Just finished my S.E.X.

[SilverS]

Oh and a minor update the Hum is gone, but still no right channel to speak of.

[cmason84]

I want to piggyback on this thread as I am having the same issue... sort of. I just finished my SEX kit as well and when playing my ipod w/ Grado RS-2 headphones plugged in, the amp seems to work fine out of both channels. However, when I plug in my speakers, the right channel is not working.
I troubleshot to ensure that the speakers and cabling were not the issue, and they were not

So, I retraced all of the steps, paying very careful attention to the wiring from the headphone jack to the binding posts, which seems to be correct. I triple checked my solder joints which all seem to be good (I even moved one wire from the twisted teflon pair of wires to the outside terminal of the bottom pair of terminals on the headphone jack, as the inside terminal was crowded and made me suspicious that that terminal may have been a bad solder joint with how crowded it was). However, the problem remains the same.

I'm at a loss as to what else I can try, so I'm going to list a couple of inconsistencies that I found with the resistance/ voltage checks to see if someone can make sense of what might be going on...

RESISTANCE
19, 39 = 5.5K ohms at minimum volume (should be at 0 ohms w/ volume at minimum)
A4, B4 = 6K ohms at minimum volume (should be at 0 ohms w/ volume at minimum)

VOLTAGE
PT terminal 1= 0 VAC (should be at 120 VAC)
PT terminal 7= 188 VAC (should be at 0 VAC)
PT terminal 10= 188 VAC (should be at 0 VAC)
*Terminals 6 and 9 on PT are at 188 VAC as well.

[Paul Joppa]

SilverS, those voltages are low, but not a lot low. Makes me wonder if your power line voltage is low, or if your meter is reading accurately. Let us know when you've replaced the headphone jack, I still suspect some internal damage for the intermittently missing channel. The fact that it once worked indicates the electronic portion is wired correctly.

cmason84, the voltages on the power transformer 6=7=9=10 do vary with different meters, so if the voltages at the tube sockets are correct you can ignore those power transformer measurements.

The zero volts at power transformer terminal 1 indicates you have the neutral connected to that terminal, not the hot. Check your wiring carefully, then if necessary check your house wiring - it may be that your power is wired incorrectly. (I am assuming you have true 3-wire sockets with a good safety ground.)

You say you get both channels on the headphones - first thing is to be sure it's really both channels, and not one channel in both ear pieces. The latter would indicate a bad connection between the headphone plug and the jack, which might be a mechanical problem rather than an electrical one. If you do have both channels in the phones, then the problem is in the wiring from transformer to jack and speaker connectors.

[cmason84]

Thanks Paul, all is well now.

The power was wired correctly (voltage check sheet lists incorrect voltages for terminal 1 and terminal 2 on PT; they're switched).

The problem was the wiring from the jack to the binding posts. When the directions said to solder the wires to the red and black binding posts, I was looking at the red and black on the underside of the chassis instead of the topside of the chassis. All I had to do was swap the wires at the two inside binding posts and I'm getting sound from both of my speakers now.

[SilverS]

I have already replaced the headphone jack, which fixed the hum. As for it transmitting on both channels I checked again, and it turns out it was just transmitting a the left single to both sides. So even at the time when I posted to worked on both, it really was just a mono signal being transmitted on both sides.

[Paul Joppa]

Good, that's progress!

OK, we'll do some signal tracing, starting at the input and output. First, find a song that is fairly consistently loud. Unplug the source from the SEX amps and measure the AC voltage at the RCA plugs coming from the source. You should see a fraction of a volt on each channel - I'm just making sure your meter can measure a signal that small, and that both channels are working on the source.

Now it's the right channel that's dead. That would be hhe "A" tube which is on the left when the amp is upside down, correct?

Then plug that source into the right channel (the dead one) and measure the voltage at T19, with the amp still turned off. You should see the same voltage if the volume control is all the way up. Then check at the tube socket pin 4 - that's the grid, input to the tube, and should be the same as T19.

If the signal has gotten that far, then we'll check the other end. Measure the AC voltage at T20, where the output transformer brown wire is connected. Do this with the amp turned on. You should see a much greater voltage. If it's there, check at T5 which is the transformer output - should be less again, maybe a volt or two.

[SilverS]

I'm really confused right now. I just tried testing those terminals and when I had the negative lead connected to the ground wire from the power socket, and the red one in hand touching nothing, it was reading 1-1.5V~. Then when I connect the positive lead to terminal 19 it drops to .0003V~

Also I had a question about terminal 19. I recall when soldering resistors to those terminals, the guide called for the B side to have the resistor soldered to the lower hole of terminal 19, while the A side should have it soldered to the top hole of terminal 19. Is this a mistake in the guide? And perhaps why I'm not getting a signal from the right channel?

Also, considering speakers are picking up the right channel wouldn't that mean the terminals around the tubes and the tubes are all working properly?

[Paul Joppa]

When the meter lead is not touching anything, it acts like an antenna and picks up whatever electrical fields are around. Once it is connected to something, the low impedance of that something (less than the 10,000,000 ohms of the meter input anyhow!) shorts out the antenna function, leaving the measured voltage.

The top and bottom holes of the terminals are all the same metal, so they are all connected together. I'd call it an "inconsistency" in the manual ...  sounds better that way.  :^)

You said previously "As for it transmitting on both channels I checked again, and it turns out it was just transmitting a the left single to both sides." Now you say the right channel is working with speakers. So I don't know what the real problem is anymore. If both channels work with speakers but not with headphones, then the headphone jack/transformer output/speaker terminal wiring is in error somewhere.

