[TenTec] SB220-Tubes and QSK

[N4YG]

First, I would like to say that I am delighted to have set off such a  
nice discussion.

Second, getting back to the SB-220, even with only a fraction of a dB  
gain in output power, I am still exceptionally pleased with the  
installation. The increase in output power which I said was 20% is  
actually more like 50% depending on how you calculate it. I was  
getting 600-700 watts out on 40m and now I am getting about a KW.  
Some might say that is an increases of over 50%.

Third, power output is not the primary reason that I am so pleased. I  
had seen the reviews saying that the SB-220 ran cooler after  
installing the new tubes. Reading this casually, I sort of  
disregarded it. But when I observed it for myself, I was impressed.  
It is beginnng to make sense. The input power was about the same  
before the new tubes. If the amp is 60% efficient now, it must be  
dissipating about 670 watts. If the additional power I am now getting  
out was previously being dissipated, the amp was dissipating 300 -400  
watts more before or about a KW. That explains why it is running so  
much cooler. If all this logic is sound, the efficiency with the old  
tubes was only about 40%. Now that is a good reason to buy new tubes  
even though only a dB or two power gain is realized.

Joe