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

[powerdoc]

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)?

 

[Phil Allison]

** Groper alert.

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)?

** 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]

"Phil Allison"

** The voltage rating of the first filter electro is a good guide - allow
about 20 % under that figure.

** 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

 

[Homer J Simpson]

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)?

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

 

[powerdoc]

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.

 

[Phil Allison]

"powerdoc"

The filters are 40v and the regulators are 15v so I figure a 36v ct
transformer is the ticket.

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



......... Phil

 

[powerdoc]

"powerdoc"




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

........ Phil

Yes it does. Thanks to all. dk

 

[Homer J Simpson]

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.

 

[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.

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