Sir Mark. . . .




Here's about all I know or can find out about it . . . with no "freebie" schema to be had currently:


EICO Model 1020 Power Supply

Provides continuously variable 0-30 vdc.

Full-wave silicon diode rectifiers. Fused primary.

Current range: 150ma from 0-12v ---200ma from 12-24v --- 300ma from 24-30v

Voltmeter range: 0-6, 0-30 v . . . Max ripple at full load: .005%

Cabinet Size: (HWD) 5" X 4" X 5 1/2" . . . Weight: 4 lbs

$19.95 (1962) $25.95 (1970)


With the units current spec's, I'm xpecting it only requiring but a single series pass transistor, it being inserted between the main power supply raw DC supply and the DC output treminal.


That power device unit probably being in a diamond shaped TO-3 housing and mounted on its heat sink. Probably an additional
lower powered transistor being tied in via darlington configuration to its base circuitry.

The most suspect might be that main power pass transistor itself , since, after all, it WAS of the "geranium" based transistor technology. Being subject to leakage or possibly even having "crashed" and having Coll-Emitter continuity. That would give your present symptoms.

Also some where down there in the regulator initialization portion, there should be a Zener diode reference to be compared against a feedback sample from the units final DC output level,

Therein, the two values are compared against WHAT your control setting mandated as being your desired output voltage, and the degree of base drive . . .or diminishment . . .is then fed to the Power pass transistor, which then corrects to that desired level.

If this was using an NPN as the pass transistor, its quite foward in its circuit design, main power supply feeds into collector of power pass transistor, base regulates to required output voltage, emitter output is the regulated voltage source then presented to the power supply + output terminal .

WITH it using a PNP transistor, the circuitry most probably is the rectified and filtered power supply feeding directly to being the actual power supply output at its + output terminal,

HOWEVER, the return negative leg terminal of the power supply is fed to the collector of the PNP power pass transistor and then the base receives its corrective drive to determine the degree of conduction from collector-emitter, with that Pass transistors emitter being connected to the negative buss of the power supply. You might say its a vairiable grounding agent of the power supply.


Try this testing first:


In order to enact an evaluaton of that 30 VDC now present on the power supply, take a separate metering and measure the DC level present. Next you load down the supply with a 100 ohm 10 watt resistor and see what the reading is then, jot down, then you lift the load and locate an ~1ufd. . . .upwards is ok. . .at 50VDC + rating capacitor. . . NON ELECTROLYTIC TYPE,(NO leakage wanted) and use it to series couple from the power supplys + output, to your meters + probe.

Then you switch the metering to its AC mode, switch on the power supply as it was, use the 100 ohm load resistor and NOW you see what the meters AC reading is. What we are wanting to know is the health of the filtering of the power supply,

If you are now getting a healthy reading of ripple under load, that alone can be the problem with the regulation circuitry not functioning as it should.

Sir Mark . . . .




Praise be. . . . to The Right Honorable and Esteemed. . . .Bob Zeeeeeeee. . . . in his coming up with the 1020 schema, no more stabbing at the circuit design, and looks like you also don't have to parts trace and reverse engineer a schema. . . . even though it's a quite simple circuit.



In consulting the attached schema we are seeing the designers / draftsmen dead set on having to see the placing of the active elements at the top of the schema, thus having to revert to the placement of the B+ buss at the very bottom of the schema.

The first thing that I am going to point out is the number of "2" derivative resistive parts, since you did mention the
22 k resistor , and the eventual trimming it down in value via a shunting 1K resistor and its desired effect of further reducing
the power supplys attainable lower voltage range, downwardly.

If this was a kit, we can see the two 220 ohm values and the 2k and the 22k values, all of which could be subject to possible error in their installation. I would think that the like functioning and positionally placed 220 values ended up being installed in their proper places.



That would only leave the 2K and the 22 K to be in error, if the 2k. . .R4. . ended up installed in place of the R2 neon pilot lights current limiting resistor, they would have had one VEWY BRIGHT pilot light for as long as the two components would hold up to it.



