01-12-2012, 01:53 PM
Thanks for the PDF Gary, the SX 28...I thought it might be...Ok, when up to spec. they work very well, as you are probably aware it was Hallicrafters top of the range when it was in production, the one in the photo looks very good from the outside, the only thing missing from looking is the tuning lock, this is common, they can be fabricated.
I have worked on two of these receivers, I have one left (In the Gallery) below is my observations when when restoring the ones I did:
The mains transformer: both were ok, there are two versions, one 115v primary, one 115/230v dual primary, the dual primary is usually refered to as the SX28 U although the U isn't engraved on the panel. A good transformer will not usually run "hot" If the transformer is duff then the requirements of a replacement are fairly simple or you can power it externally via the octal socket on the rear chassis apron.
The output transformer: Push pull, both mine were ok.
The PSU filter choke: Ditto.
Capacitors: Most will probably need replacing except for possibly the micas. the filter electrolytics can be restuffed without a can opener (there's a knack)
Resistors (carbon comp.) Most will have drifted though the receiver might still work, I replaced most of them.
Resistors, Wire Wound: The HT screen divider consists of resistors in series all in the same heatsink envelope, both mine had duff sections, I did not attempt to strip and repair them, just bridged them with Welwyn types of a suitable rating.
The RF box, all C's and R's should be replaced were poss. In the Osc. section of the RF box access is very difficult for a couple of low value resistors and the micas, all checked out ok in both the ones I worked on. Somewhere on this forum I gave a full strip down and reassembly description for the RF box, it will take a day at least if you want to do a good job.
Wafer switches: all were ok apart from being noisy/intermittant etc, usual cleaning/contact tightening techniques apply.
Pots: No specials in there, clean/replace.
IF cores: All were free in both of mine.
RF cores: Ditto.
Adjustable capacitor trimmers (Adjustability): Air spaced dielectric ones ok.
Solid dielectric ones (The more conventional looking ones) all ok.
The wiered looking ones on top of some of the coils in the RF box, can be very stiff or siezed, approach with care when attempting to free them, only adjust if needed.
Xtal in Xtal filter: Ok in both sets, I opened the holders up and cleaned them any way, easier to do when replacing components in that area as you can gain a bit more room to unsolder.
RF coils/IF/BFO Coils: All were ok. capacitors inside IF cans etc, I never touched them, all seemed ok.
Mechanicals: Tuning and bandspread drive, apart from clean up, checking anti backlash offset and greasing/oiling etc all ok.
Band change indicators (The fingers of doom as I call them) the carraige and indicators were completely missing on one receiver (receiver will work without them) on the other receiver all present but drive cord snapped, replaced cord, can be fiddly but work it all out first then restring no problem, I think somewhere on this forum I posted a pic from a manual on this showing wot's wot, there were slight differences as to what was published and what you will find in the receiver (as usual)
Shaft Couplers: make sure when reassembling that they are not stressed, some times the coupler on the Xtal phasing capacitor can get a little bent if the front panel is not aligned properly.
S Meter: They work backwards! The S meter casing (brass) often cracked in many places, should not affect meter performance it wont fall appart, some say it helps ventilate the heat from the illumination bulb, some bind them up with metal based tape, I left mine as is, no problem.
Dial scales: Usual rules, if they still have the red print on that signifies the amature bands then be extra carefull as the red print can come off very easy. Usually when removed you will see some discolouration due to bulb heat, all part of the charm, ditto for the S meter scale, appart from a dust off I left mine as is.
Front panel: It's engraved, not done mine yet, just cleaned it up a bit.
Not covered everything Gary just some of the basics.
Tips: Make a large size copy of the circuit in sections say on a few individual sheets of A4, join 'em up and pin or paste on to a sheet of cardboard/hardboard, annotate the circuit with the component values, somewhere on this forum is a circuit diagram that I annotated.
If the mains transformer has a 115/230v selector switch on top: Be carefull if turning the chassis over and putting it down on the bench upside down that the switch doesn't slip into an unwanted voltage selection.....It can happen...I was lucky and caught it just in time.
I temporarily fix with silicon a 1" wooden block on top of the transformer to avoid that happening again, also gives a safer clearance for the valve tops etc.
