[Milsurplus] Best BC-348 if any

[Ray Fantini]

The term of "Complex and Elegant" are personal preference, you have yours and I have mine.  The tube line up is true, but external grid caps require external shields and additional wire length, Hams modified the front end of the 348 using 6AC7 tubes and played around with the screens and cathode circuts to produce better noise figures from the sets.
The use of a pentagrade combined oscillator and mixer was common place in many receivers and stability does not appear to be lacking in any of the Q receivers I have used. Maybe if you were running teletype or SSB but the none of the radios were designed for that.  And as in regards to the antenna trimmer, I use to have a Q that someone modified to accommodate a trimmer and it was fun to play around with, the same receiver also had separate RF and AF gain controls that was another common Ham modification but the Q receiver that I have been using  for the last ten years or so lacks both modifications and it does not appear to be an issue in its use. At least for me.

Ray F

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Mike Morrow
Sent: Tuesday, July 14, 2015 4:05 PM
To: milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] Best BC-348 if any

It is technically inaccurate to term the non-Wells-Gardener BC-348 sets primative in comparison to the Wells-Gardener J/N/Q models.  The more complex and elegant (both technically and mechanically) design of the other models offer higher performance above the J/N/Q designs.  The fact that the J/N/Q design mets minimum specifications does NOT in any way mean that they perform as well as the other models.  I'll use the R model to represent the so-called primitive set, and the Q model to represent the so-called advanced set.

1.  All models use an eight-tube design with the following stages:

    RF1, RF2, DET1, HF OSC, IF1, IF2, IF3, BFO, AVC, DET2, AF.

The stages most critical to RF performance are the two RF and three IF amplifier stages.  In R model those are mostly 6K7, and in the Q model those are mostlY 6SK7.  The 6SK7 is essentially a single-ended 6K7.  There is no RF performance difference that results from the tube lineups in these two sets.  Except as noted next.

2.  The R model uses a separate DET1 tube (6J7) from its associated HF oscillator tube (6C5).  The Q model combines both stages into a single tube (6SA7).  The R design is more advantageous to HF oscillator stability.  In addition, the R model HF OSC is run on low HV that is regulated by a 991 neon bulb.  The Q model has no such regulation.  The R model HF OSC tube is enclosed in a aluminum box on top and all four sides.  The Q model enclosure is open at the top.

3.  The R model compensates for increased internal noise as the receiver is tuned from low frequency end to high by use of a potentiometer that is ganged with the main tuning capacitors.  This resistor is in the cathode circuit of RF2 and is used to lower stage gain as frequency is tuned higher.  The Q model has nothing that is comparable...it was eliminated to cut costs.

4.  The R model has a very useful manually-operated antenna circuit trimmer.  Such a control would be no less useful on the Q model...but it was eliminated to reduce costs.

The BC-348-R and the -Q were both given the JAN nomenclature on AN/ARR-11 as part of their inclusion with the T-47A/ART-13 as part of AN/ARC-8.  I have flown in 1970 next to an AN/ARC-8 with the R model.

They both were modified to become part of AN/MRC-20 in the 1950s.

There was no preference for Q models over R models.  The R model was a better design.  I am unaware of any post-WWII gear for which the Q model set the pattern for construction...except maybe ham gear and table radios.  :-)

Mike / KK5F