Pharmicia EPS500/400 Power supply - tube use - diyAudio
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Old 4th April 2009, 07:36 PM   #1
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Default Pharmicia EPS500/400 Power supply - tube use

After seeing a thread here where someone picked up a cheap Electrophoresis power supply to use as a HV supply for tube work. I did an eBay search and found a local seller that had a pair of Pharmacia EPS500/400 power supplies for a VERY reasonable price. these are 0-500Vdc 0-400ma supplies. I picked up a pair for $40 not a bad buy.

These have some cool features and one things are digital displays for V and I and a set limit for each. I like the current limit. might come in handy to save a tube in a project should a clip lead pop off or something.

When i first got the units. I thought they had a problem. they have a front panel HV on/off switch. and when you would switch the HV on, the display would read EEE and no HV came out. but interestingly. 12V appeared at the output terminals. Suspecting that this was some sort of load check. I connected a 120v 7 watt light bulb and cranked the V down to 100V and flipped the switch and flash the bulb light up bright then settled down at 100V. so the supply works!

But there in lies the one if not 2 problems with this model of supply. No matter what voltage you set the control too. when the HV comes on, it spikes and then settles to the voltage you have set on the controls. the only way around this i have been able to find is to set the Voltage control to zero, flip the HV on and then raise the Voltage. then no spike and everything is grand. but kind of a pain.

The 2nd thing. which is a minor issue is that, without a load, or a load of a certain resistance. no HV. a resistor across the terminals should fix that issue. i just need to determine the minimum value to get the supply to come on.

The bulb flash/spike may also be related to the light bulb resistance changing as the filament begins to glow i don't know. I will have to experiment with it a bit.

Web research turned up very very little info on these. pharmacia was bought by pfizer and then merged with GE and split and several generations after the fact, the brand has sort of become lost. after a few phone calls i was able to get in touch with a service division of GE that sounded promising at first. they were aware of the model. but apparently they don't keep any sort of info on non current products.

opening the unit i see it is a switching supply with a TDA-1060 controller chip at heart. the TDA1060 is supposed to have a soft start function so im curious now if the spike at HV turn on is a planned thing for Electrophoresis work?? Kind of a drag to have the thing spike at 400-500 volts when you hit the switch.

If i can get around that spike issue. then these will be some really nice cheap supplies for tube experimenting. the output seems to be very clean and well regulated from what i could see in my initial test's.

I'm curious if anyone else has played with this model???
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Old 9th April 2009, 11:28 PM   #2
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Have you made any progress? I have a couple of the same units, with the same problems and then some. When I hook the power supply up to the tube amp, the "voltage leakage" light comes on.

Needless to say, the amp will not work.

Any insights/advice/possibilities?

Thanks in advance.
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Old 14th April 2009, 05:57 AM   #3
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I have not had time to work on these again. But if you find the TDA1060 IC inside and connect a switch between Pins 2 and 10 you can then manually turn the HV supply on and off. Goolge the data sheet and there is a note about the enable pin that states this. But this still doesn't get around the spike issue. you have to turn the voltage control to zero. not -0 or -1 but 0 and then it wont spike, you can then raise the voltage control up to whatever and everything is ok.

I will try and get back to this later this week.
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Old 20th April 2009, 07:10 AM   #4
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I did some testing and what i found is that the output of the supply is bipolar with respect to ground. If you set the supply to 100V, you will have 100Vdc across the terminals, but you will also have +/-50vdc with respect to chassis ground.

I have one of these torn apart. I will see if i can trace the secondary side and post it here. maybe we can come up with a solution.
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Old 22nd April 2009, 05:36 PM   #5
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well I managed to draw out the output side of the power supply for this thing last night. but ran out of time to put in the values.
Attached Files
File Type: pdf drawing1 model (1).pdf (5.9 KB, 49 views)
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Old 22nd April 2009, 05:56 PM   #6
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Looking at the 5 control lines from top to bottom. I suspect that the first line is where they inject 12V to the output terminal. this is how they sense if a load is connected.

Line 2 is at the junction of 2 resistors forming a voltage divider. they must be sensing output voltage at this pount.

Line 3 is grounded to the chassis.

Lines 4-5 im not sure what they are doing here. The resistor in series with the two diodes is a large 2-3 watt wirewound type. The diodes are small. possible zeners? maybe that is a V-reg stage with voltage monitoring?? or maybe this is how they are monitoring the output current??

The control circuits run off there own supply and get powered up right away. and the switcher stage doesn't even turn on until you flip the HV switch.

By connecting pin 2 to pin 10 of the TDA1060 controller IC you can manually enable the supply bypassing all the safety features such as the leak detection. But now that we know this is a bipolar supply, connecting the -side to the ground of anything is not a good idea.

Some reconfiguring of the output side of this supply is going to be necessary it seems to be able to use this up to +500V

by jumping pin 2-10 and adding a ground jack on the front you can turn these into a +/- 250vdc supply.

or if we can reconfigure the monitoring and control lines and change the ground point of the output stage and wire the two halves in series.....

I will work on getting the values put into the drawing. I am not going to draw out the control side. too much work. but maybe research where those 5 lines go and maybe we can deduct some info from that....
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