<VV> Replacement radio speaker options - late model

[Les]

Hi,

Original speaker on my '65 (AM pushbutton) is dead. Plenty of 4 ohm 6x9s 
available; original speaker was 10 ohm. Can I use a 4 ohm 6x9, or do I 
need to rig a pair of 5" or so speakers in series to get close to 10 
ohms? How about a 6 ohm resistor in series with the 4 ohm speaker (I 
know that's resistance and not impedance)?  I tried a 4 ohm speaker here 
and the output transistor gets kinda warm...

Les
corvair at mts.net