S-40B Question

[Richard Post]

Alan,

An S-40B and an S-77A (AC-DC version of the S-40B) are next in line 
to my "latest on the bench".  Both have the red high-lighted 
settings.  Sensitivity control has a red dot.  If yours has no red 
coloring at all, then I assume Hallicrafters reduced its cost by 
using a  single-color silk screen.  The only native glass tubes are 
the rectifier (5Y3GT) and the audio output tube (6K6GT).

Substituting glass tubes for metal seems to make very little 
difference except for circuits with very critical capacitance or 
shielding needs (see my notes on the SX-43 where I found out the hard 
way that the second oscillator MUST be a metal tube).  In a circuit 
such as a S-40B, a slight alignment tweak might be needed in the IF 
or RF stages where the substitution is made in order to get peak 
performance due to minor changes in tube capacitance.

I ran across a 1938 Philco in great cosmetics where the opposite had 
been done, metal tubes substituted for glass tubes that originally 
had shields.  Resulted in the mother of all howling feedback!  The 
circuit with glass tubes had no connections at pin 1.  Therefore the 
metal substitute tubes had pin one NOT CONNECTED to ground. The metal 
shells acted like capacitors from one tube to the next.  After the 
"fix", probably very early in the life of the set, In assume it just 
sat in the attic.

73 de Rich KB8TAD

<http://tinyurl.com/hexco>


At 9:56 AM -0400 5/18/07, Alan W. Fremmer wrote:
>Fellow Collectors/Restorers,
>
>Recently acquired a Hallicrafters S-40B receiver on eBay.  This model  was
>the first shortwave radio I got as a gift from my father when I was 14 or 15 
>years old.  Of course, haven't a clue as to what became of the original and 
>regret losing track of it. This radio works quite well and I'm 
>pleased with it 
>overall. 
>
>My first question has to do with whether there were variants of this 
>particular model.  Most I've seen have the normal dial and switch settings 
>highlighted in red.  Mine has a white dot over the normal settings. 
>The radio does
>not appear to be modified in any way.  Manufacture date is  August 20, 1953.
>
>The second question has to do with tubes that were replaced by the previous 
>owner.  There are several glass envelope tubes present as opposed to the 
>usual metal envelope types.  Would this have any adverse affect on 
>performance?
>
>Thanks in advance for any responses to my query.
>
>73, Alan - KB2HEI
>

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