The AM Forum

I've recently acquired an SX-28 in not too bad shape.
The line cord's insulation has crumbled off, for example...
The innards are not shiny, but not rusty.
The metal dial parts inside are rusty, not shiny.
Obviously the old paper caps are dunfors, etc.

Any experiences, tips, don'ts & do's for bringing this puppy back would be appreciated!

I'd like to avoid mistakes and learn from your experiences... before diving in.

             _-_-bear

Get a digital camera and take lots of photos.....

Replace all the caps and resistors (except the stuff inside the IF cans - mine were ok). Taking the thing apart is a real pia. If ur gunna go in, go in all the way.

When you flip it over to work on it , suport the cornors so you don't mash the IF cans and break the pretty litl glass things.

Take your time, this is a bear to work on.

this is a good link -

http://antiqueradio.org/halli12.htm

klc

Before you go to all the work of changing out the caps and resistors, make sure the IF's are ok and also the output transformer. If all ok, first place to start is in the audio section. Replace ALL the components in the audio circuit except the transformer. I dont care if that resistor checks ok, REPLACE IT. I have done several of these receivers with good results. I would also throw out the line by-pass caps and install new ones rated at 1.5KV. The old ones are no good. Also add a line fuse if there is not one. Good luck and have patients. This receiver has excellent audio and its a pleasure to tune.
Regards,
Gary...WZ1M

Re-capping the RF compartment is gonna be a, uhhh.... BEAR!  ;D  There were several versions of SX-28s and some of the RF compartments come apart easier than others.

I've successfully re-capped the RF compartment with a small diagonal cutter, a hemostat, and a tip for my Weller made out of solid copper wire that was extra-long.  There's a dude named Phil Nelson who has a website that has step by step instructions on how to re-cap the RF compartment.

If you take some care in lubing/cleaning the tuning gearbox, you'll be more than pleased with the smoothness of its operation.  Also I'd be wiling to bet that the string that pulls the dial pointer up and down is busted.  You can do it without removing the front panel, but you're gonna wanna clean/wax it and all the escutcheons anyway... so it's easier if you just pull the front panel.  You'll still want a hemostat to help along the way.

There's nothing really complex about this receiver but the components are laid on in a less-than-logical fashion.  It could take a bit of tracing to find a particular resistor or capacitor. 

One thing that I've noticed on several I've had (and one that Slab Bacon had) was the substitution of a 6AC7 for the 6AB7 first RF tube.  The 6AC7 is a sharp cutoff pentode and with this sub the radio will overload on strong signals and the S-meter will read high everywhere.  The 6AB7 isn't very common, whereas the 6AC7 was, so it was a popular (albiet ill-advised) sub.

Good luck!

73 John

I didnt take out the rf deck when I did mine years ago. I used hemos, the small yellow AES caps instead of orange drops ( which I hate due to the axial leads)
a small dental mirror which revealed the hidden caps underneath, but it was real trouble to get them all.

At one time, I had the following fully restored with each radios matching speaker: sx-16,sx25,sx 28, 28A, 42, and a s 40. I think the most I paid for any one of them was 100 bucks.

I have done several of them over the years, and am about to do another one for a friend and fellow AMer. this radio is a royal pain in the ass to recap, but definately NOT the worst one out there to deal with. Replace ALL of the paper caps, and all of the filter caps, and most likely, it will come right up and play.

The first one I did, I did like everyone else and played microsurgeon with hemostats and long soldering tips. That was a royal pain in the a$$!! The hot lick is to remove the 2 center bulkheads and their coils from the coil catacombs. This will allow EASY access to all of the rest of the caps in the front end. Believe it or not is is by far less work to dissasemble the coil catacombs than trying to "surgically" replace those capz in the front end. If yours is a 28A it is even easier to remove the coil banks, as the rf section is "modular".

Also, do not use any kind of cleaner on the bandswitch wafers that leaves an oily or greasy
residue ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! It will go up in flames, and you'll be hatin life!!

When you are doing it, you will definately invent a few new cusswords. But the first time you use it, you will agree that it was worth it!!

                                                                                 The Slab bacon

Take the 'catacomes' out to do the parts replacement... Document before you change anything, take notes , drawing and digital photos.....  I used the yellow caps from AES 'caus they were cheep...if you have spaghetti , use it. I spent a lot of time making drawings, the camera is the only way to go if you want to be really sure; but still do drawings... That and do a Griefkit  by printing out the schematic and mark/highlite the components and wiring changes as you go ....  DONT loose the thin brass washers on the gang switches.......   klc

Bear-
Look me up at Nearfest. I will have my restored SX-28A there for sale. The guy that did the electrical (K1VYU) work will be with me and happy to give you hints. We will have the radio running if we can find power 

73

Carl

Bear,

I've rebuilt 2 of them, a 28 and a 28A.  To do it right, you need to completely break the radio down, which includes removing the front panel, shafts, transmission, etc.  Getting at the RF section is the by far the major problem.  It is a little easier with the 28A.  I don't agree with replacing the electrolytics per the earlier post.  If the radio doesn't hum...why bother?  They tend to last.  One thing to change:  the big power supply dropping resistor kluge Hallicrafters riveted onto the chassis near the rear on the side.  Mine smoked one day...so save yourself a future repair by replacing it from the start. 

Check every IF and RF stage screen resistor.  They tend to be way off.

The audio output xformer is known to go south in this radio.  It is no big deal to replace it though. 

I'll be at Nearfest!  C everyone there!

Pete
n1ps

Reinstalling the dial cord is a pain in the neck, but easily done.

In second everything the others said. I restored an SX28A using an SX28 as a parts rig, so mine is kind of a hybrid. One thing I could add; take your time, go section by section, testing and replacing anything in there that needs it (or anything that even "looks" funky). Also, undo any previous user mods. After I tangled with the SX28, restoring an SX-62 was like a vacation.

So who bought the SX-28?

David Goncalves
W1EUJ

I'd add to what Slab says about spraying cleaner onto the phenolic band switch wafers. Even if it doesn't go *poof*, the wafers tend to soak the stuff up and swell to the point that the switch is very difficult to turn.

IIRC, there's also a resistor in the S-meter circuit that changes value so much that the meter is rendered useless. Plenty of info online, if you still need it. If it's the receiver you brought to NEAR-Fest, it looked pretty nice at first glance.

Dave, dunno who got it!

Todd - yep it was! Sold it...


             ;D

                       _-_-bear

Pete,
        replacing all of the paper caps, whole bunches of resistors, and other assorted parts, and not replacing the lytics in a 67 year old radio is like taking a shower and putting dirty drawers back on!!

Electrolytic technology has improved 10 fold since then. Dont kid yourself, those caps can go shorted at the drop of a hat. Its a cheap insurance policy to replace them with modern caps instead of risking an old and somewhat hard to find power transformer. not to mention a whole lot easier to do.

                                                                              The Slab Bacon


And it lookz like Bear chickened out ;D ;D

Cluck     cluck     cluck    cluck


"...man's gotta know his limitations..." C. Eastwood



                _-_-bear

Uhhh Bear.... it was Dirty Harry Callahan. ( A fine line..... maybe !!)  ;) ;)

Yeah, I have CRS, I thought it was Dirty Harry... but rather than misquote...

"...make my day..."


              _-_-

How about, "right turn Clyde"

Inspector H. Callahan