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IMG_2293.JPG (361210 bytes)  Jump to the second 1204 chassis




Zenith 12-S-256 number one.

One or more of these tubes needs to be wiggled to make this radio play.  I found tubes two and five to cause problems.  

I went over this chassis cleaning up solder connections, wrapping lead wires around solder lugs, cleaning and lubricating.  This chassis received a full alignment.  

The dial scale was cleaned and the dial needle stripped and painted white.

Any original resistor was replaced and the Candohm resistor which is known to go bad or intermittent was replaced with wire wound cermet resistors.  

If the speaker is intermittent, (audio output transformer, voice coil,  field coil, plug or wires), it would render the radio silent.  The dial lamp and tube filaments lit and glowing.  The B+ high voltage flows through the field coil and the audio output transformer.  The audio modulates the voice coil from the secondary of the audio output transformer.  I do not have the speaker here to test. 

I should mention the 456 kHz IF transformers were way out of alignment.  It is surprising how this radio received at all.  Perhaps the IF misalignment inhibited the radio from receiving.  It was simple luck that moving tubes and cycling power allowed the radio to receive.  The band adjustments were considerably out of adjustment as well. 


Tubes 2 and 5 caused the radio to quit playing when moved around.  I cleaned and retentioned the sockets. All the tubes were tested with a Heathkit emissions tester and passed.  Tube 12 the eye tube is a bit dim.


IMG_1977.JPG (1772084 bytes) IMG_1979.JPG (1736287 bytes) IMG_1980.JPG (1966022 bytes) IMG_1981.JPG (1759055 bytes)  
IMG_2006.JPG (284356 bytes) I replaced the remaining dog bone and original carbon composition resistors with new carbon film resistors.  IMG_2015.JPG (227657 bytes)The restorer did a nice looking job.  Unfortunately with beauty can come intermittent operations.  These leads were not twisted around the terminal posts and a flux joint and not a solder joint can easily form.  It has happened to me. 

I went around the chassis securing lead wires and resoldering the joints.   These joints may or may not cause problems.  However with the client complaint of intermittent operation I am not taking any chances.

IMG_2020.JPG (200465 bytes) Just about every bench has a mirror.  
IMG_2112.JPG (177303 bytes) The wire from the lower right goes through the solder terminal straight.  This is poor practice.  A physically weak solder joint. IMG_2108.JPG (88810 bytes) This resistor shows flux on the right lead wire where it was pulled from the solder blob.  That flux is between the lead wire and solder. No crimp and too little heat.  . IMG_2109.JPG (230459 bytes)This is the same resistor (left) reinstalled with crimped lead wires for a good physical connection.   IMG_2111.JPG (163480 bytes) The capacitor from the volume control wiper received the same wire wrap before resoldering How can I boldly comment on these solder joints?  Well I have made the same mistakes that lead to failures.  

Taught at the EIHK,  "Electronics Institute of Hard Knocks". 

IMG_2026.JPG (256494 bytes)These capacitors were changed.  The 25pf is made by MicaMold company.  They are waxed paper, not mica and are to be replaced.  This brought the dial scale in to better agreement with the indicator.   The metal bar with tabs in the rear is a Candohm resistor.  These are know to go intermittent.  I replaced the three sections not previously replaced with ceramic/cerment wire wound resistors. IMG_2029.JPG (271908 bytes) IMG_2027.JPG (177835 bytes)RF bypass cap was a regular capacitor.  This is a UL approved Y2/X2 capacitor is specially made for this application.
IMG_2048.JPG (230730 bytes)Power cord before. Unsoldered and not wrapped around strain relief slots.  IMG_2049.JPG (221081 bytes) Tinned wire ends and wrapped around strain relief.  I am just picky about some things.  The red dot when aligned with the hot side of the plug yields the least amount of chassis leakage.  IMG_2032.JPG (321468 bytes)Dial scale lettering cleaned.  IMG_2034.JPG (184127 bytes) Frequency indicator stripped in paint stripper and repainted white.
IMG_2036.JPG (178717 bytes)The tuning shaft is rubbing against the band selector.  It is dragging the motor down.   IMG_2039.JPG (475239 bytes)I loosened the shaft collar and allowed it to relieve the tension.  IMG_2038.JPG (630426 bytes)Adjusted the play in the band selector bracket to free the motor driven tuning shaft. IMG_2040.JPG (289325 bytes) IMG_2041.JPG (289771 bytes)
IMG_2042.JPG (299952 bytes) IMG_2043.JPG (273539 bytes)Lubricated the shutter mechanism. IMG_2044.JPG (270463 bytes) Pivot points and shafts. IMG_2045.JPG (155183 bytes) Drive pulley to the capacitor gang is quite cruddy.  IMG_2046.JPG (165728 bytes) Oil saturated drive belt. 
IMG_2047.JPG (183780 bytes)Alcohol cleaned drive belt with rosin (It looks the same as the oily belt).  Use a few drops of denatured alcohol to dissolve and transfer the rosin to the belt.  IMG_2051.JPG (46315 bytes)Original tuning indicator is a bit dim. This picture is over exposed. IMG_2050.JPG (239831 bytes) Home Brew pin converter to an octal socket eye tube. IMG_2052.JPG (419353 bytes)6E5C Brand New Russian made eye tube.  
IMG_2053.JPG (31597 bytes) IMG_2055.JPG (734617 bytes)Much brighter! IMG_2062.JPG (286341 bytes)Touch up some scratches.  IMG_2063.JPG (207370 bytes)Blend matching colors.   
IMG_2067.JPG (156910 bytes)Once you make one adjustment another goes out of alignment.  The shutters are hitting this shaft splice and interfering with the band switch's ability to settle in to on of the bands.   IMG_2066.JPG (165695 bytes) The shaft splice had to be clearance (ground down) to allow the shutter to fully open thus allowing the band selector shaft to fully rotate into the detent. Now you begin to figure out why other things (motor driven tuning shaft) were out of whack.   
IMG_2070.JPG (268525 bytes)The dial scale alignment is still a bit off near the middle of the bands.  Heating of the oscillator coil and the band switch wafers drive off moisture.   This helped.  The band switch wafers were washed and scrubbed (gently) with a tooth brush to get off any crud.  The Denatured alcohol washed away contaminates and oil  The heat gun drove off the alcohol and any moisture.  This improve the dial scale frequency alignment.   This is a Windows Media file.  A video of the motor tuning drive.  It is 4  minutes long.




In conclusion, this radio was restored by some one.  And I think they cared.  Each lead wire was dressed and formed to look good.  Unfortunately I think the persons soldering technique fell a bit short of reliable solder joints.  I could not prove any of the solder joints caused the intermittent failures.  I could not also find a hard failing tube socket.  

The three main contributing factors as I see it, in order, are:

1) Tube sockets, cracked when wiggled,

2) Candohm resistor, an old

3) Solder Joints, easy to miss when inexperienced even when consciences.  

There is one electronic system left unchecked.  The original speaker with the frame mounted audio output transformer.  I used a test bench speaker and transformer.  If this failure happens again some person will need to check the speaker assembly with the transformer.

Keep Practicing!  and remember, Soldering is Fun!




This is the second 1204 chassis in for restoration.  

So far all If transformers and the antenna transformer show good DC continuity.  One bad 6L7 tube totally dead.  The two 6V6 push pull tubes are "?" questionable.  I will later see if they still work or need replacements.  


  IMG_2273.JPG (807963 bytes)

I am going to look for a new outer bezel. 

IMG_2272.JPG (724903 bytes)  This outer bezel is in some rough shape. IMG_2271.JPG (592189 bytes)Sooner or later one will come up for sale.  IMG_2275.JPG (790200 bytes)
IMG_2276.JPG (618612 bytes) IMG_2277.JPG (731385 bytes) IMG_2278.JPG (581086 bytes) IMG_2264.JPG (741481 bytes) IMG_2265.JPG (617396 bytes) The output transformer works.  I used it to diagnose and test the above chassis. 
IMG_2266.JPG (653362 bytes)  This needs re-coned.  But it works.  Sounds crappy but works.    IMG_2280.JPG (225412 bytes)  The Eye tube socket adaptor for the 6E5C octal tube. IMG_2281.JPG (232667 bytes) The antenna terminal strip has been replaced and mis-wired.  Also seen is the rectifier socket.  Jumpers have been added to accommodate a different rectifier pin out.  All the operating parameters are the same.  And the jumpers accommodate the original speced tube.   IMG_2284.JPG (121327 bytes)A little fuzzy but properly wired.  It makes a great improvement on the non BC bands.
IMG_2279.JPG (228692 bytes)I color matched the black dial scale, scraped off some rust and touched up the scale. IMG_2292.JPG (637093 bytes) IMG_2293.JPG (361210 bytes)    




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