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PostPosted: Jan Sat 29, 2011 3:29 pm 
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Thanks a lot for the info. I'm getting a Voltage reading off the plate, its at B+ potential. So if I remember correctly that's like 268v. I used the original transformer I mentioned at the beginning of this thread. Here's the parts list for the not-defined parts:

Image

I'm using two 6L6's mainly for more power, I had changed the original power supply to use both so the only thing I may need to change is the resistors. I'm thinking that until I get this working correctly I'll only be using one of the tubes, and then i'll modify it in once the oscillator is working properly.

Steve


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PostPosted: Jan Sat 29, 2011 3:54 pm 
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Quote:
I used the original transformer I mentioned at the beginning of this thread.
You will recall that I suggest that this might not work (wrong turns ratio)

Quote:
I'm thinking that until I get this working correctly I'll only be using one of the tubes, and then i'll modify it in once the oscillator is working properly.
Good plan

Recall also that I suggested that the antenna coil you had was not going to be appropriate for your circuit.

Now that you have the parts list with values, you can look for coils and transformers that are correct. Do you have access to an impedance bridge or some other means of measuring inductance?

All this aside, I would suggest getting the oscillator working before worrying about anything else.


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PostPosted: Jan Sun 30, 2011 1:36 am 
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A little update. I have tried a few different combinations on the OSC coil, including the specified one for the 6SA7. I'm not getting it working. What I don't understand follows:

1. If one of the windings on my coil is attached to B+, should I get a reading on the other one? For the record, I'm not, and this doesn't seem right since I thought it was an inductor.

2. Using the setups on the data sheet for the coil I can also only get one side of the tuning capacitor to B+ potential. Here's the kicker- the rotor and stator are hooked up to different windings on the osc coil. so IF any current were flowing through the coil I assume that would fix that.

Here's the example of how they have the 6SA7 set up on the data sheet:

Osc Grid (Pin 5 of the SA7) goes to pin 1 of the coil, on the secondary tap.

"Ground or Padder" (Obviously one side of the padder goes to this pin in my case, but I have no idea which- I just picked the stator for the hell of it) goes to pin 2 on the secondary wiring of the OSC coil.

SA7 Cathode to Pin 6 of the coil, on the primary winding.

Ground to Pin 5 on Primary winding.

*Also note that I had the rotor hooked up to the Plate of the sa7.

--- When I hooked everything up like that, here's what I got:

B+ voltage on the Primary winding (where the cathode and ground are hooked up)

Zero DC voltage on the secondary winding (where the Osc Grid and stator are hooked up)

Rotor at B+. Stator at zero. No "detectable" oscillation by putting a small radio close to it.

I just don't understand?????

-Steve


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PostPosted: Jan Sun 30, 2011 1:50 am 
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Quote:
If one of the windings on my coil is attached to B+, should I get a reading on the other one? For the record, I'm not, and this doesn't seem right since I thought it was an inductor.
Your schematic shows a tapped coil---which I understand you are emulating by using your Miller coil wired as we discussed. This means that ALL terminals would be at the same DC potential. If they are not, then you have an open winding somewhere.

Let's get this one resolved before proceeding.


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PostPosted: Jan Sun 30, 2011 4:11 am 
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Alright, copy that. At current config I have DC on both windings. Sorry for the confusion.


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PostPosted: Jan Sun 30, 2011 3:32 pm 
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Ok--I went back an looked at your previous post and you are talking about various connections that do not relate to your schematic.

For example, these statements:
Quote:
SA7 Cathode to Pin 6 of the coil, on the primary winding.
Ground to Pin 5 on Primary winding.
Neither of these correlate to your schematic.

Please post voltage measurements for the configuration on the schematic.

In re the Miller data sheet for the 6SA7: What they show is for a different kind of circuit than yours---you cannot mix the two.

And--I think you are eventually going to need to check the inductance of that coil against what your parts list calls for. It may well be that the Miller coil is simply not going to work.


