Author Topic: POWER DESIGNS PRECISION POWER SUPPLIES  (Read 369087 times)

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Online F4

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #950 on: December 29, 2024, 11:10:28 am »

I found one problem, but am unable to diagnose the transient I am seeing around what looks like the oven going on and off.

If you find your are out of spec at the 0000 calibration step, investigate R24.  I added 1k in resistance to that location and it brought my readings from +30mv down to +1.2mv. I have dialed that 1.2 down to 0s and am waiting on the unit to stabilize before dialing it in further.

As far as transients, has anyone ever investigated their cause?

This unit had 4 problems, these are the mitigation steps taken. 
1. The failed calibration with R24
2. Too much ripple solved by recapping
3. Voltage drift upwards, this was resolved incrementally from all steps but benefited the most from fix 4.
4. I spent several hours digging into the issue with transient voltages appearing on the output. The supply is supposed to stay stable at .0000, this one was doing that but had a lot of variance past 4 zeros, so 0.0000.001 to 0.0000.999. When the transient appeared it was sending the signal up to 0.0002.xxx every 20 seconds or so, some instances more intense than others. It also continued to voltage drift upwards with 0000 on the dials (no output).

I tested the transistor paths back to the power supply, saw the transients everywhere I put the scope leads:

2471815-0

The transients were even across pins on the power supply itself, which got strange as I thought it was the power supply that was the problem. I tool a look at the schematic again and noticed the heater circuit goes right from the 115v AC source, which maybe explains how the transient was seen everywhere:



Up until here I didn't realize the tap for the oven was at the transformer. I looked at the 2 caps across pins 9-11 on the oven, C9 and C14. I changed both caps and added 2 resistors to form more of a snubber on the feedback.  This worked, I ended up with 270 ohms, 75 ohms, and a 10nf ceramic cap, and 2 x 10nf to make the 20nf cap.

I still get the transient, but after several hours in stable conditions, the transient (from cold start) maxed out at 0.0000.400 versus 0.0002.000, a 5 fold decrease.




In summary, at rest, powered on, the unit is much more stable at 0000s, spends most of its time at 0000.010 or below, and after being stable 12 hours shows only two transients in a 15 minute test exceeded 0000.010, one hit .039 and the other .024.

Moving on to the 20v calibration, hopefully the stability translates there...

Edit: its a 220 ohm resistor, not 270.
« Last Edit: December 29, 2024, 11:49:13 am by F4 »
 

Online F4

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #951 on: January 09, 2025, 10:30:35 pm »
Following up again, I have narrowed the transient mentioned in a previous post down to the thermostat. I figured it was the thermostat or the oven bulb as they were the only things in the path other than the heating element itself. I converted both the power on bulb and oven bulb to LED to eliminate the oven bulb as a root cause.


(Attachment Link)

Monitoring pins 10 and 11 I observed the voltage stay close to 0, and on the scope monitoring the output I see the transient when the thermostat appears to signal for heat, but before the heater jumps to 120v across pins 10 and 11.

I couldnt find a picture of the thermostat anywhere, and eventually decided to open up the oven and see what was servicable. Turns out the thermostat and oven casing look tack welded together, or somehow soldered with the heater unit.  Not servicable.

2479429-0


I was thinking of changing the heating element on the can to one of these:

https://www.amazon.com/Coliao-Adhesive-45mmx100mm-Elements-Polyimide/dp/B0CM6KKHXX/?th=1

My problem is that I am not sure what a simple way would be to get this different heating element to run at a constant temperature from the oven.

Would these work?

https://www.amazon.com/gp/product/B0861C3ZNB/ref=sw_img_1?smid=A1THAZDOWP300U&psc=1

 

Offline PKeithM

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #952 on: January 15, 2025, 11:10:12 pm »
I can add a little history about this company if you are interested at all.
I worked at Power Designs Inc (Westbury NY) summers from 1973 to 1977, while going to school to for my BSEE.

