Homebrew Power Supply

Discussion in 'The Projects Forum' started by Cadmandu, Nov 16, 2014.

  1. Cadmandu

    Thread Starter New Member

    May 27, 2013
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    Hi All,
    I built a power supply with a bucking transformer to get the AC filament voltage down, it is measuring 6.4 vac and the rectified DC is 312 vdc. Here is what I built the power supply is for the BC-1A Heatkit Tuner. Here is what has me confused. The output of the 6X4 rectifier is going through a 1K 2 watt resistor and then off to the rf amp, then it goes through a 10K 1 watt and off to the audio amp. I am reading 312 vdc at all three points, before the first resistor in the middle and at the end of the string. I thought that these were voltage dividers and that they should be dropping the voltage by some small amount. I do not have the supply under any load. Please advise. The ac HV is 446 ac before rectification.
    Thank you test bed small.jpg test bed small.jpg bc-1a.gif
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    By simple Ohms Law, if the current through the 1K and 10K resistors is zero (you said the supply is unloaded), then the voltage drop across the resistors will be zero, therefore the same B+ will occur at all three filter capacitors...

    The progressive voltage drops would only be valid if the various stages connected to the supply are drawing their nominal design current...
     
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  3. Cadmandu

    Thread Starter New Member

    May 27, 2013
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    Thanks Mike, I thought that the resistors were a type of load and that I should find a voltage drop across them. What you said makes perfect sense. I was hoping that I would find the correct voltages after hooking up the tuned RF amp and audio sections. Nice plane and thanks again.
    Dan tuner2.jpg
     
  4. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    762
    Resistors are the most common load. Point is that if you do not have current flowing thru them no drop would happen.

    Are you relaying on resistors to ensure the proper feeding voltage for other stages?
     
  5. Cadmandu

    Thread Starter New Member

    May 27, 2013
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    photo 3.JPG photo 4.JPG Well to tell you the truth I have no idea what I am doing, that was probably already known. According to the test voltages sheet I am to have a reading of 220 vdc at the plate of the 6BA^ RF amp and 145 vdc at pin 6 of the 12AU7 audio amp. I assumed that the 1K and 10K formed a voltage divider and the 470 ohm resistor at the plate of the RF tube dropped the voltage down to the 220 that I am suppose to read from the plate to chassis. And the and the 1K and 10K would drop the voltage to 145 for the pin 6 on the 12AU7 audio.
    Thanks Dan
     
  6. BigD61

    New Member

    Nov 8, 2014
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    The voltage at the plate of these tubes depends on the plate current through the tubes. The plate voltage being common suggest they are not conducting. Either they are in cutoff state due to high grid bias (negative) or they are all defective. Check pin 1 of RF amp, be sure you are using a high impedance voltmeter >10meg. Negative dc greater than 5 volts could be the cause. Your power supply B+ is something like 24% high. 312 vs 230 (max at 6X4) It has been a long time since I worked with valves, I thinking higher voltage would lower the tube life, circuit should still work and cause high plate current effecting the power across the various series resistors.
     
  7. Cadmandu

    Thread Starter New Member

    May 27, 2013
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    Welcome to the forum, how many servos do you have in the D61? Did u build it? The 312 vdc is a measured voltage with no load. I have 446 vac coming out of the HV secondary and this is the actual transformer that was in the BC-1A. I would like to check the ripple that is left in my rectified and filtered supply. What do I have to do to run this into my 5441 Tek Scope. Do I need to buy or build an attenuator, or buy a special HV probe. Also, do the three caps all equally filter the output or does the first do 75% and the 2nd do 15% and the third do the rest.
    Thanks Dan W3DKY
     
