[Hammarlund] HQ-170A drift reduction progress

[Richard Knoppow]

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "Mitch" <mskobier at charter.net>
Cc: <Hammarlund at mailman.qth.net>
Sent: Sunday, May 15, 2011 12:15 PM
Subject: Re: [Hammarlund] HQ-170A drift reduction progress


> On 15 Apr 2011 at 11:32, Mitch wrote:
>
>> Input to receiver coax antenna connection from signal 
>> generator for
>> all tests -- 3 microvolts
>>
>> 14.2mhz            No discernable drift until the house 
>> heating system
>> kicks on. Then it shifts in frequency about 100-200 hz.
>
> How quickly does it shift frequency? Instantly (as soon as 
> the heating system
> kicks on) or after a brief interval when the warmer air 
> starts circulating? What
> kind of heathing system does your home have? Hot air? Hot 
> water? What?
>
> The reason I ask is that the FIRST thing that leapt to my 
> mind when I read
> this was that there was some VOLTAGE change that induced 
> this shift, not
> temperature.
>
> If, as I suppose, the B+ to the oscillator (HFO) is 
> regulated, and there is no
> discernible change in THAT voltage, perhaps the problem is 
> a change in
> filament voltage.
>
> Many military receivers used some means to regulate the 
> filament voltage to
> the HFO: the R-390/390A, the SRR-11/12/13, and others.
>
> There is a fairly simple circuit you can add to the 
> filament circuit that will
> regulate the AC voltage. This circuit, using two Zener 
> diodes, was developed
> by RCA for their SRR-11/12/13 receivers to eliminate the 
> ballast tube which
> was previously used to regulate the filament voltage.
>
> Anyway, before proceeding further, please answer my 
> questions above.
>
> Ken Gordon W7EKB

     I found my S{-600-JX drifted quite a lot when a 
thermostatically controlled electic heater was being used. 
This is a very old house and there is some reduction in 
voltage when something draws a lot of power. Its the 
filament voltage changing that causes the problem. The cure 
was putting the receiver on a Sola constant voltage 
transformer. Not all receivers are suseptible, for instance, 
my R-388 does not change at all over a very wide range of 
line voltage and does not have regulated filaments.


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