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VF14 tube: other uses?
Author: Posted by Bruce Harvie
Date: 11/16/2000
What other applications was the VF14 used for other than a U47? Is it possible to find a VF14 being used for something other than a Telefunken mic? Thanks!  
Re: VF14 tube: other uses?
Author: Posted by Uwe Sattler, Neumann|USA
Date: 11/16/2000

The VF14 was originally developed in the mid 1930s as a standard universal pentode for military field radios, where it was employed mainly in RF-front ends, mixers and fixed gain IF-stages, and rarely in AF stages. Much less of this equipment survived than U47/48 microphones though ...  
Re: VF14 tube: other uses?
Author: Posted by Oliver
Date: 11/27/2000

The VF14 is identicle to the EF14 and UF14 with a different fillament current. There is also the VF15 the remote cutoff version of the VF14 and connected as a triode it works great. Only problem the pin connection is a bit different so you have to change the socket... In 1956 Telefunken stoppped the Stahlroehren production and changed to the glass types Rimlock and Noval. The glass version of the EF14 was the EF42 with a different base, it came also as the UF42 version that can be retrofit inside the U47/48.... The other company that made VF14 up to 1965 was RFT Muehlhausen in east germany there came in a black glass housing.  
VF14 tube: are there 'identical' substitutes?
Author: Posted by Klaus Heyne
Date: 11/28/2000

Thanks for the expert info, Oliver. That's quite some array of VF14 substitutes you list, few of them I ?ve ever heard of. As on this board before, I quarrel only with the assertion that any of these substitutes is sonically 'identical' to the original VF14. I do not have a scientific answer to explain why different supply voltages and current draws of a filament create an audibly different dynamic behavior and timbre of the mic's impedance converter/amp. However, I continue to maintain that the different physical tube structures necessary for different voltage/current draw requirements, which is what distinguishes the three tubes I am familiar with (EF, UF, VF14), do matter, sonically. Not because I wish it was so- a $20.- EF14 is certainly tempting- but because I have tested and repeated these tests enough to be certain. I did these tests not by comparing the audio of two mics with two different kind of tubes in question, but by using the same mic, the same capsule, the same everything, except for the one variable, the tube. I'd be interested to exchange notes and views with those who have also done that kind of test which I regard as the only valid form of comparison in this case, because it eliminates any other variable which might be larger than the tube's influence.
By the way: of the three tubes, the VF14 came out ahead as the only tube contributing the characteristics I associate with a U47. The UF 14 was less robust in the mid range and softer in its dynamics. The EF 14 even more so. This tube almost made the U47 sound like a Church mic. (6072 tube is used there)
Klaus Heyne  
About different filament voltage tube comparisons.
Author: Posted by Joaquín Estéban
Date: 11/28/2000

Hello dear mic lovers: About comparisons among different filament voltage tubes, I can say some things about. I was employed two different tubes: EF89 vs. UF89 in a prototype of mic some years ago. As everybody knows, this two tubes are the same, a remote-cut IF pentode that works finely as impedance converter in condenser mics. Well: I was feed the filament of both valves in a constant-power circuit configuration, one of that (UF)is 12,6V/0,1A and other (EF)6,3/0,2A. Feeding in one case at 10V and at 5V in other, I was not found any sonic difference between EF and UF tubes. Of course, NOTHING (capsule, transformer, passive components...) onto the microphone was changed, only the TUBES. I ignore if VF14, EF14 and UF14 are so different one of another to produce big changes in mic sonic performances particularly in U47's, but I think that if all of these tubes are '14' suffix, maybe all equal. Filament voltage differences only affects to filament lenght and thickness, not to cathode diameter nor cathode-to-grid or grid-to-grid or grid-to-plate distances. Perhaps VF, EF and UF14 tubes was made purposely different among its to achieve another particular performances, but differences between heater voltages not necesarily implies differences in tube caractheristics. It's at least, that I think. Best regards. J. Esteban.  
EF14
Author: Posted by M. Schneider / Neumann
Date: 11/28/2000

Hello,
by the way, the EF 14 is specified for 6,3V / 0,47 (!) Amp, meaning 3 Watt. UF14 for 25V / 0,1Amp, VF14 for 55V / 0,05 Amp.
Best regards, Martin Schneider Neumann Mic. Development  
Re: EF14
Author: Posted by J. Estéban
Date: 11/29/2000

Dear Mr. Schneider: Thanks for your always valuable information. Yes, differences btw. heating characteristics are so great, but the question that are 'floating' over this pinboard is if really this filament differences affects to valve performances, mainly in its characteristic curve enough to create sonic differences on amplified signal supossing other electronic components and voltage remains the same? Of course, we assume that filament in every cases are correctly heated appliyng the correct voltage and admitting the right current.
Thanks in advance and best regards. J. Esteban.  
Re: EF14/UF14/VF14
Author: Posted by Oliver
Date: 11/29/2000

