I have a B&K CS-117 preamp which has a defunct power transformer. The B&K folks won't sell parts and the cost of the parts, shipping and labor will be more than the worth of the unit. I'd like to keep it in service but the transformer is unmarked as to manufacturer and the manufacturer of the unit won't give me the specs. I guess that I see their point, in some ways, but at least they'd profit from selling me a transformer and I could speak well of them. Is there a way to estimate the output needed (it looks like a center-tapped output from the 3 wires that go to the circuit board)?
How to estimate transformer voltage for audio preamp B&K cs117
Mar 13, 2007
8 Replies
** Groper alert.
** The voltage rating of the first filter electro is a good guide - allow about 20 % under that figure.
Similar size and style trannys have the same VA capacity.
Also, trannys with the same primary resistance have close to the same VA rating.
....... Phil
"Phil Allison"
** Of course, also allow the peak transformer voltage to be 1.41 times the rms value quoted by the maker and allow for the quoted regulation percentage too, if the load condition is not constant........ Phil
What's the voltage rating of the main input filter cap?
The filters are 40v and the regulators are 15v so I figure a 36v ct transformer is the ticket. There is a model in the Allied catalogue that has the same form factor and maybe the same manufacturer although the original is just marked with cryptic numbers.
"powerdoc"
** Long as that means an 18 - 0 - 18 tranny......... Phil
Yes it does. Thanks to all. dk
There's no power tapped off before the regulators? If so you are close enough IMO. Try that tranny, hook up a variac, drop the voltage until the post regulator voltage drops slightly, then go back up 10%. If you're back at close to 18 - 0 - 18 you're set.
Unfortunately, there is something else wrong. After hooking up the transformer, the output of the vr's was 14.88 v but one ic got really hot. I guess there was a reason for the transformer to fail as the power is always on on this unit. More looking I guess; IC's are relatively cheap to replace
Join the Discussion
Have something to add? Share your thoughts — no account required.
Didn't find your answer?
Ask the community — no account required