Voltage test after shut regulator install.

[Tom228]

Here's the images from tonight:

http://imgur.com/a/QyjGR

Nice shiny high-res ones

[Paul Birkeland]

I'm not seeing the errors that would cause this.

Can you:

1.  Meausre the DC voltage on both sides of the 270 Ohm resistor?

2.  Verify that you have MJE5731A transistors on the board (not TIP50's or anything else)

We'll get this sorted out.

-PB

[Tom228]

Hi Caucasian Blackplate.

Thank you for all of your help with this.  While I'm pretty good at following directions and putting stuff together, I'm not great at troubleshooting.  So, all of the help is most appreciated.

When I measure the DC voltage on teh 270 Ohm resister - is that the big 5w one on the power supply?  Do I leave the - probe on the back resistor both times?  Do you want that with or without the shunt regulator attached?

I'll post a picture of the transistors tonight.

[Paul Birkeland]

With the regulator attached, place the black probe in the ground post at the front of the chassis plate, then use the red probe to measure the voltage on each side of the 270 Ohm resistor.

-PB

[Tom228]

I've got MJE5731AG (AFB43) transistors on the shunt regulator.

Off to re-attach it.

[Tom228]

Ok:

2 -270k resistors:

Resistor closest to the top of the power supply board:
Bottom pin (red band):  142v
Top pin (gold band): -0.001v

Resistor closest to the bottom of the power supply board:
Bottom pin (red band):  286v
Top pin (gold band): 142v

[Paul Birkeland]

Sorry, I may not have been clear enough, I'm interested in the voltages on either side of the single green 270 Ohm resistor.

-PB

[Tom228]

Right side - 280v
Left side - 292v

[Tom228]

Hi all.

Can I keep moving along with assembly of my preamp?  I'm to the point of wiring up the 3 tube sockets and the stand-offs.  Or should I wait until we get this figured out?

[Grainger49]

Tom,

I haven't dug into this since you were getting responses.  Bottlehead hosted a meet yesterday, so your responders were busy.  I'm headed to Church.  If you don't have a response when I get home I will open the manual and see what I think.

[Grainger49]

Tom,

I'm home.  I don't know how we got to looking at the 270 ohm resistor so bear with me as I jump from the instructions to the schematic and think out loud.  I see now that PB (Paul Burkeland, AKA Caucasian Blackplate) is looking to see how much current is being drawn through the power supply.  I=V/R so he can get a handle on what the circuit is drawing (current).

I think there are three things to verify.  First you need a good ground for the power supply board.  You tested it on the top of page 45 in the manual.  Or at least that is where it is in my manual.

It comes off the board at the top of page 52 on a pad labeled "375V DC -".  It is the first instruction on that page.  If you measure resistance from this solder pad to the chassis plate it should be less than an ohm.

The 270 ohm 5W resistor is part of the power supply filter.  It is between the first and second capacitors in the high voltage DC supply.   If the tubes are in, the circuit should be regulating, as Paul Joppa posted.  When this happens there is a fixed voltage across this big white resistor.  The output of the power supply, before regulation should be about 275V (within 15%).  And 225 with a close tolerance after being regulated.

You said, "5w resistor - 276v (this was up around 362 when I did the voltage check prior to installing the shunt regulator)"  This is good. The first measurement had no current being drawn, 276V with the regulator hooked up is 1 volt higher than I stated above.

BTW Cc caps don't have an orientation. 

When Paul or Paul post back they can give you better guidance as whether the circuit is pulling the right current. 

As PB said, we will get you through this and you won't believe the sound you will have created!

Hang in there.

[Tom228]

Hi Grainger49.

Thanks for the tips.  While I am jonesin' to get this thing done and off of the bench (read: kitchen dinner table), I don't yet have a TT or a amp.  So, it's not like I need to be in a rush to get it done (contrary to a couple of TT having friends who are anxious to try this thing out).

I measured the resistance as you requested.  Red measure lead on the negative 375v pad and the black measure lead to the chassis plate and I got 0.2 ohms.

The voltage on the +375 lead has come up a bit during the course of testing and moving stuff around.  When I first turned the power supply on, it was indeed showing 362v.  I tested it again just prior to putting the shunt regulator back on the board and the voltage had come up to a closer 371v w/o the shunt regulator attached.

My 5w 270 ohm resistor is green and round.  Voltage on its pins are (left): 292v (right): 280v with the shunt regulator attached.

[Paul Joppa]

...
My 5w 270 ohm resistor is green and round.  Voltage on its pins are (left): 292v (right): 280v with the shunt regulator attached.

It's not exactly what I predict, but pretty close - close enough to draw the following conclusion:

* The current through the shunt regulator tube is no more than the C4S target

We already know the following:

* The bias on the shunt reg tube (terminal "kreg") is as low as the 431 can make it.

* The bias voltage for a new tube should be at least 7 volts.

* The plate voltage on the reg tube is closer to the supply voltage than to the target 225v regulated

* The shunt reg tube is getting adequate filament power (the heater glows visibly, the tube gets hot,  and the measured 6.3 volts is correct)

Based on these observations, it sounds like the 12BH7 tube is just not conducting enough. Contact Eileen on Monday and get a replacement tube - mention this thread and someone should test the replacement before shipping it.

It is possible the cathode was poorly formed at the factory and it will eventually conduct better - typically 50 to 200 hours of running will do that. However, the tube should not be run for any extended time without the rest of the circuit - it will be get too hot - so I cannot recommend doing this in the Eros circuit.

[Tom228]

Thanks Paul!  I will give her a call tomorrow.

Is there any way I can test the tube?  Or do you need special gear for that?

[Tom228]

Good news everyone!

The new tube came in.  Installed it and checked D1 and D6 and WAMMO BLAMMO!  223v! 

Soldered D1 and D6 into their homes, completed the circuit checks and then the big moment came.  "Please don't catch fire, please don't catch fire" I chanted as I plugged the cord into the wall.

No fire!  And all of the voltage checks came out in spec!!!

I could not see the two X79 tubes glowing.  But I know they had voltage.  Is that normal?  The center tube was glowing.  May have to wait until it gets dark to see the glow.

Sadly, I have nothing to hook the preamp up too at the moment. 

I picked a ProJect Experience 2 from the Needle Doctor.  It should be here later this week as should the new AVR (Denon 4520).  Hopefully late this next weekend I'll be enjoying it all!  Thanks very much to everyone for their help!!