# 0-30v and 0-6v power supply schematic?

#### PrincessWoona

Joined Nov 30, 2015
53

ak

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#### PrincessWoona

Joined Nov 30, 2015
53
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).

#### dl324

Joined Mar 30, 2015
12,238
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.

#### ISB123

Joined May 21, 2014
1,236
I'll post a circuit later today or very early tomorrow.Do you have a budget for the project?

#### AnalogKid

Joined Aug 1, 2013
8,806
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

#### dl324

Joined Mar 30, 2015
12,238
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.

#### dl324

Joined Mar 30, 2015
12,238
Nonlinearity isn't pronounced for the values involved:

#### PrincessWoona

Joined Nov 30, 2015
53
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.

#### spinnaker

Joined Oct 29, 2009
7,835
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.

#### dl324

Joined Mar 30, 2015
12,238
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?

#### dl324

Joined Mar 30, 2015
12,238
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.

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#### AnalogKid

Joined Aug 1, 2013
8,806
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