Sunday, May 25, 2014

N7ART Audrey II 432MHz Amplifier 240V Conversion

A week ago I was taking stock of my 432MHz amplifier collection. The one I had used the most was the N7ART Audrey II 2x3CX800A7 amplifier I bought 20 years ago. Steve made a wonderful job of building the amplifiers as the pictures below show. Unfortunately the PA was wired for 110V so couldn't be used in the UK. The 2600V PSU was not an issue as it was wired for 240V. It was time to investigate what would be needed for conversion.

Luckily I still had the original Documents in which Steve gives the part numbers for the 240V components used in his 240V version. The relay supply transformer in the amplifier (Triad FD-4-12) was already dual voltage primary so did not need changing. The heater transformer was a Stancor P8857 which being 115V only primary would need changing to a Triad FD-7-16 which would also mean changing the resistor in series with its primary from 20ohm 20W to 150 ohm 20W. The blower was a Dayton 4C446 115V 50/60Hz which would need changing to a Dayton 2C915 230V 50/60Hz. The search was on
The Dayton 2C915 is no longer made but I found an equivalent on ebay for $68. Mouser had the FD-7-16, but on 4 week delivery but someone had one on ebay at $10 shipped, so both were bought along with a 150 ohm 30W resistor from the local emporium
This weekend the components were installed. The blower had a different shaped outlet flange so some chassis filing was needed but fitted otherwise. The new transformer had different fixing centres which needed to be drilled along with the mounting holes for the new resistor.
Top View of amplifier after modification
Bottom View of amplifier after modification
  The amplifier is now ready to go on UK mains!

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