HELP - - Something went bad! [resolved]

[glynnw]

My Seductor had been working fine for months- only non-stock parts are matched JJ EL84 tubes and 3.9uF Mundorf caps and they have been in the amp almost from day 1.  Yesterday I changed the output impedence from 16 Ohm to 4 Ohm to match my new Spatial Audio speakers (yummy).  I was very careful, knowing I have a tendency to screw things up.  When I turned it on after this the right channel was out - I tried it in 2 systems to make sure it was really the right channel being out.  I checked the input RCAs and speaker terminals for continuity to the underside - all OK.  I very carefully inspected the transformer wires where I had soldered to make sure they were still OK -  they appear to be.  So now I have done a full check of all the resistance and voltage values.  A few of the 0 resitance points measure .1 or .2 Ohms, but I figure that is OK.  The only errors were on some voltage readings as follows:

Terminal  Should be  Actually Is

4                100            144
5                  95            varies frim 140 - 150
6                  380            337
7                  100            150
12                30-55        150
13                100            150
14                100            150
15                360            290
22                380            360
31                360            330
34                425            398
42                100            153
43                370            308
45                370            345

I am really not aware of touching anything or doing anything wrong when changing the output impedence.  I have checked all my work with a very bright LED light and it looks OK to me.
Any help would be appreciated before I give up and contact Bottlehead to send it in for repair.

 

[kgoss]

Can you post  a picture or two?

 

[glynnw]

Looks just like one on Bottlehead product page - http://bottlehead.com/seductor-single-ended-el84-amplifier-kit-specs/

 

[Paul Birkeland]

I too would recommend post photos of your build, especially where the wires connect to the output transformers.

-PB

 

[glynnw]

OK - Here are pics of left and right OT-2.  The wires going to binding posts were not changed - only the two short red and blck wires were added

 

[glynnw]

I apologize to Kgoss for my rude answer.  I didn't see how a couple of pics of the amp could help and I should have asked for clarifiaction of what you needed. After hours of screwing with this thing I am kinda burned out.

 

[Doc B]

Are the wires connecting the transformer secondary to the binding posts soldered to the binding posts? Also, the lower joint of the short black wire on the right output transformer looks kind of like a cold joint. I would guess that you simply need to reflow all of the new transformer connections that you made with this change.

 

[glynnw]

I just  resoldered the 8 OT-2 lugs that I had soldered in switching from 16 to 4 Ohm.  Right channel still out.  And the output trans wire is not soldered to binding posts, but very securely attached with the bolts that come with the posts.  I checked connectivity by putting 1 probe into banana input slot on topside of plate and other on the small copper wire going from OT-2 lug into the tans.  All test as good.    I notice on the voltages I listed as being off that most are reading 150 or so when they should be reading 100.  Does this provide a clue to anyone as to something I should check?

 

[kgoss]

No worries about the response. We have all been in your shoes and a little frustrated tracking down a problem. I can't tell from the angle but the red wire twisted with the black one looks like the insulation has been melted in the first picture. Make sure there isn't a short causing your problem. If not the Bottlehead crew will help you find and fix the problem. They are amazing and have some of the best customer service I have ever seen.

 

[Doc B]

Did the output cap for that channel get hit with the iron and melted a bit, maybe? I have seen amps lose a channel from a cap that got shorted that way, even done it myself.

 

[caffeinator]

I apologize if this sounds like a dumb question, or a dumb suggestion, but I didn't see anything in the thread about swapping tubes left for right to be sure it's not a tube issue.  That's easy and worth a try, if only to confirm it's not part of the problem.

 

[glynnw]

Output caps look fine and I switched the tubes - right still out..  I am out until Monday.  Pkease keep up with any suggestions.  thanks.

 

[glynnw]

OK - Part 2.  This weeekend I wired it to 8 OHMs and put the original Solens back in.  Tested continuity every which way.    I  let it warm up a while, retested all resistance and voltage points  and got slightly different readings, but basically the same as before.  All resistance points OK and a few voltages out of line.  I even tried to check individual resostors and caps in place, trying to do channel to channel comparisons, but that only confused me.  The only really out of line measurements doing that were to the 270 KOhms resistors from points 34 to 35 and 36 to 37.

Here are the outliers:

Terminal    Should Be  Measured
4                  100          149
5                    95          149
6                  380          347 - this may be within range
7                  100          149
13                100          148
14                100          148
15                360          300

42                100          149
43                370          319

As I have mentioned over the years, I am happily ignorant about how these things work, but tracing wires makes me think all these incorrect measurements relate to the non-working right channel.  Do the errors at points 42 and 43 lead to the errors at the other points or vice versa?  If anyone can suggest which part went bad I will remove it and test it.  I considered just doing a wholesale swap of lots of parts, but I don't even have any experience ordering these small parts and I really don't want to invest a lot more hours trying to figure out how to order them.  If no one can figure it out in the next couple of days Iplan to contact Bottlehead and send it to them for repair.  I have spent at least 10 long hours on this, including getting out of bed at 3 AM to test "one more thing" I thought of.  I am toasted.

 

[glynnw]

Well, well, well... I was giving up on it this evening and as a last resort, while it was plugged in and the left channel was playing I reached over and rather violently (as in angrily) shook the EL84 tube - no change - shook the 6AU6 - and the right channel popped in and out.  In trying to find the problem I have switched these tubes around gently and the right channel has remained off.  I unplugged it, turned it over and again shook the right 6AU6 to see what was loose - but the socket is so firmly mounted that I could see nothing moving.  I righted it, pulled the tube, bent all the contacts out a bit to guarantee they had contact, sprayed it with DeoxIT and put it in and now the right channel works.  All I can figure is that 1 of the contacts in the socket is misaligned and the pin had to be really bent to make contact. When I originally moved the amp around to change the output resistance that bad pin hole must have  moved enough to stop contact with the pin.  Now as soon as my cat gets out of the way I will again check those errant voltages and hopefully they will now be in spec.  Thanks for all the help.  It just took some violent action to discover the problem.

 

[glynnw]

Cat got out of way and I checked the deviant voltages, which are now all normal.