S-40B Question

[Bob Krassa]

Very good point that Rich makes about pin 1 - I encountered this once when 
installing one of those Collins plug in filter adapters that depended on pin 
1 on the octal socket being grounded - it wasn't - didn't work at all as it 
was the heater return for the adapter!  So, nothing wrong with the 
manufacturer saving some cost by not bothering with pin 1 but if you are 
going to try metal tubes it is very important to tie it down.

73, Bob Krassa KC0TDS

----- Original Message ----- 
From: "Richard Post" <postr at OHIOU.EDU>
To: <BOATANCHORS at LISTSERV.TEMPE.GOV>
Sent: Friday, May 18, 2007 11:18 AM
Subject: Re: S-40B Question


> 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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