[Hammarlund] Drift of Newer Hammarlunds? was Re: Old Hammarlunds

[Richard Knoppow]

----- Original Message ----- 
From: "Carl" <km1h at jeremy.mv.com>
To: "Glen Zook" <gzook at yahoo.com>; 
<Hammarlund at mailman.qth.net>; "Darrell Bellerive" 
<drbellerive.va7to at gmail.com>
Sent: Sunday, May 08, 2011 11:32 AM
Subject: Re: [Hammarlund] Drift of Newer Hammarlunds? was 
Re: Old Hammarlunds


>
> ----- Original Message ----- 
> From: "Glen Zook" <gzook at yahoo.com>
> To: <Hammarlund at mailman.qth.net>; "Darrell Bellerive"
> <drbellerive.va7to at gmail.com>
> Sent: Sunday, May 08, 2011 11:20 AM
> Subject: Re: [Hammarlund] Drift of Newer Hammarlunds? was 
> Re: Old
> Hammarlunds
>
>>
>> Even the SP-600 receivers are generally pretty drifty 
>> above 10 MHz.  Yes,
>> the military did use hundreds of the SP-600 in fixed 
>> links (i.e. RTTY).
>> However, those units were the "JX" series which used 
>> crystals for
>> frequency control.  Since a crystal was used to control 
>> the actual
>> received frequency the tunable local oscillator was not 
>> used and the
>> single frequency was very stable.

     One problem with the SP-600 is that its sensitive to 
filament voltage variation. Although it has a voltage 
regulator tube that pretty much just compensates for 
variations in the B+ from bias variations on the RF and IF 
stages from gain or AVC. It does not compensate for filament 
voltage variation from line voltage change. I have two of 
these receivers and they will go sailing off frequency if 
operated on the same line with, say, an electric heater with 
a thermostat. I found that if operated from a well regulated 
source such as a Sola transformer, they are very stable.
     Both of mine are quite microphonic. I have not yet 
traced down the source, its not the LO tube. I suspect it 
may be from the ceramic caps in the oscillator stage due to 
their light weight, not their electrical characteristics, 
but it could well be something else. Both of my receivers 
work OK but need work to make them right and, as usual, its 
hard to find time plus I am looking for some parts.
     In comparison my R-388 is dead stable regardless of 
line voltage and has no microphonics.


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