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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Sun 01, 2020 8:12 pm 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
I jumped the gun with buying a transmitter. I still have to take the test! So I am not buying one till I do that if I do it.

I am starting to receive my 2 watt military quality resistors that are 1% tolerance. They are really hard to find on Ebay so it took a long time finding the values I needed.

I also got a used Allen Bradley 500 ohm pot and put it in. On the back of the radio it has a plug in socket with two jumper wires. The fabric covering had worn off and the bare wire was showing. I had some multi strand silicon jacket wire so I used that to replace the old wire. Now no danger of shock by touching the bare wire.

I also ordered some old stock new mica silver caps so I will start doing those small pico farad ones next.

When I was examining one of the old dog bone caps on a tuner section by mis soldering I had turned it into a resistor by mistake.

I got two new old stock 6f6 Sylvania tubes so they are now in and working.

Close up shot of my ac 6v led bulbs. Close up of my homemade dial.

Waiting for my ceramic insulators, silver plated copper teflon coated wire which I just ordered and my rg11u coax which I hopefully will get this wk. Slowly working on my antenna. I have a 2.5 piece of carbon tubing, a 8 foot fishing pole stripping it down for a whip antenna on top of the carbon and then all that connected to 3/4 plastic 10 foot pipe. Then I am going to paint on the vertical antenna wire with epoxy. Mount a plate to the vertical somewhere maybe at the base and run horizontal radials.

This isn't for transmitting so I don't think I have to be critical with lengths for the bands.

Cheers,

MK


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Tue 03, 2020 2:54 am 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
Maple dial plate installed.

Works good on all bands. Working on a new antenna now.

Radio is 90% there. S meter still isn't working.

Sounds great. Next doing mica caps and install an audio input and speaker connector.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Tue 03, 2020 7:36 am 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
A note about my s meter. It seems to deflect slightly so if it is at 10db above s9 then it will rest there and then if I am on AM and get to a strong station it will go up to 20db above S9. It only works this way on band 1.

I am wondering if maybe my crap antenna is to blame. Maybe it just doesn't pull in a strong enough signal to move the meter!


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Tue 03, 2020 7:45 am 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 1965
I think you are correct. A good test is to apply a signal of known amplitude. The standard for a reading of S9 is 50 microvolts into 50 Ohms, or -73 dBm. The SX-25 may have a higher input impedance but we don't need to be overly accurate here.

Broadcast signals are often very strong.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Tue 03, 2020 2:05 pm 
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Joined: May Wed 20, 2020 1:33 am
Posts: 311
Location: Rockford, IL
My SX-25 is a very strong receiver.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Mon 09, 2020 9:05 pm 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
Got my carol brand rg 11 u coax. super low loss, very stiff stuff. It is carrying my signal from both sides of my dipole to my radio.

Much cleaner signal now. But.....

These cheapo radio shack 1.2 watt resistors that i got a lot of on Ebay are not cutting it.

The high voltage is screwing them all up.

Going to replace all my resistors now especially those getting hit with over 50v with 2 watt or so military grade resistors.

Crappy that they are so hard to find now.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Mon 09, 2020 11:46 pm 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
I am not saying Radio Shack capacitors are bad but just for this application they are not the best.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Wed 11, 2020 2:09 pm 
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Joined: May Wed 20, 2020 1:33 am
Posts: 311
Location: Rockford, IL
Try tubedepot.com as they have a great selection of HV stuff. They actually sell enough of caps and resistors that even DigiKey will list items they are selling on the DigiKey site. I have dealt with them for nearly 20 years and are great for resistors and common caps.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Wed 11, 2020 3:24 pm 
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Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1695
Location: Champaign IL 61822
Once working properly you will not be disappointed. It takes skill learning to
use the xtal filter. But the Phone Xtal position works wonders with SSB,
giving quite good single signal selectivity. What I did was play with
xtal phase, BFO tuning and bandspread tuning, rocking the bandspread
over a pure CW signal (actually an outboard calibrator) to get best
performace for USB and LSB and marking the correct spots with tiny
arrows of blue masking tape for USB and red masking tape for LSB,
green for CW (in CW Xtal).


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Thu 12, 2020 3:39 am 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
Thanks guys sounds good. Those tube depot resistors look much better priced than digikey and they have a nice selection.

I just received some russian resistors that were on Ebay I thought i would give a try.

I also got a diamond 24mm drill bit so I am going to put my audio in and speaker jacks soon.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Sun 22, 2020 1:56 am 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
Spent a few hours replacing most of the resistors on my SX 25 with 1% tolerance military grade resistors, I do believe these make a difference vs no name resistors. You really need some good quality especially under load.

I am getting some nice signals even though it has just been a few hrs.

I noticed a bunch of tiny bone capacitors wired to some of the tuners. Do these go bad? Any experiences from anyone?


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Sun 29, 2020 1:33 am 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
Howdy all. My latest bit of work on my SX25 is just done. Replaced most of the old mica capacitors with new dipped silver mica ones.

All get right to the bottom line. All were out of spec that I replaced some as much as 100 pf. Where I didn't have the correct capacitors I summed two in parallel to the value needed.

The ones on the underside were pretty straightforward. Band 1 and 3 pad adjustment mica was a bit harder. You have to unsolder the top right wire contact and unscrew the middle screw all the way and the nut will fall off into your radio with the lock washer. Instead of bothering with the almost impossible soldering to put it all back together I just put in a jumper wire so I could put a wire over the mount instead of under it.

The RF tower at the back of the radio has two caps that are supposed to be 150pf and both of mine were reading over 200.