It is not a big secret that Telefunken, like all other tube makers used the same tube funktions, with different fillaments, best example is the EL84, it was made 4,5,6.3,8 and 12 volt fillament. The tubes mechanic is still the same. Telefunken made most of the Stahlroehren in Erfurt before WWII, that became later RFT/Muehlhausen (erfurt). After germany was separeted, Telefunken relocated the tube manufacturiong to Ulm/Donau and West Berlin. All Neumann used VF14 were either made in Berlin or Ulm, with the date code on the tube you can identify when and were it was made. There is a difference between prewar (and later east german) and postwar tubes. It is quite easy to find out, the prewar have a bulky ring around the bakalite base, the postwar units the phenolic base is hold by the pin solder. Regarding sound? yes there is a diffrence pre/post but all postwar E/U/VF14 are all itenicle inside, the only difference is how the fillament wire is attached. I cut a few open to measure them and ten years ago you even could order the original blueprints from the Telefunken archive in Frankfurt. Why do they sound different? The Vf14 is in a neumann microfone underheated, there is a good reason why, so if you use a EF14 and run a seperate fillament at 4.95V the EF14 reacts identicle to the VF14. Only thing is you have to replace the VF14 fillament with a dummy to keep the kothode bias stiff. Stiff means that the filament current holds the cathode at the same level without the normal flux due to tube current, at high input level this keeps the cathode very stable without compressing. This circuit was first used in Telefunken gear in 1918!! So if you underheat the cathode and keep the dummy the EF14 sounds the same. This works for the UF14 as well.... The VF15 is a bid different in construction and sounds nearly the same, measuring wise it is the same... For all other different construction tubes like the E/UF42 the underheating works the same. Sound? It is the same if you do not count the lack of microphonic..... Telefunken also made the EF732 that is a subminature tube like the AC701 (RFT made those ones also!!) that is identicle in values, way smaller, less current, and no microfonie, they were made for the transatlantic phonecables. Sounds? It is a bit different. I checked all tubes in my 47, it works great, the 47 connector has a few not used pins so you can use them for the fillament supply, found about 300 meter original U67 cable that was made for Neumann that looks like the one used on U47 so the original look is the same.... It is quite funny, most 47 that I worked on had burned out VF14 there were still working but sounded nothing compared to a new one. But the owners loved them......  
Re: EF14/UF14/VF14
Author: Posted by Klaus Heyne
Date: 11/30/2000

Oliver, What a treasure trove! Thank you for the detailed historical background.
Klaus Heyne  
Re: EF14/UF14/VF14
Author: Posted by Mathias Myka
Date: 11/30/2000

To add another historical detail: in 1993, I contacted the former Telefunken tube factory in Ulm, about the possibility of a VF 14 re-issue. While my request was kindly declined, I at least got to know that between 1946 and 1957, exactly 27,548 VF 14 tubes were produced. Interesting that.
Mathias Myka  
Re: EF14/UF14/VF14
Author: Posted by Josef Schwarz
Date: 12/17/2000

Hello,
very interesting thread on U47 conversions, tubes, etc.
I've been thinking of using a C3m for conversion, a special longlife Post Office tube. It has almost identical technical data. Filament supply is 20V 125mA. What's nice about it: It's housed in an aluminium screening can, which keeps the temperature down to 120 degrees Celsius. There are nice aluminium sockets for this loctal tube, in which most of the tube sits. Mechanics may be a bit of a problem though.
Any thoughts on this?
- Josef  
Re: tube modifications of U47
Author: Posted by Klaus Heyne
Date: 12/18/2000
Owners were dissatisfied with or could no longer easlily obtain this or that piece of hardware, started drilling around, changing tuning gears, re-lacquering bodies, installing humbucking pickups in slots designed for singe-coils, and woke up one day, realizing that the same model and year Strat they had, but without these modifications, was yielding thousands of dollars more than their butchered equivalent. If someone can tell me the disadvantage of using a good, quiet, well working VF14 with a lifespan in the decades, I'd like to know about it.
Klaus Heyne  
Re: tube modifications of U47
Author: Posted by Bruce Harvie
Date: 12/24/2000

