The AM Forum

Hello,

Saw a DX 100B on Ebay that was selling for 499.00.  I thought it looked some what clean so I continue to read about it.
The seller said he had no way of testing it and didn't know the condition.

Since the Seller is from Jersey and I am here in Pa. I stated that I have seen these DX-100's sell from 150.00 to 300.00, and the 300.00 ones were working.  I then stated I could pick it up for 200.00.  Reluctantly the Seller agreed.

I brought it home and connected it to a Dummy Load and continue to power it up up.  It seemed maybe it was weak on the bands above 40 meter?  It may be just my inexperience of peaking the grid and dipping the plate?  

Anyway I bought it for 40 meter on down so I wasn't to concern at the moment.

This was yesterday, and so I went down in the shack this morning to try the audio output using a condenser mic.  
Well I was in my house slippers (!) and they were damp from walking outside.  I bumped the back of my right hand on the corner of the radio due to it hanging a little over the edge of the bench.  I felt a little tingle of voltage when doing so.  I then proceeding to turn it off remembering I didn't have a ground on the back of it.  I had gotten another hit of voltage again on the power switch.

Anyway I turned it off and pulled the electrical plug and then connected a secure ground to the back of the chassie.

When I plugged the transmitter back in, there was this "Pop" sound!

I unplugged it again and then continue to remove the outside casing so I could have a look underneath where I assumed I would find the issue.

Well it turned out that one of the caps across the AC line had blown.  I take it that these caps are the line filter caps.

My question is why would one of these blow after I installed a ground wire?

The plug is an old style non-grounded type and the two bladed plug is not the polarized type either.  Both blades are the same.

If I had by chance plugged it in with the blades reversed, would it HAD NOT blown the AC line filter cap?

Thank you,
Ken

The caps were probably leaky, that's most likely why you were getting bit.  When you grounded the case and most likely plug the cord in with the hot side on the bad cap, it shorted.

Get rid of the caps on the AC line, you don't need them.  They usually cause more trouble than they're worth.  You can install a 3 wire grounding cord.  If you do make sure the black wire goes to the fuse first  It should connect to the rear terminal of the fuse holder.

Fred

Ken

I agree with Fred about eliminating the AC line bypass caps... and converting to a 3-wire configuration. with the safety ground wire connected to the chassis.

In the original configuration, current must flow through both RF bypass capacitors (in series)... but the mid point, where the capacitors are joined, is connected to the chassis.

If only one capacitor is bad (leaky), the other capacitor will limit the flow of current (essentially none). When you connected the chassis to ground, you provided a path for current to flow from the "hot" (black) wire through one capacitor (not both capacitors in series)... and back to neutral... via the ground connection. If the bad (leaky) capacitor happened to the one that was connected to "hot", it would conduct too much AC current, heat up, and pop.

Stu

I have a DX-100 (non "B").  Absolutely agree with the above posts.  If you're still using the Heath plug with two fuses, replace the plug and cord with a three wire system.  You can save the fused plug if later someone else wants to return the rig to "original" condition.  Install a fuse holder on the chassis and put one 8A fuse in it.  The black wire is switched and fused. The white wire goes to the other transformer connection point.  The green wire goes to any convenient chassis ground point.  No more bites!

Here's a second thought:  You said you went "down" to the shack.  Is it in the basement?  Cement floor?  If so, I'd be sure to wear dry shoes with rubber soles because damp cement floors and stray voltages are not a good mix with poorly insulated feet.

With all of the noise and "buzz" on AC Power lines these days I prefer this type of input filter:

Phil - AC0OB

Okay, I removed the old two conductor cord and I am going to replace it with a 3 prong plug as suggested.  And of course I removed the old line filter caps.  Do I leave the existing inductance coil in tack?

There is not a lot of room in there to work.  I temporary removed the coil mount screws so I can solder in the new cord neatly and then replace.  Its going to be a bear holding onto the nut with needle nose pliers!  I will have to drill out the existing AC wire hole to fit a Strain relief for the new 3 wire cord.  The original was just tied in a knot. 

I will have to think it out carefully where to place the fuse holder.  Its really tight and I want to make it look like it is suppose to be there!

Does anyone know where to download a manual for the "B" version?

Thank you Fred, Stu, and others.

Ken

Somewhere on the web is a reengineering of the Viking Ranger 2 coil monstrosity. I think that the redesign took up a lot less space, 2IIRC. I guess that you could try that....


klc

Now that you removed the caps you can remove the coils.  Drill the line cord hole to size but not too big.  You'll need to file the hole to size, it's not round for a strain relief bushing.  Try to locate the fuse holder near where the AC cord enters.  Connect the black lead directly to the rear terminal of the fuse holder.  Next connection, from the fuse holder, is to the switch.  Make sure you're switching the hot lead.  Neutral lead (white) would go directly to the power xfmr via a terminal strip if there is one already on the chassis.

Most common fuse holders have a rubber washer.  The washer goes between the chassis and the holder on the front side and not on the nut side.

Fred

I found an open space to install the fuse holder.  
The black disk that looks like a capacitor is an inrush current limiter.
The diagonally mounted transformer on the right is a reversed audio output transformer that feeds the modulator tubes directly from an external audio amp. (And that, as they say, is a whole 'nother story!)  Sorry I don't have a better pic of where the power cord actually comes in.

OK FB, you can use that type fuse holder, much easier to install than drilling holes.

Keep up the good work.

Fred

In your photograph it looks like there is a stray 6-32 x 1/4 inch nut laying between the 1625 socket and the LV can electrolytic.  Might want to remove that one.

Nice find!!

Yep, I got it out before I buttoned up the rig!

