Dumb questions about resurrecting my DX-100

[wn5t]

Greetings.  Well, I'm not a complete noob to tube gear...I've had a Galaxy III Mk V ( I know...groans...) that I had to fix and a Swan 700CX that ran FB and Drake B-Line Twins (still here and not going anywhere!) that run FB.  Oh, I've read and read and read...from old Handbooks, from the 'net, from manuals...you name it.  However, I am just old enough (mid-30's) to know that questions asked are often headaches averted.  So, here goes...

In April I picked up a DX-100 at a hamfest for $30. Yes, I knew there would be things wrong for that price.  Things like...no cabinet (probably had been rack mounted), too much voltage to the VFO tube, no reading on the meter in any position.  I brought it up on a variac and the bulbs light as do all of the filaments, but without metering, I didn't want to push it.  Just the other day I put the DVM on the meter circuit....nada.  Oh, some knobs are missing and some are not original.  But...I'm cheap and I want a decent AM rig that glows.  Otherwise, I'd probably build a class-E rig....boy those look sweet, but they don't glow in the dark unless covered in phosphorescent paint. 

My plan for this rig is a wholesale replacement of resistors and caps.  Yep, every one of 'em.  As I start into this project so I'll be ready for quiet conditions for fall/winter, are there things that I should know or consider other than just making sure, for starters, that everything matches the schematic and that all the solder joints are good? (I figure that the mods can wait until the old girl is percolating.) 

All good advice appreciated. 

[John K5PRO]

Michael
Theres nothing dumb about your inquiry. Over the past winter and spring, I restored a DX100 to FB operation, and documented it on this forum. Others have also, in the more distant past, here and in Electric Radio magazine. If you jump to this link about 8 pages down, you can read a bunch of postings about it, with replies and lots of suggestions and ideas.

http://amfone.net/Amforum/index.php?topic=3789.0


 I plan to finish the job this fall once it cools off and I finish some other priorities, as I left the VFO taken apart and planned to refurbish that, cure some problems with it. Hope to get it all written into an article or put it online. Read and heed.

So have fun with 'er, its a classic inexpensive transmitter from a classic era. Just watch out for the HV, and those series electrolytics gotta' be replaced. If you go solid state for the 5R4's then you have to do something better than run the modulator screens of the center tap of the divider, as it really unbalances and stresses your new 'lytics. A pair of fresh 6146 or 6146B really makes that radio play, along with strong 1625's.

73

[WA1HZK]

There are a bunch of those operating and people with spare parts, etc. I gave away my cabinet last year but I still have VFO Wobulation when I fire up so those rigs will keep running and keep us amused for years to come. Check out my efforts. This would make a good project also.
Keith
http://www.criticalradio.com/833%20Rig%20Project/Web%20Pages/Default%20WA1HZK%20Page.htm

[Ed-VA3ES]

Steve's AM Window site's Technical Section has a couple of excellent  mods and upgrads for the DX100.   You can access the AM Window[/b] from <A href="http://www.amwindow.org/"> <b>here</b></a>.  Go to the "technical" section of his site.

[wn5t]

Thanks, guys...

John... I have read the saga of your DX-100 whilst glancing across the room at mine!  The new forum software has a neat print feature so one can print text-only.  Since I have a laser prn and lots of extra paper, I've printed it out to go in the notebook.  Looks like a nice job, BTW.

Keith...I've seen your project pages.  I have access to a rack with everything in it but the exciter.  There's just one problem... I live in an OLD house.  I'm not sure that the floor would hold it.  Even thought the electrical service was refrubed before we moved in, I'm not sure it would handle such a lovely best either! It might be nice to try it, though... 

Ed...yes I have read and read and read lots of good stuff on AM Window.  I'm probably going to to have to collect it all in my notebook and do a project plan, parts list...the whole shebang.   I'd really like to get this rig working to the point that I know that the major pieces/parts are operational and then do the mods...unless there is a compelling reason to do the mods while in the rebuild process. 

Oh...the plans and dreams.  So, why did we ever stop HB and home repair?  It's almost as much fun as putting fire in the wire...

[VA3ES - Piss-Weak Ed]

A few years ago, I published my "AM Notebook" which contained every published mod of the DX100 and Apache rigs. It also included a 90 minute tape by Tim, WA1HLR, discussing modding these rigs, and describing his  own mods to them.  The book also contained assorted info on AM, mod transformers, and other useful items. 

I've been thinking of donating the whole pile of original material to Gary, to publish on the Amfone.net, including the 90 minute Timtron audio.  (I have yet to formally offer it to him - things keep getting in the way  .

Yo, Gary, are you reading this???  (Maybe I ought to PM him?)

[wn5t]

Ed...
That sounds like a great resource.  Even it some of the info was duplicated in other places, it would be worthwhile, IMHO, to make available here in one place and in a coherent and easily navigable manner.

