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56 minutes ago
From: Grayson Evans
Subject: New info on the Drake 2B
To: "Bill Meara"
Date: Wednesday, January 23, 2013, 1:43 PMHI Bill,I was looking through the Dec. 1963 issue of 73 and came across an ad for a "New Mechanical Filter Modification Kit" for the 2A and 2B. IT says "like magic the Drake becomes a truly superlative SSB receiver" Model DMF-2 $29.. Says sold exclusively by Henry Radio, but does not say if they made it or not.Has a photo showing a module that plugs in (maybe a tube socket?) right behind the VFO. Module has a mechanical filter (Collins I presume), two IF transformers and a tube (probably the tube it substitutes for). I have been looking through a bunch of old CQ's and 73's, early 60's, and I only saw this one ad. Probably a rare accessory, but how knows.Thought you might be interested.Take care,
Subject: [BITX20] Re: JBOT taking off at 250 kHz
Date: Sunday, December 23, 2012, 9:56 PM
First. You must secure the RF decoupling of +B line. Use a bunch of small capacitors in paralell 1n and 100 nF with 22 uF electrolitic.
Second: Use 1Kohm resistor in paralell with primary of the transformers. Begin with the driver, then the 1st amplifier and then the output transformer.
Let us know results.
Edgardo Maffia LU1AR
Buenos Aires - Argentina
--- In BITX20@yahoogroups.com, "iam74@..."
> --- In BITX20@yahoogroups.com, Bill Meara
> > I'm building my FOURTH JBOT and this one is giving me more trouble than all the others combined. I seek the help of the group.
> > Here are the details of my tale of woe:
> > 20 meter rig. Double Sideband. The JBOT is fed by a simple two-diode, trifilar toroid singly balanced modulator. NO DIPLEXER TO SPEAK OF. At the output of the balanced modulator there is a 1000 uH choke to ground and a .001 uF cap to the input of the JBOT. AF amp is an LM-386. VXO is a very simple MPF-102 one stage ceramic resonator VXO with no buffer stage. 7 element low pass filter (three coils, four caps).
> > All the transformers are wound on FT-37-43 cores. T3 is four such cores stacked 2X2.
> > The arrangement works beautifully into a 50 ohm dummy load. But as soon as I connect it to an antenna (a dipole out in the yard, fed with 50 ohm coax) the output signal gets ugly.
> > Looking at it on the scope, instead of the nice figure eight pattern (similar to the two tone test pattern of SSB) I get ugly fuzzy outcroppings from the peaks. Looking at the signal more closely I can see that in addition to the 14.2 Mhz signal, there is another LF oscillation at around 250 kHz.
> > I've been struggling with this. I can't get rid of the LF oscillations. The leads are all short and the inputs are far from the outputs. I've beefed up shielding, and decoupling. I've sacrificed a chicken to Papa Legba. Nothing seems to help.
> > I THINK the feedback/oscillation is taking place in the JBOT itself -- not through the
> > audio amp or the balanced modulator or the VXO.
> > I watch the RF and the AF inputs to the balanced modulator to see if there is any difference between the stable situation (with the 50 ohm dummy load) and the unstable situation (with the antenna), I don't see any differences.
> > I even put an antenna tuner between the final and the antenna anb made sure that the antenna looks like 50 ohms non reactive. This seems to help a bit, but the ugly instability is still there.
> > Help me!
> > 73 Bill N2CQR