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hallicrafters sx-43 NO FM - Printable Version

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hallicrafters sx-43 NO FM - falcon123 - 02-14-2020

hi ya fellas.i must admit i dont know much about radios and im stymied.i came across this rather tired set that appears to have been worked on in the sixties and not very well at the time. ive replaced almost every resistor in it and all the wax paper and electro. caps cleaned it up deoxited the switches. it most certainly needs an alignment,but i still get respectable am broadcast and stations on 3,3a.and 4 at night. nothing on band 2 but i dont know if there is anything in this part of the world on that band. but no fm.i do have a signal generator and an o scope that was gifted to me that i play with but i cant really say i know i;m doing with the scope. the generator i'm quite comfortable with.  i did try to perform the 1st alignment step but i found that the if adjustments had NO effect on the the pin 7 voltage of 6al5.all the tubes are new and appear to have the correct voltages on them the only tube i cant get to to read is the the 6ba6. as buggered up as this was i should be pleased i got this far,but unfortunately i'm not built that way. is there anyone game enough to a stab at this? Icon_sad Icon_e_confused

RE: hallicrafters sx-43 NO FM - Chas - 02-15-2020

Nasty schematic to post...

http://www.nostalgiaair.org/Resources/download.asp?FN=\M0008920.pdf

All but one IF can is commonly used that one is the ratio detector. Therefore, all IF cans should be O.K.

I suspect that the FM oscillator is not working. Try cleaning all contacts on any switches associated with FM with 91% alcohol, using an acid brush and cloth scraps to catch the excess. Careful not to snag a bristle from the brush. Blow dry with compressed air if available, follow with warm hair dryer or heat gun after being sure there are no residual alcohol fumes around... De-Oxit can cause leakage in sensitive switch circuits. Manipulate the switches carefully to be sure there has been no mechanical damage to the contacts, then exercise the switch at least 50 times. That should burnish the contacts. A tiny bit of lube oil on bushings and tiny dab of grease on the ball detent helps...

Be sure there is no De-Oxit in/on tube socket/pins...

If no joy, use a 20k ohms/volt meter for voltage checks, any other meter will tell a lie in respect to the schematic readings. Look for problems in the FM oscillator.

Since the chassis has had a lot of work, shorting wire clipping, solder blobs, solder flowed across tube contacts and tie terminals, wire whiskers from stranded wire, shorting. Poor riveted connections like socket ground rings and chassis grounding lugs. A meter will not show this faults so soldering the rivet and body of the lug to the chassis is a remedy or drilling out the rivet and using hardware with serrated washers.

If you have a generator injecting a 110.7 mhz into the oscillator coil may yield reception if the front end is tuned to 100mhz. Use an insulated link for this to avoid issues like a shock or fried generator level controls.

If no joy, plan on a stage by stage signal injection or tracing. May have to make simple instruments to do...

GL

Chas

RE: hallicrafters sx-43 NO FM - Radioroslyn - 02-15-2020

Cleaner schematic here:  https://www.americanradiohistory.com/Archive-Rider/48/Rider-1948-GHI.pdf  pg 98

RE: hallicrafters sx-43 NO FM - falcon123 - 02-15-2020

well ive just bathed the band switch for the i dont know how many times/. i did have a separated contact on the front of the first wafer of the band switch 3 days ago.i thought that might be it (it wasnt). the rivet head had fallen off leaving the contact and wire from pin 2 on t19 hanging in the wind. i thought that was the ball game as removing the band switch was a non starter.luckily the chassis plate behind the knob and front cover was removable and i managed to repair it and change r27 while i was at it its quite miserable to get in there.ive got a factory schematic. ive got a national vp-8177a generator. i was advised to use a 1000pf cap as a probe or at least have it in series from the generator to any point on the radio. so a modulated signal at say c-26 at 110.7mhertz is a reasonable place to start? ive looked with a magnifying glass to inspect my work i cant find anything wrong visually

RE: hallicrafters sx-43 NO FM - falcon123 - 02-15-2020

i tried the t18 with the generator its still dead. in the interest of being clear and eliminating variables,ive previously cleaned both tuning caps with a non residue contact cleaner and have deoxited all the shaft wipers and have lubed them with fader lube. the generator was set at 107.1 at 60db. i tried to tune the fm dial full range slowly. i've several meters but am using a fluke 79iii.

