[Heathkit] Final update on the SB-630 Monitor

[jack m]

The SB-630 is now timed to the gnat's eyelash - 12 repetitive timeouts with the stopwatch reading 2 hours and 4 seconds on the last one!
 
One final modification was made worth noting to those interested.  I noticed that the relay was sluggish, and sometimes did not return to full NC which caused the buzzer to not drop out without repeated reset attempts using the button.  Apparently the residual coil voltage was sufficient to hold the contacts on the armature.  The normally closed relay contact which charges the delay RC network was not making NC (relaxed) contact every other time, so these resets produced instantaneous drops on alternating resets because there was no previous charging of the dropout delay RC circuitry.  
 
After measuring all voltages in the associated circuits and substituting a brand new NOS 6EW6 relay control tube with no effect, I placed my resistor substitution box across the 220K ohm resistor between the cathode and screen grid of the tube.  I started with a parallel 220K and worked down to 68K.  The 68K caused relay dropout too quickly, but it sure was solid.  I finally settled on a parallel 220K resistor, which resulted in 110K across the tube pins.  Everything is solid now with a 1-second delay every time.
 
I also noticed that the neon light flashes only when the 6EW6 is cold and during it's warm-up cycle when using the reset button.  I never did get to visually "catch" the pulse of the 10 minute intervals, so I can't verify that.  But the pre-6EW6 warmup period (about 15 seconds) may be an easy way to verify operation of the neon light.
 
Again, thanks to the gorup for all the help.  I am now waiting for the replacement 3AG-B's!  But - I may not replace the original!
 
Jack  W3RU