Wanna take a second here to say “thanks” to Stephen Sank, again, for his sagacity in the service of my old ribbon mics. My circa 195X RCA BK5b is one of the most popular (with vocalists) in my pile/collection of mics and it gets used a lot on sessions… and it breaks every couple of years. Pretty consistently. Luckily there’s a reliable, experienced, and reasonably-priced serviceman who really knows his way around these dusty old gems. I was afraid that the ribbon had broken and/or fried, yet again, but that was not the case. From S:
“Very bizarre problem, very easily dealt with. I have never, ever seen it happen before on an RCA, but one of the transformer taps went bad spontaneously. Wire up into the potted transformer shield casing is fine, so it happened in the core. Fortunately, the 150ohm tap is fine, so just moved a wire to it. Works great, ribbon still perfect. And there is no reason at all to suspect any future transformer issues. And that transformer is unbeatable & unobtainable, so don’t even ask.;-)”
Yeah it never would have occurred to me to suspect the transformer. Anyhow my BK5b is back and should make another recorded appearance soon. You can find Sank at this website.
One reply on “Sank Comes Thru Again”
Transformers (small signal ones) are made out of fine wire insulated, in the case of old ones, with organic materials that do not necessarily hold up and worse will corrode the wire itself. I always suspect them and will phase out any old transformer on a pro forma basis.
Some small signal transformers can be damaged by very small DC currents so it is important to use an ohmmeter of known current capacity, for measuring resistance. Low level, low current AC is always safe, you should have a good test sinewave generator. Phase is instantly apparent if you use a scope properly.
People who deride “scope jockeys” are a pet peeve of mine. I can usually judge a tech very well on how well he can use a scope.