S.E.X. amp seconde hand

[mwgrient]

Dear all,
I have a Bottlehead S.E.X. amp. Bought second hand, hence I am not feeling comfortable yet to build a complete system like the S.E.X. amp.

When I attache the power cable (220v) there is a loud sound from the headphone: It sounds "like a dolphin". I instantly shut down the amp of course.

My question is: does someone recognise my description of the sound (dolphin)? And maybe knows where to start. Could It be the tubes are dead?

Regards, hope that someone can help me a little bit further...
Marco 

 

[Paul Birkeland]

Does it have a 240V transformer or is it wired for 240V? 

If you don't know, you can flip it over and post pictures of the bottom of the power transformer.

 

[mwgrient]

Hi, hope you can see the attachments for this!

 

[Paul Birkeland]

Alright, so you have a 240V SEX amp, are you in a 240V country? 

This noise could easily be external interference from a wireless device like a router or a cell phone, or a badly polluted powerline. 

There's maybe a 0.1% chance that it's tube related.

 

[Doc B]

The sound you describe is an oscillation. Most likely it is due to dirty tube pins or a bad connection somewhere. Try cleaning the tube pins and sockets for starters.

 

[mwgrient]

oscillation: OK, I will clean the tubes! They are dirty in deed.

country: I am in a 220/230 country (Europe/The Netherlands) I have bought the amp in Norway (240). And I also will eliminate interference.

 

[mwgrient]

Cleaned the tubes, no effect. After some seconds (with the volume closed) there is my loud oscillation sound.

 

[Doc B]

Is the sound only in one channel? If you wiggle the tube can you get the sound to stop?

 

[mwgrient]

one side only! If I touch the right (this must be left) tube (having the amp in front of me), and touching the tube, the sound changes a little bit. But keeps on going loud... wiggle the tube does not effect it.

I also found that if I turn up the volume a bit, It goes away?

 

[Doc B]

Now swap the tubes in the sockets and see if the noise follows the tube.

 

[mwgrient]

it does not, stays left channel: so it is not the tube!

 

[Doc B]

Then it is possibly a bad solder joint. A good place to start would be to reflow the solder joints around the tube socket on the noisy side.

 

[mwgrient]

Gould it be the potentiometer/volume? I have oscillation when I turn off the volume, then when I turn it on, It goes away. But on 12 a clock the oscillation is loud again. Etc.

 

[Paul Birkeland]

If you have nothing plugged into the inputs of the amplifier, then noise that varies with the position of the potentiometer isn't useful information.  Your amp is just picking up ambient noise at the inputs and you're controlling how much gets into the amp by turning up the volume pot.

 

[mwgrient]

OK, thanks for the information! I have nothing in the input.

I have re-soldered every joint on both tube sockets, but no effect at all. Pitty. And did a good look at all the soldering joints. Not luck either.

 

[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)

 

[Jameson]

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?