NOW if the resultant 22k resistor ended up installed in R4's position, that could certainly produce your present situation.
If built as a kit, this malfunctioning unit might have been abandoned, since most users would be wanting the presently unattainable , popular 15-12-9 -6 and 5 volt ranges from the power supply.



Here is an analysis of the power supply's complete circuitry operation, should you, or any others, need it in the future.

Start with the dirivation of the raw B+ supply of the set obtained fom the T1 seconary and its CT tapped winding feeding CR1 -CR2
configured as a Full Wave Rectifier combo then the addition of C2 for the primary filtering, that then leaves you with one raw DC supply with its positive lead zipping right across the schema bottom [Red Mark-up Buss], to end up as the main B+ terminal of the supply. It would then be wanting to feed your load that is connected across the power supply and then complete its power loop by flowing thru the top [Broken Black Mark-up Buss] to the Raw B- Buss source.

Some hindrances now present themselves in that loop, in the form of series arranged TR-1 and TR-2, they will have to be conducting in order for that closed power loop condition to be met, and their degree of conduction will also be establishing the voltage present at the power supplys output terminals.



Here is how that is accomplished:



Note that the first circuitry to be met by the output of the raw DC supply is a series voltage divider bridge that is consisting of R3--R1A--R4.

Now, of the three, R1 A is the variable element while R3 and R4 are scaling resistors that establish the desired limits of the voltage adjustment range. The R1-A wipers sample is fed to the base of TR1 and will adjust the conduction of that transistor along with the produced voltage output created at the emitter of that transistor.


NO EXTRA CHARGE ! . . .there is an additional effect created within that stage , note that there is C3 filter capacitor and its 300 ufd value, with it being placed on the base circuitry of that stage , if there is any power supply ripple present at that point., the end effect is that ripple is reduced on the pass thru output at its emitter. That is what is called a capacitance multiplier stage. . .in addition to its other functions as a series conductive stage and a regulator stage. That 300 ufd on that base is producing the filtering equivalency of one having shunted a 1500 ufd capacitor across the power supply from reference points [C] to [B].

Its roughly the 300 ufd times the Beta / gain of the transistor, and on your old 2N256, at its max current consumption involved, would be in the order of 5 X 300 ufd = 1500 ufd .

The voltage level set by the R1-A pot will then be present across the [C]-[B] test points and THEN find ITS level being sampled in the same manner via R1-B pot with its sample at the wiper being introduced to TR2's base circuit, same proceuure again with a 300 ufd across its base, by virtue of the same capacitive multiplier effect , its producing the equivalency of there being a 1500 ufd capacitor across the [B]-[D] test points. By this time you can see the only need for further filtering, solely being the placement of a small 50 ufd C5 unit right across the output terminals for decoupling and low frequency bypassing.



That brings up another aspect mentioned in the documentation for this unit. . .it is specified as a Power Supply AND Bias Supply, the qualifier there being the BIAS aspect, on connecting this supply into the grid circuitry of a receiver, one certainly doesn't want any introduced ripple or trash to be potentially amplified. I initially had given the specs for the unit and even at that time was noting that particularly impressive spec, even though I was additionally noting the units quite bucolic 300 ma max current spec.



Sooooo. . . that should fill you in on the two series connected transistors and their manner of varying their conductance to establish the voltage output on the unit by the degree of isolation provided between the power supplys negative return terminal and the raw B- buss.


Therein. . .R1-A control provides the "Coarse" voltage adjustment and then R1-B provides the "Fine" degree of adjustment.


Of the TR-1 and TR-2 transistors, TR-1 is the most critical on leakage having adverse controlling or range affectation, so the lowest leakage of the two should be used for the TR-1 position should a problem arise on attainable range.

In your case we know that the R3-R5-R6 loop seems to be presently fine in the attaining your max output voltage, via max conduction of the pass transistors, but failure to reach a lower voltage limit , in addition to the above transistor leakage aspect, would be for R4 to be yet a lower value.



Thats it for now. . ..feed back time. . . .




73's de Edd