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Old 02-23-2018, 8:29 PM
RFI-EMI-GUY's Avatar
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Join Date: Dec 2013
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Originally Posted by RFI-EMI-GUY View Post
My friend has a Hammond toroidial transformer with 15V secondary on order. Hopefully this will drop in and work properly. Not an inexpensive part.

The R71 has a laminated transformer with slightly lower voltage and If I recall the VA rating is lower. A lot more going on in an R7000 logic wise.

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Just a follow up. the Hammond 1182J15 30VA 2 x 117 VAC primary and 2 X 15 VAC secondary was the trick. The dual primary and secondary windings must both be used. The radio is a #2 North American model so the transformer being replaced comports to that version.

The transformer is available from either Mouser or Digikey and will set you back about $40-45, which is not bad since these receivers still command $350 on the used market and they are well worth it.

Before letting the cost turn you off and go to an external supply, this transformer runs much cooler than the original one.


The secondary's are paralleled together in pairs soldered together at the D1 rectifier bridge.

Connection 1) Red plus Grey and

Connection 2) Blue Plus Yellow .

The primaries are connected as follows

Old wires = New wires

White = Black
Orange = White
Blue = Brown
Brown = Orange

Yellow = No Connection (Was 100V Tap)
Grey = No Connection (Was 100V Tap)

If you wire like this, you still will have ability to tap either a 117 VAC or 234 VAC mains voltage. The 100 VAC mains voltage option is lost.

I made some drawings for this modification and if there is interest I will put them up on the web for future. I basically walked my freind through this. He is pretty technically savvy but was a bit surprised at all the wires, the lack of an OEM transformer or specs from ICOM for a replacement. He reports the radio is working fine and operating much cooler. So it seems the originals were not very efficient. Hammond says that a slow blow fuse might be required due to higher in rush currents. My freind had a SB on hand but did not report he had to change from a FB fuse. So I would default to FB in the event that works for you.

The 4 bolt mounting base from the original transformer was salvaged and a hole drilled into its center to mount the toroid with Hammond furnished hardware. So you don't need to cobble up the radio by drilling a hole in the chassis.
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