BC-348-Q restoration

[KK4RF]

Gentlemen:
     I bought a BC-348-Q, made by Wells Gardner Co. at the Virginia Beach Hamfest yesterday.  It's been modified, the dynamotor is missing  and someone put in a very flimsy  high voltage power supply into it. Also, there is a 12AT7 extra stage put into it, I suspect an extra audio stage. The rig is in nice shape otherwise. I'd like to get it working ( as it currently doesn't.) I want to buy a manual for it. I'd like a recommendation as to who markets the best manual for the money. It would be fun to get it working again. Thanks.   ---Marty, KK4RF---

[N8ETQ]

Hey Marty,

    Look for one of the "Surplus Radio Conversion Manuals" the extra audio
stage is handy, the crap power supply is another mater.  there were 3 editions

look here:

http://www.archive.org/details/SurplusRadioConversionManualVolume3

all the editions are posted but only Volume 1 had an index posted. u may
need to Suck em all in to see which one has the 348.

 one of em has the 348. Also be aware that the "Q" is a late model and is diff.
from the early ones. 915kc IF, single conversion, No BA shack is complete
without one! Verify the early/Late thing via the tube line up as they don't
make a big deal out of it in those manuals.


GL es 73

/Dan

[KK4RF]

Dan,
     Thanks for the tip. I'll be checking out that link. Thanks again.   ---Marty, KK4RF---

[KA3EKH]

Of all the BC-348 receivers the Q is my favorite, never warmed to the "R" and the like older versions. They used big capacitors stuffed all under the deck and tubes with grid tops. With the Q you may find that the DPDT "knob" switches for the crystal filter and BFO will be flakey due to their age but other than that the construction is a lot like late forties or early fifties radio and television sets. I have a web page that has the schematic and the common conversions for that receiver at:
http://staff.salisbury.edu/~rafantini/bc348modifications.htm
The Q that’s on that page has the most common stuff that’s done to one for Ham use, the AC power supply, six volt filament string and a S meter, adding a triode amplifier before the 6K6 audio output was a common thing but think that is not necessary. The 6K6 tube works well with small levels of input. I did replace its output transformer on the 6K6 with a transformer that had a 3 ohm secondary and have plenty of audio from the radio. Have to wonder how many put second audio stage before the  output because they did not get good audio being they were trying to drive low impedance speaker from high impedance transformer? One receiver I cleaned up once had a 6SN7 audio driver and a 6V6 in the output and all that did was produce lots of heat and load down the power supply.
If you had a receiver that was original they are getting rare enough that you don’t want to modify it but if it's already had holes and stuff in it the typical Ham mods make it a way better radio. Used mine the other day just to listen in on 80 and 160 AM stuff and was surprised how well it worked.

[iw5ci]

Hy Marty... i just finished the restoration of my 348R and i am really pleased of it.
i tought that military WWII radios where not suitable for modern HF activity, until i finished my AN/ART-13 station + BC-348R receiver.

The AC power supply is a necessary mod because in a silent environment i think that is not a good idea tu run a dynamotor.

The extra audio stage is not necessary. My BC-348 has a 5000 to 4 ohm trasformer, so i drive the LS/R speaker directly bypassing the internal trasformer.

There is plenty of audio power in this configuration (not a push pull of 6v6 like an RCA AR-88 or SX-28 but sufficient for a nice reception).

It is very important that you replace at least all the paper condensers you find, because they are prone to leakage.

After restoration you will discover a really nice receiver it will please your ears, your eyes and your nose (i like the smell of antifungus wormth by tubes heat).

Yesterday i was able to discriminate 2 AM stations in 40 meters band , less than 5khz one from the other with heavy electrical noise from a thunderstorm.

http://www.youtube.com/watch?v=yGX0hWkGPCM

not bad for a 70 years old receiver

[WU2D]

I find that almost ALL conversions on these and most other surplus sets can be traced to the CQ conversion manuals and 73 Magazine Articles and all are generally reversible with the exception of when a meter gets added! The added audio stage is sometimes found but the stock receiver works OK with plenty of speaker volume with a proper matching transformer. Separating the RF and audio gain controls can be a nice mod as improving the AGC can. The XTAL filter and IF, when lined up properly work pretty good on CW. The 348 tunes a bit fast on 20 meters and a Q multiplier tuned for the IF can work wonders.

Mike WU2D

[KK4RF]

Gentlemen:
     Thanks for all the replies, tips and the neat YouTube videos. This repair job will take me a while but I think I can do it this Fall and Winter. I'll be printing out these postings to keep in the notebook I'm assembling for the BC-348-Q. Thanks again.   ---Marty, KK4RF---

[MikeKE0ZUinkcmo]

Here are some VERY good FREE copies of the original manuals available for down load.   He also sells paper copies, and sells CDs on ebay quite reasonably.  I was very impressed.

