[Hallicrafters] SX-28 help please

[Carl]

Powering up for 5 days is pure lunacy; reforming those old electrolytics 
properly is a myth waiting to fail. A fried transformer will stink. A power 
surge likely popped a mains breaker or a below chassis added fuse. Also 
check/replace the AC line bypasses.

Always start with no tubes using the Variac to at least confirm the 
transformer is OK. Then always replace the filter caps, and the paper caps 
in the audio stages for the SX-28 and other sets prone to losing the audio 
transformer.

Then install the tubes and slowly power up while monitoring the DC; if its 
well below whats expected turn it off as the xfmr is drawing excessive 
current. Replace 3-4 caps at a time working back towards the RF amp. (You 
can also concentrate on just the plate and screen bypasses as those are the 
ones likely to be causing the current draw.) At some point the voltage will 
be somewhat normal and the radio will show some life. Keep doing 3-4 caps at 
a time and checking your work. When under the RF deck replace out of 
tolerance resistors and any silver mica which has DC on it. No need to 
revisit that area more than once unless you enjoy the effort involved.

Finish up with any other out of tolerance resistor and then get into the 
alignment, tube swapping, switch and control cleaning, etc.

Carl
KM1H


----- Original Message ----- 
From: <hallicraftersx28 at aol.com>
To: <Hallicrafters at mailman.qth.net>
Sent: Wednesday, May 05, 2010 2:32 AM
Subject: [Hallicrafters] SX-28 help please


>
> 90 V over 5 days !! Were  you  slowly trying to ROAST the rcvr ?
> Powering a 60 plus year old rcvr even on a variac isn't a good idea 
> without first doing  an 'under the hood check 'for past repairs ,condition 
> of components etc.
> I'm assuming the rcvr is totally DEAD ,no lights nothing ! Looks like a 
> blown power transformer .Do a continuity check on the primary and 
> secondary windings.
> Nick
>
>
>
>
>
>
> -----Original Message-----
> From: KV5I <elh54 at sbcglobal.net>
> To: Hallicrafters at mailman.qth.net
> Sent: Tue, May 4, 2010 11:09 pm
> Subject: [Hallicrafters] SX-28 help please
>
>
> I was powering up for the first time. I had worked up tp 90 volts over 
> five
> ays. We had a Spring power outage and now she's dead. No blown fuse. 
> Surely
> t didn't take the transformer? what's the next best guesses to check?
> 3,
> d-KV5I
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