the noise problems?
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After some unsuccessful attempts at restoring one of my original Preh sockets, I picked up a replacement socket (and suspension assembly) from Flea. Nickel plating. Here's a couple pics. This way I can be without the Preh and still (hopefully) have a working mic while I take subsequent steps (re-plating the silver contacts) on the Preh. Just thought I'd post in case anyone else is in the same boat.
* No affiliation with Flea or anything. In fact, it's the only time I've ever dealt with them.
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Can you share the cost?
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Going well, but extremely slowly. Which I don't mind at all. I am pretty happy with my Preh which you can see in an earlier post. Kontakt 60 soak, Kontakt WL wash, IPA wash. Tx Kia.
Cleaned the body and basket with warm water and washing up liquid. Tx K. It looks lovely now, still obviously old, but now obviously cared for. I have stalled for the moment as I feel a need to replace the two high value Resistors. The 100M has drifted to 133M, the 60M has gone to 125M.
It is proving impossible to find a 60M or even combinations to achieve that value.
I will keep the originals in case of a future sale, but for now I am looking for performance. Best shot so far seems to be these. https://ie.rs-online.com/web/p/through-hole-fixed-resistors/8492750/ But I will have to accept 10+47+ 57M and a different composition for the grid R.
Tele USA are also willing to supply a nice looking gold plated socket with suspension for 149 bucks.
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Have another search at RS, lots of high ohm resistors in different styles. You can get a single resistor at 68M. and resistors up into the Gigohm.
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LOL I have spent hours on there. Trying to stick to one brand, size, and appearance. Just when you think you have it....... next delivery june! I have spent time on Farnell and Digikey also.....
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Can you share the cost?
Well, it was 180 Euros for TWO of the socket assemblies including express shipping to Canada, so I think they were 65 Euro each before shipping?
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Going well, but extremely slowly. Which I don't mind at all. I am pretty happy with my Preh which you can see in an earlier post. Kontakt 60 soak, Kontakt WL wash, IPA wash. Tx Kia.
Cleaned the body and basket with warm water and washing up liquid. Tx K. It looks lovely now, still obviously old, but now obviously cared for. I have stalled for the moment as I feel a need to replace the two high value Resistors. The 100M has drifted to 133M, the 60M has gone to 125M.
It is proving impossible to find a 60M or even combinations to achieve that value.
I will keep the originals in case of a future sale, but for now I am looking for performance. Best shot so far seems to be these. https://ie.rs-online.com/web/p/through-hole-fixed-resistors/8492750/ But I will have to accept 10+47+ 57M and a different composition for the grid R.
Tele USA are also willing to supply a nice looking gold plated socket with suspension for 149 bucks.
Very cool. So, did it clear up the noise issues you were having? Or is the mic still in pieces?
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LOL, listen I may be slow, but at least I'm expensive.......
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LOL, listen I may be slow, but at least I'm expensive.......
Haha. OK. I'll be patient. Just super curious if it was the socket, and if your restoration is successful. I'll be popping my new Flea socket in when this session wraps...
Best of luck.
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I am back on the horse. Long story but..... I have resumed my U47 cleaning project.
There is a lot of fine black dust, or even mould? Originally it was just high level noise, and removing some of that dust with cotton buds, no liquid, was enough to drop the noise way down. So I intend cleaning all the detachable bits in a small Ultrasonic bath.
The high Rs are 130M and 68M so I have replacements. I will talk to a jeweller re silver plating next week.
One of my advisors is worried about the insulation resistance of the Preh valve socket material. He tests at High Voltage and wants to see Gigohms. I have a cheap LCR meter which is showing nothing on the 2000M range. He thinks it is Bakelite? Is that true or is it something exotic with very good insulation that doesn't fail?
DD
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Unless contaminated, Prehs are perfectly fine and do not suffer loss of surface resistance over time.
I am curious about the high impedance resistor values you cite: U47 stock ones are 100MΩ and 60megΩ respectively.
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Thanks Klaus. My resistors appear to have changed in value quite a bit I guess. They are indeed measuring 130 and 68 Megs.