Problems with Seduction C4s

[viridian]

Well, it's fitting that with the venerable Seduction being retired, mine is acting up a bit. I had an occasional very loud snapping sound coming through the speakers and tried a few things but it persisted and I decided to let the thing fail and deal with it from there. That day has come to pass. Some specifics from my tests. All LEDs are lit with the exception of the two on the C4s that are closest to the outside edge of the board. The LED between B3 and B9 is not lit and the voltage on B3 is only 1V. Tube A seems to be working correctly and the associated channel sounds very good with music. Any guidance or insight is greatly appreciated and it's easy for me to do more tests if necessary. Thanks in advance for any, and all, help in the matter.

[Doc B.]

The 2N2907 transistors sometimes blow due to intermittent contact of the case with the PC board traces. Check to see if one of the transistors is touching a trace.

[Paul Birkeland]

Also swap the tubes to see if the LED issue on B3 goes to A3.

[viridian]

Gents, thanks so much for the input. Doc, no the transistors are clearly standing proud of the board, though I think that something is wrong in C4s land. Paul, that was my first move and the problem did not follow the tubes.

[Paul Joppa]

The voltage checks are the next step; it sounds like one (at least) of the C4Ss is not supplying proper current to the associated tube plate. You can start with just the tube pin voltages; they are the most informative.

[viridian]

Mr. Joppa, thanks so much! I am enjoying a bit of Dexter Gordon on your Paramours driven by Foreplay 2 C4s, whispers, etc. as I write this. Eileen is sending me out a new transformer form my Foreplay III extended, but that's for a later time. You are the author of  gear that gets me much closer to the music that I enjoy, and puts the life in the long dead musicians that haunt my listening room. At any rate the voltages are as follows:

Tube A                Tube B
1   65.8               jumps around 1v
2   0                       0
3   1.54                  0.97
4   0                        0
5   5.8                    5.9
6   80.2                  73.1
7    0                       0
8    1.56                  1.56
9     0                       0
 
Thanks again for taking the time to sort me out!

[Paul Joppa]

OK, sure enough, the C4S is not feeding the first plate (pin 1) of tube B.

There is a wire from that pin to the C4S, which connects to the middle leg of an MJE350. Check the voltage on that pin (carefully, don''t short it to either of the adjacent pins! If you get a high voltage then the problem is probably in the wire or solder joints along that path. If you still get nearly no voltage, then it's either the solder connections around that transistor or the nearby small transistor, or one of the transistors. Think bright light, powerful magnifying glass, and much patience.

A most likely candidate is the solder joint to the middle pin of the MJE350; that pin connects to the heat sink and absorbs heat from soldering, so it requires a bit longer contact with the soldering iron to get the pin hot enough for a good solder flow.

[viridian]

Mr. Joppa, thanks so much; that did the trick. And my 55 year old eyes had no trouble at all. I really appreciate it!  Thanks as well to Doc and Paul for getting me on the road.

My Seduction was derelict, hence some bad solder work, but I rebuilt it. The previous owner drilled the top full of holes to hang caps off of. While I was filling the holes, with a metal loaded epoxy, I filled the holes for the Hammond shield as well and finished it off with stainless screws. I used Sonicaps in the RIAA because they come matched to 5%. I have some nice Audio Note copper foil in oil caps for the output couplers, but have not gotten around to putting them in yet; the current coupling caps are Auricaps. It sounds so good as it is.