[Jeffhs]

You will have an excellent set once you replace the selenium rectifier in your K731. These radios were great in their day (late '50s-early sixties) and are still very good performers today. I have one, an ebay score a couple of years ago, that still looks great and sounds excellent even after 44 years (I believe mine was made in or perhaps after 1963, as it does not have the Conelrad [Civil Defense] icons on the AM tuning dial; the Emergency Broadcast System replaced Conelrad in 1963).

I second the warning as to the hot chassis. I will add to what has already been mentioned, however, that the knobs are captivated to the cabinet, so they cannot be removed; this is a safety measure which should not be defeated. Note also that the K731 has an AC interlock on the back cover, as did most TVs of that era. This is also a safety measure which must not be perrmanently defeated, although it possible to temporarily bypass the interlock with a cheater cord for service purposes. However, it is always best to disconnect the AC cord from the wall socket before attempting any kind of repair or service work on the chassis. The only time it is really necessary to have this radio, or any kind of electronic equipment for that matter, under power with the back off is during alignment procedures (and troubleshooting, of course), and even then only when the receiver is powered through an isolation transformer (the safest way by far to work on any AC/DC radio, phono, stereo or TV). There is a 50-50 chance that the chassis will be grounded through the power line, depending on which way the AC plug is inserted in the socket, but the problem with relying on that system is there is just as much of a chance of inserting the plug so that the hot side of the line is connected to the chassis (it is all but impossible to tell whether or not the chassis is grounded or hot unless you use a light bulb tester between the ground screw on the outlet plate and either side of the AC line). Today's polarized AC plugs eliminate the guesswork, as they can be inserted in the wall socket only one way (so that the grounded side of the line is connected to the chassis), but the K-731 was manufactured decades before this type of safety plug was in any kind of widespread use. I would play it safe and unplug the radio if you must work on the chassis for any reason. (Watch out for charged filter capacitors as well; always discharge these before beginning work on any kind of equipment in which they are used.) It is always better to be safe than sorry.