Hi everyone,
I have a broken Bruel and Kjaer microphone preamp type 2619 and would appreciate it if someone can let me have a copy of the circuit diagram.
Any anecdotes from anyone who has successfully repaired/found replacement FET's, transistors?
Any help would be greatly appreciated.
Thanks in anticipation
Dave
I have a broken Bruel and Kjaer microphone preamp type 2619 and would appreciate it if someone can let me have a copy of the circuit diagram.
Any anecdotes from anyone who has successfully repaired/found replacement FET's, transistors?
Any help would be greatly appreciated.
Thanks in anticipation
Dave
Hi Dave. I have just acquired a manual for my 2619s (I have quite a few). Should be here any day now and I would be happy to send you the schematics. Finding a FET to replace the orig should be very easy. Although there may not be any exact part number equivalents there will be many easily obtainable devices with a very close (or better than original) parameter match, lower noise etc. than the original FET . The early FETs had a very wide ranging distribution of parameters for a given part number. Because of much more advanced manufacturing techniques most of these have been replaced by families of devices which fit well inside the parameter range of the original devices and with many improvement over the original including being much less susceptible to static charge destruction!.
I am not that familiar with the workings of the member contact mechanisms on DiyAudio but contact me through my email if still interested.. Or leave me contact info and I will check back on this thread occasionally. Chris
I am not that familiar with the workings of the member contact mechanisms on DiyAudio but contact me through my email if still interested.. Or leave me contact info and I will check back on this thread occasionally. Chris
Hello, I am brand new to this forum and it is your posts have prompted me to join. I also have a non -working Bruel & Kjaer 2619 preamp and any information on servicing or a schematic would be greatly appreciated. One thing I would like to know is how do you open it up? 😕
Does anyone know reasonably close replacement for U2002 (Teledyne corp) used as the front transistor in 2619? Or just parameters?
replacement for B&K U2002
Almost any small signal, N-Channel, >50v junction FET with Low noise parameters will work.
Early transistors of any given type hade a very wide parameter spread (particularly FETs). Modern fabrication technology has allowed for much better control over these parameters and there are doubtless many modern devices that will fit within the parameter spread of the original U2002 - which is the device I believe you wish to replace
The OEM FET was probably “hand selected” for low noise which was very necessary at that time. It should be easy to find a modern device that will easily satisfy the noise requirement.
I have rarely had a problem when substituting modern transistors for older – no longer available – devices and have usually improved the performance and durability of the circuit (I have done this many many times in high end pro-audio equipment and instrumentation).
At worst you may have to do a little experimentation for best results but a little research on the most appropriate device should eliminate that. The B&K circuit is very straightforward and there is nothing magical about it.
Good hunting.
Almost any small signal, N-Channel, >50v junction FET with Low noise parameters will work.
Early transistors of any given type hade a very wide parameter spread (particularly FETs). Modern fabrication technology has allowed for much better control over these parameters and there are doubtless many modern devices that will fit within the parameter spread of the original U2002 - which is the device I believe you wish to replace
The OEM FET was probably “hand selected” for low noise which was very necessary at that time. It should be easy to find a modern device that will easily satisfy the noise requirement.
I have rarely had a problem when substituting modern transistors for older – no longer available – devices and have usually improved the performance and durability of the circuit (I have done this many many times in high end pro-audio equipment and instrumentation).
At worst you may have to do a little experimentation for best results but a little research on the most appropriate device should eliminate that. The B&K circuit is very straightforward and there is nothing magical about it.
Good hunting.
The input FET for the 2619 is not really generic. The capsules can have as little as 7 pF total capacitance so the low noise Jfets will have enough capacitance to seriously attenuate the output, even with the bootstrap. The low noise Jfets have large areas to get the low noise but can have higher current noise and much higher input C.This is often recommended for the application: https://www.onsemi.com/pub/Collateral/2N5457-D.PDF but some of the RF Jfets may have lower C without more noise. Its a tradeoff.
What is the problem with the preamp you are trying to fix?
What is the problem with the preamp you are trying to fix?
B&K 2619 Pre amp input fet replacement
Certainly the input capacitance of the j-fet is important however because of the heavy bootstrapping in this circuit the effective input capacitance is reduced to a fraction of a pf. This is evidenced by the overall gain of the preamp which despite the approx 8 -> 10 pf summed input capacitance of the devices and wiring in the circuit ( junction cap + cap of the SF115 + other stray Cs) is only about .2 dB below unity.
½ inch B&K capsules typically have capacitances in the range 14pf to 18pf only ¼ inch and 1/8 inch capsules have capacitances lower than 8 pf. I would not recommend using this preamp with a ¼ inch (or 1/8 inch) capsule for anything other than high SPL measurements.
Certainly the input capacitance of the j-fet is important however because of the heavy bootstrapping in this circuit the effective input capacitance is reduced to a fraction of a pf. This is evidenced by the overall gain of the preamp which despite the approx 8 -> 10 pf summed input capacitance of the devices and wiring in the circuit ( junction cap + cap of the SF115 + other stray Cs) is only about .2 dB below unity.
½ inch B&K capsules typically have capacitances in the range 14pf to 18pf only ¼ inch and 1/8 inch capsules have capacitances lower than 8 pf. I would not recommend using this preamp with a ¼ inch (or 1/8 inch) capsule for anything other than high SPL measurements.
Hello! I am trying to get life in a 2619 and am wondering if anybody has the schematic and what jFETs have worked for others? Given the 200v polarization voltage I am guessing it needs a special-jfet?
Are you folks still looking for the schematic? Here is a link to the service manual:
Dropbox - Password Required
Password:
diyaudio
Link will be good for a month or so.
I have a zillion B&K manuals scanned. Here is my most complete collection:
PDF 400+ BRUEL&KJAER MANUALS 100 SERVICE INSTRUCTION SCANS 5 CATALOGS 3 DVD-R | eBay
I have a couple more limited collections on eBay as well.
If you need a particular manual, let me know.
Dropbox - Password Required
Password:
diyaudio
Link will be good for a month or so.
I have a zillion B&K manuals scanned. Here is my most complete collection:
PDF 400+ BRUEL&KJAER MANUALS 100 SERVICE INSTRUCTION SCANS 5 CATALOGS 3 DVD-R | eBay
I have a couple more limited collections on eBay as well.
If you need a particular manual, let me know.