BC-348 and ART-13

[iw5ci]

After 1 year of research i managed to find a companion to my an/art-13 transmitter, a BC-348R receiver.
I have discarged several BC-348 because of their lack of originality.. some where equipped with pl connectors , s-meters, holes, and one was painted of a horrible purple color and many stickers !

The one i choose is almost in original conditions, except for a 220V power supply instead of dynamotor (I agree for this convenient mod).

It was sold AS-IS at a very reasonable price, the front panel is in very good shape and also the cabinet. Only the covers of the speaker / earphone connector are broken, but i hope to find spares at flea market.

I decided anyway to power-up the radio with a variac, and it's working !
but the dial scale was innaccurate, the bfo was not centered and the xtal filter was not operative.

After one hour of power up , the radio became dead and a cloud of smoke came outside the chassis.... the burnin test was completed

One of the micamold capacitor became short and this caused the burning of a resistor. I measured some micamold capacitors and i found that all of them where leaking even at 20V ... i replaced almost any bypass and coupling capacitors except those in the cans , and the receiver came to life again working very good.
I realigned the logging scale as in the service manual and also che crystal filter and bfo.
The receiver is now alive and very lively and it works very well

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

I never tried a BC-348 before so i am asking a couple of questions:

In avc mode, if i put the volume control ccw i can ear the stations at a low volume but never completely muted. In MVC yes.

Is it normal that the xtal filter is very narrow for AM and SSB reception? with the xtal inserted there is a consistent reduction of volume level. In CW the xtal works great so i suppose it is suitable only for CW reception and for AM/SSB only with very strong nearby interference (maybe the BW is about 1 KHZ?!).

73 de iw5ci

[KA3EKH]

Had more than a couple 348 receivers and found that the crystal filter as originally designed left much to be desired. Check the frequency of the crystal first and then aligned the IF so the center frequency of the IF is on the frequency of the crystal. Don’t be surprised if it's not 915 kc. When working normally they tend to cut audio level way down. Also don’t be surprised if some of the controls stick and don’t work correctly, more of a problem on the newer Q series then the old R series. I refer to the Q as a newer radio but think the R may have been in production at the same time. If you are using a external power supply or something different for the B+ don’t forget that there is a resistor in series with the B- and if you directly ground the B- the radio will have issues. Have a web page on common modifications to the 348 at:
http://staff.salisbury.edu/~rafantini/bc348modifications.htm

[w3jn]

ALL the square micamold capacitors will be bad in that radio.  Despite their name they aren't micas, they're paper bypass capacitors in a molded bakelite block.  The actual mica capacitors (small value, 1000 uuF and less) should mostly be OK.

The xtal filter isn't great, but taking it apart, and cleaning the crystal element and contacts with some cleaner will make it a lot better.

As I recall in AVC mode the RF gain is full on and only the audio gain has any effect.  In MVC both the audio and RF gain are active.  Could be you have a volume control pot that's open at the ground end and isn't completely shunting the audio to ground.

It's a pretty good receiver other than the selectivity.  I have a BC-348C with the dynamotor (I removed the horrible hammy hambone power supply and installed a dynamotor donated by Steve K4HX), and has all original parts (so far as I can determine) except for one RF trimmer that I replaced.

[WU2D]

The Xtal filter when cleaned up and centered on the peak IF frequency as described by Jim EKH works very well on CW. It is strictly a CW filter. And yes the volume is lowered as the crystal filter is lossy. I use mine mostly for CW and AM.

Mike WU2D

[iw5ci]

Yesterday evening i made some checks on the resistors near the Micamold capacitors, and found a couple of the completely out of tolerance. One of them was 200 ohm instead of 4700 ohm, another splitted in two while i was desoldering one end.....
So i replaced many resistors.

Now i need instructions to open the if and rf boxes because i don't' know how to disassemble those units... are the boxes full of leaky micamolds capacitors?