I applied at the start of the summer 1973 to be a repair technician for new (power supplies that failed tests) and returned units.
Even though all I had was electronics in high school (three years), a Ham radio license and a 1st class commercial radio license (I was 18 when I started), the president/owner of the company, Herb Roth (sp?), hired me anyway after a series of interviews with many folks including the Chief Engineer Mischa Vamberg (sp?).  Herb's wife ran the front office. I can credit much of my career to the tutoring I got from Herb and Mischa on practical engineering and especially on feedback circuit design.

 During the week I worked as an assistant to Mischa helping him develop/improve some of the power supplies you folks are talking about and a lot of special project supplies (power supplies for Grumman jets, High Voltage/high current supplies for IBM research, NIM supplies,  and so on). I distinctly remember working on the temperature stability enclosures to improve voltage stability and reduce noise used in many of the supplies. I built hundreds of these as the zener diodes we received had to be selected by hand and then the assemblies were tested over weeks to meet the power supply specs. For some reason the ones I built worked really well and I was rewarded with getting to build a wholes years supply over each summer.

On weekends I worked with Herb at adjacent test benches fixing  supplies that the regular technicians were unable to troubleshoot (or just help him clear the backlog of testing new supplies). There was no scrapping out of spec supplies, we figured every one out.

Herb loved to talk on the weekends, and here is the story he told me how he got the initial money for starting the company.  Apparently, he was a radio technician (or worked with radios) during WW II and many years after the war a whole lot of surplus radio radio equipment was sold for pennies on the dollar and ended up in warehouses located around Canal street in Manhattan. Herb was aware that a certain class of vacuum tubes had grid wires that had a high gold content and he bought thousands of them (every one he could find) for very little money (nobody in the surplus chain realized the gold wire was there). Herb and his wife spent weeks breaking each tube and stripping out the gold wire. They then sold the gold and used the proceeds to start the company.

Herb was focused on exceeding published product specs. As you probably realize, that certain parts in the supplies were selected to meet very tight margins (more than the manufacturer was willing to meet). We had in house  built equipment we used to select the parts. If it survived over time, you would see this as various colored dots (actually cheap nail polish) on parts (mostly semiconductors) that were selected out for a specific set of characteristic depending on use (this varied by supply and even in a single supply). This practice was very prevalent in the higher reference supplies (those with the temp chambers) and the NIM supplies. So while the schematic may call out a part number, the internal documentation would include a specification of the colored dot(s) the part had to have to be used in that specific application.



 

Online rsjsouza

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #953 on: January 17, 2025, 02:46:38 am »
Thank you for the bit of history about the company.

However, are you sure the designers / owners weren't aliens?  ;D The lore in this and other threads about the legendary quality of Power Designs is the following:

As someone else hinted in a past discussion, I am suspicious they were in fact from another planet and graced us with their designs...

Glad someone else believes this, since there is no internet history on them.  If something exists then it will be on the internet.  Since "they" do not exist but their products exist, something must be going on.  A logical explanation is aliens made them for some purpose that we do not know about.  Like help develop something for space flight that will take us to another planet.  Once this theory is proven then the value of these supplies will greatly increase.  I just hope humans will not become a food source like I think about every time I look at my power supply.  God forbid, the PD is not the alien (but just in case I use kind words when I talk to my power supply)
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 
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Online F4

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #954 on: January 19, 2025, 12:08:58 am »
I can add a little history about this company if you are interested at all.
I worked at Power Designs Inc (Westbury NY) summers from 1973 to 1977, while going to school to for my BSEE.

I applied at the start of the summer 1973 to be a repair technician for new (power supplies that failed tests) and returned units.
Even though all I had was electronics in high school (three years), a Ham radio license and a 1st class commercial radio license (I was 18 when I started), the president/owner of the company, Herb Roth (sp?), hired me anyway after a series of interviews with many folks including the Chief Engineer Mischa Vamberg (sp?).  Herb's wife ran the front office. I can credit much of my career to the tutoring I got from Herb and Mischa on practical engineering and especially on feedback circuit design.

 During the week I worked as an assistant to Mischa helping him develop/improve some of the power supplies you folks are talking about and a lot of special project supplies (power supplies for Grumman jets, High Voltage/high current supplies for IBM research, NIM supplies,  and so on). I distinctly remember working on the temperature stability enclosures to improve voltage stability and reduce noise used in many of the supplies. I built hundreds of these as the zener diodes we received had to be selected by hand and then the assemblies were tested over weeks to meet the power supply specs. For some reason the ones I built worked really well and I was rewarded with getting to build a wholes years supply over each summer.

On weekends I worked with Herb at adjacent test benches fixing  supplies that the regular technicians were unable to troubleshoot (or just help him clear the backlog of testing new supplies). There was no scrapping out of spec supplies, we figured every one out.

Herb loved to talk on the weekends, and here is the story he told me how he got the initial money for starting the company.  Apparently, he was a radio technician (or worked with radios) during WW II and many years after the war a whole lot of surplus radio radio equipment was sold for pennies on the dollar and ended up in warehouses located around Canal street in Manhattan. Herb was aware that a certain class of vacuum tubes had grid wires that had a high gold content and he bought thousands of them (every one he could find) for very little money (nobody in the surplus chain realized the gold wire was there). Herb and his wife spent weeks breaking each tube and stripping out the gold wire. They then sold the gold and used the proceeds to start the company.

Herb was focused on exceeding published product specs. As you probably realize, that certain parts in the supplies were selected to meet very tight margins (more than the manufacturer was willing to meet). We had in house  built equipment we used to select the parts. If it survived over time, you would see this as various colored dots (actually cheap nail polish) on parts (mostly semiconductors) that were selected out for a specific set of characteristic depending on use (this varied by supply and even in a single supply). This practice was very prevalent in the higher reference supplies (those with the temp chambers) and the NIM supplies. So while the schematic may call out a part number, the internal documentation would include a specification of the colored dot(s) the part had to have to be used in that specific application.

This was a great read, makes it more meaningful to tinker around with the units. I do indeed have some of those dots inside.

The boards, were they made in house or outsourced?  It's a nice experience soldering with the lugs.

Please do stick around, we'd love to hear more.
 

Offline Melt-O-Tronic

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #955 on: January 20, 2025, 05:40:25 pm »
Please do stick around, we'd love to hear more.
YES, THIS!

Most of us have a lot of older equipment that gives us great service.  These tangible artifacts represent our under-appreciated history of innovation,  People are recognizing that.  But rarely are the records & stories of the design & production evolution of this gear available to those of us who are interested.  There is a lot to be learned for our throwaway society right now about the experiences and genius that went into this gear; gear that paved the way to the successes we enjoy today.
 

Offline mawyatt

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Re: POWER DESIGNS PRECISION POWER SUPPLIES
« Reply #956 on: January 20, 2025, 06:01:16 pm »
Please do stick around, we'd love to hear more.
YES, THIS!

Most of us have a lot of older equipment that gives us great service.  These tangible artifacts represent our under-appreciated history of innovation,  People are recognizing that.  But rarely are the records & stories of the design & production evolution of this gear available to those of us who are interested.  There is a lot to be learned for our throwaway society right now about the experiences and genius that went into this gear; gear that paved the way to the successes we enjoy today.

Agree we tend to forget the great innovations and stories from the past. While an adjunct way back in early 2000s we tried to convince the university while on the Presidents Advisory Board to offer a course on engineering history, unfortunately this fell on deaf ears!!

Much of the great stories like Power Designs soon will be forgotten, hopefully others will come forward with important and interesting historical stories from our past engineering life!!

Best
Curiosity killed the cat, also depleted my wallet!
~Wyatt Labs by Mike~
 
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