[Hallicrafters] S-27 Help Needed

[Richard Knoppow]

----- Original Message ----- 
From: "Joe Connor" <joeconnor53 at yahoo.com>
To: "Joe Connor" <joeconnor53 at yahoo.com>; 
<hallicrafters at mailman.qth.net>
Sent: Sunday, May 05, 2013 5:32 PM
Subject: Re: [Hallicrafters] S-27 Help Needed


Thanks for your help, guys. We're making progress, and I 
think this receiver will be a keeper.

1. Yes, the problem in the 1st RF stage was dirty pins on 
the 956 tube. I cleaned them with a .22-cal. brass 
gun-cleaning brush. This set now receives well.

2. To have the AVC on, should the AVC toggle switch be in 
the open (no continuity) or closed (continuity) position? 
All of the toggle switches in this receiver have problems 
(i.e., frozen/corroded either open or closed)

3. The front panel is cleaning up nicely, which sort of 
surprises me because it looked really bad when I first got 
it. Permatex hand cleaner and 0000 steel wool really do a 
nice cleaning job.

4. The innards of this receiver are interesting. It uses a 
fair number of .01 caps for bypass and coupling. It's about 
a 50-50 mix between the notorious black lozenge Micamolds 
and square tan Aerovox caps. The Micamolds are all bad. The 
Aerovoxes seem to be good. From the soldering on these caps, 
the Micamolds and Aerovoxes all appear to be original. 
Weird.

5. Several of the set screws on the knobs are badly rusted. 
I currently have lubricant soaking in. If that doesn't work, 
I will be back to ask about the best way to remove rusted 
set screws or, if that fails, how to drill them out.

Joe Connor


    For the set screws try a good penetrating oil like 
Liquid Wrench or PB Blaster.  The latter gets very good 
reports. Kano also makes an effective loosener but I've 
never tried it.  You may have to put doses in several days 
in a row to get it to work.

    Micamold made a variety of capacitors.  The flat lozenge 
shaped ones are paper caps with plastic impregnated paper. 
The ones I took out of my AR-88 were mixed, some fairly good 
some with a lot of leakage.  These were good caps when new 
but any very old paper cap is likely to be bad.  The square 
Aerovox caps may be micas. There is a dot code for mica vs: 
paper, on mica caps the upper right dot is always black, on 
paper caps its always silver.
    At the time these receivers were made mica caps may have 
been in sort supply.  I think this is the reason some paper 
caps are used in the AR-88 since the illustrations of the 
earlier version shows the RCA-made pink lozenge shaped micas 
where the Micamold caps are. Hallicrafters was notorious for 
using whatever parts they could get.

    The AVC switch, which Hallicrafters show unhelpfully (as 
does National) as an X is shorted to ground in MANual gain 
and open for AVC.  However the AVC bus is disconnected for 
FM although the instructions say a small amount of delayed 
AVC is applied to the limiter tube. This may be from the 
limiter itself since there will be a small amount of 
rectification there.   The Manual RF grain is in the 
cathodes of the two IF amplifiers so it works all the time. 
When advanced to maximum gain these two stages probably 
enhance the limiting action of the driver/limiter tube 
preceding the FM discriminator.
    Check the AVC switch and the FM/AM switch to see that 
they are working.  Note also that the FM/AM switch changes 
the meter from a signal strength meter to a zero-center 
tuning meter for the discriminator.
     Depending on the design you can sometimes clean toggle 
switches by squirting contact cleaner around the terminals. 
If they stick out through holes in the case this will often 
work.
    Contratululations on getting the panel clean.  Sometimes 
really awful looking stuff responds to simple cleaning.  I 
am not sure about the S-27 but my S-36 has genuine crackle 
finish. This is not the familiar "wrinkle" finish but a 
finish that looks like dried, cracked mud.  General Radio 
used a very similar finish.  I think its supposed to 
resemble old leather.  My understanding is that its a 
difficult finish to apply, done in layers with a couple of 
baking treatments.  When done right it looks quite elegant. 
Whatever shortcomings Hallicrafters may have had their stuff 
was always classy looking.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com