[Collins] 30L-1 vs 30S-1

[Glen Zook]

The thing is that the average power, duty cycle, with SSB is generally considered to be 20% of the peak power, and CW is generally considered to be 40% of the peak power (by the FCC).  Even if this is somewhat higher, for SSB, the average plate dissipation is considerably lower then it would be in a key down CW condition.  That is why Collins rated the 30L-1 for no more than 30-seconds key down CW and that is really pushing the 811A tubes.


The duty cycle is why the 6293, which is basically the same tube as the 6146A/8298, is rated for 1000-watts input when used for pulse.

 Glen, K9STH

Technical Adviser Collins Collectors' Association

Website: http://k9sth.net
      From: Dr. Gerald N. Johnson <geraldj at netins.net>
 To: Glen Zook <k9sth at sbcglobal.net> 
Cc: "collins at mailman.qth.net" <collins at mailman.qth.net>
 Sent: Sunday, December 13, 2015 8:51 PM
 Subject: Re: [Collins] 30L-1 vs 30S-1
   
Yoiks. I was thinking 125 watts, probabaly the data sheet rated power 
for a pair in class B. Generally with linears there's about 50% 
efficiency so the available RF power out is about the same as the 
available plate dissipation. The 30S-1 has 1 KW plate dissipation and 
the manual rates it at 1 KW PEP output. The 30L-1 manual doesn't show 
output, but limits the input to 1 KW PEP so the output would tend to be 
about 500 watts PEP, still driving the tubes way beyond their rating for 
intermittent service and even further beyond their Continuous Commercial 
Service dissipation rating of 45 watts per tube. So the Collins rating 
dissipates about twice the tube manual (RCA TT-5) which means the plates 
probably glow a bit. Its a wonder the glass doesn't get soft like some 
over driven sweep tubes had been known to do and then the vacuum pulls 
the soft glass into be against the tube plate. Using sweep tubes for SSB 
linears brought a new era to ham radio where the intermod products were 
a lot greater than the Collins 32S transmitter standard.

Or the RCA rating was very conservative allowing those antique tubes to 
survive that much abuse.

Usually when a tube or gang of tubes is worked very hard to intermod 
products are significantly increased. The 30S-1 manual specifies 
intermod products, the 30L-1 manual does not.

So for the original post, the 30L-1 puts out no more than half the 
output power of the 30S-1 and probably with considerably more splatter 
from over working the tubes.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.