Final Voltage Check

[Paul Birkeland]

If you pull the tubes out, do the voltages at the 6.3V pads change?

[bradtsakeris]

Paul,

I just pulled the tubes and am getting a reading of 30.8 on the + and 30.6 on the - of the 6.3V

[Paul Birkeland]

There's all sorts of wrong with this.  Can you slip just the shielded twisted pair connections out of the + and - pads where the 6.3V is supposed to be and recheck those outputs?

[bradtsakeris]

Paul,

Sorry, I'm a bit of a newbie with all this stuff. Do you want me to remove the shielded wire from the board at the 6.3v? What do I need to do after doing that?

[Doc B.]

Let's slow this down. Don't remove the wires yet. If you recall I explained during our phone call that you want to measure with black test lead to 6.3v - and red lead to 6.3v+. For this measurement you don't want the black lead connected to the ground post. Give us that reading from 6.3+ to 6.3- . And please let us know if you double checked the values of the 124 and 499 ohm resistors mentioned in my previous post.

[bradtsakeris]

Hi Dan,

Sorry, I should have been more clear on my end. I'm getting 3.12v on + and 1.86v on - when I have the black lead connected to the ground post. I am getting 30.8 on + and 30.3 on - when I have both the red and the black touching the 6.3v. I also checked the 124Ohm and the 499Ohm and both are reading correctly.

[Paul Birkeland]

This still isn't making sense, you should put the red lead on +6.3 and the black lead on -6.3 at the same time and report the DC voltage you get there (not two different voltages). 

[bradtsakeris]

Paul,

My bad. The reading with red on red and black on black of the 6.3v is 30.8. I could explain the 30.3 reading but you'd probably call me an idiot, haha.

[bradtsakeris]

Hi Guys,

Quick update. I noticed in the picture with all the finished wiring that I had the wiring incorrect coming from the where the power cord gets plugged in to the on/off switch. I went ahead and re-wired and have attached a picture ( I accidentally put both the switched in backwards when I first got started on the kit). Anyway, I'm still not getting proper voltages on the 6.3v but at least wanted to show we can cross this off the list.

[Doc B.]

Your meter is set to DC volts when you check those 6.3V pads, yes?

[bradtsakeris]

Hi Dan,

Yes, the meter is on DC. I just did a bunch of different tests of the 6.3v and here are the readings:

1. Tested with tubes in, turned on, and plugged into outlet.

52.6v on + (black wire on ground)
51.7v on - (black wire on ground)
1.26v with red on + and black on -

2. Tested with tubes removed, turned on, and plugged into outlet.

13.86v on + (black wire on ground)
1.85v on - (black wire on ground)
11.3 v with red on + and black on -

Let me know what I should try to do next.

[Doc B.]

OK, this has circled back around pretty close to what you were measuring when we were on the phone. The 52v is good and indicates that the regulator that biases the heater supply up is working fine. But the 13v means something is not right with the regulator circuit for the 6.3vdc heater supply itself. That the heater voltage drops so dramatically when tubes are installed seems to imply something is not installed correctly because it's not functioning as a regulator and also not able to pass enough current to the tube heaters without the voltage getting pulled away down. If the 124 ohm and 499 ohm resistors are installed in the right positions it makes the lm1085 chip a suspect in my book. Let's see if PB concurs before you take anything aprt.

[Paul Birkeland]

Take the power supply board off, flip it over, then post some pictures of what the bottom looks like.  Also take a picture of the 1085 regulator and post it as well.

[bradtsakeris]

Hi Paul,

Here is a picture of the the underside of the board and the 1085 regulator.

[Paul Birkeland]

I would reflow the joints on the 1085 and the two resistors by it.  The top side of the board shows that the solder has not been heated enough to flow through the board.