[R-390] Re: Pearl tube shields

[W. Li]

Interesting thread: reducing operating tube temperatures is one maneuver that will definitely prolong their life. Note that there are TWO types of IERC shields, one that merely slips over the the JAN socket, and one that actually mates mechanically to a special add-on sleeve bolted to the socket. The latter has an advantage in that a large area thermal connection is made to the chassis for conduction of heat away from the tube. This arrangement makes the most sense for those tubes below the chassis in the R-390 series, and not all that advantageous for those above the chassis. As Roy correctly points out, a fan is far more important to dissipate heat away from the tubes. On the market today are 80cm ball-bearing fans that are incredibly quiet that can be mounted strategically to dissipate heat... most useful for those of us that have the unit housed in a cabinet. My preference would be to mount the receiver in a ventilated rack with both top and bottom covers OFF.

Stictly speaking, this group (of all groups) ought to take the trouble to actually document operating temperatures of our units in a scientific way. After all, we are compulsive types, and prefer to pay attention to detail.  Inexpensive battery operated LCD temperature monitors can be acquired from shops that sell customized computer case accessories for around $16-$22. These come with small temperature sensors that can be mounted anywhere on (or inside) a shield. Such results would be an interesting post for the ambitious members in this group.... 

Another point that has been brought up earlier, is to leave the unit on all the time, not only for temperature stability, but to avoid power surges through thermally vulnerable portions of our tubes. My own practice is to use a Variac to power up, with a thermal delay for B+, as described by another list member. 

W. Li
Mercer Island, WA