I'm looking to build a 0-30v and 0-6v power supply in place of an old Eico transistorized power supply model 1020. This ones bad in that there sparking in a potentiometer and half of one range is dead. And the two 94004 transistors(must be bad) at $30 a pop really make me feel like making it a reliable modern supply. It doesn't have to be much current but simple, cheap and effective. I don't have enough experience in electronics to be able to design circuits. I can barely read a schematic! Any help is appreciated. Thanks

Mod Note: Reduced image file sizes to accommodate slower connections.

 

What's purpose of the power supply?
0 ~30V.

Or using LM317 plus 2N3055 to increasing the current, it's easy to get the schematic from google.

 

You should be able to make substitutions for the transistors if you decide you want to repair. If you could trace the existing circuit and make a schematic, many here will be able to help.

If you want to start over, you should decide on what current you require and whether you really need a 0-30V range. If 1.25V min is okay, you can use an LM317 as Scott mentioned.

 

You should be able to make substitutions for the transistors if you decide you want to repair. If you could trace the existing circuit and make a schematic, many here will be able to help.

If you want to start over, you should decide on what current you require and whether you really need a 0-30V range. If 1.25V min is okay, you can use an LM317 as Scott mentioned.

I'm going to post a picture of the schematic for this currently. The original is 0-30v or 0-6v 300ma max. I don't think I'll need more then 1amp max if I did a new circuit. I'll probably just use it mainly for testing vacuum tubes heaters without having to use a variac(hard to get precise values). I wanted the 0-30v and 0-6v ranges because of the original volt meter. But just a 0-30v range would work.

Also I stole the power cord off of this for use in my zenith console(12H090). Needed a new cord but I wanted a vintage cord. This can just get a new modern style cord for all I care.

Mod EDIT: Reduced image file size.

 

There isn't much that could go wrong with that power supply; but there's not much good about it either. If you wanted to repair, you'd probably only need a new potentiometer and a couple power PNP transistors.

If you want a power supply to provide 1A, you'll need a different transformer. Having a 6V and a 30V range isn't an issue, but if you really need it to adjust to 0V, I don't know of any voltage regulators (offhand) that will adjust to zero. If 1.25V minimum works, you can use LM317 and a power PNP transistor.

What will you be using the power supply for? Anything that requires a well regulated supply (which the Eico doesn't appear to have been)?

 

There are plenty of LM317 power supply projects out there. That would be the easiest why to go.

Here is one http://www.ladyada.net/library/equipt/diypsupp.html.

Edit: You won't get this supply to got to zero, 1.25V maybe (as mentioned above).


I built my own supply when I started. Even added an LCD panel to display voltage. It all worked great but quickly bought a supply. Mine came from Circuit Specialists and I was very happy with the price and features.

 

Get a kit on ebay ready made or self assembly, and put it into the psu case using the meter.


http://m.ebay.com/sch/i.html?isRefine=true&_pgn=1&_nkw=Lm317+kit&_sop=15

 

Do you really need it to go to 0V ?I doubt that people ever go under 1.5V.

 

Nice job posting the schematic; you saved many electrons from a horrible fate.

You've probably gotten the message by now that contemporary adjustable 3-terminal regulators do no regulate down to zero volts output. Separate from that, you can substitute 2N2955 PNP power transistors for the original parts at considerable savings.

The kit has many parts you don't need, but for $2 and free shipping it is an excellent way to go. Note that in the original design the range switch adjusts the meter only; it does not shift the adjustability of the pot. Spray contact cleaner might resurrect the switch, or you can find a replacement at any distributor (and ebay).

ak

 

Nice job posting the schematic; you saved many electrons from a horrible fate.

You've probably gotten the message by now hat contemporary adjustable 3-terminal regulators do no regulate down to zero volts output. Separate from that, you can substitute 2N2955 PNP power transistors for the original parts at considerable savings.

The kit has many parts you don't need, but for $2 and free shipping it is an excellent way to go. Note that in the original design the range switch adjusts the meter only; it does not shift the adjustability of the pot. Spray contact cleaner might resurrect the switch, or you can find a replacement at any distributor (and ebay).

ak

I don't need it to go to zero volts. That's just the range I used. A 30v and 6v range were what I was looking for. As for the potentiometer I think the one is dead. There are two and the power switch in one assembly but one has considerable sparking in it. And magic smoke. I tried cleaning it many many many times with contact and control cleaner. No fixing that issue. I'm trying to find the right schematic one online to put in it. I found a few but all seem to be 5amps. I don't need that much. For the most part I'll probably just it to test vacuum tubes heaters. No more than a amp needed. I don't have a tube tester so for them making sure the heaters working right at voltage is a start to knowing if a tube works(but it won't tell me if ones worn out on the cathode. Please don't restate that).

 

Here's a basic LM317 circuit:

To get to 30V, you'd need to decrease R1 to around 200Ω. To actually limit the voltage on the 6V range, you could switch in a different pot; 1K would give you 7.5V. Lowest output is 1.25V.

With sufficient heatsinking, LM317T will provide 1A; or you could add an external power transistor.

For more info, check the datasheet; National Semiconductors will probably be the most informative.

 

I'll post a circuit later today or very early tomorrow.Do you have a budget for the project?

 

HTo actually limit the voltage on the 6V range, you could switch in a different pot ...

Or switch a resistor in parallel with the pot.

An LM317 is rated for 1.5 A output current. An LM350 is rated for 3 A output current. One thing you need to know in advance is the peak voltage across capacitor C2 with no load on the supply.

As noted above, the switch does *not* change the output voltage range; it only changes the range of values that can be displayed on the meter. To make it a true range switch with improved adjustability on the lower range, change to a DPST switch; one pole shifts the meter range and one pole shifts the adjustment range.

Also, for any new circuit you will need only a single-gang pot (plus the AC power switch), a much easier thing to find as a catalog standard part.

ak

 

Or switch a resistor in parallel with the pot.

That would make more sense, but doing that will affect adjust linearity. I've done that before to increase adjust sensitivity on one end of the range.

 

Nonlinearity isn't pronounced for the values involved:

 

Or switch a resistor in parallel with the pot.

An LM317 is rated for 1.5 A output current. An LM350 is rated for 3 A output current. One thing you need to know in advance is the peak voltage across capacitor C2 with no load on the supply.

As noted above, the switch does *not* change the output voltage range; it only changes the range of values that can be displayed on the meter. To make it a true range switch with improved adjustability on the lower range, change to a DPST switch; one pole shifts the meter range and one pole shifts the adjustment range.

Also, for any new circuit you will need only a single-gang pot (plus the AC power switch), a much easier thing to find as a catalog standard part.

ak

So I may get the lm350 just so I don't have to worry about a heat sink as much. As for the transformer, I got a problem. I can't find any 30v transformers that output enough current. All I find is expensive or too low. What shall I do? As for a budget I don't really have one. I don't have much money so the cheaper the better.

 

What is wrong with the transformer in the current power supply?

The LM350 is rated at 3A with heat sink. It would be a good practice to add one even if you don't push it that far.

 

So I may get the lm350 just so I don't have to worry about a heat sink as much.

Both parts will dissipate the same power and require adequate heat sinking. Both parts have built-in thermal protection and will throttle without it.

As for the transformer, I got a problem. I can't find any 30v transformers that output enough current. All I find is expensive or too low. What shall I do? As for a budget I don't really have one. I don't have much money so the cheaper the better.

Any surplus stores in your area?

 

Nonlinearity isn't pronounced for the values involved:

Nonlinearity is pronounced if I get the spreadsheet right...

First half of adjustment range gives deltaV of 3.25V, last half gives 1V.

 

So I may get the lm350 just so I don't have to worry about a heat sink as much.

Watts is watts. At 1 A output current and the same input voltage, the 317 and 350 will dissipate exactly the same power and need the same heatsinking. The advantage of the 350 is that if you have adequate heat removal it can pass a greater sustained output current.

I thought the goal of this project was to keep the EICO framework and replace the regulator.

ak