[Hammarlund] HQ-120X Restoration

[Carl]

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: "Carl" <km1h at jeremy.mv.com>; "Joe Connor" <joeconnor53 at yahoo.com>; 
<hammarlund at mailman.qth.net>
Sent: Saturday, February 19, 2011 3:00 PM
Subject: Re: [Hammarlund] HQ-120X Restoration


>
> ----- 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.

They contribute minimally, this is not a Hallicrafters.


Different tubes can make some difference but the
> above suggests essentially re-engineering the set.


No engineering required, just a tech who can read.


 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.


Totally different tubes, no interchangability at all.


>    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.


My comment already assumes a full overhaul and there is no basis in fact to 
not use discs in audio stages of that radio. I only use film when the value 
and voltage makes a disc more expensive or the customer requests it.


>    Check the power supply ripple and voltage before replacing the filter 
> cap, it may still be OK.


And then it lets go a week later, are you offering replacement parts at no 
charge? Leaving 70+ year old filters in place is poor thinking at best.


>    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.


The HQ-120/RBG  was contemporary with the SP-200 family and the SP-400 and 
HQ-129 shared the stage postwar.

Carl
KM1H


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