SX100 5kc filter.

[ke7trp]

Has anyone bypassed the SX100 5K filter?   I love my SX100 and it matches my 40 meter AM station perfectly. I wish I had a wider band pass though. 5K is just to narrow to hear great AM.

Clark

[nq5t]

Hmmmm..  I'm not sure how you would do that.  Perhaps modify components in the 50Kc IF strip in the 5Kc position (maybe change the resistors/capacitors that set the bandwidth -- lower C, bigger R).  I suppose you could try bypassing maybe one set the 50Khz tuned circuits with a network to equalize gain and see what that looks like.



Grant/NQ5T

[ke7trp]

Yeah.. I as hoping it was going to be a simple jump operation.  I lost my SX100 manual and they are no longer on BAMA as someone purchased the Halli rights. The guy is charging for all the manuals now.  If someone has the manual, I would love a copy.

Clark

[Pete, WA2CWA]

Yeah.. I as hoping it was going to be a simple jump operation.  I lost my SX100 manual and they are no longer on BAMA as someone purchased the Halli rights. The guy is charging for all the manuals now.  If someone has the manual, I would love a copy.

Clark

Hallicrafters manuals, if you can read them, are still on BAMA.

[ke7trp]

man.. I just checked for that thing over the weekend and they where all gone.. I found it on the Mirror site.. Thanks pete!

Clark

[ke7trp]

Yikes.. Not going to be easy..  Oh well... One can Dream. I will just use it as is.

Clark

[Pete, WA2CWA]

man.. I just checked for that thing over the weekend and they where all gone.. I found it on the Mirror site.. Thanks pete!

Clark

The Heathkit stuff was removed, not the Hallicrafters.

[ke7trp]

Your right..  My mistake.  I was looking for a Heathkit manual!  Sorry!

Clark

[WQ9E]

Clark,

Properly tuned and aligned, the SX-100 provides audio response out to 5 Khz. at the 6 db down point.  It is designed to receive the carrier plus one sideband at a time and is equivalent to 10 Khz. selectivity in a conventional receiver.

Proper tuning requires placing the carrier at one side of the selectivity curve.  Assuming your SX-100 is properly aligned, set the BFO to 0 and set the receiver for SSB reception.  Now tune the carrier for zero beat, then turn the BFO off, and select the sideband with the least interference.

If you center the carrier in the passband as you would with a traditional receiver then you will have very narrow recovered audio.

The alignment is critical so make sure that it (and the BFO frequency) are set properly.  The SX-100 is a great AM receiver both for good and "battle" conditions.  I used one for several months with my Ranger/Desk setup and it was much better than the HRO-50T1 it replaced.  I now use an SX-88 which looks cool but isn't as easy to use on AM (requires retuning to select the desired sideband rather than flipping a switch).  The SX-88 selectivity is definitely better on CW but I sometimes miss the SX-100 on AM (just not enough to substitute them though).

This same advice (using the BFO for tuning) is applicable to the Hammarlund HQ-170/180 twins and also the Heath RX-1.

Rodger WQ9E

[ke7trp]

Thanks Rodger!  I have been zero beating the RXer for 2 years.. LOL. I will try this tonight.  Mine has a mellow low sound. No mid and no highs.  I might have to check the alignment.

Clark

[WQ9E]

Clark,

It could very well just be your BFO alignment so check that before you mess with the IF transformers since it is easy to set.  You can pick up the third and fourth harmonics of the BFO easily in an external receiver to check that it is at the proper frequency when set to zero and this is easier than hooking up a frequency counter.  You need an external receiver that tunes down into the longwave region and just make sure when tuned to WWV at 5 or 10 Mhz. that your "test" receiver is at zero beat or adjust it as needed.  Then tune it to the stated BFO frequency of the SX-100 or its lowest harmonic and make sure the SX-100 BFO is correct.  If it is then it sounds like realignment time.

You should have plenty of highs on the SX-100; it definitely is not "muddy" when working properly.

Rodger

[ke7trp]

Ok.. Its way off Rodger.

WWV shows as 5.2 mhz on the main dial with the bandspread at 0..   So the dial is off.  Thats problem number one.

Number two is the BFO was WAY WAY WAY off.  When Upper Side band zero beated, Lower was SUPER high pitched.  I removed the knob and spent a Frusterating 30 minutes trying to find a way to make the shaft beat upper and lower together. I finaly found a compromise that was almost perfect.. I put the knob back on but now, O is Zero for both upper and lower.. But I can only turn the knob ONE section over before it hits the stop. In otherwords, the has little turning to the left and ALOT to the right. 


Even so.. I now have lots more treble and a wider band audio.  Any advice?

C

[WQ9E]

Clark,

There is a mechanical collar stop that determines how far the pitch control can move either way; it is either locked in place with a hex or bristol set screw depending upon when yours was made. 

To provide a known baseline, check the manual to see what the BFO frequency is supposed to be when the pitch knob is set to zero (I seem to recall 50.75 but I don't have a manual handy).  With the set screw in the collar loose, adjust the core of the BFO coil so that the frequency is correct.  If you don't have a "test" receiver or transceiver that goes down to the 50 Kc region you can use the 2'nd, 3'rd, or 4'th harmonic of the SX-100 BFO since it is fairly rich in harmonics.

The collar on the shaft works with a screw shaft sticking out and interfering with the set screw to limit the range of the pitch knob.  You want the collar set to center of range to allow the pitch control to go to +/-5  before the set screw hits the limit.   This same setup is used on a lot of halli receivers.

I hope this helps!

Rodger

[ke7trp]

I saw that and figured thats what I needed to do.. But the manual does not mention this. Thanks alot Rodger.. I will try again tonight. 

Clark

[WQ9E]

Clark,

If you run into alignment problems shoot me a PM or email and I will try to help you out.  Sometimes one or both of the crystals in the 2'nd mixer will drift a little off frequency and there is a procedure to work around that if they have not drifted too far.  Before you try a complete realignment, check the frequencies of those two crystals because if they are off it will affect how you align the final IF.

I am sure Hallicrafters must explain the procedure for adjusting that collar stop in one of their manuals but I haven't come across it yet. 

My one disappointment with the SX-88 was that I assumed it used the same selectable sideband setup as the later family members (SX-96, 100, 101, 111, 115, 117, 122) since it also uses the dual crystal 2'nd mixer.  But in the case of the SX-88 the dual crystals are there due to the use of two different 1'st IF frequencies to avoid having the IF range fall inside a tuning range.  So, you don't get the neat switch selected sidebands with the SX-88.

With your recent postings it sounds like you are putting together a neat collection of gear!

Rodger WQ9E