[Hallicrafters] SX-101A selectivity - Capacitor testing - observations.

[Rodney Bunt]

Duane,

I used a B&K digital capacitance checker to check the values, and the Heath was very close to
this. Then I used the Heath C-3 checker, and a Hallicrafters Capacitor Checker as it has a "pot"
to dial up any voltage up to 450v, the Heathkit has only switch at 25v 150v 250v etc....

There is a "gap" in the magic eye display. How clear/wide this is, is a measure of the quality IE:
capacitance and resistance.

Orange drops show a wide gap and a distinct "light/dark" boundary.
Older caps have a less wide gap and a more blurred "light/dark" boundary.

As an example, the capacitors inside a R-44 Hallicrafters speaker that give the
HiFi/Communications characteristics, measured fine with an ohm meter, measured fine with a digital
capacitance meter, but showed breakdown at greater than 25v. A voltage that is not too hard to get
to being driven from the 500-Ohm speaker circuit.
With peaks of 1.5 watts of power reaching 25v..
It is quite a good testing technique.
Good for finding that capacitor that is causing that annoying "crackle"....

Rodney
VK2KTZ


--- "Duane Fischer, W8DBF" <dfischer at usol.com> wrote:
> Was the Heathkit tester itself within tolerances Rodney? Did you check the
> capacitors in it first? Heath did not use high quality parts many times and an
> old capacitor is an old capacitor, in a test item or in a receiver. 	
> 	
> Unrelated: you need to discuss with your ISP its frequent failures. I have seen
> the system remove you because of these frequent failings.  You are going to end
> up off the qth.net lists if you don't get a better provider OM. Just a heads up
> alert.	
> 	
> Best 73's	
> 	
> DBF 
> 
> ----------
> From: Rodney Bunt <rodney_bunt at yahoo.com>
> To: Dave Moorman <dmoorman4 at attbi.com>; Hallicrafters List (qth.net)
> <hallicrafters at mailman.qth.net>
> Subject: Re: [Hallicrafters] SX-101A selectivity
> Date: Sunday, February 17, 2002 10:54 PM
> 
> Hallicrafters.....
> 
> The same band-pass circuit is used in the SX-100 nad the SX-101, I have found
> the caps drift by up
> to +50% and the are leaky too. I tested them on a Heat capacitor tester and they
> started to leak
> at 25volts (pretty bad for a 200v cap!). I put in some 630v Orange drops and I
> can report similar
> improved results as Dave. Note: the resistors also drift, so it is a good idea
> to replace them
> also, the IF at this point is in the order of 50kHz so any quality resitor will
> do the job here.
> 
> I have done this work on two SX-100's and one SX-101A, it is a pain removing the
> wafer switch to
> do the work, but worth the result.
> 
> Rodney
> VK2KTZ
> 
> 
> --- Dave Moorman <dmoorman4 at attbi.com> wrote:
> > I've been working at recapping an SX-101A I bought a couple of weeks ago and
> > replaced the caps on the selectivity switch this morning.
> > 
> > The results have been excellent.  The selectivity system worked fairly well
> > before, and it works even better now.  With the 500 Hz bandwidth in
> > conjunction with the notch filter, almost any signal is readable.  Sweet!
> > 
> > Dave
> > 
> > _______________________________________________
> > List Administrator: Duane Fischer, W8DBF **for assistance**
> > dfischer at usol.com
> > ----
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> > ----
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> 
> 
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