[SilverS]

Yeah I can see where the confusion is coming from. Let me sum everything up to a final conclusion:

The speakers since day 1 of the issues have only been transmitting on the right channel.
The Headphones since day 1 have only been truly transmitting on the left channel (when I said they were transmitting both it was just the left channel being sent through both sides for some reason)

So where do we go from here?

[Paul Joppa]

Thanks, that makes better sense now - guess I just got lost in teh many posts.

OK, the amp is generating output on both channels. The output (autoformer secondary connections are T5 and T25 for the hot lead (the black primary and white secondary are both connected here. The cold side of the outputs are the secondary black wires, connected at T10 and T30.

The hot outputs (T5 and T25) go to the headphone jack, and from there to the hot (red) speaker binding post on the top side for that channel. You may have to trace the physical wires, because the output transformer secondary winding has a fraction of an ohm resistance, making it hard to tell with a meter which speaker terminal is connected directly, and which is connected through the winding. Also, the speaker terminals in the manual are coded red for one channel, black for the other channel - but on top there's a red and a black for each channel - it's the binding post color, not the base color referred to. I'm not sure if the current speaker terminals are identical to what's in the manual now, so I can't be certain this is clear, but this seems to be the most likely place for a wiring error.

Similarly the cold outputs go to the headphone jack (lowest terminals, which are connected) and from there to the black speaker binding posts.

It might help to first unsolder the wire that goes from T5 to the headphone jack, and also the one at T25. In both cases, these are one wire of a twisted pair. Then those wires can be traced with an ohmmeter, as can the cold wires (the other wire of the twisted pairs).

[SilverS]

Alright I desoldered the wires connected to T5 and T25, no sound on either channel now. I'd also like to add I never plan on hooking speakers up to the amp, so trouble shooting the binding posts is at the bottom of list for me.

[Paul Joppa]

So, now we trace the wiring to the headphone jack and binding posts. (I am including the speaker binding posts because an error in that wiring could cause problems with the headphone wiring, and I don't want to complicate matters by deviating from the manual.) At every terminal you test, inspect the solder joint while you are there in case the solder hasn't flowed properly.

First check the ground wiring. With one meter lead to terminal 17 or 18, check that there is zero resistance to terminals 17, 18, 15, and 10 (and to A3 on the tube socket). Then check resistance to the lowest terminals on the headphone jack. Finally, you should find zero resistance from this ground to the two black speaker binding posts (one for each speaker).

All OK? Then measure the resistance to ground of the wire that used to go from terminal 5 to the headphone jack - it should be infinite. Do the same for the red speaker binding posts which should also be infinite resistance to ground.

Repeat for the other side, terminals 37, 38, 35, 30, and B3 for ground, and infinite resistance at the wire that used to go from terminal 25 to the headphone jack, and the red binding posts.

If all that is OK, then we will trace the hot leads. With one meter lead connected to the wire that used to go from terminal 5 to the headphone jack, put the other lead on the middle terminal of the headphone jack on the side nearest the volume control - the should be connected with zero resistance. At the other end of the 120 ohms resistor, you should measure 120 ohms. The resistance to the other resistor on the headphone jack (the top terminals) should be infinite. Finally, at one of the red speaker binding posts you should read zero resistance, and infinite resistance at the other red terminal.

Repeat for the other side - meter to the wire that used to go from terminal 25 to the headphone jack, read resistance at both ends of the resistor on the top of the headphone jack (should be zero and 120 ohms) and the other red speaker binding post.

[SilverS]

Here are the results of the tests:

All resistances in Ohms
T17 ~ 1.1
T18 ~ 1.4
T15 ~ 1.1
T10 ~ 1.6 - 1.8
A3 ~ 1.6 - 1.8
Black Binding posts (L/R) ~ inf./inf.

T37 ~ 1.1
T38 ~ 1.4
T35 ~ 1.1
T30 ~ 1.6 - 1.8
B3 ~ 1.6-1.8
Red Biding posts (L/R) ~ inf./inf.

As for the wires going from T5 and T25 to the headphone jack, was I supposed to desolder them from the headphone jack or the terminal strips?

[Paul Joppa]

Man, it's really hard to describe things fully with just words! Sorry about that, I means to desolder from the terminal 5 and terminal 25.

The ground buss resistances are all low, showing they are connected properly. However, those resistances should not differ by even 0.1 ohm, since they are all connected by short lengths of wire. It may be the solder connections are not good, or it may be that the connection to the meter was not good enough to get that kind of accuracy. It can be quite difficult to get a good, low resistance connection with a meter probe or even a cliplead.

You did not report the resistance from ground to the bottom terminals on the headphone jack, but they should also be near zero. There are two twisted pairs of wire, from the headphone jack, one to each speaker output pair. One of those wires is the ground and should go from the bottom terminal of the headphone jack to the black binding post. You did report that none of the speaker binding posts are connected to ground, but the black ones should be. So there is a failure of ground connections somewhere along that line.

[SilverS]

Whats really confusing me is that the speaker posts get their signal from the headphone jack, which means they're getting the right channel from the headphone jack but the headphone jack doesn't appear to be getting the signal in the first place.