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PostPosted: Jan Sun 30, 2011 7:21 pm 
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When hooked up as you specified it reads B+ on all pins, and the tuning cap has both stator and rotor at B+.

This coil has an adjustable core, but idk what I'm doing with something like that...

UPDATE:

I realized I was running some sort of ground loop that Was causing all connections to B+ to be at over 250v. After fixing this I have about 70vdc on the whole oscillator coil circuit.


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PostPosted: Jan Mon 31, 2011 11:17 am 
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Quote:
This coil has an adjustable core, but idk what I'm doing with something like that...
See my comments as to whether this coil is going to be suitable----checking the inductance against what your parts list specifies, etc. In your circuit---assuming we get it working with that coil---the adjustable coil will be used to set the frequency range that it will tune over. For fine adustments, set the coil at the low end, and then the tuning cap will determine the high end.


Quote:
After fixing this I have about 70vdc on the whole oscillator coil circuit.
Fix this first. First, have you removed the extra 6L6? (remember the comment that bias settings may have to be changed with 2).
Please post readings for the B+ and the oscillator---starting with the cathode of the 5Y3, then C1, C2, top of R3, and top of R4 (6SA7 cathode).
Also, confirm that all component values are the same as the schematic and parts list.

One thing I noticed on your schematic is that they have B- floating (connected to chassis ground with a 0.1mF cap). Please confirm how you have it wired.


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PostPosted: Jan Mon 31, 2011 11:22 am 
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PS:

Just noticed that some part values are different on the schematic and the parts list.

Please post the schematic with the actual values installed for every part.

I am starting to wonder where this design came from.......do you know if anyone has successfully built one of these using the info you have given us.


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PostPosted: Jan Mon 31, 2011 7:51 pm 
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OK. Here's the deal. The part values on the parts list are what was used, when I asked the supplier of the schematic he said he wasn't sure why those were on there anyway. So go off the parts list. Here's the thing with the power supply:

1. I have a seperate chassis for the power supply. It uses a slightly different set up but the readings off the connection for the umbilical cord are correct and at full B+. Now. Here's where I am confused. The "floating ground". I originally wired it like this: Chassis Ground -> .1mfd cap -> B-. This was causing everything in the chassis to be at full B+ potential. When I removed that capacitor I was getting different readings for different parts, which I assume is how it's supposed to be, but I was getting barely any readings on some areas like the 6L6 plate. (And yes, I'm only using one). I don't know if this is due to the current not wanting to flow through the multimeter or what.

PS, my analog multimeter has a 300v setting, but the scale only goes to 250v. There is a red dot at 150V, how the hell do I read this thing above 250?

Here's the webpage of the schematic and the tranny:
http://www.vacuumtuberadio.com/AM_Transmitter/Mod1/

Steve


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PostPosted: Jan Mon 31, 2011 8:55 pm 
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Quote:
I originally wired it like this: Chassis Ground -> .1mfd cap -> B-. This was causing everything in the chassis to be at full B+ potential. When I removed that capacitor I was getting different readings for different parts, which I assume is how it's supposed to be, but I was getting barely any readings on some areas like the 6L6 plate.
This makes no sense at all. Connecting a capacitor from B- to chassis will not cause the chassis to be at B+ potential.

Please post the actual as-built schematic.

Quote:
PS, my analog multimeter has a 300v setting, but the scale only goes to 250v. There is a red dot at 150V, how the hell do I read this thing above 250?
I have no idea, but I would simply go buy an inexpensive digital multimeter. Mine is a Triplett and I don't think it was more than $30 or so.

I looked at the website you linked---and went back to the version before "Mod 1". He shows you how to make the various coils. Why not do it his way instead of trying make it work with other parts? If you want to use your parts--eg the coils---you'll need to measure the values as I requested.


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PostPosted: Jan Mon 31, 2011 9:01 pm 
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DMM:
http://www.amazon.com/Triplett-1101-B-C ... 888&sr=8-6

Mine is similar to this one


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PostPosted: Jan Mon 31, 2011 9:01 pm 
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pixellany wrote:
This makes no sense at all. Connecting a capacitor from B- to chassis will not cause the chassis to be at B+ potential.


