Resistance checks - couple of issues

[Oldlistener50]

All the resistance checks check out per the manual, with these exceptions:

6 - reading 1.4 ohms
9 - reading .3 ohms

my build looks exactly like the color JPG on the CD and the photo on page 21 at the top.

Are the readings on 6 and 9 ok or is something wrong?  I have inspected everything and rechecked the instructions for terminals 6-10, everything appears to be in order.

Thanks...

 

[Grainger49]

You don't say what 6 and 9 should be.  9 should be considered zero ohms or shorted to the ground/signal common buss.  If you short your meter leads to each other you will most likely read 0.3 ohms.

6 is almost there.  The resistor in the heater circuit is the only thing I remember being in that resistance range.  Is 9 in that circuit?

 

[Grainger49]

I have an Original Seduction and manual, the paper one.  There is no resistance reading for either Terminal 6 or Terminal 9.  That tells me that they are not critical if the others measure well.  Wrong manual, ignore this statement. 

Looking at the schematic, T6 is at the output of the full wave bridge for the heaters.  It "sees" a 1.2 ohm resistor and  a string of capacitors in parallel to ground.  But... if you measured with the tubes in, the heaters short to ground, they are just wires.  So your 0.3 ohms plus the 1.2 ohm resistor are 1.5 ohms.  That is a hair off of what you measured.

If so (you had the tubes in) you can go forward to the voltage checks.

 

[Oldlistener50]

Hi, no these resistance checks were made without having the tubes in.  That's the way I interpreted the instructions.

In my manual, 6 and 9 are marked with a * meaning they are some that will wander (as the meter power charges the capacitors) and should be >10K ohms.

 

[Grainger49]

Ok, I got my head screwed on right and realized I grabbed the wrong manual.  T6 is supposed to charge the capacitors, same with T9.  But a low resistance indicates a ground somewhere it shouldn't be.  Check the diodes around terminals T1, T2, T6 & T7.  Verify that the band is as you see it in the manual.  (I'd give the page number but mine is paper)

If one or two are pointed the wrong way you end up with T6 grounded.  T9 would be 1.2 ohms to ground plus the meter lead resistance.

Anyway that is my first guess.

 

[Oldlistener50]

Yeah, I checked that whole area and compared to the manual.  From what I can see it's right.

Here's some photos:

and the transformer:

(just to confirm on the transformer,  since mine is the current version, the 3rd and 5th terminals down on the left are the ones that are supposed to go to Seduction terminals 17 and 22, correct?  The center tap (4th one down on the left) goes to Seduction terminal 16 (which has a ground loop  tied to it as well).


Now, I took the red lead off terminal 9 to test; when I do that the resistance between 6 and the ground plane and 9 and the ground plane jumps all over the place (what I would expect).  If I then read across the black lead on 10 and the (disconnected) read lead (which was on 9) I read essentially no resistance (.2 ohms).  But here's a question - if I read resistance across the Z5U capacitors they read the same resistance.  So since there is one of those tied across A4 and A5 and also B4 and B5, the reading should be essentially no resistance, correct? 

 

[Grainger49]

Oldster,

I agree, your diodes and the capacitor associated with the heaters are properly oriented.  That would mean that there is a short to ground further down the line.

Try measuring from T9 to T10; the red lead on T9 where the red STP is.  That is directly across the blue capacitor.  It should charge.

 

[Oldlistener50]

With the red lead off T9, and the DMM test leads right on the blue capacitor,  yes it appears to charge.

I have peered deep at all the connections to A4 and A5 and B4 and B5 and cannot find anything wrong.  Ugh.

Some up-close pics.  Maybe someone can spot something wrong (the tape on B3 is to ensure the LED leads don't touch anything... that's a tight one!):

 

[Doc B]

The polyethylene insulation on the wires in the STP is rather easily melted. I would look to see if maybe the red wire has a bare spot where there should be insulation right where it comes out of the outer jacket, and that is maybe shorted to the drain wire.

 

[Oldlistener50]

Ah ha!!  Found it.

Uncut extraneous lead on B5 touching T38 (grounded).  Now I'm getting proper readings.

Thanks friends!  

Update: voltage tests fine, hooked up and sounding nice!  Time for a few beers.  Thanks again for all the help - much appreciated!

 

[Grainger49]

You deserve a tall cold one!  I was betting on the tube pins since they are so crowded.  They about drove me bonkers!

 

[randy@matrixq.com]

Oldlistener50, enjoy your build!  I just finished mine over the Holiday break.  I've been really enjoying the sound ever since.  It's a tight build in spots but it matters sonically.  The tight, sometimes crowded connections keep the noise down and make these amps what they are. 

Congratulations, you've jumped one of the high hurdles.

 

[Oldlistener50]

Sure is a nice feeling to sit and listen to something I built!  Been a long time since I've put an electronic kit together.  The glow of the tubes along with the brass connectors reflects nicely on the shiny black top.