A shotgunning look into my random thought patterns, turning up surprisingly non-random, non-trivial connects on several hoopy wavelength. Your Mileage May Vary.
While I wait for #3 to bug me about her radio again, I'm working on my 10DE7 project.
Here's the skinny:
I took some parts that look like this:
and turned them into this:
and in the processed learned something about phasing.
Some project notes,
I did make the connection between taps 9 and 7 permanent, that is, soldered the wire in place. I made a short jumper with spades so I could experiment with places to put them on the taps. The first time, I soldered a jumper wire between pins 8 and 9, and didn't get the results I wanted. I thought for a minute that I had a bad transformer. I learned a couple of things in the process.
1. Autoranging digital VOMs can mess with your head. I kept getting jumpy measurements in the milivolt range, and it kept making me nervous. Verifying some readings with an analog meter really helped me settle down.
2. When dealing with AC transformers phasing matters. I should have realized from the schematic of the taps that the phasing a the bottom of one set of secondary taps would be out of phase with the top of the next set, but it took a little experimenting to figure that out.
3. When dealing with an unknown quantity, don't solder things down. I know better, but sometimes I don't do better.
4. Alligator clips for VOMs have their place.
I got to bed pretty late last night, so probably no shacktime tonight.
I have to think some more about plate voltages anyway.
I've decided to call my One Tube MOPA project "Operation Rock Garden." Because it is another project that involves a crystal controlled oscillator, I figured, why the heck not?
Phase one deals with power supplies. Not supply in this case, but supplies. There are three distinct voltages for this project, 2 different DC B+ voltages, and an AC filament voltage. Each one needs to be able to handle a certain amount of current as well. bBcause of this, I'll probably need a few solid state parts, like diodes and voltage regulators, for creating a rectifier circuit, or voltage doubler.
Step 1 of this phase is to light the filaments. To do this I need a circuit that can supply 9.7V at 600 milliamps. The easiest way to get there is to take the massive milsurp filament supply voltage I have, and series up the proper combination of taps to get as close to 9.7 as possible.
It came from a homebrew power supply for a Heathkit SB-102, and other than that, I don't know much about it, but I figure if I connect tap 8 to tap 9, and take my voltage from tap 7 and tap 11, I should have somewhere in the neighborhood of 9.45 Vrms, maybe a little more, because this primary is listed at 117 Vrms, and I'm around 120 consistently here.
Backside, showing taps.
I don't see this as an optimal solution, but it can handle the current, and the voltage should stay reasonably under the max. The supply has this lug sticking out of it.
The lug is behind taps 5 and 3. I think it's there so the core can be grounded, but I'm not sure the core needs to be grounded in the application I'm using it.
I will take advise in this matter.
Here's the plan for tonight when I get home from work:
1. Hook up the Transformer, ground (or not) the lug.
2. Construct tube base breadboard.
3. Go to bed. Light the sucker when I'm sure I have at least 9.4 Vrms, and after I've rested.
I'll be listening to 3579 KC while building, and the NoGA Twin Tube 80 will be standing by...
***EDIT*** General concensus is that the lug can be grounded with no ill effects, and the filaments should be ok at that voltage.
We'll see if I can get 'er done tonight!
******
So Here's what I have been able to discover:
I'm still not 100% certain why the unit failed the first time. Initially I suspected the power supply, but I'm reinvestigating, I discovered another loose solder connection on one of the tube sockets. I'm not sure that's what did it, but I'm always suspicious of any changes I made. I changed tubes, the supply blew up. Thems the facts. Whether changing the tube caused a supply malfunction remains to be seen.
You can notice from the pic that I changed out the crystal holder part of the circuit. I did this to keep the metal case of the crystal WELL away from the supply voltage terminal, and because it looks better put together up and off of things as opposed to flopping around all dangly like. The bad news is my thumb is sore today because I think I poked it with a wire. If things don't improve soon, may have to go see the Dr about lockjaw! Heh!
how you 'spain that one to the XYL?
The second time the supply failed, I am 100% certain was because I used a severely underrated rectifier diode. I used a 1N4001 blindly following a misprint in the schematic I was using, instead of a 1N4004. So I'm beefing up to a 1N4005 just to make sure, and that's only IF I can't find any 1N4007's laying around the junque box. Next I will isolate the 150 B+ part of the circuit from the line, and instead of using one diode, I will go ahead and use four, building a full wave bridge rectifier. This is because I got diodes, and math is on my side...
From an awesome mess
Comes a beautiful circuit
Arise O Phoenix!
OK:
so you take a half wave rectifier like W3IRZ(sk) first designed into this rig, and you take the caps he had for smoothing, do some funny math, and using the max transformer rating of 1 amp. I'm not expecting to actually draw more than about .05 amp here, and yes, I know about derating the transformer current rating in a bridge rectifier, the actual rating is 1.2 Amp. Radio Shack sells a 3 Amp transformer too, it is part number 273-1511 you can ship it to my address from QRZ.com or hit the donate button in the top right hand corner of this webpage :)
anyway,
you do the math found at MIT: and discover that there is 24.1 Volts of ripple voltage when the load draws 1 Amp.
