On May 2, 8:11 am, Wiebe Cazemier wrote:


Hmm, there seems to be some disagreement over whether a H-K short can be fixed.
Will the filament also be killed if you tie its pins together? That way, a
current path other than through the entire filament always exists.

The current required to clear a short needs to pass through both
elements, the cathode and the heater. Even with the heater pins
shorted, current will pass from the cathode to at least a portion of
the heater, which is subject to fail at the point of contact.


Floating might work, but not in this case, because the problem exists in two
guns.

That's true. If you have contact between the filament and more than
one cathode, the tube is garbage.


Additionally, it would decrease image quality (at least when the short
exists; it might clear up when the short disappears when it's warm)

Not true. In the vast majority of tubes I've isolated over the
years, there had been no picture issues when the short occurs. The
only way that you could tell the short was still there was by
measuring the DC component of the filament above ground, and actually
watch it vary from virtually nothing to a couple hundred volts.


Another thing; if I measure the filament voltage, it's 5V. Is that normal
deviation from the 6.3 which is common? And, when isolating, is it useful to
use some kind of regulation, like with a couple of diodes and an LM317, to
make sure the voltage is exactly what it should be?


If the filament is AC supplied from the flyback, it's at the scan
rate, not 60hz. A true RMS meter is needed to accurately measure the
voltage. I use a Fluke 87 for measuring high frequency AC. Non RMS
DMMs usually read scan derived filament voltage below 5 volts. If the
filaments are DC and regulated, they will read exactly correct with
any DMM.

John