[Hallicrafters] R-274 Problem

[Richard Knoppow]

----- Original Message ----- 
From: "Chuck" <ka6uup at comcast.net>
To: <hallicrafters at mailman.qth.net>
Sent: Wednesday, May 21, 2014 3:53 PM
Subject: [Hallicrafters] R-274 Problem


>I have an R-274 I am trying to get working. It shows signs 
>of having been restored or updated at some time in the 
>past. There are olive drab disk capacitors and the typical 
>tan ones both in it. Also there are at least 2 of the old 
>square type caps in it. I am not sure whether I should 
>leave them alone or not.
>
> It was given to me because the previous owner could not 
> figure out what was wrong with it.
>
> In the process of trying to get it to work, I removed the 
> turret and the problem was apparent. Many of the contact 
> loops were either folded over or broken. I got some 
> fingerstock and drilled out the rivets and fabricated 
> loops which I bolted in place with 2-56 screws.
>
> That solved the problem and the radio started working.
>
> I started tuning the IF stages and while doing so, it 
> suddenly died. No noise etc. just dead.
>
> I immediately thought of the ballast but it checks fine at 
> 4 ohms.
>
> I ran most of the check in the manual including the signal 
> substitution and get audio and 455 khz through the radio 
> until I came to V7. I went to the relay and did find a 
> cold solder joint on one to the contacts. That fixed that 
> and I heard the 455 khz signal at pin 5 but, when 
> injecting the 6 mhz signal at pin 7 heard nothing.
>
> I then started checking voltages at the tubes. The B+ is 
> high in many cases, (the transformer is set at 115 volts 
> and my line voltage runs about 117 to 119vac.
>
> However many of the voltages are missing, + when they 
> should be -,or in the mv range. So it looks like I have 
> some tubes in a cut off condition.
>
> Interestingly enough, V3 on all the manuals (R274 and 
> SX73) shows as a 6BE6.
>
> But in this radio V3 is a 6C4.
>
> Can anyone tell me what the voltages should be for the 6C4 
> and why does this not show up in any of the manuals?
>
> So that is where I am at the moment.
>
> Any suggestions would be greatly appreciated.
>
> 73,
>
> Chuck KA6UUP
>
    I saw your correction on V4.  My R-274 book has a 
partial schematic showing the B+ distribution. It would be 
helpful to know exactly where you are getting incorrect 
readings particularly where the polarity is wrong.
    The square caps are probably silver-mica types. They do 
not often go bad but can develop a problem with leakage due 
to corrosion of the silver plating. The symptoms can be a 
jump in value as the capacitor heats or a rapid variation of 
value.  I would not change out the mica caps unless you have 
definite signs of a defective one. Ceramic caps also do not 
often go bad but can. I don't know how many paper caps are 
used in this receiver (the SP-600 has a ton) but they should 
all be changed. Modern plastic film caps will do fine.  The 
contacts in the turret bother me, some real ham-fist got in 
there.  I know how contacts in SP-600 turrets get bent up 
but thought the ones in the SX-73 were less vulnerable. 
Evidently not.


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