SEX Amp transformer problem

[jelx]

Dear Forum,

I just completed building my Bottlehead SEX Amp.  All the Resistance checks are OK.  The Voltage checks all check out, except the Power Transformer.  I am getting the following volt meter readings on the Power Transformer:

Terminal 1  50VAC instructions specify 120VAC

Terminal 2  60VAC instructions specify 0VAC

Terminal 4  OK

Terminal 5  OK

Terminial 6  OK

Terminal 7  188VAC instructions specify 0VAC

Terminal 9    OK

Terminal 10  189VAC instructions specify 0VAC

I have checked through the build against the build instructions, rechecked all resistance tests, rechecked all voltage tests, and heated/added solder to all the solder joints I could get my iron to.

Does any one have any suggestions?  Could it be that the Power Transformer is not working properly?

Sincerely,

John
Washington, DC AKA Puzzle Town, USA

 

[JC]

Just a guess, but it seems like there is a grounding issue, either with whatever the black lead of your meter is connected to, or with the outlet your amp is plugged into.

The reason I say this is that it looks like you are reading approximately half of your AC line voltage at transformer terminal one, and the other half at transformer terminal 2.

How I would start is to unplug the amp for awhile, then set your meter to the lowest Ohm scale, or to a 'continuity' setting if it has one.  With the black lead clipped to the round ground prong of the power plug, check the other safety and circuit grounds for very low Ohms or continuity.

If those points all seem good, it may be worthwhile to check that the grounded outlet you have the amp plugged into is, indeed, a grounded outlet.  You're not using a ground-lifter adaptor, right?

This is just the 'starter' stuff, to try and make sure that the readings you are getting can be trusted.

 

[Paul Joppa]

Your measurements at power transformer terminal 1 and 2 indicate that either the safety ground is not connected to the chassis, or your house wiring is not properly safety grounded. Normally, one prong of the wall socket is Neutral and connected to safety ground where the electricity enters the house; the other line is Hot and should be 120v, more or less. This will not affect the rest of the circuit as long as everything is operating normally, but it will make many fault conditions (such as internal shorts in the power transformer) unsafe. If it is a house power problem then all other appliances with 3-prong power plugs are also at risk of being unsafe.

Transformer terminals 6, 7, 9, and 10 often read funny depending on the particular meter you use. Many inexpensive meters do not read AC correctly unless there is no DC present, and those terminals have both. If the other voltages are correct, the circuit is probably operating properly.

 

[jelx]

Thank you Jim C. and Paul Joppa for your replies to my call for help!

1ST.  I eyeballed all the ground wires and pulled them up a little so they did not touch the chassis plate.  I had originally installed the grounding wires nearest the mains-input touching the chassis plate.  I felt that they probably should not directly touch the chassis plate.

2ND.  I moved the amp to a three prong outlet that I am 95% sure is grounded.

  Note:  I live in a 100 year old Apt. Bldg. that originally had gas lighting with some electricity circuit.  I    guess that the Builders were not sure if electrical circuitry was the future.  Consequently, over the years, a lot of renovation has been done on the Bldg wiring.  I am not 100% sure that my Apt three prong plugs are grounded.  I normally plug my stereo into a two prong socket with ground-lifter adapter.

3RD.  I then checked out the grounding continuity with my meters black lead clipped to the the ground plug of the power cord.  I registered continuity from all the ground wires and the chassis plate.  Thanks for the tip Jim C.  I hadn't realised that I could check grounding continuity.

4TH.  I then remeasured my kit "Voltage checks".  Now they are all different from the kit instructions?

How do I check to ensure that my three prong plug receptacle is in fact grounded?

Any other suggestions?

Sincerely,

John L.

 

[jelx]

I might add.

That the SEX Amp Headphone Jack registers continuity at each binding post to each of the upper, middle, and lower point circuits on the headphone jack.  In other words if I connect the black meter lead to one binding post.  The red lead will register continuity as I move it to the other three levels of Headphone jack circuitry.