Mike

[KK4RF]

Mike,
     I'd seen that website but have had trouble downloading the files due to their size. I'll keep trying. I finally did order a manual from ManualMan. Hoping it will be a decent help in this project. I have a week off in November and that's when I hope to at least get the rcvr going, using an outboard power supply for a while at least. Thanks again, Mike.  73s, Marty, KK4RF

[KK4RF]

Gentlemen:
     I got my manual from Manualman.com today  and I figured out how to power up the old RCVR. Amazingly it came to life and actually sounds pretty good on cw and ssb. I was even able to listen to the top end of the AM broadcast band. I've spent  the last 4 days trying to figure the radio out but was afraid to sock the power to it until I had the manual. I used an outboard power supply and had to figure out the filaments and to figure out the mods that had been previously made to it. But it works and it was a real "high" to actually copy cw and ssb signals on 80 and 40. I hope to actually be able to use it with a transmitter on the air  sometime this winter. Thanks to all.
     ---Marty, KK4RF---

[MikeKE0ZUinkcmo]

I met my first 348 in 1953 and learned CW with it.   We moved into a new house and a ham, now K6LG lived over our back fence.  Bought this early version receiver from Fair Radio in the 70s, and have done absolutely nothing to it except install an AC supply, and the occasional tune-up.  This pic was taken last month, listening to the 3885 morning net.   Still get a kick out  it, brings back a lot of memories.

[KK4RF]

Mike,
     Your '348 looks great! Actually, mine looks almost as clean as yours. Other than powering it up and listening on the bands, I have not started replacing old electrolytics and old bypass caps yet or even checked for out of tolerance resistors. It needs a lot of work, but looks like a receiver that is worth some effort. I get a kick out of old gear.
     I viewed the slideshow of your rigs and shack. Thanks again, Mike. 73s, Marty, KK4RF

[KK4RF]

     I had the afternoon off today as I had worked the weekend. I took the '348 off the dining  room table and hooked it up to my 40 meter dipole in the radio room. It's incredible how good the receiver works connected to a real antenna. I had been testing it with just a 10 piece of wire the past few days in the dining room. The dipole antenna makes this radio sound fantastic. I'm tempted not to change out any of the old caps/resistors, and just use the radio the way it is. I heard lots of good cw/ssb/ and AM signals on 80/75/and 40 meters tonight. What a pleasant surprise. This old radio actually sounds pretty darn good. I only paid 40 bucks for it at the hamfest. Got a bargain! Thanks again to all who gave advice.   ---Marty, KK4RF---

[W7TFO]

You might put a milliampere-rated fuse in the B+ if you elect to not re-cap the old girl.  Otherwise a failure could cost you other parts.

An easy temporary mod.

73DG

[KK4RF]

DG,
     Excellent idea. I have an old 1938 Philco console I was trying to restore. I had it turned on with a Variac, turning the voltage up slowly, and a component shorted and with it the filter choke burned up internally.
     Will definitely put in a low current fuse. Thanks again.   ---Marty, KK4RF---

[KA3EKH]

I have owned several BC-348 receivers ,  most of them Q models because I like them better than the older design with the grid top tubes and have had very few if any capacitor failures. If it's still there the big stupid 8 uf cube under the dynamotor chassis is usually good. Have seen many of the paper capacitors that hams installed for different mods go bad and short but the old original sealed capacitors tend to hold up real well, at least on the BC-348. Funny thing that BC-342 doesn't and I had a HRO RAS where almost every wax paper capacitor was leaky but the 348 for some unknown reason holds up better. On the subject of a fuse there is a fuse holder right up from where the original power plug is. I used that for the AC fuse for a internal power supply on two or three that I did but with you using a external supply maybe you can use that for your B+ fuse? Going to post any pictures of this radio?
RF

[KK4RF]

RF,
     The big 8 uF cap is gone and the fuse holder also is gone. I'm going to install the B+ fuse on the external power supply.
     I've never posted pictures before. I'm not sure how to do this. I do have a camera. Are there instructions on AMFONE for posting pix? I'll try to figure it out this weekend.  ---Marty---

[Todd, KA1KAQ]

Marty, all you need to do to post a photo is look below the text box where you type your post for the word Attach. Simply click the Browse bar to locate the photo on your computer that you want to post, select it and go.

I've got 2 BC-348s, R and Q models. The Q has the usual AC supply mod, otherwise is unhacked. It's fun to play with, sounds great on AM signals. The R model is in nice shape, completely stock including dynamotor, shockmount, and power connector. It is destined for a new home as soon as I can find the time to deal with it. Need to track down one of the small knobs that fell off during the move.

[KK4RF]

Todd,
     Thanks for the info on how to post pix on this website. I'll be getting some pictures of my rig on Friday night when I have a bit more time.
     I'm listening on 80 meter cw right now with the BC-348. It sounds ver nice. 80 and 40 have been pretty good the past couple nights.. 73s and thanks again.   ---Marty, KK4RF---

[N0WEK]

Russian copy of the BC-348 built into the 1980s?


http://www.ebay.com/itm/USSR-Russian-Military-Air-US-9-BC-348-Radio-Receiver-/130582697740?pt=LH_DefaultDomain_0&hash=item1e6755d70c

[w3jn]

When a couple of B-29s landed in far western Russia in the closing days of WWII after running low on fuel, the crews and aircraft were interned by the Soviets as they were not at war with Japan at the time.  Stalin ordered that the B-29s be copied exactly; that included the BC-348 and ART-13 that were on board.  The Soviet copy of the B-29 was the TU-4, after a few years the Soviets had both an atomic bomb and the strategic bomber necessary to deliver it.

