I'm having a similar experience with one of my 30L-1 linears. It will tune
okay on all the bands,but is squirrely on 40. I can't find a dial spot where
it will tune. Works just fine on other bands, butI spend most of the time on
20.
> Date: Fri, 15 Jun 2012 11:33:30 -0700
> From: jerry@tr2.com
> To: amps@contesting.com
> Subject: Re: [Amps] Squirrely 30L-1
>
> > The first sensible step would be to measure the parasitic resistor values.
>
> *** That would be hard. I would have to unsolder the coils around them.
> And I'm not convinced that the squirrely-ness is an actual VHF parasitic.
> I do have a spectrum analyzer good to 450MHz - wouldn't be too hard to
> set up some sort of voltage probe thingie to sniff the output ( without
> actually connecting to it ).
>
> What I *might* do is verify the grid resistors and caps, make sure that
> the grids really are well grounded. I can measure the reactance to
> ground with my MFJ259B. And look for RF ground loops from aged
> metal-metal connections.
>
> > The second thing would be to accept that Chinese 811A's will never be
> > completely stable on 10-15M
>
> *** I wonder why? Does that caveat extend to Chinese 572B's ( Taylor et
> al )? I might stick some American tubes in it this afternoon and see
> what
> happens. And if the Chinese 572B's are not good, I might need to cancel
> my order with RF Parts.
>
> >
> > The third would be the ability to understand that 2dB additional NF on
> > 10-15M might only make a difference
> *** This is certainly true :).
>
> - Jerry Kaidor
>
>
>
>
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