John L.

 

[sl-15]

How do I check to ensure that my three prong plug receptacle is in fact grounded?
there is this little gadget that you can buy at most hardware stores. it is an outlet tester and looks like this:

http://www.acehardware.com/product/index.jsp?productId=3099774&CAWELAID=166610897

you probably get them cheaper online somewhere. i am not sure if there is another way how you could measure it with a multimeter for example.

 

[JC]

The safest, easiest way to check grounded outlets is a little checker you can get at the hardware store or home center electrical department.  It looks like a grounded plug with some indicator lights on the end, and depending on the combination of lights lit and extinguished when you plug it into the outlet, it can tell you if the outlet is wired correctly and functioning and what the mis-wire is if it is not.  Just a few dollars, totally safe and very useful when you have doubts about an outlet.

Of course, you can use your meter on the appropriate VAC scale to check an outlet, though sticking your meter probes into a live outlet requires great attention and care to avoid a visit from the bright blue Jeebus!  You will notice that, of the two flat slots, one is wider than the other.  The wider one is supposed to be neutral, the narrower one "HOT".   The round hole is safety ground.  So, if you measure between the two slots, you should read line voltage of approximately 120 VAC.  Measuring between the wider slot and the rounded one (Neutral to Ground)  should give you virtually nothing.  Measuring between the narrower slot and the rounded one (HOT to Ground) should give you 120 VAC again.

I cannot stress enough that you should only try this if you feel comfortable that your meter probes will fit comfortably into the slots on the outlet, and that you can take the measurements without running the risk of the probes ever touching each other!  A pair of leather gloves would be a nice safety item, as well as shoes and sox!

Or, just spring for the outlet checker and avoid the worry.

Another, perhaps easier, way to do this would be to just plug the amp in and check this at the power inlet on the amp.  You will notice on page 16 of the manual in the upper left hand corner of the picture the terminals are marked "L" for "Line" (HOT), "N" for "Neutral" and "E" for "Earth" (Ground).  If the amp is plugged into a correctly wired grounded outlet, there should be approximately 120 VAC from "L" to "N", virtually nothing between "N" and "E", and approximately 120 VAC from "L" to "E".

If that checks out, then you should get correct readings at transformer terminals 1 and 2.  As Paul points out, the readings you get at some of the other  transformer terminals can be dicey depending on how well your particular meter discriminates between AC and DC voltages on the same node.  But, if you get things squared away on transformer terminals 1 & 2, it will indicate that you have a good safety ground, and your earlier checks seem to confirm that you've got a good circuit ground, too. That is important, both for safely operating something with a metal chassis, and for the circuit to behave properly.

After that, the DC Voltages will tell you if the amp is operating within normal parameters.

If in doubt about any readings, just post them as you did before, and I'm sure someone will chip in, either with an explanation or something else for you to check!

 

[jelx]

Jim C,

Thank you for your detailed input.  I checked the "Power Inlet" on my SEX Amp according to your recommendations.  My Amp was plugged into a three prong plug that I assumed was grounded.

Assumming that L = hot and N = neutral and E = ground.  My results showed the following:

L to N =122 VAC
N to E = .88 VAC ...... This seems close enough to zero??
L to E = 1.23 VAC ..... This seems close enough to zero??

Trans 1. manual desires 120VAC.  I tested at 122 VAC.  -OK-

Trans 2. manual desires 0 VAC.  I tested at .93 VAC.  -OK-

Trans 4. manual desires 3 VAC.  I tested at 3 VAC.  -OK-

Trans 5. manual desires 3 VAC.  I testd at 3 VAC.  -OK-

Trans 6. manual desires 163 VAC.  I tested at 167 VAC.  -OK-

Trans 7. manual desires 0 VAC.  I tested at 190 VAC.  -??-

Trans 9. manual desires 163 VAC.  I tested at 191 VAC.  -OK- I feel this may be close enough?

