Seduction troubleshooting

[grosen]

Hi everyone. I recently swapped in some NOS 7308s.  Everything sounded great for a couple of days, then one channel started to get softer and then eventually died.  Switched in new tubes and all was again well for a couple of days, then the same things happened.   Two bad tubes in row? Possibly.  But I just checked the resistances and voltages.  Everything is pretty good except:

Resistance   spec.               actual
B3                1M                 26k

Voltage
B1                70V                 46V
B2                 0                   -20V
B3                 1.6                 0.7
B7                 70                  86V

Also:  the diode between B3 and B9 is not lighting up. 

Any help much appreciated.

[Grainger49]

Is this with the bad tube in?  It might be a bad diode between B3 and ground, it goes through B9 to either H or Q on the ground plane.

You can check the diode with your meter.  Try on ohms, the red lead on B3 and the black on B9.  Verify that B9 is grounded.

The LED might light with the leads as I describe.  Then try ohms with the leads reversed.  Post back.

Good luck!

[grosen]

Thanks for the quick response.  I get the same readings when I switch the tubes.  Resistances:  B9 is grounded.  B3 -> B9 = 26 k ohm; B9->B3 = 29 k ohm. 

[Grainger49]

This Seduction has been working well and the NOS tubes started the problem, right:

All problems are in the B channel.  And you are saying you have one good tube, one bad tube and that the bad readings do not follow the bad tube.  Right?

It sounds like a bad HLMP 6000, the LED.  It should light or be a low resistance in one direction, or both.  With both readings above 20k the LED is most likely fried for some reason.  There is no replacement except another HLMP 6000.  Bottlehead can supply one.

[grosen]

Thanks ... That's right.  Will try new LED.  (Not sure the NOS tubes caused the problem, but it did come on shortly after the switch.  Tried again with a second set of tubes, with same result.)

[Grainger49]

One of the first steps is always swapping tubes from right to left to assure yourself that the tube is not bad.  In your case, where you think that the Seduction is eating tubes in one channel, you should swap the bad tube to the other channel and see if it is bad there.  

If not, your problem is that the bad channel starts to drop volume and goes dead.  

BTW, the diode should work or not, they are kind of binary in that regard.  Check the other channel HLMP 6000 with your meter.  You have a good channel and a bad channel so you can compare the two easily.  Do the resistance check on the good HLMP 6000.  It should be low resistance one way.  

The problem is meters vary with what they indicate.  Some have a "diode check," indicated by the diode schematic symbol, where it will read the forward voltage drop, 1.7V for this diode.

[Paul Birkeland]

Resistance   spec.               actual
B3                1M                 26k

Voltage
B1                70V                 46V
B2                 0                   -20V
B3                 1.6                 0.7
B7                 70                  86V

Also:  the diode between B3 and B9 is not lighting up. 

Either the 47k resistor at the input of that tube or the 1M resistor that goes from the 0.1uf cap to ground is not making contact properly.  I am kinda leaning toward the 1M resistor.  I am also quite certain that the LED should light up when this issue is resolved.

-PB

[grosen]

Just got a chance to work on this and ... it was definitely the diode.  Replaced it and all is well.  Thanks as always.