SX-100 Audio

[N8UH]

Hey everyone! This little beastie followed me home a couple weeks ago. It's quite a nice little performing receiver. The audio on the other hand...

I searched the site, and found a thread from JN who had a couple mods, but they never got published.

SOoooo, does anyone here have any insight in de-heyellerfying the audio in this little guy?

Thanks!

[KM1H]

Its a SSB radio that doesnt even do that very well so what is your problem boy

Seriously, are you fussin about the restricted audio, distortion, or ??

Carl

[WQ9E]

It may sound stupid but make sure you are tuning the radio properly.  The SX-100 is designed to only receive one sideband at a time on AM so you do not tune in AM like you would on many amateur receivers.

Assuming the radio is properly aligned, set the selectivity to either of the two widest selections and then with the pitch control set to zero turn it to sideband mode and tune for zero beat.  Then turn BFO off and choose whichever sideband has the least interference.  The SX-100 (and its close Halli relatives) provides the equivalent of 10 Khz bandpass in its 5 Khz. mode by only receiving a single sideband of the AM signal but if you try to center the signal in the passband you will get truly horrible audio.

The SX-100 instructions are not great because it implies you can receive both sidebands in the normal and treble cut positions.  However the receiver architecture is such that it is always going to receive only one sideband and the two "AM" positions on the response control are both either LSB or USB (I can't remember which but you can look at your schematic and it will indicate whether the 1600 or 1700 Khz. conversion crystal is used.)

Alignment is VERY critical for this entire family of 50 Khz. final IF Halli receivers (starting with the SX-88 and includes the SX-96,100,101,115,117,122 etc.)  If it is off the receiver will not work right.  The same is true of the Hammarlund HQ-170/180 and Heathkit RX-1 which use a similar selectivity setup.

My original Ranger/Desk KW setup included a National HRO-50 like the Johnson advertising.  After my first session as net control for a regional AM net I substituted the SX-100 for net sessions because it was much better under adverse conditions.  I don't dislike the HRO-50, it is a great receiver but the ability to select the "best" sideband on AM and narrow selectively as needed is a powerful weapon.

[w3jn]

Get rid of the .047 cap (C81) that's in the ANL circuit.  That will markedly improve modulation acceptance at higher modulation levels.

There were some other mods I did associated with the 6SC7 as the BFO section is in line even in AM mode...

[N8UH]

Get rid of the .047 cap (C81) that's in the ANL circuit.  That will markedly improve modulation acceptance at higher modulation levels.

Ahhh. That's the little bugger you were talking about in the other thread...

There were some other mods I did associated with the 6SC7 as the BFO section is in line even in AM mode...

How did you go about bypassing this section in AM mode?

Thanks!

[w3jn]

I'm cornfusing this with the SX-101.  The .047 mod is the one to do; the BFO/prod det mod I mentioned above doesn't apply to the SX-100.

Be advised the ANL is pretty much worthless with that cap removed but the improvement in audio is worth it.

[N8UH]

I'm cornfusing this with the SX-101.  The .047 mod is the one to do; the BFO/prod det mod I mentioned above doesn't apply to the SX-100.

Be advised the ANL is pretty much worthless with that cap removed but the improvement in audio is worth it.

Gotcha... You had me scratching my head a bit there.

I'll give the cap a try. Thanks!!!