[Drake] T4XB dirty CW signal on 20 meters

[Andy Bullington]

I've been working more and more with my R4C and T4XB lately and just noticed 
something strange. For the last year I've been working only on 80, 40 and 30 
meters with the Drake setup and everything has been fine. Today, being 
snowed in and having some free time I decided to try the higher bands. On 20 
meters the T4XB seemed to tune up fine but I noticed the spot tone sounded a 
little harsh and a tad distorted. When I listened on another rig using a 
receive antenna, sure enough...the CW note was not the powerful clean note 
I've come to expect from the Drake. 80, 40 and 30 sound great but 20 sounds 
pretty bad. Any ideas? I've never updated the power supply and wonder if it 
could be leaky filter caps. Is it possible I've got a failing crystal for 20 
meters? I've cycled the band switch and other switches and they all seem 
fine. Thanks!
                          Andy W1AWB