Voltage checks - puzzled and… UPDATE: operator error. I don’t deserve this amp

[e2o]

UPDATE: Aw geez. Spare yourself the time. This thread only shows three things:
1) the Bottlehead folks are an amazing (and very patient) bunch; and
2) the documentation is astonishingly good; and
3) I’m a knucklehead. My assumption that wasted a lot of time: “it’s plugged into my wall outlet, my wall outlet supplies AC power. Therefore I will be taking all voltage measurements in AC.” Nope.

—————

Howdy!

OK, so doing my voltage checks. I bought a new meter for the project, and got a true-RMS meter by Greenlee (re-branded Brymen) after reading excellent reviews. I also have my big box store Sperry multimeter as backup.

I stick both in the wall outlet and get unequivocal 123 Volts. Then I do voltage checks on the crack and things get weird.

The Greenlee does the same thing no mater which terminal 1-10 I measure: With black on 12U, I place the probe on the terminal being measured, the auto-range voltage kinda flashes at 20ish Volts, then rapidly marches downward, slowing gradually and coming to a restless bottom at .005ish Volts. Each measurement 1-10 do the same thing with the Greenlee. (Ok, unit is still within the return period, let's get the Sperry out...)

The Sperry at least gives me some different results. Here is what I get, compared to the expected results in the manual:

Note: the result "1__." below means the meter displayed a "1" followed by two blank spaces, then a "." dot for this reading

Terminal  ||  Voltage Expected  ||  Voltage Measured
1  ||  50-100  ||  171.3
2  ||  170  ||  1__.
3  ||  0  ||  0
4  ||  170  ||  1__.
5  ||  50-100  ||  168.1
6  ||  0  ||  0
7  ||  90-115  ||  1__.
8  ||  0  ||  0
9  ||  90-115  ||  1__.
10||  0  ||  0

So, I'm puzzled why expected on 2 and 4 are 170, but the Sperry reads 171 and 168 on 1 and 5 respectively.
The expected zeros on 3, 6, 8, 10 I'm getting (yay!).

So, to me, the 170ish expectation on 2 and 4 - it kinda appears I'm getting in that ballpark on 1 and 5

Aaaack - so that's the "puzzled" part...

The "peeved" part is - what's up with this new meter? Is there something with the "true RMS" that is messing with me?

Additionally, the LEDs are lighting, and the tubes are glowing at this point. What is my next step?

Thanks!

- eric

[Doc B.]

How were your resistance measurements?

[e2o]

Resistance all good. The two input center posts were more different that I would have liked, but ok (99 and 88). But, yeah, both multimeters said "you may proceed"...

[e2o]

A few photos...

[Paul Birkeland]

Are both the black wires on the headphone jack captured by solder?

Your voltages being what they are would not indicate that the LEDs would be illuminated, so I would suspect a loose ground wire in the amp. 

[e2o]

Are both the black wires on the headphone jack captured by solder?

Yes, confirmed.

Your voltages being what they are would not indicate that the LEDs would be illuminated, so I would suspect a loose ground wire in the amp.

LEDs illuminate within 10 seconds of the amp getting power. Both tubes glow, both sides.

[e2o]

Are both the black wires on the headphone jack captured by solder?

Your voltages being what they are would not indicate that the LEDs would be illuminated, so I would suspect a loose ground wire in the amp.

So, looking through it again. If I’m concentrating on ground wires as you suggest - (sorry) should I be looking at a particular wire color or, um, any other distinguishing characteristics?

[lanson]

should I be looking at a particular wire color

To my (very limited) understanding: red wires are live, white wires are neutral, green wires are signal, and black wires are ground.

[Doc B.]

Black wires in the amp will be wires that are part of the ground buss. But other components also connect to ground. So the best way to address the possibility of a loose connection is to go over all of the solder connections, except for the LEDs which are a little sensitive to reworking. Since they are lighting up you know their connections are good already.

The reason PB mentioned the black wires at the headphone jack is because there has more than one wire connected to a terminal and it is the most common point where a connection has been missed or didn't get enough solder on all the wires.

[e2o]

...So the best way to address the possibility of a loose connection is to go over all of the solder connections, except for the LEDs which are a little sensitive to reworking. Since they are lighting up you know their connections are good already.

OK, back to my 4th careful check. Is there a way continuity tests could provide more information to simple visual inspection? Or something else?

Is "checking" meant to be "looking", or wicking solder off and re-soldering?

Is the fact that resistance checks being OK consistent with a problem with the ground?

thanks,

- eric

[Paul Birkeland]

Pull on each black wire with a needle nose plier (with the amp off and unplugged).  It's likely that one will either pull completely out from where it's sitting or will move a lot more than it should.

Alternatively you can heat up your soldering iron and reflow all of the joints on all of the black wires that work their way from the RCA jacks to the volume pot, then to terminal 3, then to the headphone jack, then back up to the two 6 lug strips at the rear of the amp.

[e2o]

Pull on each black wire with a needle nose plier (with the amp off and unplugged).  It's likely that one will either pull completely out from where it's sitting or will move a lot more than it should.

Alternatively you can heat up your soldering iron and reflow all of the joints on all of the black wires that work their way from the RCA jacks to the volume pot, then to terminal 3, then to the headphone jack, then back up to the two 6 lug strips at the rear of the amp.

OK. The tugging has been done during previous inspections. I will go again concentrating on the sequence you suggest.

The fact my voltage reading of very close to 170 on 1 and 5 INSTEAD of 170 expected on 2 and 4 - is that consistent with the ground bus theory?

[Paul Birkeland]

If the voltages on 1 and 5 are higher than 2 and 4, that definitely suggests a loose ground wire in the amp.  This is especially true if the LEDs on the socket are also illuminating, as those three pieces of information don't exactly fit properly into the same puzzle.

[e2o]

Ok. The joints are all wrapped and crimped, and soldering looks great. Continuity is good through the chain you suggest. I guess I have to wick and resolder even though it will mess up a tidy(ish) job.

Something doesn’t seem right to me. Can you explain your comment about the puzzle pieces not fitting?

[Paul Birkeland]

Can you get an actual measurement on terminals 2 and 4?  If 1__ is what you see on your meter, maybe post a picture of your meter and we can make some suggestions based on what's going on.