[Milsurplus] BC-348-R BFO problem

[Ray Fantini]

If, with if being the operative word you wanted to use a BC-348 for SSB operation best results are obtained by operating in MVC where the volume control acts as a RF gain control. That allows you to back the RF gain down and produce good audio. One of the many modifications for the receiver is to have two separate gain controls, one for audio and a second gain control for RF gain but that involves drilling a hole in the front of the radio. The stock receiver a great AM and fair CW receiver but considering the broad tuning and stock detector using the BC-348 for a SSB receiver is a little like putting a saddle on a cow, yes you can do it and it will work but what's the point when there are lots of good SSB receivers out there that will be far superior to anything you can do with the 348 unless you want to do a lot of work, like separate gain controls, product detector , improve the audio stage for more gain and use with a low impedance speaker and then maybe a huge knob to slow down the tuning rate, but after all that it isn't going to be much of a BC-348 anymore.

RayF

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of John Hutchins
Sent: Monday, January 28, 2013 7:26 PM
To: milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] BC-348-R BFO problem

Jim -

Speaking of BC-348-R -
Per QST article November 1947 on ANL fix, the author, Wayne Parcel, noticed that the Cathode, VT-98, 6B8, pin 8  would modulate the IF grid under large signal conditions thus the root of the ANL poor performance 
problems.   "In fact", or in my opinion, the ANL circuits are basically 
the same as published in the Surplus Conversion Manual volume 1 1947.  
The cure was to add a lager capacitance between Pin 8 Cathode and ground.

Now with this simple mod, how is the over all SSB reception with the AVC and MVC mode, is the reception improved? Per the author Wayne Parcel, November 1947 QST.

Presently, observations on my BC-348R are that when receiving strong signals I need to detune the receiver antenna to get intelligible SSB reception.

This may be a good fix to cure more that one problem.

Hutch


On 1/28/2013 3:15 PM, Laura and Jim wrote:
> The bypass cap (#11-2, .01uF/500V paper) in mine failed and smoked the associated resistor (#62, 68k, 1/2W). This resistor appears to drop the B+ for VT-70 (6F7). I don't have a direct sub, but close (60k and 80K).
>
> My question: which way would be better for BFO operation? I think use the 60k for higher B+?
>
> I hope to have it and the BC-375-E on the air for the coming AM CX.
>
> 73 ALL DE JIM K6FWT