'If someone can tell me the disadvantage of using a good, quiet, well working VF14 with a lifespan in the decades, I'd like to know about it.'
Uh, cost...? I recently found a Telefunken U47 for 1000.00 US that someone 20 years ago poorly fitted with a nuvistor. The original socket was missing as well, and I'm looking at 900-1100.00 for a VF14 and socket, which, frankly, I think is ridiculous, but understandable. But I just can't bring myself to plunk down that kind of money for a tube that may need replacement in a year or five if I'm unlucky... Why not go with the EF14 and socket (I found a socket/tube for under 50 bucks) with the idea in mind that if a VF14 comes my way in the future, I can convert it then? If I had a mic that was originally fitted with a VF14 (and still had it), I wouldn't hesitate to find another, but in this case, this is the route that makes the most sense for me, and I'm sure others as well. To analogize this to routing out the body of a '54 Strat for a humbucker is moot--the 'routing' in my case, and countless others, unfortunatly has already been done... Frankly, I never dreamed of ever owning a U47. I have an extensive mic collection, including many ribbons and condensers, but never could imagine being able to afford a mic that sells for what I usually pay for a car. Even if I have the cap rebuilt on this mic, I'm in at under 1.5K--a little over the price of an original tube and socket...  
Re: tube modifications of U47
Author: Posted by Klaus Heyne
Date: 01/11/2001

'To analogize this to routing out the body of a '54 Strat for a humbucker is moot--the 'routing' in my case, and countless others, unfortunatly has already been done... Frankly, I never dreamed of ever owning a U47. I have an extensive mic collection, including many ribbons and condensers, but never could imagine being able to afford a mic that sells for what I usually pay for a car. Even if I have the cap rebuilt on this mic, I'm in at under 1.5K--a little over the price of an original tube and socket... '
Lucky duck- 1.5k for a U47! I still feel comfortable with my Strat analogy of bastardization: EF 14s need a separate wiring/electrical component/ routing and power supply setup for getting the separate 6.3V heater to the mic's innerds. Not that you could not retrofit at a later date back to VF14. No issue for you, for obvious reasons. Possible sound differences? I've said enough about this subject on this pinboard already.
Kind regards, Klaus Heyne  
Cm3?
Author: Posted by Oliver
Date: 12/27/2000

Hello Josef,
sure the Cm3 is a nice tube and similar to the E(V)F14, it was only made by Siemens for special applications, and was also used as a 'Postroehre', I got a hole bunch working in my J78(psophonemeter) and the prewar version the J38 was set up with EF14... The circuit and schematic is the same. So those tubes are very close. Only one minor problem, the Cm3 was designed for very low impedance input and doesn't like the high grid leak resistor used in a condensor. You will get crackling noise due to reverse space charges of the grid, this effect happends also with nearly burned out tubes.
Best regards,
Oliver  
Thanks for historical Info!
Author: Posted by Joaquín Estéban
Date: 11/30/2000

Dear Oliver: Thank you for this complete historical appointments. I hope that all mic and tube lovers we will can read some posts than this. Best regards
J. Esteban.  
Re: EF14/UF14/VF14
Author: Posted by R. M. Burrow Jr.
Date: 12/11/2000

Oliver, since VF14's are hard to find and very expensive, have you tried using the 407A as a substitute? This tube is a 9 pin miniature dual triode with a 40 volt heater. If you connect the two sections in parallel, the effective plate impedance becomes reasonable. The difference in heater voltage can be taken care of with a resistor. Also, the 407A is very low noise, originally used in telephone repeaters and other applications.
I remember posting some comments about the 407A about a year or so ago here that didn't exactly get the blessing of Neumann, but something needs to be done to keep the old classic mics running at reasonable cost.
I would like to get hold of one of the old AR-47 nuvistor conversion kits simply to make a quick plug-in conversion to a 407A.
Morgan Burrow  
Re: EF14/UF14/VF14
Author: Posted by Oliver
Date: 12/27/2000

Morgan,
I tried nearly all tubes that are out there that are somehow useable for VF14 replacement. Only ones that realy work are the Telefunken made EF14 (UF14), the E(U)F42 and the EF802s. All those tubes have nearly the same system construction. Sure the 407a works somehow, but it dosn't sound right for my taste. The Nuvistor solution is still made by some crasy company for $180.00 what is real funny. The Neumann guys are very helpfull regarding the old stuff, they helped me very kindly with some info to get some new live in my BV8. reasonable cost? If you own a 5K mic, you shouldn't think about cost, some people spend over 1K$ to get a EF86 and a bad copy of a M7 in their mic installed. So for about $200.00 you get all parts for a EF14 replacement plus 1/2 an hour work and the old bottle works again. In case you need some infos were to get EF14 tubes and Stahlroehren sockets, please send me a mail...
Regards, Oliver  
Re: VF14 tube: other uses?
Author: Posted by Michael Rolf
Date: 01/08/2001

Another use for the VF 14 was in antenna amplifiers due to its large amplification bandwith. But I think there won't be around so many old antenna amplifiers fitted with a VF 14 in the junk or as surplus items these days ...