[TMC] PRogress report No. 3?

[Sheldon Daitch]

Most of the time, we've replaced mercury vapor rectifiers with diode stacks.

The problem with mercury vapor rectifiers is an arc back, or flashover,
roughly the same, I guess, when the tubes have either been moved or very
cold.

If the tubes have not been stored in an upright position, they need to be run
with filaments only, for 20-60 minutes, depending on ambient air temperature
to make sure the mercury is properly dispersed in the tube.

In one small MW tranmsitter that I had years back, pair of 866s and 8008s
for the low and high voltage power supplies.  The TX was in an unheated room
in the station and we had so much problems in the early years with the tubes
taking too long to warm up during the winter that we left the filaments on
overnight.  The cost of electricity beat the problems with lost time at 6AM
sign-on.

I guess I could have rewired the filament primary circuit to be
separate from the remainder of the AC, but I never thought about it.  Eventually,
we got some solid state replacements that cured the warm-up problem.

73
Sheldon
WA4MZZ



telegrapher at att.net wrote:

> Well the only way to put HV on them in the transmitter anyway is to
> apply High B+ like your going to operate the rig.  I don't suppose it
> would make any difference.  The transmitter was designed for 24/7 duty
> so how do i as a ham with maybe once a week operation treat them?  Is a
> 15 minute warm-up time adequate and will just applying primary power for
> the filaments be considered adequate for the warm-up period?  I don't
> want the transmitter setting here running 24/7 when i'm not even going
> to be around it for periods of time.  besides electricity here isn't cheap.
>
> Larry
> W0OGH
>
> Mark Foltarz wrote:
>
> >
> >>872A's, and their more common cousin, the 866A, can be unpredictable. In my
> >>early experiences with a TMC GPT-750, the HV breaker would pop often and
> >>more or less predictably until the 872's had "cooked" for quite a long time.
> >>
> >
> >
> >
> > Yes they can be!  I had fits with a home brew supply using 866's.  Went through
> > a bunch of them. Never could get more than a few hundred MA. And the darn thing
> > was never reliable on start up - blew fuses left and right.I swithed to 3B28s
> > and the probems went away.
> >
> > Is there a more modern eq. of a 872?
> >
> > Mark
> >
> >