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 Post subject: DX-100 Restoration
PostPosted: Aug Mon 29, 2022 3:03 pm 
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Joined: Apr Sun 26, 2020 1:43 pm
Posts: 38
Location: Cumberland, Rhode Island
Greetings to the Forum,

I’ve taken on a new long-term project. This past weekend I picked up a Heatkit DX-100 (original) from the Northeast Hamxposition fleamarket. The seller had intended to do a restoration but never got around to it and had never even tried to power it up. Price $50. Examining the radio, I find that all tubes and major components are in place. At least I think they are. Time will tell.

Before attempting to power up on a variac I’m cleaning and going through the more mechanical components. The final amplifier knob is tough to turn. I also noticed that the tuning capacitor (EF Johnson 350.E.20) rotor blades are not exactly centered between the stators. Is this an issue? Image attached. The capacitor seems relatively clean it is hard to rotate. What is the best method for freeing this up?

Lloyd Merrill - W1LBM

Attachment:
Rotor blades.jpg
Rotor blades.jpg [ 566.11 KiB | Viewed 1024 times ]


Attachment:
Fin-amp-tuning-cap.jpg
Fin-amp-tuning-cap.jpg [ 562.25 KiB | Viewed 1024 times ]

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 Post subject: Re: DX-100 Restoration
PostPosted: Aug Mon 29, 2022 3:26 pm 
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Joined: Jan Fri 27, 2017 7:41 pm
Posts: 501
Location: Springwater, NY
lmerrill wrote:
Before attempting to power up on a variac....


Lloyd, fun project! Are the power supply filter caps new? If not, you might want to attend to them before applying power.

Here is a link to the manual:

http://www.radiomanual.info/schemi/Surplus_Radioamateur/Heathkit_DX-100_user.pdf


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 Post subject: Re: DX-100 Restoration
PostPosted: Aug Mon 29, 2022 3:46 pm 
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Joined: Jan Fri 11, 2008 11:25 pm
Posts: 330
Location: Kingwood, Texas
Location: Kingwood, Texas
The plate tuning capacitor has mechanical issues. The rotor plates should be centered between the stator plates. I’d remove it and take a close look to determine if it’s repairable. If not, you’ll need to find a replacement.

Darrell


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 Post subject: Re: DX-100 Restoration
PostPosted: Aug Mon 29, 2022 5:53 pm 
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Joined: Nov Sun 15, 2015 7:32 pm
Posts: 284
Location: Poteau, OK
Location: Poteau OK 74953
There is a similar variable capacitor, EF Johnson 154-2-98 16-358pf on eBay auction
#134208511376

The current bid is $14.99 with 1 day and 4 hours left on the auction.


https://www.ebay.com/itm/134208511376?hash=item1f3f735d90:g:to0AAOSw0eBjBUyR&amdata=enc%3AAQAHAAAAsGDNdItsCYJbejr6ylWPpGU6%2F201XqfwZVH3bSc100UwoLtNIAx0xOtTYDJM%2B4h%2FD3Z%2F%2FYH59YDVOyqva1RECrSef0E8uBmGUL2yk0%2Fnim1d0ur8saXDEjxtia3Fg1QmO7c2CewXDm3lpHT7kVtNOUYB%2BAONOFb9kfpnjTw09EYLgRJcBVYNpRzMvA0HvMKb61N%2F6vClfSFJj5vls6y2f80r3otY45N0H55%2BafMGYloJ%7Ctkp%3ABk9SR-i54ardYA


I have the same idea, fully restore a DX-100. I have fully restored quite a few pieces of Heathkt ham gear so I thought
I would try a DX-100.

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Mike W5RKL
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 Post subject: Re: DX-100 Restoration
PostPosted: Aug Mon 29, 2022 7:16 pm 
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Joined: Jun Sun 19, 2011 1:31 pm
Posts: 8510
Location: Minier IL
It has been years since I ran into this but I recall having to recenter a Johnson variable like this several years ago. If I recall correctly, the centering adjustment is at the rear (short shaft protrusion end) of the capacitor.

It is hard to turn because the shaft is binding in their bushings at either end of the capacitor frame. If there isn't a lot of crud build up, a few drops of light oil in the slots in the bushing ends will free it up again.

Rodger WQ9E


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 Post subject: Re: DX-100 Restoration
PostPosted: Aug Mon 29, 2022 7:27 pm 
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Joined: May Wed 16, 2018 11:16 pm
Posts: 432
Location: Edmonds, WA USA
Location: Edmonds Washington
Yep, just center it the rear nut is a tension nut so will keep the adjustment. Turning it is the adjustment. Someone has played with it. A little good oil should make it easier to turn. You don;t want it too easy, either.

