[Hammarlund] SP600 Characteristics

[David Wise]

If you go back through the message archive, you should find a post containing a cure for strong-signal distortion.  I modified the bias on the last IF amp to make saturation less likely.  The details vary depending on the production level of your radio, so you'll have an opportunity to get very familiar with it.

Dave Wise

-----Original Message-----
From: hammarlund-bounces at mailman.qth.net [mailto:hammarlund-bounces at mailman.qth.net] On Behalf Of Wes Bolin
Sent: Thursday, May 30, 2013 1:40 PM
To: hammarlund at mailman.qth.net
Subject: [Hammarlund] SP600 Characteristics

Thanks Richard for your comprehensive reply.  I would like to comment on some of your points (and continue to ponder them).
1.  I did use new metal film self healing 1000 volt capacitors to replace the BBODs originally.  I used both .01uF and .022uF in
     the original positions.  The RF deck was recapped with Z5U .01uF ceramic capacitors.  I found two obvious bad BBODs:  One was
     leaking and one had a split in the case. (caps made by Panasonic and CDE and Vishay from Mouser)
2.  I was concerned about swapping the metal film caps with ceramic caps, especially the .022uF with .01uF ceramic discs that I had on
    hand.  Even calculated XL for them at IF and BCB frequencies.  A MWO was referenced that Hammarlund did go to all .01uF ceramic
    disc caps, so that did build my confidence. 
3.  I left metal film bypass caps in the FCU (2)  and T1 (1) on side of RF deck cause of hassle to replace them. 
4.  The audio distortion I hear on BCB and SW is on strong stations.  I see what you say about the Carrier Meter slightly dipping during
     modulation on some stations. I tried to back off RF gain and turn up the audio and the distortion was still there.  Other stations of
     similar power levels (meter) had no distortion.  Some were downright terrible. Lot's of strong carriers and weak mod too.
5.  I painted the inside of my tube shields flat black, and they got quite warm to the touch.  Put a fan on low speed behind the chassis and
     they were ok to touch. Then I took them off and kept the fan running, and could hear no difference cause of lack of shielding. I think
     I'll stick with air movement when the radio eventually goes into a cabinet.  Have used in the past a 240vac muffin fan on 120vac to
     run quiet and get air flow.  Really good on a KWM2 or 51S1.
6.  The capacitor looked untouched when I pulled the RF deck, and calibration is very close on all bands. Alignment is not a critical
      issue, but will be done eventually.
There are now 33 used metal film caps in a plastic bag that might be used somewhere else.  Something I did different was to move the
disc caps to where their leads were shorter by grounding them where the other caps were too large to fit. Maybe that helped.  Very
surprising that there is a hearable difference for the better.  It was a lot of work, but glad I did it.  I appreciate your comments.
Wes
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