B&W 5100, SX-101 station

[K1ZJH]

I just ended up owning a B&W 5100 and an SX-101 receiver. Any comments on the B&W?  Good transmitter, or a dog?  One of those deals where you a make an offer and end up with a lot of iron.  Wish it was a Johnson  and a 75A4, but....

Pete

[KB5MD]

I wouldn't frett if I were you, those are really good pieces of gear.   

[WQ9E]

Nice setup and the SX-101 does a great job on AM and CW.  It is one of my favorite vintage receivers since it does well under normal conditions with nice audio and does a very good job under "battle conditions" also.

I worked on a 5100 a few months ago and had a slight problem with neutralization since it didn't want to; it was close with the piston trimmer in the minimum capacity position.  I made a change which created two improvements:  By angling the neutralizing cap slightly outward it made adjustment much easier and dropped the stray capacitance just enough for proper neutralizing.

I think you will be very pleased with that setup.

Rodger WQ9E

[Jim, W5JO]

You won't hear much about B&W 5100s.  Probably because there aren't that many floating around.  I, personally, like them better than the 32V series Collins transmitters.  They are easy to repair, they sound good and they are built substantially. 

The plain 5100 does not have neutralization because it was AM and CW only.  The B model does have neutralization that is switched in on SSB.  If you have the 5100 (no suffix) then you have a very good AM transmitter that will do 100% negative modulation and about 95% positive.

I am not a fan of the SX series of receivers.  It is a good receiver, but Halli is not my favorite.  Many people like them and prefer them to any other brand.  It is sort of like the difference in Ford and Chevy.

So all in all, you have a nice station that once operational, will be fun to operate and give many hours of pleasure if you have a good antenna.

[K1ZJH]

I'm not sure of the SX or B&W versions--they were stuffed into an attic crawlspace and weren't overly accessible.  The son is going to drag them out and get them downstairs for me. I guess I'll find out exactly what I bought next Saturday morning when I go pick the stuff up.  I'll need to make room for the station since I am running out of room. (Who isn't )

[WQ9E]

The earliest SX-101 versions do not have a product detector; the SX-101A loses 160 meter coverage in favor of a converter band.  Most versions had an always on heating element (a resistor across the line cord) to keep the chassis warm and the later versions had a separate filament transformer to keep the 12BY7A HFO filament always on.  If the one you get has a separate oscillator filament transformer you may need to add some series resistance to drop the filament voltage to the proper value-particularly if your line voltage is on the high side.

No matter which version you get, the alignment of the low IF is critical for best performance and audio; you really need a signal generator which goes down to 50 Khz. to do a proper job. Under tough conditions, being able to narrow the selectivity and choose the sideband with the least interference is most helpful and this receiver provides these options.  When aligned properly, the best way to tune the receiver on AM is set the Pitch control to zero and then tune for zero beat on the AM carrier.  This establishes the proper positioning of the AM signal in the passband.  Then choose the sideband with the least interference.  With proper choice of selectivity and sideband my SX-101 receivers can pull signals out of the QRM as well as my Drake R-7A and modern Yaesu and Icom gear.   

[W3SLK]

Pete said:

I'll need to make room for the station since I am running out of room. (Who isn't )

Make sure you have a sturdy table........

[w3jn]

Some notes on the SX-101:

1)  The 12BY7 oscillator tube runs hot 'n' heavy.  Most times they're bad and/or have crusty sockets.

2)  The AM detector has WAY too much capacitive loading which creates distortion at above 70% mudulation.  Clipping the .1 uF capacitor associated with the ANL circuit improves this drastically, at the expense of the ANL.

3)  The thing is full of those miserable bumblebee capacitors.  99% chance you'll find some split and leaking oil.  Replace 'em all.  Someone with too much brainpower wrote an article in Electric Radio a few years ago with the idea that the inductive reactance inherent in these was part of the selectivity determining circuit.  A bunch of crap; the iductive reactance at 50 KHz in these things is negligible.  Replace 'em with orange drops or equivalent film caps.

4)  Enjoy it, it's one of the better ham-band boatanchors.

[K1ZJH]

All of the caps and out of spec resistors will get replaced as a matter of course. I suspect both rigs will have some issues considering they were stored in a hot attic for decades. 

Any links to the audio mods to improve the audio bandwidth in the SX-101? I get the feeling the B&W is going to be a kick ass AM TX!! 

Pete

[w3jn]

I'm not aware of any published mods to increase the audio BW.  You could increase the coupling cap on the grid of the output toob.

As far as the mod I mentioned above, it dosn't increase audio BW but decreases distortion.  I can't remember the designation on the schematic, but it's pretty apparent which one it is (goes to ground in the ANL circuit somewhere).  Just clip one end of it.  Makes a big difference, at the expense of the ANL.

[N2DTS]

From memory, the 5100 uses a pair of 6146 tubes as finals and modulators.
I never had any luck getting 6146's to work to my satisfaction as modulators, but I have heard good sounding 5100's.

Built like a tank I think.

I like the 32v series better, but the 5100 is likely a lot easier to work on.

Brett

[K1ZJH]

I'm not aware of any published mods to increase the audio BW.  You could increase the coupling cap on the grid of the output toob.

As far as the mod I mentioned above, it dosn't increase audio BW but decreases distortion.  I can't remember the designation on the schematic, but it's pretty apparent which one it is (goes to ground in the ANL circuit somewhere).  Just clip one end of it.  Makes a big difference, at the expense of the ANL.