Since the chassis is isolated, should I instead isolate the ground? Or should I use an earth ground. the Power Supply chassis IS grounded already and does NOT use an earth ground. It uses the neutral wire. I will admit I had the power supply up to right past R2 built for me because I didn't want to deal with it. I had him verify the correct output.

I am going to try winding his coil, that should work, was just hoping for a more "professional" output. Not sure about my winding abilities.


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PostPosted: Jan Mon 31, 2011 9:09 pm 
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All I can do at this point is suggest how to think about things....

Trace the flow of HV DC current ("B+") from the power supply through your circuits. The node where it all returns to the supply is typically called "B-" The more modern term is "return".

For the circuit to work at DC or very low frequencies, nothing needs to be connected to "ground". The grounding of things becomes important as the frequency goes up. In audio, it matters at 60Hz, and in radios, it really matters at RF frequencies.

Regardless of where "ground" is, you have to maintain the integrity of the DC current paths.

I will try to post a sketch to illustrate.


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PostPosted: Jan Mon 31, 2011 11:16 pm 
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filmmaker516,

I feel bad to dash cold water on your project, but you need to know that your project is likely to be very frustrating, as you attempt to complete it and get it working. And in case some other reader is thinking of making such a "phono oscillator", he should be warned that this ain't the one to try building.

Someone needs to state very clearly that the circuit you are working from is a very bad bash-up. It falls short of being a design. Contrivance, perhaps.

Peter Bertini attempted to point this out a couple of weeks ago, but perhaps he was a bit too subtle:

"Posted: Jan Sat 15, 2011 8:37 pm

The design is beyond bizzare.

Cathode modulated, and no RF bypassing on the cathode. I'll stop there.

Pete"

The original example may have sort-of worked, and the photos do look very impressive, but it is not a good model for newcomers to follow. Nearly every element of the circuit shows poor choice of components, and "bizarre" circuit topology.

Even if the "design" were reasonably good, the schematic is incomplete, with missing and apparently incorrect component values.

I'm afraid that if you don't understand why the "design" is so poor, you are likely to have great difficulty making changes and parts substitutions.

And you may expend great effort acquiring things such as "1m" resistors. They do make these, but a couple of short pieces of wire will work the same in this thing.

I suppose struggling with this project might be a real learning opportunity, but it can be difficult enough to build and troubleshoot a good design. This one may mostly result in aggravation, with little reward.

I suggest posting the original schematic & parts list in the "Homebrew" forum. Ask for constructive criticism. That may get it the sort of attention it needs.

As Pixellany pointed out, if you want useful help with what you actually built, you do need to create an accurate schematic, with parts values, showing the separate chassis and any connectors, etc. If you post this, the help from ARF members might be a little better focused. Again, this really should be on the "Homebrew" forum.

Anyhow, I wish you luck!

Ted


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PostPosted: Feb Tue 01, 2011 4:50 am 
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Here a scribble showing how the power supply might b wired to the other unit.
http://pixellany.com/ps_wiring.jpg


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PostPosted: Feb Tue 01, 2011 9:58 pm 
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pixellany wrote:
Here a scribble showing how the power supply might b wired to the other unit.
http://pixellany.com/ps_wiring.jpg


Thanks. I fixed the grounding issue. I built my coil to Rick's specs, and I think I have oscillation occurring. I have no idea how to test it tho. If I plug a radio in on the same circuit and tune it below about 900 all the channels have a horrid buzzing on them Which stops if I turn off the TXmitter. Not sure whatnthat means.

Still have to build that damn antenna coil...


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PostPosted: Feb Tue 01, 2011 10:11 pm 
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I'm going to make a new thread in "home brew" as suggested. Fully redone sche,atic and parts list to be included.


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PostPosted: Feb Tue 01, 2011 10:52 pm 
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Sounds like good progress---will look forward to the new thread.


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