[Hammarlund] Tube Shields?

[Roy Morgan]

On Feb 11, 2015, at 7:19 PM, K3PID <Ron.K3PID at sbcglobal.net> wrote:

> What possesses someone to open a nice vintage receiver and take out all the tube shields?

Perfectly good question, which has at least some good answers. This has been one of those recurrent topics on the R-390 list.  My comments are taken mostly from there:

- It was well established (in studies by tube and equipment manufacturers and by the military) that normal tube shields measurably raise the tube operating temperature.

- Tube envelope temperature is one of the primary factors associated with shorter or longer tube life.  Cooler tubes last longer, sometimes much longer.

- In military and mobile equipment, tube shields were often installed to keep the tubes seated in their sockets where vibration and shock were expected.  Your HQ-180 is unlikely to see such conditions.

- In the R-390A receivers in particular, only a few of the tubes needed shields to reduce spurious signals within the radio.  Maintenance instructions were issued to remove all the others.

Based on the above:

- Having no shields may be a good thing.

- If you find and install replacement shields, you may decide to stock up on spare tubes.

- The presence of spurious signals in the HQ-180 due to lack of shields is an unknown.

- Based on pictures I have here, it appears that the shields in the HQ-180 may not be the normal shiny, nickel plated ones that fasten with a bayonet type socket ring, but may be held in place by spring fingers at each socket.  The more common bayonet type may or may not fit right.

- Avoid running your HQ-180 in tanks, jeeps, or Navy carrier aircraft.

> My HQ-180 has NONE, NADA, ZIP shields!

The tubes in your radio *may* well be better off.

> Anyone have one, some, or all of the shields for said receiver? 

Sorry, none where I am now.  You may be well advised to search for the IERC type black thermal conducting type.  You may pay more for a set of those shields than you did for the radio.  Adding a small fan to your radio would also help a lot.


Roy


Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958