That is a tricky one. Top nut on the rf can comes off. Than flip the radio upside down and with a tiny socket like the kind on a multi screw driver you pull the two bottom nuts surrounded by wires. Flip the radio back over and gently lift up the can. Ditch the pieces of insulating paper taped on. Then you have to solder off the old mica caps but there are tiny wires three of them going to solder points where you mount the new caps. If they break which they are bound to do you have to gently scrape the ends with a knife to get bare metal. Then wind them with needle pincers around the contact again and solder up. Take photos so you have a reference should you be distracted.

I put it all back together and thought I had a dead radio. Checked and re-checked everything. I realize I had desoldered a resistor when I heated up a joint.

Back together barely a peep on band 1. Once these tiny pf capacitors are changed you need to really retune everything to get sound.

Result the noise floor seems much more silent now. Do this fix on your radio. This makes a big difference.

I haven't done the BFO micas yet. They are next and last. I think this might be one of my final fixes on this radio. Working great.

The last RF Tower you can really crank out the volume on band 4 now. It behaves different from the other towers.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Sun 29, 2020 4:22 am 
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Joined: May Wed 20, 2020 1:33 am
Posts: 311
Location: Rockford, IL
I have wanted to do this myself - I have not replaced caps in any of my sets IFs. Of course the IFs would need re-tuned with the caps so I would not think anything would get messed up as long as the nominal value is used.





mk2020@ wrote:
Howdy all. My latest bit of work on my SX25 is just done. Replaced most of the old mica capacitors with new dipped silver mica ones.

All get right to the bottom line. All were out of spec that I replaced some as much as 100 pf. Where I didn't have the correct capacitors I summed two in parallel to the value needed.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Nov Mon 30, 2020 2:11 am 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
I have never calibrated a radio. I have a frequency generator. Do you just send a signal into the antenna and calibrate it that way?


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Dec Tue 01, 2020 2:03 am 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
Hi this might be a dumb question but oh well. When you are making adjustments to the radio for calibrating do you have both dials at zero?

MK


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Dec Tue 01, 2020 4:13 am 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
The hallicrafters manual for that set has a pretty good step-by-step set of instructions for doing this.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Dec Thu 03, 2020 3:30 pm 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 76
If you have a frequency generator is there an easier way to calibrate the radio. I also have an oscilloscope.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Dec Thu 03, 2020 4:44 pm 
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Joined: May Wed 20, 2020 1:33 am
Posts: 311
Location: Rockford, IL
The SX-25 is somewhat tame to align - the sticky point is aligning to the crystal as with any crystal filter radio. It took me a few times to get it right (I seem to need 2-4 times to get it where I am happy with it) - if you make it past the IF alignment then the rest of it is a cake walk. The instructions need to be followed to the T (somewhat) and I use elements of SAMs, Riders, and the Hallicrafters procedures depending on the radio.

Bare minimum you will need a signal generator and a VTVM (because of its sensitivity). A Fluke 87 like I have is less than desired as I found out: accuracy and precision are nice but sensitivity of small deflection changes seem to be king in getting a good alignment. A scope helped me with my SX-43 in getting all of the 10.7Mhz IF trimmers all agreeing and working together. I have not needed one with the SX-25. Also I bought a slick RMA antenna with BNC connectors and clips from some guy on eBay that builds them (KK4HXJ). I have many of his items and the dummy antenna is a great piece of gear to make an alignment easy.

I highly recommend using a frequency counter to do the alignment properly - keep in mind as I understand the IF/Crystal alignment process you must align to the crystal's variation from what it actually is to make the crystal and BFO action work as you want it to so strict 455Khz is off the table. My first set I ever worked on and aligned was a SX-43 and it was an uphill learning experience (the three day festival of the alignment ceremony). The SX-25 is along the same lines but not quite as bad. The frequency counter helped my keep the signal generator honest in the band alignment process - I cannot imagine working on a radio without a frequency counter somewhere in the equation.

Note that the 3A band is aligned specially (main dial AND band spread changes). The instructions are clear on what to do - otherwise the band spread needs to be set as per the instructions so the dial aligns to what you are doing. Watch for the sensitivity of the three trimmers for each band and the pad. I found that rocking the dial on the set to the trimmer and (not trimmer to the dial) is needed when it is so small of a change it is ninja expertise to turn it.

I can tell you that properly aligned the SX-25 is a downright amazing receiver in performance and sound!


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Dec Thu 03, 2020 6:29 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1652
Location: Peekskill, NY
A few words to the wise:

1) have the set in the cabinet, with the bottom cover ON when you do the alignment. The trimmer settings
will change markedly if you do it with the bottom cover off and put it back on later.

2) have the set warm up for a LONG time, like an hour, in the orientation that it will be used in. Then turn it up
to access the trimmers on the bottom.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Dec Fri 04, 2020 2:35 am 
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Joined: May Wed 20, 2020 1:33 am
Posts: 311
Location: Rockford, IL
This is the best advise: I learned it the very hard way on both points. I did not realize how things drastically change once the set is in the case until I did some (careful) live experiments with my SX-43.

I got to admit I was initially a little nervous sticking even an insulated screwdriver blindly into a 6mm hole into a device 75 years old with 340 volts in it. :shock:

jim rozen wrote:
A few words to the wise:

1) have the set in the cabinet, with the bottom cover ON when you do the alignment. The trimmer settings
will change markedly if you do it with the bottom cover off and put it back on later.

2) have the set warm up for a LONG time, like an hour, in the orientation that it will be used in. Then turn it up
to access the trimmers on the bottom.


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