Philco Dry Battery Eliminator for 33-37 turned MP3 Player!

Thread Starter

W7NUK

Joined Mar 12, 2017
17
I'm building a battery eliminator for my beautiful Philco 33-37! The radio requires 5 voltages! That must have been pricey for new batteries back in the day. Well luckily I only need to build 4 voltages. I have converted my radio from, well a radio into an MP3 player! So I disabled the RF side of things and hooked up an aux jack into the chassis. So I no longer need to build 90V. But I still have 2, 3, 9 and 135V! That's a lot! Well I only have two NTE956's currently. And as the data sheet says, I can use them as a high voltage regulator as it is floating. Well I want to get that 135V without a ton of resistors. So I need the advice of anyone here on building that WITHOUT frying anything. I don't want to attempt it without help first. While the second NTE956 can go towards making my 3V supply.

But wait? How do I get the rest? Well my plan is to use a resistor to get my 2V supply. I already know my current draw for the vacuum tubes and what resistor I need. I have a 2.5ohm 5watt picked out. Need an idea on how to mount though. The 9V I will have to get another NTE956 for that. I don't have enough space inside my project box to fit a 9V battery. But it's used only for bias so I might be able to use a few resistors as a voltage divider and get it. It's only used a bias on two tubes so the current draw is not important.

I have my project mostly set up and ready for parts to be thrown in. I drilled holes to mount my connector so I can disconnect it from the radio. The only problem with that is my panel mount connector is male pins. So if someone is dumb enough to touch it with the power on they will get shocked. However, I couldn't fit it on the radio without causing too much damage. Wasn't comfortable drilling a big hole when the original wires for the battery already had a big hole. Just wouldn't fit there without the flange sticking above the chassis. Also got my holes drilled to fit my protoboard inside. I don't have the equipment to make my own circuits boards so I'm using one of those universal type prototyping boards. Also have a fuse, power switch and light mounted. Well I'm cheating. Those were already there from an earlier project.

My project box is an old Heathkit oscilloscope transformer cage. Don't worry. I only took it to pieces thanks to the post office. No need to thank them for that kind action I didn't even need to ask for!. I'll attach images of what I have so far. I won't get any of the radio until I open it to add in my wires to the power supply. Kinda a pain to do so. However this will be an awesome MP3 player! The first thing I will play out of this as it's initiation will be some Korn!

Bought the radio for only $40! I think that's a great deal! Only missing one tube and shield. And my pilot light's burned out. And all wires on the backside are torn right up. And the veneer is coming off. And the AM radio doesn't work;). But who cares? It looks perfect to me! And everything so, everything appears like it will work perfect. At least I don't have to align it anymore! But I always make sure any mods I do are as easily revered as possible. So I can bring it back to the boring non Korn side of things in maybe a few hours at most.

So if anyone can provide some information on using an NTE956 aka LM317 as a high voltage regulator please let me know! I'd rather not blow one of mine up just yet! At least not while I only have two! I will for sure keep updating this for others to follow if you have a vintage battery powered radio or interested in vintage radios like me. That's Kapton tape around the transformer. It has a high voltage winding of 900V and I added heat shrink around the leads then wrapped them up in different layers of tape to prevent shorts. It ain't having a party without my permission now! The pretty sticker is mine. Added because of the last failed project built in this case. A high voltage electrolytic capacitor reformer!
IMG_20180202_203851846.jpg IMG_20180202_203909475.jpg
 

Thread Starter

W7NUK

Joined Mar 12, 2017
17
Ok, so some building and testing later. I don't need nor can use my NTE956 on the 135V side. I wired it up. And it did work as I wanted without blowing it to pieces! It did drop 30V off as I wanted. My unloaded voltage for the filtered DC is around 168V without anything other then the diodes and filter cap. However using the voltage regulator my voltage was 98V out. Input was around 120V. There is enough impedance somewhere to drop my voltage down with only the load of the multimeter and voltage regulator. After some thought, I have removed the voltage regulator and decided that simply wiring it straight into the radio will not kill it and should work fine. There should be enough impedance that as the radio draws a small load, it will drop closer to the expected voltage. I measured current by shorting through my multimeter, it can supply a max of 320mA. This should be more than enough for my simple battery powered radio. When a 1200ohm load is attached to the output, the voltage drops to 98V. And it almost killed my poor 1/2watt resistor in a second!

I'm about to start on the low voltage side with 9V, 3V and 2V. I will use one voltage regulator for the 9V and the other for the 3V. Using a small power resistor to drop the 3V into 2V for the tube heaters. I have small heat sinks which will be used to help keep the voltage regulators cool during use. I did use a large one on the 135V side however that wasn't needed in the end. So it goes back into the parts bin. I have my transformer winding for the low voltage side already wired into my circuit board but not yet started on the rectifier side of things. I will report back once that built what my DC voltage is then I will start laying out my parts to get my voltages in check.
 

DickCappels

Joined Aug 21, 2008
6,005
Quote of the day :):

(some texxt removed for clarity)
And it did work as I wanted without blowing it to pieces!
(For future reference, you may already know this:) The reason for the large difference between the unloaded and loaded voltage is probably a combination equivalent series impedance and the ripple across the capacitor. With a DVM you will read the average are not be able to see whether the peak voltage is much higher than the average or that the minimum voltage is much lower than the average.

upload_2018-2-11_9-28-0.png
(some texxt removed for clarity)
I measured current by shorting through my multimeter, it can supply a max of 320mA.
Your 1200 ohm 1/2 watt resistor would have been dissipating 8 watts. Thankfully you were able to read the results before the resistor was destroyed.

It looks like you are making pretty good progress.
 

Thread Starter

W7NUK

Joined Mar 12, 2017
17
Thanks for the reply. I'm am almost done with the low voltage side. Turn out the 9V doesn't need or can use the voltage regulator. The rectified voltage was just above 9V. And with my voltage regulator for 3V added in it's dropped to about 8.85V. So I have that set to be wired straight to the radio as well. It's just used for bias so it isn't the most important. Probably won't notice it in operation anyways. Attempting to mount the power resistor to the circuit board. It's a little tight but I would rather have it on the circuit board rather than drilling more holes in the case. That's a pain when I only have a Dremel and a Milwaukee power screwdriver with about two drill bits left. And of course they are dull! How else do you expect me to drill holes?

Everything so far has been going properly as expected. My suicide cord has seen more use than I ever wanted, but I need a way to test without the power cord and case flopping in my face! Doing this all as safe as I can. Been using my capacitor bleeder I built using a 7.5Kohm 10watt resistor with some leads to make sure that 47uF on the high voltage side doesn't bite me! So I'm really close to being done with the power supply! Have to finish the 2V side and mount my transformer and circuit board inside the case. Then wire it to my plug. And then lastly build the power cord from my radio another day. Still need to buy a tube and shield. Missing one, and of course it's one I need! At least it's cheap. Just lazy on buying.
 

Thread Starter

W7NUK

Joined Mar 12, 2017
17
Got it mounted in the case. Just have a few wires to attach for the AC input side. And then my power connector. Was struggling to mount the circuit board. But finally found a great solution. I used rubber grommets to prevent my screws from pushing back out of the case. Super glue only temporally held them. So far I think it has turned out great. It works as I want. And only a few more wires and the power supply will be done!

What's left on the radio is to trace my wires and remove the old wires for the battery. And then attach in my new ones. And my connector on the end. Making sure I don'IMG_20180210_215255293.jpg t end up with 135V in the wrong spot. Need a new pilot lamp, 1H6G tube and shield. And that should conclude this project. Really not that hard to do. Quite simple being form 1937!IMG_20180210_215255293.jpg
 

Thread Starter

W7NUK

Joined Mar 12, 2017
17
Got the power supply finished. Well, almost. I now see I really need to add a bleeder onto the high voltage cap. The proper solution is to add a bleeder probably around 100-200Kohms. My solution is to do nothing and hope I don't fondle it. I will open it back up but now having everything wired up will make getting in and removing my circuit board really hard. My wires on the transformer terminals are heat shrunk on. And the power cord is attached to the case. Point made. It will either be a pain to fix or a serious pain if I touch it! It gives one massive spark when I short it with a screw driver. It is 47uF at around 170ish volts.

