[Hammarlund] HQ-120X Restoration

[Richard Knoppow]

----- Original Message ----- 
From: "Carl" <km1h at jeremy.mv.com>
To: "Joe Connor" <joeconnor53 at yahoo.com>; 
<hammarlund at mailman.qth.net>
Sent: Saturday, February 19, 2011 10:58 AM
Subject: Re: [Hammarlund] HQ-120X Restoration


> They were the forerunner of the HQ series and share much 
> common circuitry
> and components with the 129/140. It also became the USN 
> and Coast Guard RBG
> which was a cross between the 120 and 129.
>
> Besides the caps check all resistors for tolerance.
>
> Its main problem will be poor sensitivity on the 6th band 
> due to tube
> choices. Switching to a 6SG7/6K8 up front will be some 
> help or go full out
> with the 6X8 mixer mod.
>
> Carl
> KM1H
>
>
>
> ----- Original Message ----- 
> From: "Joe Connor" <joeconnor53 at yahoo.com>
> To: <hammarlund at mailman.qth.net>
> Sent: Saturday, February 19, 2011 1:16 PM
> Subject: [Hammarlund] HQ-120X Restoration
>
>
>>I just picked up a nice HQ-120x receiver that I plan to 
>>restore. Is there
>>anything special I should be aware of or watch out for? At 
>>first blush,
>>this receiver seems to be more similar to the HQ-129 than 
>>to the early
>>Super Pros. Is that accurate?
>>
>> My first steps are going to be to replace the filter caps 
>> and the power
>> cord. Any other tips or suggestions would be gratefully 
>> appreciated.
>>
>> Thanks for looking this over.
>>
>>                                Joe Connor
>>

    Some of the poor performance at the highest frequencies 
will be due to the nature of the inductors used in the RF 
stages. Different tubes can make some difference but the 
above suggests essentially re-engineering the set. Changing 
the RF tube to a 6SG7 (essentially the octal base version of 
a 6BE6) would improve performance but the bias will have to 
be changed and there may be other problems.
    Probably most of the by-pass and coupuling caps of the 
paper type should be replaced and that will make a 
difference in performance too. One can use either film caps 
or disc-ceramics for RF but AF should be film caps.
    Check the power supply ripple and voltage before 
replacing the filter cap, it may still be OK.
    There is a lot of service information for the set, the 
military manuals have more than the civilian ones.
    The voltage charts are probably written for a 1000 
ohm/volt meter, a modern 20,000 ohm/volt one will give you 
readings which are too high for some of the circuits.
    The main difference between the HQ-120-X and HQ-129-X is 
the use of single-ended tubes in the latter.
    The HQ-129-X was contemporary with the SP-200 series of 
the Super-Pro and was the first receiver to have the 
patented Hammarlund crystal filter in it. They are quite 
surprizingly good receivers.


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