[Hammarlund] Hammarlund Digest, Vol 115, Issue 1

[Pat & Rich McKinney]

If you have a scope feed the rig a modulated signal and look for distortion 
in the modulated signal.  Should be a pretty sine wave.  That can tell you 
where it starts.  Short of that check filament voltages or maybe gassy tube.


----- Original Message ----- 
From: <hammarlund-request at mailman.qth.net>
To: <hammarlund at mailman.qth.net>
Sent: Monday, August 19, 2013 12:00 PM
Subject: Hammarlund Digest, Vol 115, Issue 1


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> Today's Topics:
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>   1. Comet Pro Help Needed (Joe Connor)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 18 Aug 2013 19:52:59 -0700 (PDT)
> From: Joe Connor <joeconnor53 at yahoo.com>
> To: "hammarlund at mailman.qth.net" <hammarlund at mailman.qth.net>,
> "boatachors at mailman.qth.net" <boatachors at mailman.qth.net>
> Subject: [Hammarlund] Comet Pro Help Needed
> Message-ID:
> <1376880779.32041.YahooMailNeo at web125501.mail.ne1.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> I need some troubleshooting help on a basket-case Hammarlund Comet Pro 
> that I'm trying to restore. Here's the schematic:?
> http://www.nostalgiaair.org/PagesByModel/994/M0008994.pdf
>
> Mine is the early model with the only gain control a pot that varies the 
> voltage on the cathodes of the two 58 IF tubes. This one was a real mess 
> when I got it but I love these old Comet Pros so I want to get it 
> performing well.?
>
> Here are my symptoms: There is low distorted audio when the gain control 
> is turned fully counter-clockwise. As I turn the control clockwise, the 
> audio gets louder but gets very distorted. Right as it gets to full 
> volume, the audio gets clear but is very, very loud. I can't get clear 
> audio at a lower volume.?
>
> I have recapped the set (except for the 1 mfd cap right after the second 
> detector). I disconnected the gain pot and it turns from 0 ohms to the 
> full 12K ohms. (I used a DMM so I'm not sure just how smooth the change in 
> resistance is). The gain pot causes the cathode voltage on the IF tubes to 
> vary between 0 and 13 V. All voltages in the set are in the ballpark. The 
> resistors all test within 20% or so of spec.?
>
> Does anyone have any ideas?
>
> As always, thanks for your help.
>
>
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Joe Connor
>
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> End of Hammarlund Digest, Vol 115, Issue 1
> ******************************************