[Hammarlund] HQ-170 Repair Saga

[Lee K. Brown MD]

The schematic shows capacitors in parallel with the coils in transformers T1 and T2 (inside the transformer cases). This is quite common for IF transformers. see:  https://radiomuseum.co.uk/hq170.htmlProbably the designations of T1 and T2 also consider the capacitors as integral to these part numbers.

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Hammarlund HQ170


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Lee, KI7UR
Lee K. Brown MD
Emeritus Professor of Internal MedicineDivision of Pulmonary, Critical Care, and Sleep MedicineUniversity of New Mexico School of MedicineMember, Editorial Board andFounding Editor (“Emerging Technology”), Journal of Clinical Sleep MedicineCo-editor, Section on Sleep and Neurobiology, Current Opinion in Pulmonary MedicineMember, American Academy of Sleep Medicine Committee: Focused     Update of Diagnostic Testing for Adult Obstructive Sleep ApneaChair, New Mexico Advisory Board for Respiratory CareChair, Polysomnography Practice Advisory Committee of the NM Medical Board
  

    On Friday, April 3, 2026 at 04:11:27 PM MDT, Kim Elmore via Hammarlund <hammarlund at mailman.qth.net> wrote:   

 My bad! It's C134 ***NOT*** C128.

I simply can't locate it. It's called out with a separate part number in 
the manual. Also, T1 andT2 share the *same* part number in the manual.

I've just acquired a '170 off the notorious site for $128. Claimed that 
it powered on, but is otherwise not tested. I got it yesterday vyt 
haven't had time to unpack it. Box is in perfect condition so it's 
likely not damaged in shipping I'll see if it works and go from there.

N.B.: It's not a '170 I'm after: I'd simply like to repair this one as 
it has sentimental value. But I'm ready to learn that it may not be 
repairable due to parts availability.

73,

Kim N5OP

On 4/3/2026 5:01 PM, manualman--- via Hammarlund wrote:
> On my HQ-170 schematics, C128 is connected to one arm of the noise
> limiter control and not between T1 and T2.
>
>  There are dashed lines around the transformer area of T1 and T2. Items
> inside the dashed lines are in the transformers.
> The coupling cap that connects one winding of T1 to one winding of T2 is
> C134,  a silver mica, 2pf capacitor. Physically that is a very small
> capacitor.
>
> C134 is NOT in the T1 and T2 cans. However, the capacitors that are in
> the cans can dialog into an additional story.
>
> Pete, wa2cwa
> www.manualman.com
>
> On Fri, 3 Apr 2026 13:16:56 -0500 "Elmore, Kim via Hammarlund"
> <hammarlund at mailman.qth.net>  writes:
>> I need the expertise of someone with some deep HQ-170 repair
>> experience
>> to tell me where, physically, C128 is located. It's the coupling
>> capacitor between T1 and T2 and, if shorted, would short B+ to
>> ground
>> through R9. I'm beginning to wonder if it's *inside* either T1 or T2
>>
>> because under the chassis I see only a straight wire connecting the
>> two.
>> It's not shown that way on the any of the four versions of the
>> schematic
>> available and I can't imagine why Hammarlund might have done that
>> *unless* T1 or T2 were specified that way.
>>
>> 73,
>>
>> Kim N5OP
>>
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-- 
Kim Elmore, Ph

Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP 
SEL/MEL/Glider, UAS, N5OP, 2nd Class Radiotelegraph, GROL)

/“Listen, it's too big a world to be in competition with everybody else. 
The only guy I have to get better than is who I am right now.” – Col. 
Sherman T. Potter, 4077 M.A.S.H./
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