[Jeffhs]

I second Hemingray's comments. Zenith made some excellent radios in their day, until they got out of the radio business in the early 1980s (1982, to be exact). I have three Zenith wood-cabinet sets (MJ1035, C845, K731) and a high-performance 13-transistor Zenith portable (R-70) that work well and have excellent sound, although as I write this the MJ1035 has a problem with the volume control--but when it works, it sounds great.

I'd leave the original tubes in your radio if the set works.

Replacing capacitors, especially the three-section electrolytic in the power supply (the latter is almost always bad in very old radios and is quite often on the verge of failure in 1950s-'60s receivers) in old sets is standard procedure when restoring them. Replacing the caps in and around the audio stages can improve the sound by altering the audio response curve. I would be careful not to put too large or small a capacitor in these circuits, the reason being that too small a cap will emphasize higher frequencies to the hilt and then some (the audio will sound abnormally shrill); too large a cap will overemphasize the lows, resulting in an excessively bassy sound.

If you have the room in the cabinet and can find a larger speaker, by all means go ahead and replace it--you have nothing to lose and everything to gain in terms of improved sound quality. Note that you can always replace a four-ohm speaker (for example) with an eight-ohm one with no fear of damaging the radio's output stage (the only thing you will lose is a little volume), but not vice-versa. Replacing an eight-ohm speaker with a 4-ohm one or less will damage the output transformer and/or other parts of the radio. The best thing is to replace the original speaker with one of the same impedance; the use of higher-impedance speakers is an emergency procedure, to be used when or if the proper speaker is unavailable.

Good luck. I'm not really all that familiar with your particular Zenith radio, but the company's sets from the '40s through the '60s were excellent radios, with no production shortcuts. You won't be disappointed once you get your set working. These radios, as I have mentioned many times in this forum, represent a level of sound/build quality which we will never see again, in this age of cheap plastic one-chip headphone stereos. Once you get that set singing again, hold on to it. As I have also said (and believe with all my heart, as I am a Zenith radio collector and have a great deal of respect for the original Zenith Radio Corporation of Chicago), they don't make them like that anymore.