The term "death cap" is a slang term. It refers to the small capacitor (usually .022-.047 µF rated 400-600 volts) used to ground one side of the AC line to the chassis.
The cap may be switchable from one side of the AC line to the other - with a switch called "polarity", "ground" or "line" sometimes optionally followed by the word "reverse".
An amp will produce less noise with the proper side of the AC line grounded. The switch was a good thing to have back in the old days of two prong plugs since you didn't have to physically reverse the plug in the AC outlet to properly ground the AC line.
http://sunn.ampage.org/site/schematics/220s.gifIf you open this link to a 200s schematic on the lower right hand side, you can see a .05 µF 600 volt cap (the two short parallel vertical lines) connected between the chassis (three slanty parallel lines) and the common side of a two position switch, with a position connected to one or the other side of the AC line (the two lines coming from the thing that sort of looks like a two prong electrical plug with 117V 60HZ opposite it).
http://sunn.ampage.org/site/schematics/modelt.gifNow open the model T schematic and scroll down to the lower left hand side. C14 is the "death cap" in this schematic (rated at .047 and 600 Volts) and S2 is the polarity switch. This schematic switch uses the horizontal lines that get smaller as the ground symbol.
Now notice the plug - this is a three prong plug, and the line (wire) labeled GRN is connected directly to ground. This is really all you do when installing a three prong plug - the black and white wires go to whereever the existing black and white wires go, and the "new" green wire is secured directly to the chassis usually with a bolt or screw. The green line is connected to the round center "ground" at the plug side of the wire.
This should properly ground our chassis - assuming that the plug is inserted into a properly grounded socket.
PS, what is the "death cap" people keep talking about? Should I have that removed on tuesday when I have the new cord installed?
Now the question makes sense?
The model T grounds the chassis both ways - through the three prong plug and the polarity switch through the cap.
Why? ... well, the model T was introduced in a transition period in terms of AC wiring - some places may not have been wired (at the time) with three prong AC sockets. Other amps produced during this transition period may have used a three position ground switch, with the center position disconnecting the cap completely from the AC line (such as Fender).
In
theory at least, every place you are likely to play the amp should be wired properly with 3 prong outlets. If this is true, having the cap is redundant to the three prong plug and it (and the switch if desired) can be removed.
Pointless trivia: Fender, on it's reissue amps, keeps the ground switch for the vintage looks but it is completely non-functional.
===
FWIW: I estimate a 95 percent chance that the rattle is a tube. Very low quality of tubes these days and I have had more than my share of microphonic ones.
