[R-390] Filter repair

[Bob Camp]

Hi

Just be sure to start by replacing the filter with a short, that's your zero db point. You'll have to pop off the caps since they won't have anything to resonate with. 

Bob

On Mar 21, 2013, at 10:39 PM, quartz55 <quartz55 at hughes.net> wrote:

> Hmm, I may be on to something here.  I 'repaired' a FA type filter, and just to test it in my test setup, I shoot 1vrms (2.8vp-p) into the 'repaired' filter and measure out of the thing .12vp-p (.042rms) doing the math, that turns out to be 27db. I haven't checked the BW, but it sure starts to cut off at about 1K high.  I've got one of the 4K 390A filters about to be ready to test, I need to tack the end caps in the tube so they don't fall out.
> 
> How does this test setup look?  I've got the 50 ohm monitor output going to the Pamona box with a .1uf and a 100K ohm in series, a 70pf variable across the filter and on the output the same 70pf variable and a 100K resistor feeding right into the scope input with the clip leads.  It seems to peak up fine.  I haven't got the grounds set up right yet, but that will come. I'm not sure how many db I can measure for loss anyhow.  The proof will be in the pudding.
> 
> http://i251.photobucket.com/albums/gg287/DogTi/R390A/FILTERTESTSET_zps3d02da99.jpg
> 
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