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Author Topic: suggestions for soldering to chasis?  (Read 9852 times)
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ka0pad
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« on: July 18, 2005, 10:41:15 PM »

Any tips for beefing up or adding  solid ground connections in an old chasis?

My sx62 is sounding sweet after a good once-over on the bench, but gets a low 700hz (or so) buzz going once and a while. It's definately in the audio section. Since I've eliminated everything else, I think,  I'm suspecting ground connections.

Larry
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W1GFH
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« Reply #1 on: July 18, 2005, 11:04:53 PM »

I have a friend who just picked up an SX-62 for himself to restore. I'll get to look it over in a week or so. Any trouble spots (besides the mystery hum)?

The reproduction dial glass from RadioDaze seems like a good deal for $38.

One of those old 100 watt plumber's soldering irons found at flea markets will enable you to tack a terminal lug to the chassis anywhere you choose.
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ka0pad
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« Reply #2 on: July 19, 2005, 11:19:05 AM »

Thanks, I'll look for one of those 100 watt jobs.

The things I ran into with this guy were:

1. the wax cap's under the band switch. The worst are still there with one end snipped off. sometimes I was able to get the new cap grounded back at the same spot, a couple of them had the ground connection moved. But with long skinny cutters and long - long nose pliers I was able to get them all replaced. There are some resistors under there that will be real buggers if they need to be replaced.

2. My 455KHZ xtal was not right, and still isnt i believe. At first the phasing cap had no effect and there was no null to be seen anywhere. Took it out, took it apart and cleaned it, reassempled and replaced. Now there is a null preceding the peak, but it doesnt move as phasing is adjusted the reponse just opens up wide at a point, not continuous at all. I've left mine where it is with about 500HZ delta between null and peak. The intent is to have 1 KHZ between these if I'm reading iit right , to reject the audio image. See the '56 handbook pg 101.

3. The springs were missing on the pointer adjust gizzy, works nice with them there.
The tuning pointer was kind of jumpy during tuning, pinching the sides of the part that rides on the rail on top corrected this, nice and smooth now.

4. The 10.7MHZ IF seems as wide as a barn, guess that's how it's supposed to be,  I cant be sure. I just adjusted the IF so it was symmetric and then tiuned the discriminator for symmetry also. I'm still not sure if this is right, but, after adjusting this the night before last and listinening to a local fm station, on comes a live recording of Janice Joplin belting one out, cranked it up, twas a religious experience I tell you. Right or not all is well.

Good luck with it, I'd be interested in what you find.

Larry
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w3jn
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« Reply #3 on: July 19, 2005, 01:44:13 PM »

See this thread for my trials and tribulations on the almost-identical SX-42
http://amfone.net/phpBB2/viewtopic.php?t=4624&highlight=sx42

Also see my post in the restoration section on silver mica capacitors - I'd be willing to bet that's the trouble with your IFs.  The 10.7 should tune relatively sharply; if it tunes broadly the silver micas are shot.

73 John
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ka0pad
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« Reply #4 on: July 19, 2005, 11:54:31 PM »

Thanks JN, I hate going into can's, what an ugly job. Got through 4 out of 5 of them today (and still get a signal out, havnt broke it yet), one more left for tomorrow.

Larry
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K6JEK
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RF in the shack


« Reply #5 on: July 20, 2005, 02:10:49 AM »

Quote from: W1GFH
I have a friend who just picked up an SX-62 for himself to restore. I'll get to look it over in a week or so. Any trouble spots (besides the mystery hum)?

The reproduction dial glass from RadioDaze seems like a good deal for $38.



I restored a basket case SX-62 a few years ago.  It's now my favorite receiver.  The audio transformers are notorious for going -- short to the case.  Somebody makes replacements, maybe expensive.   IIRC, the neg feedback circuit relies on the 500 ohm tap so garden variety transformers won't do.  I shoehorned in a fancy hi-fi unit.  That's why your hotrod Ranger sounds so good at my QTH.  Your friend will find a huge percentage of the resistors way out of spec.   He will also find that his receiver may match no known schematic.  If he recaps with orange drops he will wish he used something else like the little yellow polys because things are very tight.  He should not neglect the tone control caps just because they are a royal pain to access.   He will have to draw some pictures because one at a time in some sections is impossible.  The caps in the RF section can be done, really.  I replaced no mica's & hope like crazy I don't have to.  Advice for the caps with the braided leads:  Unless you're sure they're leaky, leave em.  Many of the ferrite slugs are sealed with wax.  To the amazement of many who have painstakingly melted out the wax, the slugs did not need adjustment.  Unless your friend is sure he needs to tweak those adjustments just leaving them alone is a pretty good idea.  I think it's called the SX-62 because there are 62 things to adjust during an alignment.
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w3jn
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« Reply #6 on: July 20, 2005, 06:57:32 AM »

The output trannies don't short, they blow one side of the primary open.  This is due to the tone circuit design of the SX-42/62 which places a Black Beauty capacitor from the plate of one of the 6V6s to ground.  When (not if) this cap shorts it burns out that half of the output tranny.

