[Hammarlund] Rebuilding a derelict SP-600 receiver

[Mike Bracey]

 Bill,
Congratulations. It sounds like you are doing it right. I've got a house full of tube receivers and my SP-600 is my favorite band cruiser. Good luck and enjoy your great project.
73, Mike, KE5YTV


    On Saturday, September 12, 2020, 12:30:21 PM CDT, William Radmer <bradmer at comcast.net> wrote:  
 
 Greetings,

 

This is my first post after joining the group a few weeks ago. I am
rebuilding an SP-600 R-274C  purchased several years ago from the brother of
a silent key. It must have been stored for years in his unheated garage (I
live in MN) and was very dirty with light corrosion on all the metal
surfaces. It was missing the audio output transformer, several tubes and a
few knobs, but hadn't been modified to any extent. I have been collecting
the missing bits for a while, so on a hot day in July I decided to pull it
off the shelf and see if it could be put the receiver back into working
condition. I've been working on tube radios for a while, but this is the
first rebuild I've attempted of a radio of this size and complexity. After
reading about all the problems with leaky capacitors in these units (it was
full of the infamous "Bumble Bees of Death") it was clear all the molded
paper caps and electrolytics were the first thing that had to go. As those
of you who have attempted a full recap of a Hammarlund know, this requires
dismantling many parts of the radio to gain access to all the bad caps, the
RF section requiring the most effort to remove for service. After
dismantling the right side of the radio and carefully pulling the RF section
I found a previous "repair" had bent a number of the contact fingers which
connect to the band coils when you change bands. Luckily, only two of the
contact pairs had broken on one side, with a passable connection left on the
remaining contact. After the RF unit was recapped and repaired all the caps
were replaced systematically in the other parts of the receiver.

 

At this point, the rebuild is almost done! 72 capacitors have now been
replaced along with the power cord and wrongly sized fuses, a replacement
audio transformer has been installed and the RF unit will soon be wired back
in place. I plan on checking resistances on all the tube socket pins prior
to bringing AC power up slowly on a variac  while checking the B+ voltage.
If no other problems come to light,  full alignment of the receiver will
finish up the rebuild. When I got the receiver it was missing the bottom
cover for the band coil turret and I'd like to replace it if anyone has a
cover for sale or knows where I can buy a replacement cover.

 

I am excited to get this excellent receiver working again after being
neglected for so long and left for dead. Let me know if you see any issues
with the rebuild or if you have tips or advise you can share to make it
better.

 

Regards,

 

Bill Radmer

KC0INQ

 



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