[Heathkit] SB-401 driver tube shield missing

Drew P. drewrailleur807 at yahoo.com
Wed Dec 25 15:10:11 EST 2013


 On Dec 23, 2013, at 12:42 PM, Garey Barrell wrote:

> Rob -
>
> You might want to check the manual for your radio before adding a?
> shield.? That is a hot tube and may have it's life shortened?
> considerably.? I don't know for sure in the 401, but the Drake TR-4?
> specifically does NOT use a shield,even though the shield base part?
> is there.? The extended ring of the base is all the shielding?
> needed.? Worth checking!

Similar type of situation with the SB-101 I have here - instability with the shield
 removed. OTOH, that tube runs awfully hot.  A quick check reveals that the 
driver tube is normally run well in excess of its rated dissipation. I'm considering  
fiddling with the cathode resistor to cool it off a bit - probably at the expense of 
IMD performance.

Drew


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