[Hallicrafters] S-38 audio question

[Don Ehrlich]

Craig,

A few thoughts off the top ....


Dial tracking depends on the IF frequency.  If not set exactly where
Halicrafters intended it to be then you will never get dial tracking
to work.  On the S38 there is no adjustment for inductance (only
padder capacitance I think) so IF freq has to be right on.  Over the
years too many people have set up the IF transformers "for maximum
volume" and this usually results as maximum volume alright but at the
wrong IF frequency!

There is no excuse for AVC action to be poor.  My first guess is that
one of the several decoupling capacitors on the AVC line is defective,
keeping the avc voltage from building up as it should when a strong
signal is received. Check the avc voltage and compare it between the
two radios.  The IF amplifier tube is another suspect but you have
probably already checked that by substitution in your other S38.

Inability of the volume control to cut the audio down all the way
could be because of the lack of avc action.  Or, as is so common on
these old radios, the potentiometer itself is just not zero-ing out as
it should.   I have replaced more than one for that reason.

I no longer have my S38 or schematic so I am going on general
knowledge and memory.   Sorry I can't provide detailed schematic
references or voltages but I am sure that others on the list can.

Every S38 I have ever worked on played beautifully and worked far
better than I had thought any little 5-tube superhet could.  I doubt
that workmanship itself is a factor in your problems.

Don K7FJ



----- Original Message ----- 
From: "Craig Roberts" <crgrbrts at verizon.net>
To: "Hallicrafters" <hallicrafters at mailman.qth.net>
Sent: Wednesday, December 10, 2003 8:40 PM
Subject: [Hallicrafters] S-38 audio question


> I've just carefully and thoroughly restored and aligned a couple of
little
> S-38s to give away as Christmas presents to friends. One is an
S-38A. The
> other is an S-38C.  The circuitry differs a bit as does the factory
build
> quality. The earlier model was well put together with neat solder
joints and
> nicely dressed leads.  The 38C, on the other hand, displays much
sloppier
> assembly and suffers a little in performance.  For instance: the 38A
dial
> tracking is very accurate (especially considering the
unsophisticated
> circuitry). The 38C is not nearly as precise.  The 38A's audio is
clean with
> good AVC action-- even on a 50KW broadcast station just about a mile
from my
> house.  The 38C, however, can't handle the BC signal and overloads
easily.
> The 38C's volume control does not attenuate a strong signal as well
as the
> earlier model's, either.
>
> I've replaced all caps, with the exception of the micas, in both
receivers.
> Resistors have been checked and a few have been replaced in both.
Both have
> been outfitted with new tubes. Sensitivity and selectivity are about
equal,
> but the audio quality in the 38C is noticeably less than that of the
38A.
>
> Any ideas on how to improve the AVC and volume control effectiveness
in the
> 38C? It'd be fun to bring it up to snuff.
>
> 73,
>
> Craig Roberts W3CRR
>
> Oh yeah -- Hi Glen!
>
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