Original sex troubleshooting

[tsingle999]

1 channel of my sex amp is not working - no sound
The c4s leds dont light up.
The voltages at the tube pins are followed by correct value
1. -.54. -17
2. 22.5 mv 345v
3. 0 0
4. -.43 0
5. -.75 72
6. 13.7mv 2.5v
7. 9 mv 0
8. 6.2 6

Any help would be appreciated. I have rechecked solder joints and swapped tubes.

 

[Paul Joppa]

By "original" you mean version 2.0?  :^) 

OK, picky picky.  :^)  Anyhow, it would seem the power supply on that channel is not working. Is this a new build, or did it work before? Check the voltages on the PSU caps on that side, and if none of them have any voltage, measure the AC voltage across the power transformer terminals that go to the power supply.

Of course you know ('cause you read the forum!) that the greatest probability is that, in the course of this checking or as a consequence of it, you will locate a bad solder joint. Even though you already checked them. BUt maybe it's something else, so trace back the power source and we'll see what we can learn from that.

 

[tsingle999]

Yes its 2.0 i believe. I built it at the amp class in sf! Seems like yesterday! So it has suffered thru a couple moves & it was my first foray into soldering too. I also have found this is the hardest bh amp to work on (built pdg, paramour2, paramount) because of the tightness of the psu caps and the terminal strips. I would love to rebuild this amp in a more relaxed layout! I am envious of the new sex!

Ok terminal
21: 226 vdc
22: 226 vdc
24: 225 vdc
25:0
26: 453 vdc
29: -1 mv
31: -18 mv
32: -1 mv
34: -.6 v
36: -24mv

 

[Paul Joppa]

OK, good. There's a 680 ohm, 3 watt resistor from T26 to T31. It's either blown or its solder connection has gone bad. You can measure the resistance in-circuit. It's the lower holes and the resistor is kind of squished in there - there's a picture at the bottom of page 30 in the manual.

Check voltages once its fixed - it's possible that tube has gone bad and taken out this resistor.

 

[tsingle999]

You nailed it! Its blown. I should change tubes out too when i replace it right? Thanks a lot Paul!

 

[tsingle999]

Ok i replaced the resistors in each channel and the bad channel works. But...
I use brass tube coolers and i heard a crunchy glass sound when i turned the amp on. I didnt think much of it at the time but the good channel was now not working. I shut the amp off and for some reason decided to pull the tube out not noticing that the damper had cracked it. Received a very nice shock that hurt my hand through the next day. Anyways put a new tube in and still no sound.
So a couple weeks later i flip the unit and plug it in. while putting it back in base upside down my hand slips and i grab the ac receptacle and get shocked again. maybe this isnt for me! Measured the voltages:
A1 -19.2
A2 363
A3 0
A4 0
A5 74.5
A6 2.32
A7 134 mv
A8 6.25

A7 is supposed to be 0... Help please

 

[Paul Joppa]

It's close enough to zero. There might be a bit of voltage drop in the heater wiring; you can re-heat the solder joints at tube pins 7 and 8 if hey look questionable but if it's just the wire resistance the voltages won't change.

 

[tsingle999]

Um i plugged it in and this time it works! Good to have my sex back! Its back in my bedroom where it belongs i swapped out the dact volume control for the pec pot. I swapped the vcaps for the russian teflons too. The amp isnt as smooth but has more life! Thanks Paul!

 

[Grainger49]

Interesting, many things are like that.  Sometimes dynamics can influence my decisions then I take a second look.  Dynamic or not, it is edgy or fuzzy.  Can't stand edgy, fuzzy is good at the right times.