Power chord for SEX amp 3.0? (and other questions about SEX) [resolved]

[slankoe]

Greetings!

I am glad to be joining the bottlehead builder's club soon as my SEXy amp is on the way to completion. However I am stuck at the current step and would appreciate a nudge in the right direction.

Here's my sitch, I'm on the powerline voltage test, on page 28 of the manual it is telling me to use the provided power cord, but I don't have that power cord. The only one I was given is not yet assembled, and I have figured that this is the C4S upgrade. So I open up the C4S manual and is gives a very strong warning not to assemble the C4S yet. So my question is what the heck do I do?

Can I use an ordinary power cord?

Thx,
-Dan

[slankoe]

I plugged the regular cord in and I only got 8-10 volts. Shouldn't I be getting 120?

What did I do wrong...

[slankoe]

Oh right now I've figured out... I feel like such an idiot. I skipped the step where the fuse goes into the fuse holder, because I don't have a fuse holder.

edit: Wait hold on, I found it.   

121.2 volts, perfect. One question, isn't that supposed to go away when I flip the on off switch of the SEX? Because my voltage stays at around 120 whether the switch is in the 1 position or the 0 position.

My SEX just won't get turned off?

edit 2: ok she passed the tube glow test. I think I'm good so far.
If I have any other problems, I maybe post here again, and figure it out myself This is kinda fun stuff, eh? I've never built anything like it before. Cheers

[JeffYoung]

The voltage test is done from the IEC, which is before the power switch.  The power switch turns off the voltage between the IEC and the transformer.


Cheers,
Jeff.


[Edit: and you're definitely not the first to try and run a voltage test without the fuse. ]

[kgoss]

 So it's very important that you unplug the power cord before continuing the build.  Like Jeff said, there is power on the IEC regardless of the amp power switch position. And if you continue the build with the amp plugged in you risk getting shocked by touching the IEC or power switch terminals.

[slankoe]

Hey guys,

I have finally finished the SEX build (and yes, of course I only had the cord in for voltage testing! good advice anyway).
However I have run into a hiccup, actually at the very last stage voltage testing.

I began testing starting from terminal 1 and moving up like the manual said, same as when resistance testing. Everything seemed good on visual check. Resistance check was good too. Now as I got to terminal either 4 or 5 my readings were off (I can't recall what it was, wish I had recorded it...), and at terminal 6 I saw a spark. Looks like a short. I turned everything off and back on again, started testing again, this time I was getting low readings like 0.6V, or very high readings like 1.5 mV, and now I am not sure that my meter is reliable...

I did my resistance testing again just now, I got all the same results as before. However some were "unusual," but I let them slide because they weren't zero (0), where the manual that it's apparently not a problem unless it says zero, indicating a connection where there shouldn't be one. I guess I should have looked closer, as I might have assumed that it said kilo-ohms or something.
I've listed the current measurements below, and to my memory they look the same as when I first measured. 107.6 ohms is a recurring number

Terminals 30, 31, and 32 are 107.6 ohms.
Terminals H2, H3, H4, H5, and H7 are 107.6 ohms
Terminal H6, is 53.7 ohms

I also made sure that the capacitors weren't wired backwards, and looked everywhere so that nothing was crossed or otherwise causing a short. I'm at a loss for what to do, and I don't want to voltage test again if I risk screwing up my first tube amp ever, and the first one I've ever built.

Does anyone have any suggestions?

Oh yes, and I should say this also: When I was doing my final voltage testing, and that after the spark and wonky readings happened, the fuse was and is still intact.

[Doc B.]

Was the spark created by accidentally touching the test probe to two terminals at once, or did it happen by itself?

[slankoe]

Was the spark created by accidentally touching the test probe to two terminals at once, or did it happen by itself?

I don't see any other way it would happen actually, unless it's a ground fault... isn't that right? Anyway, a ground fault could electrocute me too, couldn't it? So if I touched the base with my right hand to adjust it's position while it was live and I didn't get zapped, it's not a ground fault?

Maybe the probe did touch two terminals, but my hand actually slipped just as I was about to touch terminal 6 (where the pop noise and spark happened). I am pretty confident you're right though in that two terminals were touched simultaneously.

And do the recurring numbers mean anything?!

[Doc B.]

I just want to establish what caused the spark. The most common issue is accidentally shorting two terminal together with the test probe, which seems to be the case here. But a wire that was only attached to a terminal but not soldered can also spark if it gets moved and makes intermittent contact.

this time I was getting low readings like 0.6V, or very high readings like 1.5 mV,

Both those values are very low, with 1.5mV lower than 0.6V.

Could be that you have lost DC to the heaters. Are your tubes glowing?

[slankoe]

My tubes do glow still. And I should also say that the 1.5 reading was a capital m 1.5MV as in MEGAvolts? But that seems insane. Its probably millivolts.

[Doc B.]

Those resistances aren't really conclusive. Only one seems a bit off from what I measure on a S.E.X. 3.0 here at the lab, that being the 53.6 ohm one. I would suggest starting the voltages tests over and reporting anything that does not meet spec with the values in the manual.

[slankoe]

The voltage for terminal 2 is good (85 or so), but then terminal 3 is completely weird. It goes in the millivolt range, between 200mV and 2mV sometimes there is a minus for example 02.4mV was just measured. The number keeps changing. what the hell is going on?

I'll try the rest of them...

[slankoe]

I plugged it all in and my headphones make sound out of the left ear only

[slankoe]

I hear a faint buzzing in the right channel sounds like oldschool radio. Left sounds good. Switched tubes, same thing, so its not the tube. Also when I turn off the amp, it still plays. Then fades away. I guess this is how tube amps work? Kinda neat.

Just quadruple checking the connections here and they seem ok so far

[slankoe]

Did all my voltage checks again. All were pretty normal looking. Except much of the 385V were bumped to 400V and likewise the ones that were supposed to say 400 were closer to 425. The only one that isnt normal is terminal 3 which shows in the millivolt range, which is not ZERO, but then again all the ones that were supposed to say zero as per the manual actually are close to zero, but none of them are zero. I'm assuming this is just because of the sensitivity of the volt meter or what?

Also, maximum volume on the amp with Sennheiser HD650 only reaches comfortable listening. I can't crank it any more.

With that old radio sound in the right channel, it's volume is contant no matter what I set the amp volume to.