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 Post subject: HRO-60 Engineering Observation
PostPosted: Jun Fri 11, 2021 4:01 am 
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First of all, what I'm about to bring up is probably nothing new. But it's new to me, totally fascinating, a little bit annoying, and I thought I'd share this here for discussion. I'm in the midst of restoring a rather beat-up HRO-60 and have been collecting photos, schematics, and initiating the process of replacing old capacitors and resistors. Something interesting that I've discovered is that National sometimes altered its engineering of the HRO-60 by implementing wiring changes that achieved the same objective through different means -- and those means could introduce confusion.

Consider first of all the below photo from one HRO-60. The arrow shows the connectivity flow -- two resistors and then to ground.
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One.png
One.png [ 360.03 KiB | Viewed 306 times ]


Now consider the second photo of the exact same connection from another HRO-60. The arrow shows a different connectivity flow that achieves the same thing, but can introduce confusion. The connection runs from the tube base, to an unused connection on a socket next door, then across that socket to a ground connection. Electrically, it's the same connection. But to the casual observer without the schematic, they'd wonder why that connection runs through the pin on the second connector. The answer is: because that pin isn't used for anything and National used it as a connection point only between the two resistors, and the third connection coming from elsewhere.
Attachment:
Two.png
Two.png [ 438.29 KiB | Viewed 306 times ]


My point is that these sort of engineering tricks are interesting, but can frustrate troubleshooting efforts down the line.

Steve, KW4H


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 Post subject: Re: HRO-60 Engineering Observation
PostPosted: Jun Fri 11, 2021 4:29 am 
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Joined: May Thu 17, 2018 12:16 am
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Location: Edmonds, WA USA
There are many HRO-60 Manual revisions and it has been stressed many times on this forum to get the manual that matches your receiver. Unfortunately, that is very difficult because only a few have been scanned for on line access. My advice has been to use the latest and final manual that is readily available and modify to that standard if you wish but why do it if the receiver works to specifications. It can be a daunting process so the other approach is to just replace what is actually there if it actually breaks. Tube socket pin voltages are your best guide to proper operation. That is why I have a complete set of Pomona test adaptors so I can measure every voltage from the top of the chassis.

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Real Radios Glow in the Dark


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 Post subject: Re: HRO-60 Engineering Observation
PostPosted: Jun Fri 11, 2021 4:53 am 
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Dave,

The HRO manuals specific to the engineering/production revisions are indeed hard to come by. I'm using an ER 500 schematic for the restoration of the ER 345 unit I have, and electrically the manual is (so far, anyway) correct. What's missing in spots is context. Which means that you on occasion have to trace things out from a conceptual viewpoint rather than actual. It works, but it's sometimes frustrating and is slowing me down.

What I find particularly puzzling is why National would have re-engineered things for no real electrical reason -- and in a manner that could introduce confusion. There's no electrical reason whatsoever to run the connection I pointed out over through the socket next door. Possibly, however, National did it because it may have saved a minute or two in the build sequence in the factory. The end result, nevertheless, is a somewhat dorky and "elegantly illogical" connection. It works, but you've really got to wrap you head around the schematic and the wiring to figure it out.

Steve, KW4H


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 Post subject: Re: HRO-60 Engineering Observation
PostPosted: Jun Fri 11, 2021 5:24 am 
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Joined: May Thu 17, 2018 12:16 am
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Location: Edmonds, WA USA
Good comments, I agree on all points! That was the era of newly fashionable time and motion studies so to save a few minutes of time looked good for the bottom line. When I recapped mine I changed the the ground connection of some of the capacitors in the audio and noise limiter stages for accessibility but i noticed that the original points may have been easier to access during initial assembly although my changes made, in my opinion, more electronic sense but not significant in audio stages. I think Hammarlund actually made more physical sense than National in those years.

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 Post subject: Re: HRO-60 Engineering Observation
PostPosted: Jun Fri 11, 2021 4:17 pm 
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Lolyn wrote:
That was the era of newly fashionable time and motion studies so to save a few minutes of time looked good for the bottom line.


This is all a good example of how restoring an old rig can be a valuable walk through history. I was born in 59 and most of these radios predate me. However, reconditioning them in-depth can reveal some interesting things about the times in which they were built, and how manufacturing worked when things were built in large assembly lines made up of mostly people. The choices of components and the materials used can also be absolutely fascinating.

On a related note -- judging by the way some of the component leads are wrapped tightly around the connection posts, they must have also used some sort of evil wire-wrap tool to hold the parts in place before soldering. As a result, removing some components can be really challenging -- in some cases, I have no choice but to snip out the old part and leave the remnants of the old lead wrapped around the post. It violates my principle of "full restoration"; however, it's possible to do damage trying to fully unwrap some of those leads.

Steve.


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 Post subject: Re: HRO-60 Engineering Observation
PostPosted: Jun Sat 12, 2021 1:31 am 
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Location: Mountains of Mourne. Ireland.
It violates my principle of "full restoration"

What... It's not the Sistine chapel ceiling... :shock:
Just rip the old parts out and bang the new ones in.

Maybe you've got an OCD thing going on. lol


Greg.
oh... employing unused tube-pins as tie points is not uncommon.


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