[Collins] Peculiar Request - 872A

[Dave Brown]

Quite right Jerry, Don't think a dome on the 872A would be all that clever!
Wooly description on my part- dome was for the demo triode- about the size
of a 211-and not too much dissipation.
Previous reply was meant for list of course!
 73
 Dave
ZL3FJ

----- Original Message -----
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@isunet.net>
To: "Dave Brown" <tractorb@ihug.co.nz>
Cc: <zap@xzapx.com>
Sent: Saturday, February 01, 2003 10:41 AM
Subject: Re: [Collins] Peculiar Request - 872A


> RFI WILL be an issue. The mercury vapor rectifiers were noisy. Often
> helped a little with an RF choke in the plate lead. A LARGE RF choke.
>
> With 35 watts of filament dissipation and probably a few watts of plate
> and plasma dissipation, there will likely be a need for top and bottom
> vents, then the circulation will draw in more dirt. Maybe the dome will
> not be a great idea. Just a regular dusting of the tube (with power
> off).
>
> The silicon diode won't hurt.
>
> 73, Jerry, K0CQ
>
> Dave Brown wrote:
> >
> > Probably worth putting a modern silicon diode in series as well to give
long
> > term protection against reverse conduction. And RFI might be an issue.
> > Even so, a lamp like this has been on my 'to do' list for some time now!
> > The recent acquisiton of one of those demostration triodes has got me
> > thinking about 'big tube' lamps and things again. I'm presently eyeing
up a
> > likely lump of oak for base material. Was planning on using the clear
dome
> > of an old 400 day clock to keep the dust off. Might need a vent in the
top
> > though!!
> >
> > 73
> >  Dave
> > ZL3FJ
> >
> > ----- Original Message -----
> > From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@isunet.net>
> > To: "Zap (Chris)" <zap@xzapx.com>
> > Cc: <collins@mailman.qth.net>
> > Sent: Saturday, February 01, 2003 10:05 AM
> > Subject: Re: [Collins] Peculiar Request - 872A
> >
> > The 872
> > > will demand to be upright (base down) and heated with the filament
alone
> > > for about a day to be sure there's no mercury on the plate to make it
> > > conduct with reversed polarity.
>
> --
> Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
> Reproduction by permission only.
>