As far as getting into the cans, it's not the most pleasant job in the world (at least you can pull the can cover off from the top without having to remove all the leads on teh IF cans) but not as bad as replacing the bypass caps in the RF section of an SX-28.  Anyway, you'll be well rewarded  for doing all that work by a nice performing and excellent sounding radio.

73 John
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W1GFH
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« Reply #7 on: July 20, 2005, 10:19:48 AM »

Quote
the little yellow polys


Yep, I used to use Orange Drops but have now become a fan of the yellow polys. Much easier to shoehorn into tight spots. Funny how there are tight spots in  boatanchors. And much cheaper. I get 'em from this outfit in Canada. Nice folks, fast shipping, real good prices. And I'm fascinated by the name "Babylyn".

http://www.justradios.com/orderform.html

Quote
caps with the braided leads.


If the braided-lead caps are across the AC line, I always snip them out and hurl them across the room, or replace them with the super-duper X1/Y2 safety AC bypass caps.

A RELATED QUESTION:
The SX-28 is muted by opening the contacts of the send-rcv switch, which turns off the 280 volt B+ by disconnecting the ground at the transformer’s high-voltage, secondary winding center tap - and causes over -200 volts to appear on the mute line during standby (very sporty - esp. at the exposed dow-key relay contacts at the back of the Ranger).

This arrangement is very manly, except for an annoying delay when I mute my SX-28. It lasts about a 1/4 second...a quick decay...where audio feedback (depending on recvr volume setting) into the speaker causes a high pitched PLONK, kind of like the 10-4 Good Buddy roger beep effect.

My filter caps are new ones rated same as the old ones. All the waxies are gone (OK I admit leaving some in the RF deck) replaced long ago by Orange Drops. What gives?
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w3jn
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« Reply #8 on: July 20, 2005, 01:26:02 PM »

The transmitter is transmitting before the relay contacts on the Dow Key are closing as the Dow Key is the last relay in the chain.  A better way to do this would be to have a DPDT switch control both the standby line in the receiver as well as the PTT in the xmitter.  That way the RX goes to stby immeidately while all the other relays in teh xmitter do their thing.  

You wouldn't happen to have that avatar of mine you photochopped, would you?

73 John
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W1GFH
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« Reply #9 on: July 20, 2005, 02:01:47 PM »

Quote from: w3jn
The transmitter is transmitting before the relay contacts on the Dow Key are closing as the Dow Key is the last relay in the chain.  A better way to do this would be to have a DPDT switch control both the standby line in the receiver as well as the PTT in the xmitter.  That way the RX goes to stby immeidately while all the other relays in teh xmitter do their thing.  

You wouldn't happen to have that avatar of mine you photochopped, would you?

73 John


John, my Dow Key works fine with my other receivers, no delay, no PLONK. So it's something with the SX-28 that is squirrely.

I might have the "Sprague Atom Dog Hat" jpeg somewhere still. I'll look around...
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w3jn
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« Reply #10 on: July 20, 2005, 03:14:21 PM »

Hmmm, I see what the deal is now, by opening the CT of the xformer to ground the receiver still is operational for a bit until the filter caps discharge.

This is also bad because it doesn't keep the LO running so when you come back after a long old buzzard you might hafta retune.

I think a better solution would be to just use the SPDT contacts on the dow key to select either the speaker or a 600 ohm (or 8 ohm as the case may be) dummy load from the audio outpoot.

73 John
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W1GFH
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« Reply #11 on: July 20, 2005, 05:37:15 PM »

Quote from: w3jn
Hmmm, I see what the deal is now, by opening the CT of the xformer to ground the receiver still is operational for a bit until the filter caps discharge.


Right! But the SuperPro SP 210 does it fine business, no filter cap lag. I will have to look at the SP schezmatic to see how they do it.
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w3jn
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« Reply #12 on: July 20, 2005, 07:26:46 PM »

Because the Super Pro must cut the B+ at the radio, not at the PS.  The filter caps are in the PS and the stby terminals are on the radio.

And yes I've been bit by the almost 400V on those terminals  Sad
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W1GFH
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« Reply #13 on: July 20, 2005, 07:56:07 PM »

Quote from: w3jn
And yes I've been bit by the almost 400V on those terminals  Sad


I hate when that happens.

Oh and here's your avatar....

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w3jn
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« Reply #14 on: July 20, 2005, 07:58:50 PM »

Thanks!  Going in as my avatar in a second.
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