RE: hallicrafters sx-43 NO FM - falcon123 - 02-17-2020

i saw some plans on line for a rudimentary tone generator using a pair if bc547 transistors is it in my interest to build one of these?

RE: hallicrafters sx-43 NO FM - falcon123 - 02-28-2020

ive made progress!!! i now have fm am and shortwave. it turns out there were broken wires in t21 the 3rd i.f. the first two alignment steps brought back the fm. but aligning the band four if's is proving to be difficult. after i aligned the fm i lost the bfo i cant get it to squeal. i attempted to get it close by just using my generator at 455 kc unmod. verified with my frequency counter,but the 3rd step if adjustments had no effect,band four is very quiet with no static,but will pull in a station at night.

RE: hallicrafters sx-43 NO FM - Chas - 02-28-2020

Quote:but the 3rd step if adjustments had no effect,band four is very quiet with no static ,but will pull in a station at night.
+1, the shortwave band in question, however, lacks sensitivity. Since the BC band pasess through the IF and that is OK...

Lack of sensitivity can be attributed to at least four obvious things, more, if nits are to be picked...

1 - The RF or mixer tube isn't up to snuff of there is low plate voltage...

2 - There is poor "Q" in the RF/osc coils the signals are lost in "wet" coils

3 - There is a ground connection to the chassis via a rivet that is failing.

4 - There is a leaking mica bypass cap, could be one associated with tuning or the oscillator.

5 - Propagation is poor.

6 - What ever antenna is poor or your location is, for shortwave.
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#2 can be very difficult to address. Gently warming the coils in question with a heat gun will drive off moisture...

#3 The plated chassis and the rivet react with time to set up a corrosion. Even though the connection can be measured at zero ohms, that is DC not RF. Burnish such a riveted connection with a wire brush, add small amount of ACTIVE water base flux. Apply heat from iron with large copper tip and rosin solder. If all is well solder will flow around rivet, solder-tab and chassis without forming a ball. Using a heat gun to warm the chassis helps. Alternate fix: Drill out rivet replace with hardware and serrated washers.

#4 A "special" heat gun with a silicone rubber nozzle can be used to find a leaking mica or freeze spray. In the RF the effect is either drifting of the signal or the signal fading. If the signal increases then the tuning needs work.

Any alignment adjustment that does not peak or null as expected is a problem area. Components and connections associated with that adjustment will have to be inspected.

Great so far!

Chas

RE: hallicrafters sx-43 NO FM - falcon123 - 02-29-2020

im not sure how to answer you as i am so thoroughly confused. im confused because the c2b (rear) stator section is easily located at the junction of c96 and c2b. the trouble is that this junction is grounded in all positions except band one and six. how can a signal generator get a signal through a grounded connection? this ground agrees schematically and is accomplished on sw1 FRONT sec.five. this same signal input is used in the first eight steps of the alignment procedure. that is using the hallicrafters alignment data although it agrees with sams. now i cant believe that both these manuals are wrong,so it MUST be me but i will be d**ned if i can understand where i went wrong. last night in the absence of any other ideas,i used a basic am radio alignment procedure (which i know is wrong) for aligning the i.f.'s. i set the generator at 455kc MODULATED and.attached the generator output via a mica cap to the ANTENNA connection. on band ONE and let the radio warm up and got a tone,reduced the generator output to barely audible with a meter on the speaker output. the step three procedure went on without incident. and radio performance was dramatically improved in ALL bands. BUT its not right or else the factory would have used this,and still the bfo is inop. i do appreciate your time.

RE: hallicrafters sx-43 NO FM - Chas - 02-29-2020

I did a quick web search for the radio and this popped came up:

http://boatanchorpix.x10host.com/SX43.htm

Seems Hallicrafters did some unusual designing, therein, the site seems to explain a problem area and solutions that you may be experiencing...

GL

Chas

RE: hallicrafters sx-43 NO FM - falcon123 - 03-01-2020

read that chas, as previously stated all the tubes are n.o.s. and the correct type and all the tube pins were d100 deoxit treated as well as the sockets with a pipe cleaner multiple times.any thoughts on the c2b c96 injection point? yeah the antenna sucks but might surprise you.its the concertina wire atop the wall outside the workshop