[Amps] SB220 - no power output problem

[rlm]

>Good day to everyone on the Amps list.
>
>As the subject line indicates, I am having some problems with my Heathkit 
>SB220 amp.  It currently is very intermittent in providing power out on 10, 
>15 & 20 meters.  It frequently fails on 40 meters as well, but 80 meters is 
>working properly.
>
>The amp loads up in it normal plate and loading positions for my 
>antennas,  but then completely drops out, in terms of no power being 
>displayed on a Bird 43 watt meter.  Although the power drops out, there is 
>no change in the grid meter or plate meter reading when the power drop 
>out... at least not to a noticeable degree.  The amp stays in this 
>condition on that band, but often recovers on a band change, especially to 
>80 meters.  After several attempts on band changes, it will provide power 
>out and then, in the middle of a transmission, drop out again.
>
>The accompanying drop out in power is sometimes preceded by some arching 
>type sound in the amp.  I have not been able to see where in the amp this 
>is taking place, but the occasional time, it does appear to be in the area 
>of the top of the tubs or perhaps to the side of the tub area.  It is very 
>difficult to tell as the amp is elevated on a shelf above my line of sight