[Collins] Collins 30L-1 Input High SWR

[Dr. Gerald N. Johnson]

I'd be most suspicious of the input PI network including the switch 
contacts. Look for burned capacitors, remembering that that input 
matching circuit carries 100 watts of drive plus the cathode current of 
the PA tubes which is the same as the RF plate current.

I have some suspicion of long grid leads in tubes designed for audio but 
those who fix 30L-1 more often that I do haven't detected that.

73, Jerry, K0CQ, Technical Adviser for the Collins Radio Association

On 7/3/2014 3:09 PM, Tom wrote:
> Hi All,
>
> Posted here before about this but have a follow up question.
>
> I've been told that the problem is not the tuned input ckt. but the 811
> tubes. I fully admit that I'm not an expert on RF Amps, BUT it has good
> output on all bands except 20M. The tuned input on 20M will not go below
> 4 or 5 : 1 , all other inputs go to 1:1. I kind of think that if the
> problem is isolated to just the 20M tuned input that the logical
> "suspect" is one of the caps in the tuned input ckt. or am I incorrect
> and the 811's are the suspect? I "do realize" that the 811's are easier
> to change out, but it still doesn't compute in my ole brain.
>
> Thanks for everyone's feedback on this.
>
> Tom W1ALZ
>