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THE AM BULLETIN BOARD => Technical Forum => Topic started by: WA2ROC on June 09, 2015, 07:17:49 AM



Title: SX-101 Mark III Black Beauty replacement
Post by: WA2ROC on June 09, 2015, 07:17:49 AM
Round 2 of updates:

There are a bunch of "Black Beauty" caps (BTW, they're not that beautiful, are they?) and several pinkish red caps that are of the paper and wax variety that everyone says to replace.  Well, I ordered replacements for all of them, using polystyrene metal film replacements of the same working voltage, from Digikey.  Using my company discount, they cost me about $13.00 for 24 caps, including free shipping.

Here's a few pictures of the before and after.  There are still a few BB's left but none in bad condition like some of the ones in the pictures.

( Can anyone see these pictures?  I can't.  Just a lot of garbled text)


Title: Re: SX-101 Mark III Black Beauty replacement
Post by: K9DXL on June 09, 2015, 10:07:20 AM
Yep, just garbled text.  I recapped my '101 Mk III a few months ago, and saw a huge improvement!  Now it hears really well and sounds great, too!  Hope you're as pleased with your receiver as I am with mine.
73,
Jim


Title: Re: SX-101 Mark III Black Beauty replacement
Post by: WA2ROC on June 09, 2015, 01:49:38 PM
Yes, the higher bands seemed to wake up quite a bit.

As for garbled text, I looked at other photos that were posted earlier and they too were just garbled text.

I like my 101, but it is a bit on the heavy side.  I thought my Mohawk was overweight!


Title: Re: SX-101 Mark III Black Beauty replacement
Post by: K9DXL on June 09, 2015, 03:28:29 PM
Hallicrafters didn't call it "The Heavyweight Champion" for nothing.  On the other hand, working on radios like this save me the cost of a gym membership.
73,
Jim


Title: Re: SX-101 Mark III Black Beauty replacement
Post by: N8CMQ on October 07, 2015, 11:55:29 PM
I hope you replace all of the paper caps.

I had to replace the caps and resistors in my SX-101, as everything was stressed and
out of tolerance. I even had carbon tracked tube sockets, so I replaced them all.

The first picture is of the local oscillator, and the second is some of the work performed
so far. Notice the carbon mess around the local oscillator, and that is after cleaning!


Title: Re: SX-101 Mark III Black Beauty replacement
Post by: WA2SQQ on October 08, 2015, 08:26:49 AM
All the photos look fine here. What brand caps were they? I'm going to need to do this same this winter.


Title: Re: SX-101 Mark III Black Beauty replacement
Post by: N8ETQ on October 08, 2015, 12:32:43 PM


    Pix fine here too. The group of 3 BB's are all oil covered,
There cracked and leaking. Assuming each of your 24 caps is
passing 1 or 2 mA just think of the extra load on the power
xfmr.  Of course if one of them is "Re-Biasing" a tube, The
sky is the limit.

    It HAS to be done! Glad your doing it.

GL

73

/Dan





Title: Re: SX-101 Mark III Black Beauty replacement
Post by: n1ps on October 10, 2015, 08:07:35 PM
Another thought on the recap process....make sure to check the IF/RF screen resistors.  The voltage on the screens affects the gain of the stages.  Its rare that I dont find a couple way out of tolerance.  Then make sure to do a tune-up and repeak the IF stages. 

A couple other known issues with these vintage receivers:
1. Check that the gain control actually goes to zero ohms.  Frequently the pot is still above ground with the pot fully CW.  This reduces RX gain.
2. Check the AVC resistor chain.  These resistors, like the others...all carbons...tend to go higher in value over time.  The effect can result in front end overload with strong signals.
3. Check the limiter switch for leakage.  A common problem.  The effect is the limiter is not completely bypassed and is partially on. 

Just some passing thoughts on a cool Saturday night.

Peter
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands