ARD MODEL 230A POWER SUPPLY


Another phase in the amplifier rebuild is now complete.  Thanks to the large chassis I was able to remove the transformer and HV power supply with little effort.  It’s a lot lighter with that monster Peter Dahl hypersil removed.  Only a moderate amount of contortion was required to extricate the power supply assembly through the bottom opening.  The rebuild went pretty straight forward.  Fortunately, power supplies are not incredibly complicated beasts.  The main issue I had was a couple traces came loose from the circuit board as I was de-soldering.  Thankfully, I was able to get them all back down into position when the new components were installed.  The solder is holding them in place.

Grungy bits removed from circuit board.

Grungy bits removed from circuit board.

Components removed were: six 240 uF computer grade electrolytics, twelve 150K 2W resistors, one 1M 2W resistor, and five .01 uF disk caps.  The other components looked to be in pretty good shape.  The board was pretty grungy so I took some time to wipe it all down with alcohol before soldering it back together.  I made only one component substitution.  The original carbon composition resistors were replaced with metal film resistors of the same value and power rating.

The HV power supply is designed to provide 2300 VDC at 1.0 A.  There is a total of 40 uF of capacitance for filtering the DC.  My original problem was the circuit breaker on the chassis and/or the circuit breaker in the sub panel would trip when I powered up the amp.  This would happen either right after the power switch was flipped or as the step-start circuit dropped out.  On occasional times when it didn’t trip, it would run for some time and then trip suddenly.  This was especially annoying!

I’m pleased to report I’ve successfully tested the supply several times now and it seems to be working great.  The meter on the control head shows a steady 2500 VDC.  Initial load testing with low drive (up to 35 W) has provided up to 700 W out into the dummy load.  If everything proves to be linear, as it should be, then I should easily see legal limit with under 100 W drive from the exciter (in this case a Flex-5000A).  This is also without getting Plate and Load caps fully peaked in manual tune mode.

The gear motor drives are not properly synced right now.  They should be turning from 0-180 degrees as shown on the control head indicator.  Right now one is and the other just moves from roughly half-meshed to half-meshed on the other side, never getting fully meshed.  Getting them properly adjusted will be my next project.  This portion will switch from electrical to mechanical technique.  Good thing I do this kind of stuff in the real world!

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