[Hammarlund] HQ-170 Repair Saga

[kgordon2006]

Sent from my Galaxy
-------- Original message --------From: "Elmore, Kim via Hammarlund" <hammarlund at mailman.qth.net> Date: 4/3/26  11:17  (GMT-08:00) To: hammarlund at mailman.qth.net Subject: Re: [Hammarlund] HQ-170 Repair Saga Thanks, Pete! The arcing isn't to the phenolic at all: it's from the small "finger" wiper contact onto the larger contact surface. I've been very careful with any DeOxIt applications. Whatever it is, it's a symptom of the problem, not the cause of it. There is no carbon track at all. When I measure it, I see pretty much a deadI 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 N5OPOn 3/20/2026 3:20 PM, manualman--- via Hammarlund wrote:> I haven't read the history of this Hammarlund HQ-170 repair yet but this> is one of the reasons why I also mention that Deoxit should never be> sprayed on to the paper phenolic switch wafers which were quite common on> many receivers, transmitters, etc. in the 50's and 60's.>> The Deoxit is absorbed into the wafer  material and the chemical agents> that bond the paper phenolic together react with the composition> chemicals of the Deoxit and can form minute resistive streaks in the> material and can often short one switch contact with another. If voltage> gets presented on a wafer terminal where there an internal resistive> streak has formed, maybe to another terminal, it's possible to  pass> smoke from the switch wafer.>> Deoxit should be applied minutely to the actual terminal carefully and> not sprayed on the entire wafer.>> Pete, wa2cwa>>> On Fri, Mar 20, 2026, 13:43 Elmore, Kim via Hammarlund <>> hammarlund at mailman.qth.net> wrote:>>>>> Well, following up on my foray into my HQ-170: I kept getting very>>> confusing reading when I checked for shorts to ground meaning I>> simply>>> couldn't reliably isolate the issue. I'd check for shorts to>> ground>>> through the cold side of R9 and find it open: no shorts.>> Sometimes, I'd>>> see wildly fluctuating resistance readings, but they'd quickly>> resolve>>> is I jiggled the test leads. This puzzled me, but I ultimately>> became>>> convinced that something else was happening, such as fingers on>> probes,>>> etc. It's a Fluke 79 so pretty responsive.>>>>>> Following an earlier suggestion, I decided to measure the current>> though>>> R9 using a 1500 ohm 5W resistor simply because I had one. The idea>> was>>> to simply get a glimpse of what I'm dealing with. I put the test>> leads>>> in series with it and gingerly turned on power keeping my fingers>> art>>> the ready to turn it off. I saw about 170 mA.>>>>>> 0.17 * 1500 = 255 V. That's essentially the B+ value. A short>> *clearly*>>> exists somewhere.>>>>>> But when I did this I INSTANTLY saw arcing in the front wafer of>> the>>> band switch. Power on to power off spanned 1-2 s. I removed tubes>> in>>> case there's an intermittent interelectrode short. Same result.>> With>>> power off, I moved the band switch and tried again. Same result.>>>>>> Two things are now irrefutable: the problem is in C134, a 2 pF 500>> WVDC>>> mica coupling capacitor between T1 and T2 that I have yet to>> locate. But>>> the other, more ominous issue is that the front wafer of the band>> switch>>> was damaged when C134 shorted in the initial episode that>> incinerated>>> the original R9. At that point it was destroyed for all practical>>> purposes. C134 is the only capacitor I have not been able to find>> and>>> test that is in the path through the band switch. It has to be the>>> source of the problem. Now, if I could only find it C134...>>>>>> The damage to the band switch prevented me from making reliable>>> measurements.: the voltage used by the ohmmeter was insufficient>> to>>> bridge the damage to the switch. But, at 250-300 V it's bridged>> easily.>>> In one sense, I'm fortunate that it's the front wafer because it's>> about>>> the only accessible one. The band switch is the heart of the radio>> and>>> the entire thing is literally built around it. Yet, the only way I>> can>>> repair that switch is to find a front wafer from a donor HQ-170.>> Even>>> then, I'm not entire convinced I can get enough access to do the>> job.>>> This particular HQ-170 has considerable sentimental value to me>> because>>> it was my dad's and so was my very first receiver as a Novice. It>> is>>> cosmetically perfect and was aligned almost perfectly, a job that>> took>>> me couple of days to perfect. I admit that I'm emotionally>> attached to>>> it. That said, I am not left without a receiver: a good friend>> gave me>>> his HRO-60 in perfect electrical condition with ALL the coil sets,>> and I>>> also have an electrically perfect Drake 2A. Performance-wise, both>> of>>> these are superior to the HQ-170 in many respects.>>>>>> So, I'm in no hurry. I'll look a bit more at my '170 to find C134.>> If>>> anyone has a front wafer for an HQ-170 band switch, please contact>> me.>>> 73,>>>>>> Kim N5OP> ______________________________________________________________> Hammarlund mailing list> Home:http://mailman.qth.net/mailman/listinfo/hammarlund> Help:http://mailman.qth.net/mmfaq.htm> Post:mailto:Hammarlund at mailman.qth.net>> List Administrator: Gary Harmon, K5JWK> ** For Assistance:gharmon at idworld.net **>>> This list hosted by:http://www.qsl.net> Please help support this email list:http://www.qsl.net/donate.html-- Kim Elmore, PhKim Elmore, Ph.D. (Cooperative Institute for Severe and High-Impact Weather Research and Operations, Adj. Assoc. Prof., OU School of Meteorology, CCM, PP SEL/MEL/Glider, UAS, N5OP, 2nd Class Radiotelegraph, GROL)/“I am no weather master, nor is aught that goes on two legs.” – Tom Bombadill, “Fellowship of the Ring”/______________________________________________________________Hammarlund mailing listHome: http://mailman.qth.net/mailman/listinfo/hammarlundHelp: http://mailman.qth.net/mmfaq.htmPost: mailto:Hammarlund at mailman.qth.netList Administrator: Gary Harmon, K5JWK** For Assistance: gharmon at idworld.net **This list hosted by: http://www.qsl.netPlease help support this email list: http://www.qsl.net/donate.html