Tweaking a Boatanchor Receiver?

kd4e kd4e at VERIZON.NET
Mon Jan 16 14:47:23 EST 2006

> 2.    Most tube type rigs have more sensitivity than they can use (at 
> least on most bands 20M and lower).

I am initially thinking of my just-acquired Gonset G66B.

> 3.   A receiver's sensitivity is a measure of it's overall noise figure. 
> The overall noise figure is a product of the individual gains and noise 
> figures of each of the stages up to the final detector (although the 
> noise figure is usually pretty well determined in the first few stages, 
> e.g. RF amplifier and 1st mixer).

The G66B lineup is:

6DC6 rf amp, 6U8 mixer-buffer, 6C4 local osc, 6BE6 converter,
6AU6 if amp, 6BJ6 if amp, 6AL5 det-avc-anl, 6AW8 audio amp/bfo,
6AQ5 audio output, OB2 voltage regulator.

> 4.   Usually increasing the gain in the front end is the biggest factor 
> in improving the noise figure.  Also decreasing the noise figure of the 
> front end usually helps.  What this means is a tube substitution might 
> be of advantage.

Anything you see in the tube lineup that might suggest a
simple tube change would improve anything or is Gonset's
tube selection spot-on?

> 5.   Unfortunately everything has a cost!  In this case, increasing gain 
> may (probably) lead to poorer strong signal performance (a bigger 
> problem today than back in the 'old days). A different tube may have 
> different gain control characteristics so that the AGC may be adversely 
> affected.  Etc, etc.

Understood and I am not looking to re-engineer the thing!  ;-)

> 6.   Also the inherent external noise levels on most frequencies below 
> 20 MHz or so are greater than any reasonable receiver's internal noise. 
> So you may not see much improvement (if any).


One day will locate a 160M transverter for the G77A!

> Well, that is just a rough outline. The other folks on the list will be 
> able to add to this as well as add specific information relative to 
> specific receivers. There was an article or series of articles some time 
> ago where someone measured a wide variety of representative radios (the 
> Drake radio's were one of them, I think) relative to sensitivity, noise 
> figure, intermod, etc.  I probably have that around here someplace or 
> maybe someone else can contribute some web references.

Is this the one?

Thanks! & 73, doc kd4e

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West Central Florida


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