Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Dec Mon 10, 2018 4:07 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 7 posts ] 
Author Message
 Post subject: Hallicrafters SX-117 - completely dead below 100 KHz on VFO
PostPosted: Feb Sat 24, 2018 7:57 am 
New Member

Joined: Jan Thu 12, 2012 6:35 am
Posts: 5
I have acquired 2 Hallicrafters SX-117 receivers recently. Both are working fairly well except for one problem - and amazingly, they both have same problem! Signals are heard loud and strong from the top of the VFO band range (eg. starting at the 500 KHz point) all the way down to around 75-100 KHz (ie. corresponding to 3.600 on 80M, 7.100 on 40M, etc). As you turn the VFO down in frequency below this area, the receiver output goes completely dead. This includes the CAL signal, which is heard strongly above the 100 KHz point. So receiving on the CW segments of all bands is impossible. The VFO variable cap is turning smoothly in both radios with no bent plates. As an observation, the VFO variable capacitor is completely unmeshed at the point that the audio output goes dead. I have not done any testing yet, but given that both receivers work well on SSB and AM above the 100 KHz mark with good volume, no hum, I would think the tubes are OK. This one has me stumped, especially since it's the same problem in both SX-117s. Any suggestions where to start?


Top
 Profile  
 
 Post subject: Re: Hallicrafters SX-117 - completely dead below 100 KHz on
PostPosted: Feb Sat 24, 2018 12:59 pm 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1818
Location: Costa Mesa, California
Do you have a signal generator so you can determine exactly what frequency you are listening to. If you have another accurate receiver, you can compare the dials at certain strong stations to check frequency that way.

There is an alignment sequence in the manual telling how to adjust the VFO for proper agreement with the dial. Sometimes it is as simple as repositioning the linkage between the dial and the capacitor, but you need to first determine if the frequency displayed on the dial agrees with the frequency of the signal you receive.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Hallicrafters SX-117 - completely dead below 100 KHz on
PostPosted: Feb Sat 24, 2018 2:04 pm 
Member
User avatar

Joined: Jun Sun 19, 2011 2:31 pm
Posts: 5865
The VFO tunes from 4.35 Mhz. to 4.85 Mhz. and is in "reverse" so that the VFO frequency goes higher as you tune lower in the band. I haven't been inside a SX-117 lately so I don't know if the VFO tuning capacitor has over-travel or not but IF it does reach the fully unmeshed point that won't be until the dial is at zero and it moves towards full mesh as you tune higher in the band. The first IF is a tuned variable IF AND its tuning capacitors are mechanically linked to the VFO tuning capacitor (share common shaft) so its peak response is at 6.5 as you tune to the bottom of the band and this peak response decreases to 6.0 Mhz. as you tune to the top of a 500 Khz. range.

If your capacitor is going to full un-mesh before zero on the dial then the dial must be re-indexed to the capacitor and the person who made this error likely also has played with the calibration adjustments for the VFO and the alignment adjustments for the variable first IF so both will need to be addressed. I don't have a SX-117 open right now but someone who does can look inside to see what degree of mesh should occur at the 0 and 500 index marks.

Rodger WQ9E


Top
 Profile  
 
 Post subject: Re: Hallicrafters SX-117 - completely dead below 100 KHz on
PostPosted: Feb Sat 24, 2018 3:48 pm 
New Member

Joined: Jan Thu 12, 2012 6:35 am
Posts: 5
OK - thanks for the responses so far. Yes, I had a feeling someone may have screwed around with the VFO alignment so it is out of sync with the dial/tuning variable cap. I will cross-check the readout with an accurate receiver and see where things line up. It's really strange that both radios have very similar problems - not sure why anyone would do that unless there's something in the VFO alignment procedure that is difficult to do and the screwed it up? Anyway, will report back with my findings. Bob, K3AC


Top
 Profile  
 
 Post subject: Re: Hallicrafters SX-117 - completely dead below 100 KHz on
PostPosted: Feb Sat 24, 2018 5:35 pm 
Member
User avatar

Joined: Sep Wed 10, 2014 2:01 am
Posts: 1818
Location: Costa Mesa, California
Because the VFO tunes backwards, someone may have tried to adjust it opposite to the manual procedure--in other words, they attempted to adjust the high end of the frequency range with the capacitance trimmer and the low end with the inductance. That would be how most radios are aligned, but not this one. This VFO also uses a somewhat unorthodox oscillator configuration where the coil is in series with the tuning capacitor--not parallel. Hopefully your situation only requires proper adjustment. I recently restored a SR 160 with a similar VFO and it required extensive experimentation and component changes to reach dial agreement.

Norm

_________________
KK6IYM


Top
 Profile  
 
 Post subject: Re: Hallicrafters SX-117 - completely dead below 100 KHz on
PostPosted: Feb Sat 24, 2018 5:59 pm 
New Member

Joined: Jan Thu 12, 2012 6:35 am
Posts: 5
Ok Norm- appreciate the info on the atypical VFO arrangement
In the SX-117. I’ll go over the alignment info
In the manual and see if I can figure out
The problem. Does seem like the same thing was
Done to both radios, which is what had me
Perplexed.

Thanks,
Bob K3AC


Top
 Profile  
 
 Post subject: Re: Hallicrafters SX-117 - completely dead below 100 KHz on
PostPosted: Feb Mon 26, 2018 7:47 am 
New Member

Joined: Jan Thu 12, 2012 6:35 am
Posts: 5
Well, I was able to find the solution to the 'dead low band segment' problem. As was suggested, I reviewed the alignment and found that the main tuning capacitor has a ceramic trimmer on the top (C15F) had been incorrectly adjusted ('golden screwdriver'?). It's directly in front of the tuning cap, and just under the top cover so very easy for someone to get to. I turned on the CAL signal and was able to adjust it to being pretty close to the correct 100 KHz marker. I could then hear the entire band, including CW portion. The top end was off a few KHz, and looks like I will need to remove the cabinet to get to the VFO coil on underside of chassis. The alignment has you adjust the coil until you get the 500 Hz marker to zerobeat the CAL signal, after you do the same CAL zerobeat with the 0 KHz marker using the trimmer. You go back/forth until they're off by less than 3 KHz.

I want to thank everyone who replied - made me dig into the VFO alignment and see how it's done. Evidently, someone fooled with the trimmer cap, or perhaps some corrosion occurred during non-use that caused the trimmer to go out of proper alignment.

73,
Bob, K3AC


Top
 Profile  
 
Post New Topic Post Reply  [ 7 posts ]  Moderator: Sandy

All times are UTC [ DST ]


Who is online

Users browsing this forum: Tom Herman and 3 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB