SP-600 audio mods

[W1GFH]

I have an SP-600 on the bench on extended loan. What a beast - a real hernia-maker. Black beauties are in evidence, and I'm debating a recap, but so far it plays well and is doing fine as is.

Came across this alternate to the AM Window audio mod, which i think is very clever, adding negative feedback along with the usual coupling cap mods.

http://www.webex.net/~skywaves/commrx/Hammarlumd/SP-600/Audio_Mod.gif

I did it - and response is much improved - although all I had on hand was a 390pf silver mica cap - and the circuit calls for 470pf. I may experiment next week with different values to see how it affects things.......

[W3NP]

I just did that audio mod to my SP-600 and I am VERY pleased with the result  . Very full rich audio and very clean sounding. I had a 470pf cap here for the feedback network but I doubt if a 390pf would make much difference.
I am driving a Polk 5B monitor speaker with that single ended 6V6 amp in the SP and it sounds just about as good as when using diode load audio into a Williamson PP 5881 amp and another Polk 5B.

Has anyone else besides GFH and myself tried this mod?

PS: the gain hit (8db?) is not that noticable.

[w3jn]

That's a good general mod for ANY boatanchor.  Results may vary depending upon the quality of the output xformer.  I've done similar mods with varying degrees of success with 51Js, SX-101, etc.

 BTW I see no reason for the 100 uF capacitor in series with the feedback network.

The 390 or 470 pf cap could probably be eliminated if you want a bit more high freq response as well.  This cap will INCREASE NFB at higher frequencies, thereby decreasing HF distortion at the expense of HF response.  And it's value is in no way critical.

73 John

[W1GFH]

I just did that audio mod to my SP-600 and I am VERY pleased with the result  . Very full rich audio and very clean sounding. I had a 470pf cap here for the feedback network but I doubt if a 390pf would make much difference.
I am driving a Polk 5B monitor speaker with that single ended 6V6 amp in the SP and it sounds just about as good as when using diode load audio into a Williamson PP 5881 amp and another Polk 5B.

Has anyone else besides GFH and myself tried this mod?

PS: the gain hit (8db?) is not that noticable.

Yes, I would trade another 8db for a switchable bass boost circuit.

I wonder if the NC-3-00/303 might profit from this feedback network mod? Next time I have one...........

[ke7trp]

I just got an SP600 and NC300. Can someone post this info again?  The link is dead.


C

[Pete, WA2CWA]

Found it easy with Google:
http://www.skywaves.ar88.net/commrx/Hammarlumd/SP-600/Audio_Mod.gif
Google is your friend.

[ke7trp]

Thanks..I searched on yahoo.. could not find it.  Thanks.

Can you explain what is happening down at the Audio trans? This is a bit confusing. It shows two X's.. Then a Line. 


Clark

[Pete, WA2CWA]

bullet item #3

[ke7trp]

Yeah.. I read that.. But the line through them confused me.. I thought maybe it was asking me to cut that and float it. 

I got the caps.  Going to sit down in a bit and install them.  I got the Filters in.  Very slight hum still there.  Maybe normal. I have a studio monitor on the desk right at my ear and its probably producing anything thats put into it.  I cant see any other filter caps to replace. 

The set is now working very well after Deoxit.  All bands work and stations are clear.  A few bands are off by 10 or 20 on the tuning dial.. Most bands are spot on.. For example.. wwv at 10 is showing 10 on the left dial and 32 on the right..  So that section is out of wack.. 

I can hear SW stations and BC stations comming in up to 60 on the meter very clear.. Just NO bass at all..  Going to install it in my other SP600 case today and put it in the operating position.  Going to use it with the champ and King until the NC 300 is complete.. Then the 300 will be used with the Champ most likely.

On the audio output..   Is there an easy way to feed this thing into an outboard audio amp?  What about feeding it into my Mixing board for Recording?  I got a Great looking auto gram 6 ch board and plan on feeding the audio in.

C

[Pete, WA2CWA]

http://amfone.net/ECSound/K1JJ4.htm

[ke7trp]

I saw that.. But no info on how to build the Op amp

Ok.. More work done.. Found a Bad 6AB6 and a DEAD 6AL5.  Replaced both.  Now the "AF" function of the meter works and the limiter now works properly.  It seems 100% now.. 

I have the 100UF caps for the audio mod but do not have the .05 caps.  I only have Disks and it said in another article to NOT use disks.  Only Orange Drops.  When I find some or buy some, I will perform the mod..This is as far as I plan on going with it. Its going to be used on 75 and 160 for AM.  I will post some pictures of it later today


C

[Pete, WA2CWA]

I saw that.. But no info on how to build the Op amp

Ok.. More work done.. Found a Bad 6AB6 and a DEAD 6AL5.  Replaced both.  Now the "AF" function of the meter works and the limiter now works properly.  It seems 100% now.. 

I have the 100UF caps for the audio mod but do not have the .05 caps.  I only have Disks and it said in another article to NOT use disks.  Only Orange Drops.  When I find some or buy some, I will perform the mod..This is as far as I plan on going with it. Its going to be used on 75 and 160 for AM.  I will post some pictures of it later today

C

Two of the noisiest bands around. I doubt it would make much difference between orange drops versus discs unless you enjoy hi-fi static and QRM.

[ke7trp]

Ok.. I guess I will try the disks then.  Thanks Pete. 

Here are some Camera phone pics of the JX14.  I found an old O scope case and it fit right in.  Going to make a panel to house my AADE Digital display so the FREQ counter will be flush right above the 600.  On 3870 with it now..

No mute???   Its ok to switch it for now but I am used to having mute.

Note.. I am not using the small speaker.. Its on top as the SX110 is next to it out of frame. I am using the big Hallicrafters speaker on the wall.  Sounds great with the Hammond Matching transformer.

Clark

[ke7trp]

Here are more pictures.. I know how we all love pictures!

I mounted the completed SP600 in an old O scope case.  Above it is the DBX 166 compressor limiter.  Atop it is the small mixing board.  This now Drives the Champ and the king.  Came out nice and clean. Thanks for all the help pete!

I ordered the pick up for the AADE digital display. This will sit on top of the Sp600 for the readout. Should be here next week.

Now onto the NC300 I picked up!

[N3DRB The Derb]

pix are teh schizzors. luv pix.  Nice pair.

I think I am going to take a slight detour in the road and fix JN's 75-A2. It has a bug in it....no, it literally has a dead stinkbug lying in the sliderule window. Art Collins would NOT APPROVE.  Something else wrong too besides the dead bug. meter goes to abut 20 db over 9 when turned on, stays there, no rx. no rf gain action. I bet it's a tube. I have tube tester. I fix.

[The Slab Bacon]

pix are teh schizzors. luv pix.  Nice pair.

I think I am going to take a slight detour in the road and fix JN's 75-A2. It has a bug in it....no, it literally has a dead stinkbug lying in the sliderule window. Art Collins would NOT APPROVE.  Something else wrong too besides the dead bug. meter goes to abut 20 db over 9 when turned on, stays there, no rx. no rf gain action. I bet it's a tube. I have tube tester. I fix.

FINISH UP THE MATCHBOX FIRST SO YOU CAN STAY ON THE AIR! ! !      

[K1ETP]

I've got a nice JX-17, but the dial has a real slippage problem as many of them do. I have retensioned the main dial spring without significant results.  Anyone have a real cure for 600 dial slippage??

Rich

[ke7trp]

Yeah.. That makes sense..  Mine is off 30kc now.  I would like to know about solutions.  Also.. Can someone explain how to calibrate the dial?   My 600 is dead on performance wise.. But the dial is off on some bands.

C

[ke7trp]

I guess we have no SP600 experts on the board.. Oh well.

Tonight, I had a chance to compare this RXer to my hallicrafters.  We listened to the net on 75 meters.  On the SP600, We could hear every station.. If I switched to the SX110, Some stations disapeared..  What an eye opener.  The fidelity is better on the SX110. Super clear audio.  But some stations where simply not there... Go back to the Sp600 and bingo.. I could hear everyone.  I used the 110 for a year and loved it.  Now, not so much.  I wish the Sp600 had that nice smooth tone...

C

[The Slab Bacon]

Clark,
        that is why the sp-600 cost so much more than the SX-110 when they were new. When I starting collecting receivers, (I was up to 19 or 20 of them at one time) I would get one that I really thought was the bee's knee's, then sooner or later one would show up that would blow that one away.

You will find it quite amazing the difference in personality from one receiver to another. That is the fun of "road testing" them. The written specs dont always tell the full story. I would love to hear your opinion if you ever got your hands on a properly working SX-28! ! !

I have had a JX-17 on the shelf (not working) for about 10 years now, one of these days I'll get around to repairing it and evaluating it.

so far my 3 most favorites are an R-390A, SX-28, and SX101A.

                                                              The Slab Bacon

[N2DTS]

What I do is tap off the volume control and feed audio into the hifi amp and big speaker.
Almost all the old receivers had crappy audio stages, although the scott slrm and sx17 were hifi in their day.

Getting a new receiver and checking it out is fun.
All the old ones had serious flaws though, and they always got moved on.
If it had a readout that you could tell what freq you were actually listening to, it had bad bandwidth choices and/or nasty audio.
If it had good fidelity, you could only tell what band you were on.
I would not rate any of the vintage stuff as good for AM.

Most of the new stuff is poor as well, noise and distortion, and lo fi for the most part.

The R390a was good, when it was not breaking a clamp, or you did not want to jump up to 10 meters.
A 6 Khz filter would have been nice, but it was stable, accurite and had good audio off the detector.

All the old ones (and new ones) sounded somewhat sick compaired to the homebrew, and the flex tops the homebrew. My R390a sounded good but had more noise than the homebrew, enough to mask weak signals.


I would not want anything vintage to use, but I do miss the scott receiver, with its push pull 25l6's and magic eye S meter, a very neat and different receiver, hifi and with a built in speaker.

Brett


 

[W1GFH]

There is no one perfect receiver. If I could combine them, I'd like...

The slide rule dial scale of the Collins 75A-3
The continuously variable IF of the SP200 Super Pro
The milspec build quality of the R390A
The 6V6 push pull audio and Lamb Noise Silencer of the SX-28
The black wrinkle finish and backlit amber S-meter of the HRO

[ke7trp]

I would love a nice SX28.. The one I had was a mess.  Poor sensitivity.  Great audio though!

Not a huge fan of the R390.  I have the normal and A models.  The big reason is that I am 8 miles from a 50KW Disney station for the kids on 1580.  This blasts into the R390. I can hear it out to the 3rd harmonic clearly. I can hear it mix with stations on the 75 meter band.. LOL.    NONE of my hallis have this problem.. The Sp600 is clean and clear.

We have the 75 A1  and 4 here. Not bad. Lo fi.  Also some RMEs  One real old RME.  From the 40s.  Cant remember the model.  Recievers are fun to experiment with.   

C

[ke7trp]

Completed the Audio mods on my SP600 tonight. 

The original Filters where 20,20,20.  I had 22s in with still some hum.  I increased this to 40UF each and the hum is GONE.  Nothing.  If you plan on changing the caps out in the power supply. Order three 47 UF caps at 450 volts.  Cheap and will have no hum at all. 

I added the 05s. I used 716 style Orange Drops.  I added them on as suggested. Its a real bear to cut the old ones out. My wires and resistors where fragile so I just bent them around the tabs and soldered them in place.  Big improvement in audio.  I added the 100 UF caps.  I DID NOT swap the wires and add the Feedback.  I was very satisfied with the improvement of just the 05s and the 100s. I left well enough alone.  I also did not want to have 8DB of reduction in output.  I drive a big speaker and need the volume. 

So far I am very pleased.  I listed to some SW broadcast and heard very nice tones out the RXer.  And with the HUM totaly gone its a joy.

I like this RXer so much, I might fix my other SP600 soon and juse use both as my main station receivers.  After this JX14, its real hard to use the Hallicrafters and the national.  Just no comparison.


C