The AM Forum

Has anyone used a 348 in their shack as a primary or backup receiver??? I've had one for years as a showpiece, but never really used it. Any hints for its use?

Tnx.

Philip

What hints are you looking for?  This is one of the simplest radios ever built and only has four controls that change its operation.

Any question on these?
On/Off; Volume; Band switch; Tune

Four operating controls
-AVC (automatic volume control); MVC (manual volume control); Off  "predecessor to modern AGC"
-Crystal Filter In/Out;  'a narrow filter on/off"
-CW Oscillator On/Off  --->modified by "Beat Frequency" adjust, changes the tone of the BFO just like modern rigs.

Thats it.  The radio has wide front end so you can monitor lots of QSO's simultaneously.  :)   The AVC may overload at times so switching to manual may be helpful.   bill

Should have been more specific......any way to put it in standby?

Philip,

I have been using one for years, paired up with an arc5 transmitter.  I like full QSK, so I switch the RF amplifier tubes on and off using a transistor in the tube cathodes.  It is only used for CW, and the crystal filter is very effective, and there is almost no signal on the other side of zero beat.  Aligning the IF and crystal filter is critical to correct operation.  Of course, for AM its fine anyway.  Have fun.

73,
Chris

These receivers were commonly used with both ARC-5/SCR-274 systems and with the ART-13 transmitter.    Two areas were addressed, the antenna input, and the B+ was turned off.

As you can see in the ART-13 Schematic, the antenna was removed from the receiver input, and the antenna input is grounded.   And in the case of the ARC-5 the B+ was removed, by opening up pins 2 and 6 of the 348's rear connector.

(http://i670.photobucket.com/albums/vv62/mikeinkcmo/Radios/ART-13/AntSwitchingArt13_zps6fa192fb.jpg)

(http://i670.photobucket.com/albums/vv62/mikeinkcmo/Radios/ART-13/TxMuteInstSch_zps07e922fb.jpg)

I bought mine new in the box from Fair Radio in the early 70s and used it with ARC-5 transmitters on  CW for several years.   Like Chris said, its a great A.M. radio and occasionally my early morning AM net radio. 

(http://i670.photobucket.com/albums/vv62/mikeinkcmo/Radios/BC%20348/348NTwins.jpg)

  I've been using a BC-348R that I picked up at a swap meet put on by the California Historical Radio Society at KRE in Bezerkeley. This radio was converted to a 120 vac supply mounted where the dynamotor would have been. I use it with my ART-13, my WWII bomber station.

  The receiver works well, it has really grown on me over time and is an impressive example of 1940's technology.

   The two main drawbacks are the lack of a logging scale which make it difficult to pre tune the receiver to a known frequency. The other drawback is the lack of selectivity, when the band conditions are crowded adjacent frequency QRM is a real problem.

    This is my primary AM receiver due to space limitations, I plan to reconfigure my operating position and will have a R-390A and a SP-600 to choose from when the QRM gets bad.

Keeping in the spirit of the 1940s just get an LM-21 or BC-221 hetrodyne frequency meter to preset or check frequencies. They work surprisingly well and are fun to use. Just about every one I've tried is still in calibration. :)

Phillip,

Here is the original Hallicrafters AC field mod power supply schematic.   If you click the pic you will go to my Photobucket file which has all the original Hallicrafters field mods for all the different 348 variants.

(http://i670.photobucket.com/albums/vv62/mikeinkcmo/Radios/BC%20348/Halli%20PS/HalliQPS3.jpg) (http://s670.photobucket.com/user/mikeinkcmo/library/Radios/BC%20348?sort=3&page=1)

...and here is what I made and installed in mine back in '75, The "A+" is the Filament supply.

(http://i670.photobucket.com/albums/vv62/mikeinkcmo/Radios/BC%20348/My%20AC%20Supply/BC348ACPS.jpg) (http://s670.photobucket.com/user/mikeinkcmo/library/Radios/BC%20348/My%20AC%20Supply?sort=3&page=1)

I have a web page and a YouTube video out there on the BC-348, think it may be the best item of WW2 surplus ever picked up and used by Hams, the ARC-5 junk is a lot more prevalent with many using the transmitters from that series as there first transmitter or building better transmitters using that as a starting point but the BC-348 only required a new power supply and maybe a couple other changes to be equal to many of the low to mid-range Ham receivers of the forties and fifties. I have owned several over the years from ones that were restored and all original including the dynamotor to others that were way modified for Ham use and think the BC-348Q with internal AC power supply, S meter and normal audio output transformer has to be my favorite. Couple years back I bought a hacked 348Q and striped it down and did all three of those modifications and that the basis for the one in the video and on the web page.

http://staff.salisbury.edu/~rafantini/bc348modifications.htm

All of these modifications are from the CQ Surplus Conversion books from back in the late forties. Lot of people get worked up about how if you have one of these receivers it has to be all original and the like and if that’s what they want that’s great but I have always been more interested in seeing and using this receiver in the post war Ham radio version.

Mine has been sitting here on a shelf at work for awhile. Its dirty, needs pots cleaned, and doesn't work on the lowest band, or is deaf. Need to reverse a mod someone did by adding an audio board.

Also need an enclosure, but haven't seen one of those in awhile.

When I get the Valiant to the point where it isn't breaking every other day, I'll start on the 348. Its an -N model, Wells Gardner.

Lot of people back in the day added a triode stage between the detector and the audio output tube along with changing the 6K6 to a 6V6, the original audio stage had good gain and once you got rid of the original high impedance output transformer drives a speaker or headphone real well. Many people at the time thought the audio stage did not have enough gain but that’s because they did not understand that the original output transformer and when connected to a low impedance speaker the sound sucks. Fair Radio has stacks of BC-348 receivers in their back warehouse and would imagine they will sell you a case. The J,N and Q have always been my favorite and although the more primitive E,M,P and O receivers were built around the same time I always thought J,N and Q were superior of course there are many who insist that the older E,M,P and O series are superior but not in my book. You get all this together you’ll have a state of the air late fifties early sixties Ham station. Interesting thing about the BC-348 and ART-13 transmitter (ARC-8) is that they were still in use as late as the early seventies in some older transport and cargo aircraft in the USAF.

Last tube is missing; VT-152, audio. I assume it was removed as the guy installed a solid state speaker amp inside.

I've had my BC-348J for about 45-50 years.  I just did some rework on it last year.  I have the correct speaker that works with the high impedance output xfmr.  Since I improved the power supply I built for it years ago the receiver is working very well, plenty of audio.  Getting the correct schematic really helped in getting it working right.  I also added a mute function by cutting the B+ at the correct point in the circuit.  As I remember, I rewired the filament to run on 6.3 volts.  I'm still using the 6K6 in the output stage.

Off hand I can't remember what the impedance of the speaker is, but it was something real high.  I think 900 ohms but not sure.  I think there was a xfmr inside the speaker box and that was 900 ohms to voice coil.

Fred 

The 6K6 and 6V6 are different somehow, not certain why but the 6K6 is the preferred tube. May have something to do with gain or who knows what. The weird thing is that the 6K6 also requires a bias voltage that is developed by a resistor in series with the B- of the power supply and if you exclude that resistor bad things happen. The original output transformer sucks, so I always used old audio output transformers from television sets, record players and radios although they are starting to get harder to come by these days. Cannot remember the last time I saw an all tube television set like the big old RCA sets of the sixties by they were always full of useful parts.

I like BC-348 very much...

http://www.youtube.com/watch?v=qhw-UKptBjU

http://www.youtube.com/watch?v=kF6AOo4SVAU

An absolutely fantastic............paperweight (or doorstop)!  ;D  ;D

unless you get an Ashtabula Bill "outboard slicer".

"uh, got my outboard slicer on, there's not a slopbucket
in North America that can bother me."  (Ashtabula Bill)