Mainline Voltage Check

[FS]

Hello,

I have completed my Mainline. The voltage check gave me different values for each side. When the tubes are inserted and the amp powered up, the tube filaments glow on all three tubes.
On the C side of the Amp, the D1 and D2 of the A side of the C4S board glow, D1 and D2 of the B side don't.
On the A side of the Amp, none of the D's glow on the C4S board.

My voltage measurements as per instructions pn page 73 of the manual (tubes are inserted):

+275VDC on Power Supply board: spec is 275V,  reads 243V
+6.3vDC on Power Supply board: spec is 6.3V, reads 5.33V
IA on A side of C4S board: spec is 275V,  reads 243V
IA on B side of C4S board: spec is 275V, reads 243V
Breg on Regulator board (both sides): spec is 220V, reads 3.7V on A, 153V on B
-reg on Regulator board (both sides): spec is 0V   reads 0V on both sides
Kreg on Regulator board (both sides): spec = 8-12V,  reads 2.43V on A, 1.58V on B

Could somebody please pinpoint me to the possible problem?
Thanks in advance.
Cheers,
Falko

[Paul Birkeland]

I would start by determining why you don't have 6.3V DC out of the power supply board.  This is most often solder joints.

The 243V on the high voltage side is also odd, but would still be enough for the regulator to work properly.  There may also be a flaky solder joint on this part of the board that's causing some voltage drop that wouldn't otherwise be there.

Breg being 3.7V on A makes me believe that you have a jumper on that board that isn't where it's supposed to be.

The Kreg voltages being so far off also point to jumper issues on the PC boards (you did solder the two legs of each trim pot together as advised in the instructions?).

-PB

[FS]

Hi Paul,

Thanks for your quick reply. I have touched all the soldering joints to re-flow the solder on the power board and the regulator board. I did the same on the connections to the power transformer. I checked and retraced all the steps from populating the boards through soldering, everything looks as it was supposed to. And yes, I have soldered the two legs of the trim pots together as instructed. I still have the exact same readings. Are there any other readings that I could take to narrow it down?
Thanks,
Falko

[Paul Birkeland]

It might help to put some photos up of your build, as well as to focus on getting 6.3V out of the power supply board when the tubes are plugged in.  This is still most certainly a solder joint issue.

-PB

[FS]

Hi Paul,

Thanks. I will work on this tonight. The 6.3V will be my first aim before moving on to the other boards.
Cheers,
Falko

[FS]

Hi Paul,

I have checked the identity and orientation of every single piece on the power transformer board. I have re-soldered every single piece on the power transformer board for a total of 3 times, re-flowing the solder and holding for 10 seconds, then letting it sit for a few seconds before proceeding to the next. I have also resoldered every connection to the power transformer, and the wiring from the switch to the power entry. I have done the voltage check as indicated on page 38 of the manual (no tubes). I am still unsuccessful in getting a voltage higher than 5.33V between the -6.3V and the +6.3V pads. Any additional thoughts? What else could I try? Thanks.
Falko

[Paul Birkeland]

You'll also want to be sure the 10uF yellow capacitors are oriented properly.  Next, measure the DC voltage on the banded end of either 1N5820 next to the label "275vDC".

[FS]

Hi Paul,

The DC voltage at the banded end is 10.2V for each of the 1N5820 closest to the 275V DC pad.
Voltages are 4.8V and 4.7V, respectively, at the banded ends of the other set of two 1N5820.
F.

[Paul Birkeland]

Are you 100% certain that there's a 1085 regulator mounted to the heatsink and not an MJE5731A? 

Your resistor values look right, so if one of those 10uF caps isn't in backwards, it's difficult to determine what is pulling your voltage down so low.

[FS]

Hi Paul,

It says LM1085 on the part that has the heat sink.
I am pretty sure that I have put the orientation sensitive tantalum caps in the right orientation, but can't check that as I had trimmed those leads after soldering.
I have measured the voltages at the 10uF capacitors. On the one closer the the 6.3V pads, it reads 5.33V on the +, 0V on the -, the other cap has 0V on the -, and 10.4V on the + side. Are these values correct?
Thanks,
Falko

[Paul Birkeland]

You'll need 6.3V to continue.  Can you pull each individual tube and see if perhaps one is causing problems?  Also, be sure to inspect the tube socket areas around pins 4/5 on the 6C45 sockets and 4/5/9 on the 12AU7 socket.  Debris allowing these pins to come in contact with each other can also draw excessive current.

[FS]

Hi Paul,

All the measurements that I had made in the last posts had been without the tubes in the sockets. Do you want me to repeat them with tubes inserted? I will also check the tube sockets to make sure there is no contact.
Falko

[FS]

Hi Paul,

I have checked the tube sockets, and there are no unwanted connections/solder bridges visible.
Thanks,
Falko

[Paul Birkeland]

Did these issues come up on page 38 of the manual where the power supply test is performed?  Or is this a case where those values changed once the build was completed?

[FS]

Hi Paul,
I had 5.33V at the 6.3V pad during the initial power transformer board test, but decided to move on, as I assumed that this was within the 15% range. I understand that the 6.3V vs 5.3V issue has to be linked to the very first building steps, and I have retraced those, without any change. That is why I am surprised that I cannot locate the culprit....
Falko