S.E.X. amp seconde hand

[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

 

[Jameson]

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

Will do the measurements again.

We were all new at this at one point in time or another. I still mess at least one thing up per build.

 

[mwgrient]

 

[Oyvindk]

Hi.
I buildt this amp 6 years ago and recently sold it to mwgrient. I am not an experienced amp-builder, but it worked fine all the time I had it. If anyone is interested, here is the building process documented (in Norwegian, but with many pictures)  link was not allowed, but google  “
hifisentralen Bottlehead Single Ended eXperimenter's kit“ and the thread should appear.

I listene to the amp for two hours (no issues) before it was double-boxed and shipped. Obviously, something must have happened during shipping, and therefore my first suspicion would be (besides damaged tubes, which was  ruled out) a bad solder joint, as Doc B mentioned.

The amp is wired for 8ohm output as I mainly used it with horn speakers.

 

[Paul Birkeland]

So far there isn't any indication that there's an issue with the build.  It could simply be some external interference. 

 

[mwgrient]

I have tried to eliminate interference. Other room, divert power cable and wall-plug. Shutting down the computer. Nothing.

I can hear music, but when the volume is turned off, de loud signal is back. I will try to install the noise eliminator.

 

[mwgrient]

Here is a link to my amp, with a sample of the sound it gives true my headphone left channel.

https://www.youtube.com/watch?v=0OB8lpQ58lc

regards, Marco.

 

[mwgrient]

Hi all, I have soldered the sockets lower than they where soldered. And re-soldered all the ground wires/points again and again. There is no oscillation anymore!
Only a faint hum when I connect my headphone; It is also there when the volume is turned down//closed.

 

[Tom-s]

Glad it worked out!

I have soldered the sockets lower than they where soldered.

To further explain to others on this forum.
What you've done here is relocate the grid stoppers closer to the socket pins (1,4) of the tube as a preventive measure for oscillation.


Now enjoy it!
Let us know how you like the SeX 2.1!

 

[Paul Birkeland]

Oh man, that's quite a noise! 

 

[mwgrient]

Yeah! It is still not quiet, but doing a lot better now. Pffiew!

I would like to replace the potentiometer, jack socket and RCA terminals.

Does someone know where to get the distinctive Bottlehead knop?