SX-24

 


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This page is dedicated to the Hallicrafters SX-24 Skyrider Defiant.  The tube line up is 6L6, 76, 80, 6SK7, 6H6, 6K8 and three 6SK7's.  

Un-restored this radio received on all bands.  The band switch is touchy, scratchy RF and AF gain controls and the toggle switches take a bit of time to switch.  All this is easily fixed with cleaning and lubricating.  There is an occasional popping and crackle when in operation.  This is most likely caused by a bad capacitor.  The S meter is sluggishly responding and will not zero.  This too is probably because of bad caps and a dirty zero pot.  All these radio ailments will be addressed with a complete and though chassis restoration and bring this radio back to its proud capacities as a Hallicrafters SX-24 Skyrider Defiant. 

IMG_0187.JPG (315499 bytes) Original caps and resistors. IMG_0188.JPG (340535 bytes) Nice look.  Well kept. IMG_0189.JPG (337172 bytes) IMG_0190.JPG (260024 bytes) Chassis could use a cleaning. IMG_0191.JPG (228829 bytes) Some work has been done on the S meter and pilot lamps IMG_0192.JPG (233361 bytes)
IMG_0193.JPG (431667 bytes) Chipped black paint. Easy to sand and repaint. IMG_0197.JPG (308952 bytes) IMG_0198.JPG (159053 bytes) Dial scale cover with index has scratch.  IMG_0199.JPG (332170 bytes)Black paint needs restored. IMG_0200.JPG (214363 bytes) Mystery Wire.  This will be taken care of during the restoration.   IMG_0235.JPG (286542 bytes) Naked Chassis.
IMG_0234.JPG (157710 bytes) S-meter movement protected with a pop (soda) bottle. IMG_0236.JPG (330636 bytes) Empty case.        

 

Dial scales 

Some images are large. 

bandspread.jpg (7098952 bytes) Band spread - Cracked scale and scratched cover. sx24 main.jpg (6915543 bytes) Main Tuning in good condition. sx24.jpg (1112240 bytes) Main Tuning Bezel - scratched. scan0002.jpg (599011 bytes) Rear of cover - oversized to be riveted to metal bezel.
proportions.jpg (1121553 bytes)  Ruler on top of image for sizing. IMG_0232.JPG (242659 bytes) S-meter clear cover with mechanical zero is larger to be captured in meter cover.  This cover was replaced with Polycarbonate sheeting.  sx24 Smeter.jpg (1441683 bytes)  IMG_0241.JPG (327694 bytes) S-meter scale is cracked.   

 

Dry Transfer lettering used on Dial Scale covers

IMG_0315.JPG (80667 bytes)Get your materials together.  Have a pattern or the original cover. IMG_0316.JPG (102371 bytes) I used Black Gothic letters of appropriate size. IMG_0318.JPG (71227 bytes) .015 inch thick clear Polycarbonate sheets. IMG_0317.JPG (44488 bytes)Cut out a piece a little bit bigger than your dial scale cover.  This is the Bandspread index.  IMG_0319.JPG (55740 bytes)Tape it onto your pattern.
IMG_0320.JPG (95048 bytes) Line up the transfer letter over the image and gently rub. IMG_0321.JPG (79493 bytes) Four "M"s have been transferred successfully. IMG_0322.JPG (47040 bytes) All lettering has been transferd.  I'm pleased.  IMG_0323.JPG (61538 bytes) Seal down the lettering with Decal Bonder. Trim the both the polycarbonate sheet and the layout image to proper size.  I repeated this procedure for the main Tuning dial scale cover. 

 

 

 

Pictures of the finished cabinet and dial scale cove.

Black bezel (on left) was stripped primed and spray painted.  All dials and meter bezels were cleaned and treated with Magnolia Glayzit.  New Polycarbonate dial scale covers were fabricated and labeled with Dry Transfer Letters.  The letters were protected with Testors Decal Bonder.

All from "bright" steel was power buffed on a bench grinder/buffer or with a Dremel power tool and appropriate polishing compound. 

These two pictures do not do the radio justice.  The SX-24 looks much better in person with out an intense flash. 

Side vents were stripped then pained with primer and silver spray paint.

 

Audio Output Transformer

I have received multiple questions about replacement audio output transformers for Hallicrafters radios.   I have replaced transformers in Hallicrafters radios (http://www.ppinyot.com/H/sx_71.htm and http://www.ppinyot.com/sx62a.htm) where there is a 300 and 3000 ohm output impedance.  Both times the owner(s) did not want to spend $180 plus dollars on a direct replacement.  So a universal Hammond single ended transformer was selected.  The up side is lower cost and the transformer is NEW.  The down side is there is no longer a high impedance speaker connection.  But this can be overcome with a special transformer also by Hammond just  for this challenge. 

If you must use the original 3000 ohm impedance then a direct replacement, new audio transformer, will be costly and hard to find.  There may be used transformers available from other sources.  If you can live with a standard 4 to 16 ohm output then it is easy to find a replacement.  Here is how I have done it:

Givens: 

Hallicrafters SX-24

Schematic: http://www.nostalgiaair.org/PagesByModel/914/M0008914.pdf  

Output tube:  6F6

Tube output impedance:  Class A, SE output impedance of 7000 (http://www.duncanamps.com/  TDSL)

Pout = 4.5watts

Ia = 38ma (or calculate the max I through R25 cathode resistor).

Find: 

New Output transformers at:  http://www.radiodaze.com/hammond15.htm or other reputable supplier.  HX-125BSE to handle the plate current in the primary and power output.

- If there is physical space (check the dimensions) get the HX-125CSE.  It  is less expensive and can handle more plate current and more wattage.  This is the tranny I have used.

 

Do: 

- Use the 5000 ohm impedance options.

- Connect black yellow to the speaker

- Re-label the 300 ohm output to 8 ohms.

- Abandon the 3000 ohm chassis terminals in place.

- Remove and abandoned C22 (C21 stops parasitic oscillations) and rewire the head phone jack to pick up the secondary of the new audio transformer, UNLESS I choose to drive a set of headphones directly from the plate of the output tube with B+ on it.  Personally, I do not want +200 volts, held back by a capacitor (C22), in a head phone across my skull so this cap and wiring goes bye bye.

- I would parallel the headphone jack across the secondary or hook it up to interrupt the speaker when the head phones are plugged in.

- Optionally rework the headphone jack so it switches in a 150 to 300 ohm 1 to 2 watt resistor in series with the head phone just to provide some level of attenuation. But I would remember to cut the volume before plugging in head phones.  So I would forget the resistor.

If there is an original 300 ohm speaker I would then buy and install: http://www.radiodaze.com/hammond12.htm into the speaker cabinet. This would make the Hallicrafters speaker more universal to 8 ohm radios.  But if the speaker needs reconed just specify 8 ohm voice coil from the reconer. Then use the 8 to 300 ohm transformer if you put the reconed speaker on a receiver with only a 300 ohm output.

This is how I would do and have done it.

 

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