I guess "better" might be considered the enemy of "good enough" as far as the Soviets were concerned; hence, a long production run for their copies of the BC-348 and ART-13.  That's a cool radio in the auction - that guy always has some very interesting Soviet-era receivers up for auction.

[KK4RF]

Gentlemen:
     I took a bunch of pictures of my '348 but have no cable to put it into the computer with. Sorry, but it may be a while before I upload any pix.
     I had a question about the strange "ground" potential on the '348. I've read that this rig had a chassis potential of negative 1.8 volts (or was it negative 18 volts?) which is related to biasing the audio amp tube. I made no changes to the biasing of the audio amp tube. I suspect if I connect the chassis into my antenna system (which is grounded via the outer braid of the coax to everything else) that this would drop the rcvr chassis to zero volts. I'm thinking that I will have to change the bias arrangement on the audio amp tube to get around this. Any advice from you BC-348 owners out there? I've read that if the cathode of the output tube is at ground potential that there will be excessive current through the tube and tube failure. I read an internet article on this and I might have to track that guy down. The internet article was about 10 years ago. Any ideas welcome.
                            ---Marty, KK4RF---

[KA2DZT]

Gentlemen:
     I took a bunch of pictures of my '348 but have no cable to put it into the computer with. Sorry, but it may be a while before I upload any pix.
     I had a question about the strange "ground" potential on the '348. I've read that this rig had a chassis potential of negative 1.8 volts (or was it negative 18 volts?) which is related to biasing the audio amp tube. I made no changes to the biasing of the audio amp tube. I suspect if I connect the chassis into my antenna system (which is grounded via the outer braid of the coax to everything else) that this would drop the rcvr chassis to zero volts. I'm thinking that I will have to change the bias arrangement on the audio amp tube to get around this. Any advice from you BC-348 owners out there? I've read that if the cathode of the output tube is at ground potential that there will be excessive current through the tube and tube failure. I read an internet article on this and I might have to track that guy down. The internet article was about 10 years ago. Any ideas welcome.
                            ---Marty, KK4RF---

I just did some rework on my BC-348J.  I did the original work some 48yrs ago.

Back then I did add cathode bias to the 6K6, should be 480 ohms with a bypass cap.  You're right about the -18V.  In the "J" model the Neg return for the PS runs through a winding on the OUTPUT xfmr, from there is goes to ground through two 50 ohm resistors in parallel.  I was not using the fix bias and had the Neg return grounded, so instead used the cathode bias.

Seems I always had a little background hum with volume control at min.  So, this time I decided to retry the winding in the OUTPUT xfmr as this is for hum bucking.

I did away with the cathode bias resistor and reconnected the -18V back to the resistors in the grid circuit of the 6K6.  With about 250VDC supply I was getting about -18V bias (which is correct for the 6K6).

This set-up did seem to reduce the background hum to near nothing, but for some reason this created other problems.  Seemed the audio was somewhat distorted and at higher volume levels I had a bad feedback problem.

Checking a few things I concluded the feedback was getting into the 6K6 grid from the bias voltage.  The aux winding on the OUTPUT xfmr was feeding too much audio into the bias voltage.  The receiver does have bypass cap in the grid circuit resistors.  That cap did not seem to be enough filtering.

I solved the problem by adding a 150ufd 80v cap on the -18V bias voltage.   This cleaned up the little distortion and no more feedback or hum.

The radio is now working better than I ever heard it in the 48 years that I've owned it.

Fred

[KK4RF]

Fred,
     Thanks for the nice explanation and insights into this peculiarity of this radio. I'm going to check into the Old Military Radio Net on 3885 kHz AM phone next Saturday morning as there are a bunch of guys on that net running the ART-13/BC-348 combination and see what others have done. I put mine back into its' case for the time being. I could kick myself for not actually measuring the chassis voltage to ground to see if it truly is negative 18 volts. Anyway, this "loose end" is keeping me from actually using the rig with my HB tube transmitters and antenna.
     It's been a fun project so far and I've learned quite a bit from it. Definitely have gotten my return on the 40 dollar investment. Thanks again, Fred.   ---Marty, KK4RF---

[KA2DZT]

Marty,

All the circuits in the radio work from chassis (metal frame) ground.  The only thing that is not grounded to the chassis is the neg lead from the PS.  In a FW rectifier circuit this would be the CT lead from your power xfmr.  Usually the CT is grounded but in BC-348 it is connected to the Aux winding in the OUTPUT xfmr.  It gets grounded through the winding and two 50 ohm resistors that are connected to the other end of that winding.  The 50 ohm resistors go to chassis ground (one 50 ohm is at the xfmr and the other is elsewhere in the receiver).  You will measure -18V from the chassis to the point where the CT lead is connected to the Aux winding.  That point is connected to the grid resistor circuit of the 6K6.  Hence, -18V fixed bias on the 6K6, no cathode bias, cathode is grounded.

Fred