Hiwatts"Custom 20" ptp

[Swampy]

Hey guys,

Have just installed a new PT in this unusual number (type is "AP") and have a query regarding PT primary CT.

Attached is a reverse engineered schem, it would appear that the CT is connected to a filtered voltage divider, at this stage CT is floating and output is noisy.

My understanding on this is the PT CT 'floats' about 100vDC above ground to reduce noise, I've never really understood CTs...can someone verify this??




Chur

[nickb]

Just a bit of a guess here. Might what you think is a CT just be a shield? It would be at AC ground to reduce noise yet DC 100V to minimize insulation breakdown between windings?

Edit: Ignore that about the DC offset and insulation - I don't think that's right . The AC noise stands.

You could lift the wire to the "CT/Shield" and check resistance to see if is connected to anything.

Nick

[Enzo]

I am having a VERY hard time imagining that the center tap is on the primary of the power transformer. If you connected it to the CT of a low voltage secondary, then it might elevate that somehow.

Use an ohm meter to determine which exact windings this has continuity to.

[Swampy]

I am having a VERY hard time imagining that the center tap is on the primary of the power transformer. If you connected it to the CT of a low voltage secondary, then it might elevate that somehow.

Use an ohm meter to determine which exact windings this has continuity to.

My apologies, HV CT on secondary.

This is a replacement tranny, the original (secondary HV winding is kaput) had a filament winding, a HV winding and a 5th connection which I presumed was a CT. Amplifier is fixed biased so no low voltage winding. Also, there exits zero rectification between the mystery conductor from the tranny and the cap and resistor to ground...

[Jazz P Bass]

Hey guys,

Have just installed a new PT in this unusual number (type is "AP") and have a query regarding PT primary CT.


I've never really understood CTs

Who made the transformer (datasheet would help)?
There is no 'mystery' to center taps.
The transformer winding can be looked at as a resistor.
Put a 'tap' in the middle & there you have it, a 'center tap'.
Like on a tube push pull output transfomer.

[nickb]

Another possibility is that it is a CT on the heater winding to provide an elevated heater voltage. Check the resistances, measure AC voltages and find out. Or do what Jazz P says and get a data sheet.