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 Post subject: Re: DX-100 Restoration
PostPosted: Aug Tue 30, 2022 1:00 am 
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Joined: Apr Sun 26, 2020 1:43 pm
Posts: 38
Location: Cumberland, Rhode Island
Greetings to the Forum,

Thank you for your valuable feedback. To start off I will be removing the variable capacitor and see if I can adjust the rotors to be in the center of the stators. I do see another brass nut on the shaft inside the housing that I can possibly adjust.

As for the capacitor on eBay, I'm going to be keeping an eye on it. My concerns are the dimensions and capacitance. It does have the same number of plates in total.

Does anyone have a good reference on tearing down and rebuilding variable capacitors? Any help is appreciated!

Concerning the rest of the capacitors, all of them seem to be original. So I will be replacing the caps before powering up.

Thanks again,
Lloyd Merrill - W1LBM

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 Post subject: Re: DX-100 Restoration
PostPosted: Aug Tue 30, 2022 1:21 am 
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Joined: May Wed 16, 2018 11:16 pm
Posts: 432
Location: Edmonds, WA USA
Location: Edmonds Washington
Why would you remove it? The adjustment is esily accessed. I may be wrong but my recollection from mine years ago is that that front brass nut is just a bushing and adjusts nothing. Perhaps someone who has a DX-100 handy can verify the adjustment. Virtually the old big variable caps were the same construction. I recently centered the main tuning cap on an old receiver and it worked justt the same in minatire.

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 Post subject: Re: DX-100 Restoration
PostPosted: Aug Tue 30, 2022 11:43 am 
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Joined: Apr Sun 26, 2020 1:43 pm
Posts: 38
Location: Cumberland, Rhode Island
Greetings to the Forum,

Dave, thank you for pointing that out. I had tightened up the end nut pretty tight and thought I was at the limit. I didn't want to break anything by really cranking it down. However, I slowly applied even force on the 1/2" nut and was able to bring the rotors into better spacing. The shaft is still stiff but I'll keep working on that.

Lloyd Merrill - W1LBM

Attachment:
rotor_adj_inset.jpg
rotor_adj_inset.jpg [ 597.82 KiB | Viewed 871 times ]

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 Post subject: Re: DX-100 Restoration
PostPosted: Aug Tue 30, 2022 12:28 pm 
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Joined: Jun Sun 19, 2011 1:31 pm
Posts: 8510
Location: Minier IL
A little oil should free the shaft. If needed, apply heat via soldering iron and then add synthetic oil to the bushings as it cools which will draw the oil further in. I have often had to use that method to free up stiff switch and potentiometer shafts.

Rodger WQ9E


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 Post subject: Re: DX-100 Restoration
PostPosted: Sep Fri 02, 2022 1:09 am 
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Joined: Apr Sun 26, 2020 1:43 pm
Posts: 38
Location: Cumberland, Rhode Island
Greetings to the Forum,

Rodger, thank you for that advice. I was able to get some synthetic clock oil with a 3" needle applicator. The long needle helped to get in and apply the oil very precisely. The knob now has a firm turn but smooth turning action.

I have a new question for the group. The original DX-100 had 2 concentric knobs for both the Final Grid Drive and the other for Loading, Course/Fine. On this transmitter, there is only a single shaft for Loading. In an article by Bob Eckweiler, AF6C https://www.w6ze.org/Heathkit/Heathkit_008_DX100.pdf he discusses the changes to the DX-100B. He writes "The right dual concentric control that was composed of an outer Coarse and inner Fine Plate Loading control on the DX-100 is now a single control with a geared drive hooked to a larger variable load capacitor.". I've included a picture of my rig. Did a previous owner replace the variable capacitor with a DX-100B component or was Heathkit transitioning to the new model and including the new single shaft? Either way, it shouldn't be an issue. Just the lettering on the faceplate is wrong.

Lloyd - W1LBM
Attachment:
LoadingKnob.jpg
LoadingKnob.jpg [ 634.2 KiB | Viewed 703 times ]

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 Post subject: Re: DX-100 Restoration
PostPosted: Sep Fri 02, 2022 1:43 am 
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Joined: Jun Sun 19, 2011 1:31 pm
Posts: 8510
Location: Minier IL
Lloyd,

Heathkit sold an upgrade kit because of problems with the original setup so that might have been done with your set; otherwise the previous owner used equivalent parts. It was a very common modification/upgrade given the number of original DX-100 transmitters with a single large variable loading cap instead of the switched fixed plus smaller variable original design.

Heathkit borrowed very heavily from the designs of other companies and the DX-100 is effectively a Johnson Viking 1 with the VFO built in instead of external. Johnson used the switched fixed plus variable loading on numerous rigs both before and after the DX-100. The Heathkit RX-1 was heavily influenced by the Hallicrafters SX-101 design.

The single capacitor setup is less problematic than the switched fixed plus variable original setup and has sufficient matching range for any reasonable antenna.