Now this is worst case scenario mind you, but still. at 50mA which is a lot closer to the actual current draw, it will be a lot less, like 1.205 volts ripple, which is less than 1% of peak voltage (150VDC). An acceptable number, but since the 470 microfarad caps needed to produce this performance are now BBQ in the trashcan, it's time for plan B.
I have some caps suitable for filtering, but not the exact values as before. I needed a way to lower the required amount of smoothing needed to get a usable DC voltage. I decided to build a bridge rectifier, and use a couple of caps left over from the earlier efforts. Using two 220 microfarad capacitors, I actually drop my ripple voltage a little bit, to like .95 volts at 50mA. I can handle that!
Now you can buy a bridge rectifier at the local shack, but this is an exercise in understanding, and I don't have any 1 Amp, 120Vrms AC bridge rectifiers in the Junque box. I do have 4 1N4005 diodes though, and knowledge, and a community of assorted skalawags, errrr, electrically inclined persons who can help me out.
This is the bridge, as I have constructed it. The alligator grippers are holding it at the position where I hook in the AC, one side to top, one side to bottom.
The bridge will be hooked the (originally primary) secondary of a 12.6VAC to 120VAC transformer.
Here's a closeup, showing the AC wires hooked into the circuit. I've intentionally left the 'ears' on the soldered circuit leads so I can do some testing later. You can see that the bands indicating the cathode of the diode are running from left to right. As it is layed out, the rectified positive voltage will be on the right, and the negative side is the left.
This is an overhead shot of the circuit so far, laid out on a potential housing mount. The pic is upside down from the way that I took it, but whatever.
you see that I have two identical transformers, they are Radio Shack "120-12.6VAC 1.2 Amp" available at most stores. I have rolled up and taped off the center tap of the transformer, because I don't plan on using it. The two outer leads have been tied together. I will take my 12 VAC filament voltage from this point. Hot and neutral wires will be hooked up to the primary transformer on the left, and the diode bridge is hooked up to the secondary transformer on the right. If all goes well, and I haven't done anything stupid, we will have pulsed DC ready for smoothing at the secondary end.
Here's a video showing how everything is currently laid out:
I won't be hooking AC up to it until I've got the unit planned out and tightened up a lil bit, namely I will be solving space issues, hooking up a switch and fuse set up, and hooking it up the way I will have it inside the box.
So what do you guys think?
Go or No Go?
I didn't want to button my power supply up before figuring out why the hot wire was white. Basically, I wanted to make sure this radio could work anywhere, and having a hot white wire was troubling. Like David suggested in his comment, I suspected the outlet, and then the wiring in the Mains box. Time to flip breakers and do some inspecting!
First, I flipped the breaker to the shack, and trundled back into it, hoping to find a black wire where a white wire should be. The Shack in the Back was built before we moved here, and is 'unfinished'. The guy who owned the place two owners ago built it with scraps left over from some of his contracting jobs I think. When I unscrewed the socket from the recepticle, everything looked, well, fine. I was impressed with the craftsmanship of the socket to tell you the truth, connections were tight, and in the right place. Time to check the mains box, but I knew it was going to look fine there too. It did.
Back to the thinking bucket.
Yon Thinking Bucket
I juiced the shack back up, grabbed my VOM, and began doing things my mother told me not to do, namely sticking metal things in electrical outlets. By metal things, I mean VOM probes. I always feel weird sticking things into electrical outlets, makes me make sure I do so with fear, and caution. That's not a bad thing, I suppose.
First, I checked the socket for power, Hot wire to neutral, and I got 120v AC. Good!
Then I checked for what should be the neutral wire to ground, and got no AC voltage, Good!
for the kicker, I checked what should be the Hot wire to ground, and got 120v AC, Good!
So the socket is good! Should have done that first instead of assuming it wasn't... hmmm.
Next test, the power supply strip I plug into the socket. Maybe there's something miswired there,
Just checked Hotside to ground, 120v AC. Good!
So the power supply is not the issue.
must be the power cord.
The Cord- Not Polarized
notice that in the picture of the plug end, the plug is not polarized. This plug and wire was salvaged from some piece of computer equipment, and at one point in time had a female chassis mount plug on it, the kind that looks like this:
Female Chassis Mount
On a polarized plug, the narrow slot/prong is hot, the wide slot/prong is neutral and the round prong is ground, my non polarized plug fits in the socket the way a polarized one would, but, was it wired like a polarized socket? Just where did the white wire go?
I made sure the plug was unplugged, clipped the cord out of the power supply, and I decided to idiot check the green wire first, green for ground right? Switching my VOM to measure resistance, I continuity checked the green wire to the round prong, and it was Good! Then I checked between the other two wires, and no other wire lead to the round prong, Green is good!
I then oriented the plug like I was about to plug it in.
Right is hot, left is Neutral...
As this picture shows, the prong on the right, goes to the hot side of the socket. That's the one I want to check.
First I check the black wire, no continuity.
Then I check the green wire, no continuity.
Finally, I confirm that the right prong, the prong that normally connects to the hot side of the plug is connected to the white wire.
The white wire is hot because it goes to the hot side of the socket.
Heh.
I have no idea why this cord is made this way.
I just know that I can safely button up the power supply knowing It's the Cord, not my shack!
