[Hammarlund] New to Hammarlunds

[Carl]

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: <kgordon2006 at frontier.com>
Cc: <hammarlund at mailman.qth.net>
Sent: Saturday, April 09, 2011 4:30 PM
Subject: Re: [Hammarlund] New to Hammarlunds


>
> ----- 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


I had a BC-1004 in the 60's that never stopped drifting on 20M, and I mean 
never, even after 2 days.The only thing it was useful for was to SWL AM in 
the backround while I was on the ham bands with stable gear and just move 
the dial when the signal slid out of the wide bandpass.

The SP-400 added TC part way thru production, its very tolerable for AM.

Carl
KM1H



I can understand why the USAAF developed their own crystal control 
modification during WW2