Psycho SEX zapper - help please!!

[PassionForSound]

Hi All,

We've just finished a build tonight and one of the guys has a major issue. All impedance testing was perfect, but upon applying power and testing voltage we noticed errors in the voltages and the following issues:

• 100uF capacitors aren't discharging after power off
• 22uF capacitors aren't discharging after power off
• Tubes aren't heating when amp switched on
• Voltages consistently 100V+ higher than they should be along terminals 6-10 & 16-20

Many thanks!!

Lachlan (and Billy)

 

[Paul Birkeland]

There are two 270K resistors back by the 220uF/250V capacitors - if these aren't installed, the capacitors won't discharge.

If they are loose, poke at them with a wood chopstick to get them to make contact and bleed down the supply.

If the tubes won't heat up, then there's an issue back on the "H" terminal strip, can you get the +/-3V out? (If so, are you sure the tube sockets are properly aligned?)

 

[PassionForSound]

Thank Paul.

Sockets are correctly installed. Resistors too.

When you say "H" terminal strip do you mean the terminal strips above and below each tube?

 

[Paul Birkeland]

Sorry, in the SEX manual it is the "C" terminal strip.

(do get the high voltage bled off before messing around with that part)

 

[PassionForSound]

The C strip all looked good. I did find one or two solder joints that I've suggested Billy  redo, but I cant see any glaring errors. Next step is a step-by-step walkthrough of the manual.

Anyone have any other suggestions for what could cause the tubes to not heat and voltage to stay in caps?

 

[Paul Birkeland]

The tubes not heating is not having the 6.3V power supply built on the "C" strip at the back of the chassis built properly, or a wiring error from that terminal strip to the octal sockets (pins 7/8).

That is absolutely the only reason that the tubes wouldn't glow, unless both tubes have sustained serious damage in shipping.

 

[PassionForSound]

Thanks for confirming. We'll hone in on those 2 first.

 

[PassionForSound]

I've received a message overnight from Billy saying that he's systematically re-soldered every joint in the SEX and his test figures all look good.

He's going to fire it up today for the ultimate "ear" test and will report back. So far it looks like another lesson for me about how a tiny error in soldering can create dramatic results! It never ceases to amaze me that having a solder joint that LOOKS ok, doesn't mean that it IS ok.