Trans 10. manaual desires 0 VAC.  I tested at 191 VAC.  -??-

I feel that my Transformer may check out reasonably enough that I am about to try a "Smoke Test".

Thaks again for the help,

John L.
located in the Land of Puzzling Events AKA Washington, DC

 

[JC]

It certainly appears that your transformer is working.  I suspect that the two questionable readings on the secondary are as Paul suggested: There is likely a DC component present on the node you are measuring, and it is "fooling" the meter.

The only question I have is the reading from L to E on the power inlet.  I would expect to see 122 - 123 VAC there.  N and E, as Paul noted, are eventually connected to the same point back at the power panel of your building;  the .88 VAC difference between the two is likely the result of the two taking a different path to that common connection back at the panel, and is, indeed, close enough to '0' to be negligible.

Good luck with your next checks!  I have a feeling your are close to listening!

 

[jelx]

Success is mine!!  I put my SEX Amp through a Smoke Test and then connected up speakers.  My SEX Amp works marvelously!!!!!!!!!!  And it sonds great.

Thank you Jim C. and Paul Joppa for the excellent advice and help on my Transformer problem.

John L.

 

[JC]

You're most welcome, and good for you!

 

[Frank Breech]

Hi, All, I am reading through different posts on troubleshooting around the time of the smoke test in order to shed some of my naivete RE electricity.  Basically, I just want to ensure that I live long enough to listen to my FP III, assembly of which is completed.  This thread was interesting to me but I'm stumped on one portion of it.  User Jelx was testing his apartment building's electrical ground by taking readings at the power inlet of his amp.  (see the posts for all the details).  The part that stumped me was his readings:

L to N =122 VAC
N to E = .88 VAC ...... This seems close enough to zero??
L to E = 1.23 VAC ..... This seems close enough to zero??

It seems like the L to E is not correct (should be approx 120 VAC) but it is not addressed any further in the thread.  Jelx, JC, Paul Joppa, if you see this post and can recall what happened I'm highly interested.

I will also start a thread in a more appropriate category to solicit some safety tips for my FP III smoke test.

Thank You

Mike

 

[Grainger49]

L is Line, the hot lead.  Hot to earth/ground should be 117-125V as you have surmised.  But... the rub is that the neutral is not grounded.  It looks to me like the ground is not grounded.  The service panel is old and only has a hot and neutral.  With no ground on the neutral you get odd readings to the ground which is just floating out there in the ether.

If you take Dan's suggestions for measuring voltages, put one hand in your pocket and clip on the black lead, you will be safe from getting shocked.

 

[Frank Breech]

Grainger,
Thanks for the note.  So, if the ground is not grounded, as in the readings above, that leaves a potentially damaging situation as Paul Joppa describes above:

" it will make many fault conditions (such as internal shorts in the power transformer) unsafe. If it is a house power problem then all other appliances with 3-prong power plugs are also at risk of being unsafe."

Correct?  Does this basically mean, for example, that if there is a short in the unit that the chassis could become electrically charged (since there's no place for the "juice" to escape (i.e.: ground).

I've obviously been using electricity without any idea of what it is or how it works.  Can you confirm the above scenario for me?
Thanks
Mike

 

[Grainger49]

Yes, an ungrounded circuit will be very dangerous when and if a wire gets grounded that shouldn't.  The chances are small, the danger is large.

I took some pictures today of good tools to have.  One is a tester that tells you how well your outlets are wired.  If the ground isn't grounded it says so.  These cost $10 or under so it is something every hobbyist should have.  

Look here:

http://www.bottlehead.com/smf/index.php/topic,3145.0.html

I'm about to go post the pictures.

 

[Frank Breech]

Grainger,
Thank again for the replies.
I'm going to move this conversation over the General category, I think.  Please keep an eye out for it there in the next day or so - as soon as I can get my thoughts/questions together and then get a chance to post.  I appreciate your help.

Hopefully hear from you soon

MIke