[R-390] IF alignment questions and noise issue.

[Bob Camp]

Hi

Various outfits will sell you a capacitive block in an attenuator package. The ones I have are marked CC-1000 and came from a place in Florida (ELMCO?) many years ago. They look just like a coaxial 20 db pad. Mini Circuits will sell you a BLK-6 that does the same sort of thing. Rated to a whopping 50V. They also have a BLK-222 that’s rated to 100V. 

In both cases you have a low frequency rating on the data sheet of 10 MHz. That’s not likely to be an issue feeding a signal into a high impedance grid test point.

Just about everybody who makes coaxial attenuators also do DC blocks. There are a few hundred people out there ….

Bob

> On Jan 17, 2015, at 10:05 PM, Dennis Wade <sacramento.cyclist at gmail.com> wrote:
> 
> Good evening,
> 
>       Setting out to check alignment of the variable IF stages, and the
> Y2K manual states to couple the generator through "Test Lead CX-1363/U" to
> test points E209 and E210.
> 
>       I have an HP8657B, and my guess is the test lead mentioned above
> isolates the generator from the receiver, probably through a DC block.  How
> to you all couple a modern generator to those test points in practice?
> 
>        Noise issue:  The RF deck (that some may remember had shorted B+
> cap) now seems to develop a "bacon frying" sound several minutes after a
> cold start.  I've isolated the noise to the RF deck by unplugging J208 when
> the noise is present and it completely goes away.  I've also swapped all
> the tubes in the signal path with no change.
> 
>           Any ideas on how I might isolate the noise to a stage in the RF
> deck?
> 
> Thanks,
> 
> Dennis
> 
> -- 
> "If they trust you, it is an extraordinary privilege, and you simply can't
> abuse it."
>      - A. Alan Post  1914-2011.  California Legislative Analyst 1949-1977.
> 
> -------------------------
> Dennis L. Wade
> KG6ZI
> Carmichael, CA
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