The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB

[Ryssen]

WTB: a pair of the prestage pcb`s that fits on the main board.
Dont know if it is 2 or 4 boards.

 

[Kokanee]

Back to round two with the testing of the dual rail slb. Testing is not my forte', so I thought I would attach a pic and see if I am close to what is required.

I have attached 2 alligator clips from the PV and NV output of the slb to a 25 ohm 50W resistor, and, I have a DMM attached to the emitter and collector of SA1943 transistor to measure and adjust DC voltage drop.

I would be thankful for any assistance before continuing.

MM

 

[Kokanee]

X, Anand, Hugh, BMM, others,

Any assistance to offer with the post above 🤔

MM

 

[xrk971]

The simulated load should give you 1A for 25v and 25W load. Looks like it should work.

 

[Kokanee]

Hi X, thanks for the reply. Rather than have the PVout and NVout connected to the 50W resistor, should I connect the PVout or NVout and a ground to the 50W resistor and test each side separately. Trying to baby step things and learn at same time.
Note: destroyed an LT3420 and had to replace, so proceeding cautiously🤔

MM

 

[xrk971]

Indeed, testing each side independently is better to isolate problem if one side is not working. Just check to see if it makes voltage with no load first. There should be a 1-3v drop across the 2SA1943 or 2SC5200 transistor.

 

[Kokanee]

I finished rebuilding one of my dual rail SLB's. I performed a no load test and a load test into a 25ohm/50W resistor. I tested each polarity separately with DMM set on Vdc. The results are as follows:

PV: 30.9V no load, variac at 115V
28.2V under load
Ve-c on SA1943 is 0.96V. Trim pot has no effect
25ohm/50W resistor is nice and warm.

NV: -29.5V no load, variac at 115V
-27V under load
Ve-c on SC5200 is 2.45V
25ohm/50W resistor is nice and warm

Given these results it seems that I am getting the voltage drops expected, and I am thinking that the SA1943 maybe defective. Any advice on this would be greatly appreciated.

Regards,
MM

 

[xrk971]

Looks like it is working properly - test with the amp and see how it works.

 

[Kokanee]

X, thanks for the quick reply. I am concerned about the fact that the Ve-c on the SA1943 is only 0.96V, when expecting over 2+ volts like on the SC5200. Also that the pot had no effect on the voltage.

Am I faulty in my reasoning? 🤔

MM

 

[xrk971]

I missed the fact that there was only 1v drop but I know the trim pot doesn’t do much but should be overall closer to 3v. Have you tested that transistor in a tester? With it disconnected from the circuit, measure resistance between the pins. It should never appear shorted (under a few ohms).

 

[Kokanee]

Thanks X,
I did test them with my cheap tester before installing. I blew a fuse along the way by letting the alligator clips touch each other during a power test (now I tape them apart so they do not move). Not sure if it harmed anything.

I think I will desolder the transistor from the flying leads and test with the cheap tester and my DMM. If faulty, I have another one on hand that can be used.
Regards,
MM

 

[Kokanee]

OK did some transistor testing on both the 2SA1943 transistor I used and a brand new 2SA1943 transistor. I also tested both on 2 DMM's I have and a cheap transistor tester.

Transistor tester:
Used 1943: hfe = 96 and Uf = 554mV
New 1943: hfe = 127 and Uf = 546mV

DMM#1 has resistance test max of 4Mohm
Used 1943 and the New 1943 both had OL readings on all resistance measurements using DMM#1

DMM#2 has resistance test max of 40Mohm
Used 1943: 11.8Mohm base - collector, 12.7Mohm base - emitter, OL collector - emitter

New 1943: 12.5Mohm base - collector, 13.1Mohm base - emitter, OL collector - emitter

Plans are to use the new 2SA1943 and keep the used one as a spare, unless there is wisdom that says I should not.

Thanks in advance for any comments,

MM

 

[xrk971]

It sounds like nothing was wrong with the BJT.

 

[Kokanee]

Seems so X, I soldered up leads to the new one and checked continuity with the board. All OK.

After I test this SLB, I think I will work on the other SLB and get it working. Then I will see what happens when hooked up to the amp boards.
Thanks again for the help.

 

[kurand]

Quick question showing my naivety: why are the two areas marked on the schematic below shown containing two connected parallel lines rather than just a single line? Did I miss something?

 

[Mark Johnson]

Mentally insert a new resistor "Rxxx" where the tiny vertical shorting bar is drawn. Now ask yourself which branches of the tree of interconnections, carry very large currents. And which branches of the tree carry very small currents. Does that provide any insight?

 

[kurand]

sure, no problems. its kind on unusual to show that on a schematics especially when the actual pcb layout compacts it down anyway (e.g., c15, c16, c17 & c18).

 

[vanofmonks]

Is there an eta for the dual rail board being back in stock?

 

[Kokanee]

X, AKSA, other's

I am going to put my SLB's and my AN39 build on the shelf for awhile and I am moving on to some other amp / preamp projects that require attention. After receiving the correct transformers with the 22V secondaries, I retested the one SLB that was only giving a drop of 1.0V on the SA1943 under load. The measurements are the same, 1.0V drop on the SA1943 and 2.5V drop on the SC5200.

One quote from X got me thinking I may be analyzing this wrong:

" There should be a 1-3v drop across the 2SA1943 or 2SC5200 transistor."

Does this above quote imply that the 1-3V drop does not have to occur on both transistors. only one of them. ?

Thanks for the help

MM

 

[AKSA]

No Myles,
Both regulating transistors npn and pnp should drop an equal voltage, preferably 2-3 volts from emitter to collector.
Keep on trucking, you are nearly there!
Hugh