[Boatanchors] Comarison?

[Drew P.]

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