I wonder if the ANL mod could be redone using a multipole switch to put the .1 back in the circuit when the ANL is on???

I think it was a mod done by Frank (aka the Slab Bacon) so it should easy to track
down. I suspect from a cursory read he may have changed a few coupling caps or cathode bypasses to increase the low end response. Here's part of the writeup Frank did on various receivers, this is from his comments on the SX-101:  QUOTED TEXT:

"It just does almost everything right. Well, almost! It has terrible audio, but is easily fixed. With a few simple mods, this has become one of my most favorite receivers. With one audio mod courtesy of W3JN (clip out one cap in the ANL circuit), and a few of my own (change the values of 2 caps, swap the output transformer and change the output tube from a 6K6 to a 6V6), it will make very pleasant warm audio that is not quite full Hi-Fi, but very easy on the ears. The 5 kc bandwidth is a little narrow for full Hi-Fi, but a slight detuning of the low IF’s stretches this to around 6 kc in the wide mode and makes very pleasant audio. In stock form mine wouldn’t pass any audio below 300 Hz or so."

[wa6mtz]

 I have the 5100B and is a good tx. I had two issues with it though and one was the selenium rectifier for the bias. That as replaced with a silicone diode. The other problem was the 6.3 volt filament winding showed only 4.7 volts. I was able to use a separate 6.3v transformer and used some Goop to adhear it to the top of another choke or transformer inside the rig. I cut loose the original 6.3v filament leads and extended them to the new txformer. Also all the electrolytics were replaced but worked well as it was.

[w1el/1]

I use that combination here. My 5100 had a bad mod xformer, replaced with a valiant xformer in turbo mode. Just fired up the 101 to replace the drake R4B that was there. Much nicer audio. Once I get my antenna up out of the bushes, some one might even hear me! Best Regards from eastern Maine, Eric W1EL

[K1ZJH]

3)  The thing is full of those miserable bumblebee capacitors.  99% chance you'll find some split and leaking oil.  Replace 'em all.  Someone with too much brainpower wrote an article in Electric Radio a few years ago with the idea that the inductive reactance inherent in these was part of the selectivity determining circuit.  A bunch of crap; the iductive reactance at 50 KHz in these things is negligible.  Replace 'em with orange drops or equivalent film caps.

4)  Enjoy it, it's one of the better ham-band boatanchors.

I asked about the inductive reactance of the bypass caps over on the Hallicrafters reflector. It will be interesting to see what kind of foodfight starts. I haven't found much discussion of the bypass caps in that Forum, but I only did a cursory search. That ER series on the SX-101A seems to be the "gospel according to St. Luke" on that venue, however. I'd like to see something more concrete to substantiate that claim myself.

Pete

[w3jn]

LOL you troll 

[KM1H]

ER is a lot like the old 73 Magazine. You takes your chances and occassionally something good appears.

I could understand the claim about inductance in caps if it was a pre metal tube era radio but the SX-101 claim is pure barnyard engineering at its worst.

In those old 1930's sets the placement of the paper cap is often critical to stabilize the circuit and a modern cap will give you an oscillator. The 6D6 is the worse and a 78 usually works as a replacement.

Carl
KM1H

[K1ZJH]

Some notes on the SX-101:

 2)  The AM detector has WAY too much capacitive loading which creates distortion at above 70% mudulation.  Clipping the .1 uF capacitor associated with the ANL circuit improves this drastically, at the expense of the ANL.

3)   .  Someone with too much brainpower wrote an article in Electric Radio a few years ago with the idea that the inductive reactance inherent in these was part of the selectivity determining circuit.  A bunch of crap; the iductive reactance at 50 KHz in these things is negligible.  Replace 'em with orange drops or equivalent film caps.

 

Yo, W3JN... I can't find the 0.1 mFd cap on the schematic.. my eyes are
going!

Also, going back to the ER articles; was the bypass cap inductive reactance concern directed to the higher value caps used in the capacitive voltage dividers used to control the amount of coupling/selectivity in the 50.5 kHz IF stage?  That would make more sense than the actual bypass caps; but I also doubt it is that critical.

Pete

[w3jn]

Pete, sorry, my memory's gone.  It's a .047, C-80 in the skizmatic.

Also that reminds me I made another mod to the last one I had.  The product detector is in circuit all the time.  I moved a few wires around on the mode switch to correct this.  Can't remember how I did it though.  Trace out that switch and you can figure it out.  As I recall that made a substantial improvement in the audio distortion as well.

[K1ZJH]

Pete, sorry, my memory's gone.  It's a .047, C-80 in the skizmatic.

Also that reminds me I made another mod to the last one I had.  The product detector is in circuit all the time.  I moved a few wires around on the mode switch to correct this.  Can't remember how I did it though.  Trace out that switch and you can figure it out.  As I recall that made a substantial improvement in the audio distortion as well.

TNX J.N..  I am looking for a replacement front panel, if I find one I'll
be restoring the RX. I'm tempted to replace the mixers down the
road, if I get that far and not sidetracked.

pete

[W2WDX]

The 5100 is one the best AM transmitters ever built for the Amateur market IMHO. (I own a 5100B and I am dying since I need the plate Xfmr for it). Wonderful plate modulated transmitter with very service friendly modular design.

73