However mistakes aside. I am quite pleased with how it turned out. I have my power cord for the radio almost ready to install. It was a massive PITA! Wiring it was not the problem. It was pushing my wires through the strain relief on the connector! I had to struggle for 30 minutes and use a ton of WD40! But they are in without damage or shorts! Now I need to twist the wires and I'm debating adding some long heat shrink over the cabling to cover the wires and give a more professional appearance. Probably will do that if I don't twist. I can buy at this local store some heat shrink in around 4-5ft lengths.

Maybe next weekend I will open my power supply and add a bleeder somehow. It will be a pain but it really is needed. I do hate getting shocked so I try to avoid it as much as possible. But this power supply is just inviting death! That filter has more than enough power to knock me dead a couple times! I don't like shorting it with my screw driver as that's hard on the capacitor. And I don't like touching it. Do wish I could have added the chassis connector on the radio itself as it would have been a ton safer. The high voltage terminal is not the right top most. That is ground. The high voltage is the one just under it. Do need to fix it. Guess I just won't touch it or plug it in until I have that bleeder in. Should have been less focused on mounting my circuit board!IMG_20180211_154111081.jpg
 

Thread Starter

W7NUK

Joined Mar 12, 2017
17
Got a bleeder added! It wasn't as hard as I first thought. Although it wasn't a walk through the park either. Feel much better about this. As long as I don't grabbing for things I shouldn't be while it's on I should be ok. I added a 100Kohm 1watt resistor. It discharges the capacitor to safe levels in around 5 seconds. Perfectly fine for me. As long as it drops below 100V in a couple seconds I feel a lot better about it. It drops below 50V after about 4 seconds. Although it's still unsafe considering that you can touch the live pins like nothing. But good enough for me as it's not a item I expect anyone else to be using. Just didn't feel comfortable that the 170V will sit on those exposed pins with it off. That was a serious problem waiting to happen! At least I exercise the one hand rule!
 

Thread Starter

W7NUK

Joined Mar 12, 2017
17
Ok so a few problems. First off, my 9V and 3V need to be negative, guess I should have paid closer attention to my schematic!. I may be able to just flip my ground and 9V leads and be ok there. However as I load test the low voltage side, using a 8ohm resistor I am drawing 155mA. (This is on the 2V lead). The tubes should draw about 300mA total(I budgeted for around 320-350mA as I am missing one tube). Well my voltage sags a ton. No big deal I think. I knew I'd need to adjust my voltage regulator under load anyways. Well as it turns out, my DMM reads the 9V side dropping to 5.8V and my oscilloscope shows it has massive ripple dipping to 2V at the lowest from 8V peak. 120Hz as I made a bridge rectifier. I might be able to solve by adding a ton of filtering right? If I add in maybe a 1000uF or so that may work. I currently have 100uF in there. Not sure how to know how much to add, and I figured this wouldn't need that much filtering since I wasn't drawing a ton. Maybe this transformer has too much impedance for my needs. This 8ohm load on the low voltage side also dips the high voltage side down a few volts! And I'm not even touching it!

Let me know how to tackle this. Currently I'll just flip the connections and hope it does work as intended for my negative voltage. I'm not redoing my whole circuit right now. Yes, I know the NTE956 is a LM317 and is for positive voltage. And the LM337 is for negative. I don't have anything to replace it with. And my electronics store I'd like to visit isn't open on weekends. And Fry's is a couple hours away. And online is a week. Why'd I not pay closer attention! Now where's my flog gone too? This has to be solved somehow.
 
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