[Hammarlund] New to Hammarlunds

[Richard Knoppow]

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "Glen Zook" <gzook at yahoo.com>
Cc: <Hammarlund at mailman.qth.net>
Sent: Saturday, April 09, 2011 9:40 AM
Subject: Re: [Hammarlund] New to Hammarlunds


> On 9 Apr 2011 at 8:21, Glen Zook wrote:
>
>> Welcome to Hammarlund receivers.  Although some people 
>> will disagree,
>> the Hammarlunds are notorious for drifting,
>
> Yes. I had a BC-779 many years ago that drifted back and 
> forth on 20. The
> drift wasn't too bad, and in fact, it was sort of pleasant 
> to hear it.
>
>> especially on the 20-meter
>> band and higher frequencies.  The series that started 
>> with the
>> HQ-120X, then HQ-129X, then HQ-140X, and finally the 
>> HQ-150 are
>> generally very stable after about a 30 minute warm up. 
>> Unfortunately,
>> the HQ-100, HQ-110 series, HQ-160, HQ-170 series, and 
>> HQ-80 series are
>> all known to drift.
>
> Again, yes. That 6C4 oscillator is very problematic. 
> However, there is a sort-
> of fix for the tube issues, at least.
>
> Replace the 6C4 with a 6J6 with both sections wired in 
> parallel. This can
> help in some cases.
>
> My HQ-110C drifts like crazy now, although it didn't 
> previously. I haven't dug
> into it, but suspect the 6C4 in it.
>
> Ken W7EKB
>
    The BC-799 in common with other Super-Pro receivers, has 
no temperature compensation. They have a long warm up drift 
time but eventually stablize. The back and forth drift may 
have come from the AVC working because there is no voltage 
stabilization on the oscillator and it changes with RF gain. 
These receivers can be made much more stable by adding a 
150V regulator tube for the oscillator plate. The VR tube 
should have about an 8k dropping resistor and the 12K 
oscillator plate decoupling resistor is eliminated. This 
will stop the change in frequency when the RF gain is 
changed. The VR tube can be mounted under the chassis.
     I have never understood why Hammarlund did not adopt 
both temperature compensation and voltage regulation for 
this RX since they certainly knew how to do it and had both 
on the HQ-120X.
     Note also that even with HV regulation there may still 
be drift from the filament voltage varying with changing 
line voltage. Even the SP-600-JX has this problem. There are 
oscillator designs that are much more stable with voltage 
changes than the simple ones used in most receiveers.


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