Larry -
Transformer leads are not polarized. They are AC, Alternating Current!. In the US, the 'polarity'
flips back and forth (one lead + or -, and the other lead - or +) 60 times/second.
The rectifiers form a Full Wave Voltage Doubler, providing 650 VDC full load from a transformer AC
voltage (Red wires) of about 270 VAC for the HV section. The LV section provides 260 VDC at full
load from a 110 VAC (Yellow wires) winding.
The BIAS supply is a half-wave circuit. It doesn't matter which Blue lead goes to which terminal.
It outputs -50 to -100 VDC into a 30k ohm load (2 mA) from a 100 VAC transformer winding.
The Green leads are the filament power to the radio, and since the tube
filaments operate on AC ...
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Larry Sack wrote:
OK, I've rebuilt my AC-3 and I've studied the schematics and read past posts but still have a
basic question. Are each pair of transformer leads are interchangeable? Meaning does it matter
which red lead goes where? Or blue, yellow, black? I understand it's AC in and out of the
transformer and the schematic shows each pair going through a half-wave rectifier chopping into DC
and the ripple being smoothed by the caps. But, will I be inverting the voltage by getting the
wrong lead much like the bias's blue leads? The green leads must be supplying AC directly to the
radio. How can I tell which is which if there's no reference voltage?
I'm all done with the AC-3 rebuild with Mike Bryce's AC-4R unit. Much thanks to N2FFL for posting
his info on using the AC-4R kit on the AC-3. Now on to renewing some components on my TR-4.
Larry, N8QNM
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