[Boatanchors] Comarison?

[Carl]

The SX-140 is another nice project for the creative if you want ham bands 
only.

Remove the 6BA6 regenerative 1650 kc IF, put in a 6BY6 (a less overload 
prone 6BE6 variant)and convert down. I used 262 kc and built a little sub 
chassis to hold 2 stages of 6BJ6 ( half the filament current of a 6BA6) IF's 
for decent AM selectivity.

Messed around in the detector/AGC/audio circuits. Its now used with a Knight 
T-150A with modified audio up at our Maine summer cottage.

It has a fairly decent front end as built and stability is adequate for AM 
and even CW on the lower bands.

Best part is that its not AC/DC and uses low B+. A very small sleeper with 
some TLC. Converting to 455 and using available filters is another way to 
go. I happen to have had several old auto radio parts sets to get the IF's.

Carl
KM1H


----- Original Message ----- 
From: "Drew P." <drewrailleur807 at yahoo.com>
To: <boatanchors at mailman.qth.net>
Sent: Saturday, December 19, 2009 11:56 PM
Subject: Re: [Boatanchors] Comarison?


> While were are still fresh on the topic of boatanchor comparisons and also 
> with homebrew receiver projects, I'll mention an idea of my own which 
> involves a combination of the pursuits: boatanchor modification.  Before I 
> get burned at the stake as a heretic, let me mention the object of my 
> idea, a receiver which is neither good nor desireable. It is the 
> Hallicrafters S-120, and at probably less than 10 pounds, would have a 
> tough time anchoring a swimming pool toy in a puddle.  But at that it 
> would do better than at many receiving tasks.
>
> The S-120 is a bottom of the barrel entry level receiver from the 1960's, 
> branded Hallicrafters but made for them in Japan. I intend no slight 
> against Japanese equipment; Japan was a low cost supplier and 
> Hallicrafters needed to address the economy market. The S-120 is an "All 
> American 4", that is, 12BE6 converter, 12BA6 IF, 12AV6 detector and audio 
> voltage amp, 50C5 audio power amp. The 35W4 half-wave rectifier was 
> designed out and rectification is accomplished by selenium and the 35W4
> heater voltage drop for series heater string operation from 115V is taken 
> up instead by a power resistor.  Even with good tubes, the radio is deaf 
> as a stone above 10 MHz., 40 meters is beseiged by images and 80 works for 
> strong AM stations. There is a BFO control but that is just a pot in the 
> suppressor grid of the 12BA6; the IF amp can be made to regenerate or
> oscillate by its adjustment, providing a sort of BFO (pretty much useless 
> for SSB).
>
> For such little circuitry, the radio has a rather large chassis with much 
> empty space; that and the 35 or so volts at 150 mA taken up by the series 
> heater power resistor (in lieu of a real 35W4) beg for 3 additional 12V 
> tubes with series heaters replacing the power resistor.
>
> If I were planning to modify this radio, with the 3 additional tubes, I 
> might add:
>
> 1. Second IF stage. This thing is deaf!
> 2. RF Q multiplier.  With 455 KHz IF, images are a problem.  There aren't 
> enough gangs on the tuning cap to add an RF amplifier stage.
> 3. A real BFO.
> 4. Quieter mixer with a separate L.O. (with no RF amp, some configurations 
> of this mod might cause excessive L.O. radiation via antenna).
>
> 12AU7 family of tubes could be used to get 2 tubes for the (heater) price 
> of 1.  Going further, a 12V, 150 mA tube could be replaced with a pair of 
> 6BJ6 to get a similar 2-for-1. Could use a 19EA8 or 19EZ8 for front end.
>
> I'm not actually planning to do this mod, but it is an interesting 
> exercise to comtemplate doing within the aforementioned heater 
> constraints.  So, I now solicit commentary and ideas for mods using:
>
> A. 3- 12v, 150mA tubes such as 12BA6, 12AV6, 12BE6, 12AU6, 12BZ6, etc. 
> (more rigorous constraint)
>
> B. More 6.3V, 150 mA (6BJ6, 6C4) and/or 12v, 150 mA (12AU7, etc) (less 
> rigorous constraint) And yes, the 50C5 could be replaced with a 35C5 to 
> free up more heater power for more tubes.
>
> Silicon could replace selenium, keep it half wave just because.
>
> The S-120 Sow's Ear would be transformed into a, er, not quite silk purse, 
> but maybe chintzy cotton or linen...
>
> Drew
>
>
>
>
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