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Post by thesoundmotel on Mar 14, 2018 23:07:46 GMT -6
So I just finished my 251 diy ( Beesneez capusle , Beesneez body , Cinemag transformer , vintagemicpcb.com pcb and psu ) . The output es very low and I can't seem to figure out what went wrong .
I get :
B+ 110v
H+ 6.3v
Capsule
Front : 30v
Front Back Plate : -1 v
Rear Plate 30 v ( on omni and bi )
Rear Back Plate : .30 mv
Plate testing point : 57 V
Checked de wiring and everithing twice . I would apreciate any help with this issue .
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Post by kcatthedog on Mar 15, 2018 6:12:22 GMT -6
Did you test your tube or try a different one ?
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Post by thesoundmotel on Mar 15, 2018 7:35:28 GMT -6
Yes I have . I don't know , I think I got a bas transformer . Cinemag 13114 .
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Post by svart on Mar 15, 2018 9:08:30 GMT -6
How are you probing for voltage?
DMMs usually have only like 1M to 10M input impedance for voltage measurements, which would load down the HV circuit in a lot of mics that use 1G resistors as biasing, etc..
But I don't know what the voltages should be either. I'd have to look up the 251 circuit again.
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Post by johneppstein on Mar 16, 2018 11:46:32 GMT -6
Yes I have . I don't know , I think I got a bas transformer . Cinemag 13114 . Did you check the resistance/continuity across all the windings in the trannie? It;s usually pretty easy to tell if something's wrong - the only time I had trouble was on an OT in an old Bandmaster that had pinhole burns in one of the windings - It took high voltage for it to short. You shouldn't have that problem in a mic. |
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Post by thesoundmotel on Mar 17, 2018 6:15:18 GMT -6
Thanks guys , I think I found the issue . Two of the leads on the transformer were giving up very near de transformer itself . It replaced with a 13114 I had form a C12 build . It working fine now ![]()  |
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