As for styling, well it fits the bill, the two bright metal strips on the cabinet sides make it, as does the "Jules Verne" steering wheel tuning knobs.
Anyway hope you get it.
Lawrence.
I have worked on two of these receivers, I have one left (In the Gallery) below is my observations when when restoring the ones I did:
The mains transformer: both were ok, there are two versions, one 115v primary, one 115/230v dual primary, the dual primary is usually refered to as the SX28 U although the U isn't engraved on the panel. A good transformer will not usually run "hot" If the transformer is duff then the requirements of a replacement are fairly simple or you can power it externally via the octal socket on the rear chassis apron.
The output transformer: Push pull, both mine were ok.
The PSU filter choke: Ditto.
Capacitors: Most will probably need replacing except for possibly the micas. the filter electrolytics can be restuffed without a can opener (there's a knack)
Resistors (carbon comp.) Most will have drifted though the receiver might still work, I replaced most of them.
Resistors, Wire Wound: The HT screen divider consists of resistors in series all in the same heatsink envelope, both mine had duff sections, I did not attempt to strip and repair them, just bridged them with Welwyn types of a suitable rating.
The RF box, all C's and R's should be replaced were poss. In the Osc. section of the RF box access is very difficult for a couple of low value resistors and the micas, all checked out ok in both the ones I worked on. Somewhere on this forum I gave a full strip down and reassembly description for the RF box, it will take a day at least if you want to do a good job.
Wafer switches: all were ok apart from being noisy/intermittant etc, usual cleaning/contact tightening techniques apply.
Pots: No specials in there, clean/replace.
IF cores: All were free in both of mine.
RF cores: Ditto.
Adjustable capacitor trimmers (Adjustability): Air spaced dielectric ones ok.
Solid dielectric ones (The more conventional looking ones) all ok.
The wiered looking ones on top of some of the coils in the RF box, can be very stiff or siezed, approach with care when attempting to free them, only adjust if needed.
Xtal in Xtal filter: Ok in both sets, I opened the holders up and cleaned them any way, easier to do when replacing components in that area as you can gain a bit more room to unsolder.
RF coils/IF/BFO Coils: All were ok. capacitors inside IF cans etc, I never touched them, all seemed ok.
Mechanicals: Tuning and bandspread drive, apart from clean up, checking anti backlash offset and greasing/oiling etc all ok.
Band change indicators (The fingers of doom as I call them) the carraige and indicators were completely missing on one receiver (receiver will work without them) on the other receiver all present but drive cord snapped, replaced cord, can be fiddly but work it all out first then restring no problem, I think somewhere on this forum I posted a pic from a manual on this showing wot's wot, there were slight differences as to what was published and what you will find in the receiver (as usual)
Shaft Couplers: make sure when reassembling that they are not stressed, some times the coupler on the Xtal phasing capacitor can get a little bent if the front panel is not aligned properly.
S Meter: They work backwards! The S meter casing (brass) often cracked in many places, should not affect meter performance it wont fall appart, some say it helps ventilate the heat from the illumination bulb, some bind them up with metal based tape, I left mine as is, no problem.
Dial scales: Usual rules, if they still have the red print on that signifies the amature bands then be extra carefull as the red print can come off very easy. Usually when removed you will see some discolouration due to bulb heat, all part of the charm, ditto for the S meter scale, appart from a dust off I left mine as is.
Front panel: It's engraved, not done mine yet, just cleaned it up a bit.
Not covered everything Gary just some of the basics.
Tips: Make a large size copy of the circuit in sections say on a few individual sheets of A4, join 'em up and pin or paste on to a sheet of cardboard/hardboard, annotate the circuit with the component values, somewhere on this forum is a circuit diagram that I annotated.
If the mains transformer has a 115/230v selector switch on top: Be carefull if turning the chassis over and putting it down on the bench upside down that the switch doesn't slip into an unwanted voltage selection.....It can happen...I was lucky and caught it just in time.
I temporarily fix with silicon a 1" wooden block on top of the transformer to avoid that happening again, also gives a safer clearance for the valve tops etc.
As for styling, well it fits the bill, the two bright metal strips on the cabinet sides make it, as does the "Jules Verne" steering wheel tuning knobs.
Anyway hope you get it.
Lawrence.
