U87i with U87a filter?

[VanguardAudioLabs]

Never seen this before. Admittedly not as many U87s have passed through my hands as other folks on this forum.

My first assumption is someone kludged together two mics for a repair, but that seems odd for something like an XLR connector. SN 21422.
View attachment IMG_4018.mov

 

[Khron]

Oh wow / oh no...

 

[OneRoomStudio]

I believe that was a standard circuit revision. There were a few versions of the U87i before the "A" version came out. Here are two versions - the second one has the LC filters.

 

[OneRoomStudio]

Also, that transistor near the the meter is likely "D1" in the second schematic, which is absent from the first.

 

[VanguardAudioLabs]

I believe that was a standard circuit revision. There were a few versions of the U87i before the "A" version came out. Here are two versions - the second one has the LC filters.
View attachment 138573
View attachment 138574

Thanks for this, I hadn’t seen this revision.l schem. I only had the first schematic and the A schematic in my files.

 

[VanguardAudioLabs]

Also, that transistor near the the meter is likely "D1" in the second schematic, which is absent from the first.

the serial number rang familiar. Looked at my notes - I just had serial # 21024 in my hands a few weeks ago and it was revision 1 (no LC filter or transistor). This is SN 21422. Funny to have gotten two on my workbench just on either side of the revision!

From the limited info I’ve found in u87 serials and manufacturing dates that puts both of these some time in 1973.