Rodger WQ9E


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 Post subject: Re: DX-100 Restoration
PostPosted: Sep Fri 02, 2022 2:41 am 
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Joined: May Wed 16, 2018 11:16 pm
Posts: 432
Location: Edmonds, WA USA
Location: Edmonds Washington
There are two versions of the "original" DX-100. You have the later vcersion with the concentrick knobs. The tuning range is narower but still just fine. I have had both. If you look at various DX-100 manuals on line yu will ssee both versions.

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 Post subject: Re: DX-100 Restoration
PostPosted: Sep Fri 02, 2022 5:40 pm 
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Joined: May Fri 01, 2015 1:33 am
Posts: 1874
Location: Roslyn,Pa 19001
There were three mods that heathkit came up with to
update the DX-100 to make it more like the newer TX-1. They were named the MK-1,2, and ,3.
https://vdocuments.net/heathkit-dx-100-mods.html?page=6
GL with your new project they're fun transmitters. Have had few operating in the shack over the
years. Have one that is in line for an overhaul at some point. Just
watch your back there like picking up a V8 car engine!

Terry N3GTE


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 Post subject: Re: DX-100 Restoration
PostPosted: Sep Sat 03, 2022 2:28 am 
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Joined: Apr Sun 26, 2020 1:43 pm
Posts: 38
Location: Cumberland, Rhode Island
Greetings to the Forum,

Terry, thank you for the DX-100 mods document. Having these resources available makes the understanding of the rig much easier.

I’m happy to see the page on voltages of all the tubes by pin. Unlike some of the later Heathkit manuals where some voltages are on the schematic the DX-100 has none.

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 Post subject: Re: DX-100 Restoration
PostPosted: Sep Mon 19, 2022 8:23 pm 
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Joined: Apr Sun 26, 2020 1:43 pm
Posts: 38
Location: Cumberland, Rhode Island
Greetings to the Forum,

It's been a few weeks since my last post. I've now received a DX-100 recapping kit from Hayseed Hamfest who I've used a few times before. I believe that I have identified all of the caps that need replacing.

There is one area within the chassis that will present a challenge and I'm looking at the collective knowledge of this group for suggestions. The audio section is built on a sub-chassis mounted vertically towards the front of the rig. There is no clearance to gain access to the 5 capacitors that need to be replaced. Above this assembly, there are 2 tubes that also have connections. Obviously, this needs to be unbolted and moved, but I'm concerned that leads may be short and present an issue. I'm just looking for the best way to attack this. Here are a few pictures of what I looking at.

Attachment:
SubAssembly.jpg
SubAssembly.jpg [ 803.95 KiB | Viewed 346 times ]

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 Post subject: Re: DX-100 Restoration
PostPosted: Sep Thu 22, 2022 12:55 am 
Member

Joined: May Fri 01, 2015 1:33 am
Posts: 1874
Location: Roslyn,Pa 19001
Sorry don't have an answer for the question at hand but I do have a general recommendation.
That is to increase the capacitance of the 510mmfd caps to .01mfd at 630v, both 2 mfd 50v
to 10mfd at 50v, and the both .1 600v to 10mfd at 450vdc. This is to accomplish better
bypassing and audio frequency response.

Terry


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 Post subject: Re: DX-100 Restoration
PostPosted: Sep Thu 22, 2022 11:25 am 
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Joined: Apr Sun 26, 2020 1:43 pm
Posts: 38
Location: Cumberland, Rhode Island
Greetings to the Forum,

Terry, thank you for that recommendation. When I eventually tackle this subassembly I'll evaluate changing out those components.

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 Post subject: Re: DX-100 Restoration
PostPosted: Sep Thu 22, 2022 11:26 pm 
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Joined: May Fri 01, 2015 1:33 am
Posts: 1874
Location: Roslyn,Pa 19001
I did some nosing around and checking with some friends over on the AM Window.
The best I could find is to remove the screws that hold the tie strips and the rf
shield to the chassis. Then you can remove the shield. This will give you access
to both sides of the parts that are soldered to the tube sockets. It's not great
but that's about it.

In sounds familiar as I'm pretty sure that's what I did yrs ago. I've got one
to go.

Terry N3GTE


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 Post subject: Re: DX-100 Restoration
PostPosted: Sep Fri 23, 2022 4:46 am 
Member

Joined: May Wed 16, 2018 11:16 pm
Posts: 432
Location: Edmonds, WA USA
Location: Edmonds Washington
Thats what I also did years ago. Take a real good set of pictures of where the wires terminate so if one breaks off it wil lbe eeasy to figure out whee it goes. Make the capacitor changes als, they ae found in many articles on he wed, The real bottleneck is the audio interstage transformer but the cap changes will help/ The DX-100 was purposely desighned for restriced "communication grade" audio on the old busy am bands of yesteryear not the relatively empty am bands of today. It was typical good Heathkit engineering for its time and purpose/

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