[Elecraft] A few possible explainations with Collins Amp amd K2 AMP

[WA2JJH at aol.com]

I had the same problem with a ts-850 and a Heathkit HL-2200(SB-221 same  
ciruit)
 
   Some tube amps(especialy Heath kits) have to be modified for  proper 
operation.
Tube amps may present as much as a 2:1 SWR to a transistor final rig.
 
   With a tube rig, this is compensated for by the final load  control. In 
fact some tube rigs load control will match up to a 3:1 SWR. An  antenna tuner 
may not be needed in fact.
At tube rig can be run without an antenna tuner If the SWR is not that  high.
Indeed the older antenna tuners used a PI network .
 
   Of course transistor finals do not have a load control. One  will use a T 
network type tuner to match up to greater than 10:1  SWR's 
 
   So transistor finals need power fold back protection. It could  be your 
power fold back was not set right and you had a 2:1 or greater SWR. Over  time 
the transistor final may go into thermal runaway.
 
  Also the older Kilowatt amplifiers used up to 100VDC for the key  down T/R 
relay.
ALC on my heathkit is -55 VOLTS !  Just about any solid state final  rig use 
12V max for that T/R relay. The new 1-2KILOWATT amps also use much lower  ALC 
control voltages. -6-8V.
 
  Did you use a relay or opto-isolator to prevent the K2 from switcing  the 
higher voltage.
What is the ALC's max voltage of the vintage Collins amp?
 
2) You may have had a ground loop situation too. I have seen 50 VAC ground  
differentials.
That is why one should Ground the rig and linear together.
 
3)Perhaps your bias was not set right on the K2 finals. You said you get  20W 
output.
The Finals should output 16V MAXIMUM. K2;s  rated output is  `10-15W.
 
4) You could have just been unlucky and got a not so good final
 
Hope this helps
 
73 DE Mike