  8. BigD61

    New Member

    Nov 8, 2014
    20
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    The plane is/was a Great Planes Ryan STA, Servos used were standard Futuba S3004, 2 elevator, 2 aileron, 1 rudder & 1 throttle. I did not built it, but cause it's unpleasant demise. If your scope has a 50V scale you would be good to 500 v with a 10:1 probe. Ohms law say the circuit drew about 40 mA. So 82 volts could be dropped across a 2000 ohm 10 watt resistor with a proper voltage rated capacitor, something like 100 mfd at 350V, kind of hard to find these days. To test your PS you would need to connect a 5.6K (15 - 20 watt) to the junction of the 2K / 100mfd to your PS output (312 V). In other word: PS output to 2K 10 watt, junction to 100 mfd and 5.6k with the free end to the PS return, ground. Scope the junction of the 100 mfd/5.6 20W. I would expect less than 2 V Pk-Pk of noise.
     
  9. Cadmandu

    Thread Starter New Member

    May 27, 2013
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    What happened to that beautiful plane? Can you send me either a schematic or better yet a pictorial of what you just said. I really appreciate what you told me but I am not sure what it was. I have a 5441 Tek and a 7623A Tek
    Should I use AC coupling and a 50 ohm terminator.
    Thanks
     
  10. BigD61

    New Member

    Nov 8, 2014
    20
    2
    Ha, that was a matter of the fingers not keeping up with the mind, a botched landing. Oh well I didn't quit and there are a couple more waiting for a good flying day. As for the scope, I've use many Tektronic scopes the old one were 475s. Anyhow, were only use 50 ohm terminator when working, measuring RF and not for what you are doing. High Impedance probe typical 1 megohm 10:1 is what you want. My calculations points to some hard to find parts. Big wattage resistors are a lot harder to locate these days. As I am new to this forum I try but can not attach a file. I ginned up a cad schematic and saved it as a PDF. The System reject the file with error file is empty. However I can open it with Adobe just find. So how do I better describe what you need to do? If you had the parts laid out on a flat surface like so: the 2k 10 watt connect to the + 312 V lead of Power supply, the free end connect with the + lead of the 100 MFD/300V capacitor and one end of the 5.6K 15 Watt resistor, the other end of 5.6K 15W resistor connects the negative lead of the capacitor and both connect back to the power supply negative lead. Needless to say, be careful 300 vdc can do more than hurt!! Do NOT run this very long as the 5.6K will heat up fast, 10 watts.
     
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  11. Cadmandu

    Thread Starter New Member

    May 27, 2013
    10
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    Is the engine and controls okay? Here is a list of my probes which would be best?

    1) P6006 (10X 7pf 10 Meg) P/N 010-128. It has a screw on tip with two pinchers and a ground wire.

    2) P6028 (1X 47 pf + Instr C) P/N 010-0121-00. It has a screw on tip P/N 013-0071-00,and a ground wire.

    3) P6122 (10:1 Atten 11 pf 10 Meg) missing push on tip, no Tek P/N

    4) P6053B (10X 12.5 pf 10 Meg and an indent button) push on tip, ground wire and the sensing ring pin

    5) P6105 (10X 13pf 10 Meg 100 Mhz ) indent button, tan collar with a jumper) no ground wire,sensing ring pin

    Please send your files to

    danyoder.cs@gmail.com

    Thank you for your help. Is this suggested circuit dropping the voltage down to protect my scope? Since this is a full wave rectifier should the ripple be 120 hz and the ac volts be under 2 vac ripple. What % of ripple is acceptable? If I put a choke in the circuit where should it be placed and what size and current rating should it be. This is a test bed power supply so later I want to add a 12.6 vac filament supply and a regulated output for audio. So I can go bigger than what the BC-1A requires. I retire in 18 months and building and flying remote control is on my bucket list. When I was a kid i built a flew many stick, rib, and paper covered planes with .049 and .029 Fox engines. They were all wire controlled. I love the art of plane building. Have fun and thank you for your help.
    Mikwml has a real putter. My son Justin is a commerical pilot and was a flight instructor for a few years. Picture 757.jpg Republic_Airlines_E170_N822MD.jpg
     
  12. BigD61

    New Member

    Nov 8, 2014
    20
    2
    The old RYAN probably could have been rebuild. However as I did not have plans for it, rebuild would be bigger project than I wanted to tackle. After retirement I found completely an ARF was a lot faster than scratch building a kit. After all flying is a big part of why we enjoy or in some case so aggravated.:mad: I was able salvage all of the equipment and the engine and radio receiver are in another plane. I designed and fabricated a complete electrical system which has several years in development is working very well. My goal is to have big WWII war-bird all scaled out and have the skills to safely fly it. Talking serious $$.
    Your project; the resistor/capacitor network is meant to simulate the BC-1A based on the schematic provided. The 2000 ohm 10 watt resistor and the 100 mfd/300v capacitor would be required to match your supply to the receiver (BC-1A). The 5600 ohm 15 watt resistor is equivalent to the 4 tubes in the BC-1A. and are only to test your power supply.
    Scope; Just to be on the safe side, find a .1 MFD@350V rating and connect the scope to the circuit through it. Problem solved, scope is isolated for power supply DC. As the 5600 ohm resistor is constant I do not expect to see very much ripple. Anything over 2 volts would need to be investigated. Once the PS is connected to an active circuit the ac noise may increase, still 5% would be just over 1 volt.
     
  13. Cadmandu

    Thread Starter New Member

    May 27, 2013
    10
    0
    Okay, I think I see it now, please answer and correct as needed.
    1) The res/cap network is a simulation of my entire radio load.
    2) The .1 uf 350v axial cap is a DC blocker just in case.
    3) If you look at my schematic I have the HV CT chassis ground along with the bottom winding of the filament coil. So that is considered the "and both connect back to the power supply negative lead" Can I just make a chassis connection for these
    Send me some pics of your home brew airplane. Do you need any 3D software?

    Look what I bought.
    http://www.ebay.com/itm/150484659803?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT

    3k 9o watts 2 of them
     
  14. BigD61

    New Member

    Nov 8, 2014
    20
    2
    We're closing in on it.
    1) You will need to incorporate the 2000 ohm 5 watt resistor and the 100 mfd@350Vdc capacitor into your power supply. The two 3000 ohm resistors will be the test load to simulate the radio. You must tie the 2000 ohm and the two 3000 ohm resistors in series across the power supply + & - points. Very important you properly load the power supply. Tell you have the 2000 ohm 5 watt available.
    2) yes, using the capacitor will protect/isolate your scope from the 230 vdc and will couple any noise signal present to the scope vertical input.
    3) that is correct. you will need to tie the scope low side to this same point. I did a ACAD drawing for this project, however I can not get it to upload, this time I tried it as a jpg same results, error message "file is empty". Any help with how to accomplish uploads would be beneficial.
    FYI, I'll be traveling next couple of days, I can & will log on and see how you are doing.
     
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  15. Cadmandu

    Thread Starter New Member

    May 27, 2013
    10
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    I took pictures and made them 256k and uploaded them. Can you send the acad files to danyoder.cs@gmail.com ?
    If the two 3k 90 watts are the load that take place of the radio what do the series 2k 10 watt and the 100 uf 350 vdc cap that is built into the power supply do?
    Thanks for your help have fun on the trip
    look what i bought
    (1) OHMITE 2k 2000 OHM FIXED 50 WATT CERAMIC WIREWOUND RESISTOR NIB NOS
     
    Last edited: Nov 20, 2014
  16. Cadmandu

    Thread Starter New Member

    May 27, 2013
    10
    0
    Man I just spent 35.00 to pull this little experiment off. Can you tell me if these will work? How do I hook up the .1 uf 630 vdc mylar to my vertical input?
     
  17. BigD61

    New Member

    Nov 8, 2014
    20
    2
    ouch, check your gmail
     
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