S.E.X. amp seconde hand

[Paul Birkeland]

How about a voltage check?

[mwgrient]

That's my first. I do have a meter, but will come back with my measurements since I have the PDF with the build instructions.

[mwgrient]

I would like to check something: is the cable shown in the red cirkel OK? It is soldered at the power socket (as ground), but not soldered in the power switch? See the attachment.

(I am digging into the volt meter lessons before doing a voltage check on a live system)

[oguinn]

Yep that’s fine.

[mwgrient]

Ok, thanks for confirmation.

The measurements:

Terminal - Voltage
1 - 452
2 - 0
3 - 0
4 - 903
5 - 451
6,16 - 856 / 856
7,17 - 0 / 0
8,18 - 0 / 0
9,19 - 0 / 0
10,20 - 902 / 902
11,21 - 766 / 768
12,22 - 0 / 0
13,23 - 0 / 0
14/24 - 0 / 0
15,25 - 38 / 37
A1,B1 - 0 / 0
A2,B2 - 802 / 803
A3,B3 - 38 / 37
A4,B4 - 0 / 0
A5,B5 - 0 / 0
A6,B6 - 4 / 4
A7,B7 - 0 / 0
A8,B8 - 7 / 7
C1 - 0
C2 - 8
C3 - 0
C4 - 0
C5 - 7

Certainly not what it should be?

[Paul Birkeland]

If those voltages were correct, many of the capacitors in the amp would explode almost instantly. 

Since this has not happened, I would suggest trying to measure the DC voltage of something like a 9V battery to be sure you are using the meter correctly.

[mwgrient]

I see 

I have chosen the 600 V˜ since I am using a 220v amp; see pictures. A 9 volt battery measures 16 ?
What am I doing wrong?

[Deke609]

Try putting fresh batteries in your meter.  For some reason, a lot of meters read high when the battery is low.

If new batteries don't fix the problem, I'd get a new meter.

Edit: and note that in the pic you have the meter set to read AC voltage (wavy symbol), not DC voltage (straight dashed and solid liness), which will work for taking measurements of the incoming line voltage, the power transformer terminals and AC heater voltages -- but everything else in the amp will be DC.

cheers, Derek

[Paul Birkeland]

You have the meter set to measure AC volts and you are trying to measure DC volts.

[Thermioniclife]

The V with the squiggley line is for measuring AC volts The V with the straight line and dotted line underneath is for DC volts.
If your meter is not auto ranging select the scale that is one step larger than the voltage you expect to measure.
This will give you the most accurate reading.

[mwgrient]

Oh lord, thank you: I am in the learning mode now.

Will do the measurements again.

[mwgrient]

The measurements again:

Terminal - Voltage
1 - 204
2 - 0
3 - 0
4 - 410
5 - 204
6,16 - 390 / 389
7,17 - 0 / 0
8,18 - 0 / 0
9,19 - 0 / 0
10,20 - 411 / 412
11,21 - 354 / 353
12,22 - 0 / 0
13,23 - 0 / 0
14/24 - 0 / 0
15,25 - 17 / 17
A1,B1 - 0 / 0
A2,B2 - 364 / 364
A3,B3 - 17 / 17
A4,B4 - 0 / 0
A5,B5 - 0 / 0
A6,B6 - 2 / 2
A7,B7 - 2 / 2
A8,B8 - 3 / 3
C1 - 2
C2 - 3
C3 - 0
C4 - 2
C5 - 3

[Paul Birkeland]

You have a lot of voltages that are the numbers we are looking for, but not listed on the terminals where we wold expect them.

What jumps out at me is that A5/B5 are 0V, but A6 and B6 are ~2V.  This isn't really a likely/possible set of circumstances.  I would recheck A5/B5.

-PB

[mwgrient]

on a recheck

a5 - 71
b5 - 72

[Paul Birkeland]

Well, I can see enough there to say the amp is operating as expected in terms of the tubes doing their jobs.

You could try adding this modification, which will interrupt several sources of noise:
https://forum.bottlehead.com/index.php?topic=11676.0