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How to estimate transformer voltage for audio preamp B&K cs117

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)?

Reply to
powerdoc
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** 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

Reply to
Phil Allison

"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

Reply to
Phil Allison

What's the voltage rating of the main input filter cap?

Reply to
Homer J Simpson

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.

Reply to
powerdoc

"powerdoc"

** Long as that means an 18 - 0 - 18 tranny.

........ Phil

Reply to
Phil Allison

Yes it does. Thanks to all. dk

Reply to
powerdoc

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.

Reply to
Homer J Simpson

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

Reply to
powerdoc

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