On Mar 14, 12:22 pm, wrote:
On 14 Mar, 12:41, "powerdoc" wrote:

On Mar 14, 4:05 am, "N Cook" wrote:
wrote in message
oups.com...
I have a CS-117 with a defunct transformer. The factory won't sell me
parts and the value of the unit will be exceeded by the repair costs.
Is there a way to estimate the value of the ac output (it looks like a
center - tapped output with 3 wires) so I can get this back on the
road?
The voltage regulators are 15v and electrolytics are 40v.

I remember asking the type of Vregs, without this you cant work it out
accurately.

Lets guess at 4v drop, which is on the generous / safe side, so that
means you need minimum 19v dc input.

Its a preamp so low current supply, so say 2v BR drop and perhaps a
25% regulation transformer. Allow for 15% mains drop. So your
transformer ac voltage will be

(19 + 2 ) /.85 x .707= 17.5v.

You'll need to allow for copper loss too, so 18+18 wont be enough.

Top voltage limit will be dictated by margins & cap rating.
If 25% transformer regualtion and 10% mains overvoltage get us to 40v,
running loaded v = 40/1.375 = 29v.

25v ac would be a good guesstimate. If its a split secondary with 2
diode rectifier, 25-0-25.

NT

I figure
that the transformer is prob 36v. c.t. with a fractional amperage.
Will try that with a variac and see how it works.

The 36v ct transformer gave me about 25v on the high side of the vr
and 14.88 on the low but there is something else wrong as one of the
ic's got really hot. Time to start looking at other ic's in the
circuit but since I don't have a schematic it may be replacing all of
them.