Integration shunt regulator voltage check

[kjwcb2]

Hi guys, wondered if I could run a couple of test figures by you. The Integration manual quotes figures of 110-120VDC on the metal tabs of the MJE5731's and around 130V on terminal 56 for the shunt regulator voltage check. Mine are 118.2 on the MJE5731's and 118.6 on terminal 56, but that's from approx. 230VAC mains power. How do they look to you? The voltage at the transistors is pretty close, but the terminal 56 reading is a bit low? Good to go or good to blow?
Thanks for any help - much appreciated

[Paul Birkeland]

What DC voltage do you get at terminal 50?

We want to see a bit of a voltage difference between the tabs of the MJE5731A and terminal 56.  Checking the voltage at terminal 50 will let me calculate how much current is being drawn through your power supply.

Also, what is your exact mains voltage?

[kjwcb2]

Hi Paul. Voltage at terminal 50 fluctuates but is 130V give or take. The reading at 56 is 112.5 now. Mains voltage reads about 217.5 at the moment. This is Greece. The voltage is all over the place :-(.

[Paul Birkeland]

217V just isn't enough for the circuit to work properly.  There are a few ways that we can help you tweak things to work properly.  One would be to get a small 220:240 step-up transformer and use that in front of the Reduction.  Another option would be to substitute a couple of chokes for the power supply dropping resistors to increase the available B+ voltage for the regulator.

The expensive but best option would be to use an AC regenerator, but I can totally understand if that's not an option.

[kjwcb2]

Ah. The Reduction seemed to work fine with the existing voltage, but maybe the upgrade is more demanding. I must admit I'm no expert when it comes to electronics. Looking at ebay, I can see a lot of Chinese 110-220V step-ups, and I found a Goldsource automatic voltage regulator which can regulate input voltage from AC 75V-130V or 180V-260V to output voltage: AC 110V+-4-percent or AC220V+-4-percent. Not sure if something like that would suffice. What is the minimum stable voltage that I need to run the upgraded pre-amp?

[Paul Birkeland]

Yes, the Integration is going to work much better with some extra line voltage. 

Here is an example of an autoformer that would work for what you need to do:
https://www.foster-transformer.com/product.aspx?GUID=e3ede396-dc23-43de-a42b-d0896abbf3cf

Your incoming AC connects to the 0 and 220V connections and the output connects to the 0V and 230V connections. I would not recommend using the 240V connection unless you plan to connect more devices, as the 1500VA rating means that 220V coming in will make more than 230V on the 230V tap.

As far as how to actually do this safely, there is some enormous convenience with this unit because it has wire leads.  You can take a spare power cord and cut it in half, strip the big jacket and small wire jackets off, then solder and heat shrink it to the transformer leads.  Though I can't see the datasheet for the autoformer, there is likely a ground wire that should be connected to the ground lead on your power cord.  If such a wire is not present, I would use a machine screw, nut, and solder lug to add one to one of the mounting legs of the autoformer.

-PB

[kjwcb2]

Thanks for all your help PB. I really appreciate it. I checked the link but they want $256 to ship it to Greece, so no! I've taken new readings, this time at the point where the device will actually be connected rather than my kitchen where I've been assembling the upgrade (yes, why didn't I do this in the beginning?). They are: Mains: 228VAC / MJE5731 tabs: 110/109.0 / Terminal 56: 123VDC / Terminal 50: 142VDC. These look a bit better don't you think?

[Paul Birkeland]

Those are proper voltages.  That shipping price, however, is not so proper!

-PB

[kjwcb2]

Excellent to hear that the voltage readings are finally proper. Yes, I was shocked at the shipping price. That was the cheap option too! there was a higher shipping cost at around $280. Almost cheaper to fly over and pick it up in person! Thanks again for your invaluable help and advice. Very much appreciated.