[Hammarlund] HQ-129-X Mixer Noise

[`Richard Knoppow]

    If the noise disappears with no antenna its coming from 
outside the receiver. While the mixer is a noisy one the RF gain 
should overcome it. I am not sure why its noisier than the S-40B 
although the S-40B has a quieter RF stage, the mixer tube is 
actually noisier.
    The RF tube is relatively noisy but replacing it will require 
re-designing the AVC. The 717 was an octal base prototype of the 
6AK7. Its a sharp cut-off tube that does not work well in AVC 
controlled stages.
     Note that below about 20Mhz the atmospheric noise will be 
greater than receiver noise.
     You need a calibrated signal generator and known dummy load 
to check the receiver sensitivity. That is, how much output it 
has for a given signal strength. From that you can figure out the 
amount of noise.


On 5/22/2019 8:57 AM, Frank Barnes wrote:
> I'm new to the group and have an old subject which I'm sure has been
> discussed multiple times.   I've restored an HQ-129-X and I really like
> it.   It was a lot of work to bring it back!
> I really like the quality and love the 3-IF system.  I'll use it mostly on
> 40M CW and for some general SW listening.
> However it seems to have a lot of "noise" - sort of a background hash.
>   More than some other receivers I've used, including my Halli S-40B.
> Disconnecting the antenna eliminates the noise so I think that means I'm
> hearing noise radiated from power lines, appliances, etc.
> 
> Am I hearing mixer noise?  I've read about replacing the 6K8 mixer with a
> very expensive 6SB7Y (requires some rewiring).
> 
> Does anyone have advice regarding quieting the mixer noise, other than tube
> replacement?
> 
> I'm also interested in replacing the RF tube with a better one - 717A?
> 6AC7? 6BZ6 mini?  Any advice/experience?
> 

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