NC-183 Product Detector?

[W7POW]

I have a National NC-183 (not the D version) and was wondering if anyone has info on addition of a product detector for rare reception of SSB signals.  I fired it up on 75 meters tonight to try it out after a full re-cap and was pleased with its performance.  However there was narry a AM signal to be found but lots of SSB signal right on and around 3885 and 3870.  I turned on the BFO to listen and was barely able to copy the SSB signals if I turned the RF gain down and fiddled.  Just for giggles I tried on 20 meters and could not get upper side band signals tuned at all no matter how much I played with the settings.  Sure, I really dont plan on using this national for much more than a companion for my Viking II for AM reception but it would be nice to be a ble to copy the SSB as well.  There is an extra socket in the chassis for some sort of accessory that would be great to add a tube for a produect detecotr.  Does anyone know of a skizmatic for adding a PD to the 183?  Thanks again for looking folks.
Chris Simmonds

[KM1H]

The older ARRL and West Coast HB's had lots of PD circuits.

OTOH I have no problem copying SSB on my 183, NBS-1 variant, or 183D. Turn down the RF, and use the BS dial and BFO tune to bring it in. You have to offset the BFO from zero beat either side for LSB/USB.

Carl
KM1H

[W7POW]

Never mind folks!  I tried a different bfo oscillator tube and now it is alot easier to tune in the SSB signals.  Also was able to copy some nice AM signals on 75 meters today and they sounded GREAT with this NC-183.

[KM1H]

There is no 100K bias resistor or voltage divider iin the HFO or BFO

Carl

[KM1H]

Sorry, I read bias and missed "screen"    Reading the forum on the fly while doing work in the attic.

I just increase the value of the injection cap to around 50pf or whatever the scope tells me to on all the radios I redo for myself. I dont like messing with oscillator voltages unless absolutely necessary.

Carl

[W7POW]

Thanks for the suggestions guys.  I will give those a try and see if it makes an improvement.

[Pete, WA2CWA]

Electric Radio, Dec. 1992, has an article for adding a product detector to a NC-183D. Probably wouldn't be that difficult to roll it over to a NC-183. Lots of circuits floating around for both solid-state and tube type product detectors. Not much parts either. Check the ARRL Handbook. Here's one using a 1496/1596, http://www.seekic.com/uploadfile/ic-circuit/2009625212847909.gif

[w3jn]

Don't try this trick with a NBS-1, kids, the BFO switch grounds the BFO tube screen.  If you mess with the screen dividers enough you might end up with some smoked resistors.

Believe there's at least one other National that switches the BFO in this manner.

I built up a 6SN7 product detector for the NBS-1, plugs right into the accessory socket.  Had to cut a jumper on the PHONO/CW/AM switch and run some coass over to the accessory tube, but it works FB.  4 resistors, 4 caps.

[w3jn]

Just move the BFO knob 45 degrees.

[KM1H]

Just move the BFO knob 45 degrees.

Great comeback

Post yours John, Im sure several might be interested. Ive used my NBS-1 on CW, but not SSB other than to ID QRM a few times, dont need a PD for that.

Carl
KM1H

[w3jn]

Someone posted the manual for the Universal Radio product detector not long ago.

I used the PD in the '66 ARRL handbook.

I very much prefer a variable BFO rather than crystal controlled, you can put the BFO where ever you want it on the nose of the passband.

[KM1H]

Agree John, I dont like being at the mercy of crystal drifting, now you need a trimmer for each one. This aint rocket science or requiring hard to find surplus crystals or buying new ones.

Carl

[KM1H]

I think JN and I prefer twiddling the BFO knob; if I want crystals I'll use one of the SSB rigs. I cant see spending $30-40 for a couple of crystals that will rarely get used if you can even find them for 455 kc tube service.

Carl

[w3jn]

Yep, zactly.  Grid resistors 100K, cathode resistor 270 ohms, plate resistor on right tube 47K.  I used the 150V regulated supply, just because it was there.  I always end up having to do up a capacitive divider on the grid where the IF input is.  Every radio seems to be different, it depends largely on the BFO level.

[The Slab Bacon]

That is a pretty popular circuit. (right out of an older ARRL handbook)
Also if space is a problem, you could use a 12AU7 instead of the 6SN7 and stuff it all into a very small minibox.


My 183-D has the self oscilating 6SA7 product detector / BFO mod. (done by a previous owner) and still doesnt have enough BFO to work well without backing the RF gain way down.

The nice thing about the twin triode circuit is with the IF input going into a cathode follower, it gives a wimpy BFO a good bit more "leverage" over a strong incoming signal.

I have found that in some receivers a few mods to de-wimpyize the BFO can make all the difference in the world and sometimes even make adding a product detector somewhat unnecessary. The SX-17 that I had (it got sucked into the "Vortex") had such a strapping BFO that it would swamp out the incoming signal completely if you turned the injection control too high. It worked extreemly well on SSB for a receiver that was designed before SSB. The adjustable injection feature was really kool.

The old staple used to be that you needed 10 times the BFO injection voltage as you had IF outpoot into the detector. 10x, I question, but there is no substitute for a stable STRAPPING BFO!

                                                            the Slab Bacon

[KM1H]

This is another application where a Pullen mixer really shines if you have the space to implement it. Most any dual triode can be used for the PD. The BFO can be changed to a oscillator/buffer or a seperate buffer/amp added. This boosts the voltage to the PD as well as isolating the oscillator from pulling. The various Nationals with the accessory socket are ideal for this.

Yep, the SX-17 is a very nice radio, I have 3 of them. One Ive fully restored and is often in use. It is far superior to the later SX-25 and even the HF range of a SX-42 IMO. I equate it close to the SX-32. Another will get various mods just to see what is possible, the chassis cosmetics are too rough to make like new so it will make a fine candidate. The other will become a parts whore if needed.

Carl

[w3jn]

You can use a single triode as a product detector in a radio like the R-388 or 51J-4.  Just rewire the 1/2 12AU7 that's used as the IF output cathode follower.  90% of the work's already done for you, but you need to drop the front panel to add a wire to the CW/AM switch to switch the audio.  I did this in my 51J-4 and it works FB.

[w3jn]

I did something similar with the 6SN7, Brian, I used one of those Vector octal sockets with the terminal board extensions on the bottom, and wired it to an old octal tube base.  You still hafta remove one wire from the accessory socket (I removed the 250V B+) and use it for the BFO input.

[WU2D]

For octals the 6SC7 is a good tube too because it is commonly found in metal (shielded) and it has a common cathode. It would probably work better as a product detector than as an RF mixer as I used it in the super-pro.

Mike WU2D

[w3jn]

Unfortunately the audiophools have discovered the 6SC7, and they're getting pricey.

A decent 7-pin sub would be a 6J6.

[KM1H]

The 6J6 is often overlooked and they are still a $1 tube with millions of NOS JAN surplus available. Makes a good Pullen PD also.

Or simply stuff 2 or 4 1N5711's outta sight