 AMFone and AM Window have been wonderful reading for me as I try to gain sufficient knowledge to fully participate in the AM part of the hobby.  Perhaps, in addition to your collection, a nice series in the "Handbook" section of this site would be a thorough dissertation on topics that newcomers to the mode should know.  I worked to find stuff on modulation methods, only to find out that my tube rig (a Swan at the time) was SSB only to learning that my current tube stuff (Drake B-Line) is a mediocre performer.  So, Elmers, help those of us coming from SSB/CW/FM learn why plate modulation is better than screen modulation.  Oh...how about "what test equipment do I really NEED and what equipment is a somewhat lower priority?"  Or...how do I select an O'scope and use it to test and monitor my AM rig?  What are all those neat traces telling me? (w/pics)   The list goes on and on and on...

One thing that is important, I think, in AM and that is one of the things that fascinates me so much is that you gotta be able to work on this stuff yourself.  Sure, I could send my DX-100 to RTO in Benton Harbor and get back a FB rig...for parts, labor, and $150 in shipping.  I'm fortunate to have some old handbooks from the 40's, 50's and 70's to peruse.  The books are a poor substitute for a guide to selecting, using, and repairing/maintaining tube gear that is written for kids like me who cut our teeth on rice boxes only to become frustrated with $75/hr labor for repairs and have a "need to know" the deep info on how this thing really works and how to fix it. 

I know first-hand that building a site takes a lot of time.   Writing thorough primer and advanced material takes even more time.   I cannot express how deeply I appreciate those who started/maintain this site, AM Window, ClassERadio, and others in their spare time and those who don't mind helping folks like me along the trail. 

BTW, I have reviewed the printed copy of John's journey with his DX-100.  Boy, there's a lot of work documented there.  I don't have the equipment or experience to make such detailed measurements, but I hope that my results are qualitatively similar. 

Here's to a 100K roll-off on the bottom end...

[KB2WIG]

Dumb q?? Asking  sure beats sittng there not knowin' and thinking that u doo.  Anyway, what may help you is "A Course In Radio Fundamentals", by that publishing firm the ARRL. THe william Orr books are gud also. That and some experience.  Like.  Keep one hand in your pocket when working with High Voltage ......   klc

[wn5t]

Three years ago at the Mena, AR, hamfest I picked up a copy of the Bill Orr book for $5 and a Galaxy for $45.  The Galaxy is gone...donated to a buddy in NW Arkansas...but not before it bit me.  I have learned the lesson about not becoming part of the circuit!  I have poured over the Orr book many times, and will keep on going over it and my older Handbooks.  Too bad my dad wouldn't support me getting my ticket 20 years ago, I'd have learned much by now.  (He worked in a shipping whse. and only knew about CBs...so when he heard "radio" he thougtht "CB" and said "no.")  Alas, I was really just an elmer away from being a novice.  My friend who had an elmer and got his ticket put it to good use; he's an RF engineer at a TV station.  Back to the Orr book....  BTW, that book was the best $5 I've ever spent.

[WA1HZK]

Such A Deal!!
I came across a cabinet that looks exactly like the DX-100 one I had last year. I gave that one away but this one I rescued from the dumpster looks OK except for the paint will need to be done. It's yours for the postage to send it to you. Just e-mail me the address & I'll send it over. See, it works to make some noise.
Keith, WA1HZK

keith@criticalradio.com

[wn5t]

Thanks, Keith...  The e-mail is on the way.  Wow.

BTW, the bite I took from the Galaxy was from the final plate supply!  It took me a moment to realize that I was still breathing and that my heart rate was steady!    Then I got down to bandaging the cut on my hand and cataloguing the entry and exit points of the HV.  I'll never forget that lesson. 

[wn5t]

Hi Mark...

Since the title of this topic is "Dumb Questions...," I'll bite.  Could you tell a little about the rationale for including a thermister in the Ep?

[wn5t]

Okay...here are a couple more questions... 

I was specifying resistors and capacitors on mouser.com and these questions popped up:
1) When replacing the silver mica caps in the DX-100, what is the preferred replacement?  I'm having trouble finding the correct values of mica caps.  Almost everything is rated for 500V, not 600V.  2) There is a 30Kohm 50W center tapped resistor in the DX-100.  I haven't found anything similar.  I don't know that mine is bad, but if I'm going to do a wholesale rebuild, might as well assume it needs replaced.  Does anyone know of a currently available replacement?  If not, what is the resistance at the center tap?  Perhaps it could be replaced by two resistors of appropriate value?

Thanks, again...

[Jim, W5JO]

You won't find the fixed tap resistor to replace the one in the transmitter.  I agree, it is is ok, leave it alone.  Should it be bad, you can get a 30 K slider resistor and set the tap to 15K.  The slider resistors are available at Mouser or Digi-Key. 

[WA1HZK]

There is a color TV transformer supplying the low voltage for mine and a Valiant filter choke on the chassis. Anything will work if you screw with it enough!!!

[WA1HZK]

Did you get your cabinet?
It went your way a while ago.
Keith

[wn5t]

Yes, I rec'd it the last week of August.  The box looked FB. I haven't opened it yet...still trying to get time and space to get the rig going.  I hope you got my check ok...

[Glenn NY4NC]

Wow! I didn't know there was DX-100 info in there!!!! 

Anyway, what may help you is "A Course In Radio Fundamentals", by that publishing firm the ARRL.