[AMRadio] too much HV Fin.

[Todd, KA1KAQ]

On Wed, Oct 19, 2011 at 11:42 AM, Bernie Doran
<qedconsultants at embarqmail.com> wrote:

> Now if someone want to get paranoid, consider that when replacing the vacuum
> tube rectifiers in a receiver, usually 5Y3 or 5U4 type animals, with silicon
> diodes and equilivelant series resistor. The full B+ plus more than a few
> volts will be available on the tube plates and all other components as none
> of the tubes have warmed up and have initally no current flow.  With a VT
> rectifier it also had to warm up a bit before it would conduct and it rather
> served as a slow start device.  Ideally one should probably have a time
> delay prior to turning on the B+.

Another facet not figured in by most is the elevated line voltages
today, sometimes 10-12 volts higher at the AC receptacle than when the
equipment was designed. None of these things taken on their own seems
like much, but when you add it all together and multiply through HV
circuits and such, it starts to become more significant. Still nowhere
near close enough to account for a 1000v difference, but IMO, worth
paying attention to if you're using old equipment.

The easy answer for me has been to switch the MV rectifiers to their
xenon equivalents (3B28, 4B32) which still has a small voltage
difference, but is closer to the original design. Having paid for a
couple pricy transformer & choke rewinds, you can put me in the
slightly paranoid category. Maybe none of it matters, but doing an
easy swap and sticking with tubes is cheap insurance in my book. If I
never need it, nothing is lost beyond a couple minutes of my time.

~ Todd,  KA1KAQ/4