Ken,

I have a DX100B on the bench, but haven't replaced the line cord yet.  I will add a 14 gauge 3-wire cord w/strain relief and chassis mount fuse holder, wired as the other guys have specified, which is what I did with my Heathkit Apache (see photo).  The white & green wires are not connected together, although it looks that way in the photo because of the angle.  I removed the stock pass-through caps and used one of the available holes for the fuse-holder.  I think I may have had to slightly enlarge the hole for the fuse holder with a round file.  I decided to replace the pass-through caps with new 1KV disc caps.

Brad

Hello Brad,

I will also be going with a chassie mount fuse holder as you did, I haven't done it yet, I need to buy a new cord from the hardware store.  Also I have to alternate working on the DX100B and renovating my house which feels like it is taking forever!

So you still installed the pass through caps?  Was this for line noise or just another form of line protection?

Ken

 " I need to buy a new cord from the hardware store'

I'll carry a nice big wire cutter in the ca. When I drive down the road and see tv/computer monitor/ vacuum cleaner alongside the road, out comes the cutter. Crude but effective.

 I had lots 'o fun when the transition from CRT monitors to SS came along. Mouse cordage is fine also.


klc

Actually I have several cords from extension cords to the ones that have those complex outlets.  I have a couple that has burned out with nice heavy cords.  But...they are to heavy!  The outer shells are to thick with the strain relief that I plan on using.  Plus there isn't much room to play since I will be adding a fuse holder as well.  The original hole is right up against a transformer mount.  So I have to be careful there if I want to do a nice install.

I know I have some other cords around, but I won't find them until I buy one!  Isn't that how it goes!!! 

Ken
 

You can power that xmtr with a 16ga cord, even a 18ga cord will work FB.  The lighter cords require a smaller strain relief bushing since space for one is limited.

Fred

Hi Ken,

I know what you mean.  Since spring, I have been working on house projects in my spare time and have neglected the DX100B.  In this unit, all the iron appears to be good.  I have replaced the electrolytic caps in the PS, and I'm replacing other caps as well as out of spec and open resistors.  There was a strange modification to the speech amp, which I have removed, and I will return the speech amp to stock configuration, perhaps changing the value of the interstage caps.  A couple of the front panel knobs are cracked or broken, so I will need to find replacements.

In the Apache, I got rid of the stock pass-through caps and installed new 1KV disc caps.  As noted above, some of the guys get rid of the caps and coils.  But after reading up on it, for me there was no compelling reason to leave the caps out.  I bought my 6 ft. AC cord at Lowe's.  It is made in U.S.A., came with the plug installed, and the black, white and green leads were tinned.  Probably a good idea to look at the copper wire ratings chart in the back of a handbook before deciding on which wire gauge to use.

Brad

consider adding a separate fuse for the low voltage/filament xfmr ... sooner or later solid stating the supplies will come up .... please remember it is a system and should be considered as such ...73  John

Hello Fred,

I finally drilled a hole for the strain relief that I also finally found!  No one seems to have any locally.  I was lucky enough to find one in storage, imagine that...

I also went with a 14 gauge wire with a ground.  I had to cut the strain relief ears off on the part that folds over the wire.  The strain relief that I had found could had been a little larger, but I managed to get it altogether and looking like it should!  Pics will follow later...  

I haven't done anymore.  The DX-100 is still sitting on it's side.  Brad K4RT had me thinking about those Caps, so I did a little research here and there, and it made me think that I should put them back in?

Can you Fred or anyone else elaborate more on the Caps?  At first I was just going to remove them because I thought "what the heck this isn't a receiver".  If the Caps are made for line noise, is it a possible that some noise can make it through to the transmit audio circuit?  I am just throwing this out there.  

Please don't get me wrong, I appreciate all the help I can get.  I just want to learn about what I am doing or not doing.  This way I will know for any future modifications and perhaps I can help someone down the road as well?

Ken

Ken,

FB on installing the new AC cord and strain relief.

I reviewed everything I could find on the subject and just did not see a compelling reason not to put caps back in.  My impression is that those caps and coils were intended to address TVI issues back in the day.  But I don't think there's any significant down side to doing away with the caps and coils nowadays.  If you do away with them you'll have more room to work in that section under the chassis.

Brad

depending on the size of the line filter caps and how they are connected, you may have problems with ground fault circuit interrupters "false tripping".....

if this gives you the 'deer in the headlights' look just ask ....

Ken,

The caps were put there to reduce TVI which today is a thing of the past.  As far as worrying about line noise, not much line noise (if any) is going past the power xfmr.  I built many power supplies for rigs, never put any line caps.  They're just something that can short and give you problems.

Today with many products, TVs etc, there are special line filter caps that are used.  The reason, most all these products have no power xfmrs.

Fred

Hello,

Okay the install is complete all but the the Plug.  So No Smoke Test as of yet!

I think I mentioned I had found a fuse holder but I also had bought one too. (It's a Good Thing...)

The one I found was a little slimmer and shorter, so I thought I would go with the one I found.  Well the soldering tabs holes where one would insert the wire wasn't large enough to accommodate the 14 gauge wire.  So I started to drill it out and turning it from one side to the other in hopes not to have the drill bit catch and twist the fuse holder.  Well it did and the tab was toward off.  But it turned out that the new fuse holder stuck out beyond the case more getting it away from the new power cord.  So it worked out in my favor.

Also if you look at the pic with the red arrow, I am trying to point out that the once countersunk hole that held the coil connections had left a beveled edge.  This was due to not drilling the hole perfectly in the center.  I purposely did this to move the hole away from the new power cord install.

However this would leave an issue with the fuse holder nut not being able to tighten flush.  So if you look at one of the other pics with the cutter and grommet, you will see I had cut a grommet in half so to use it as a way to accommodate the offset.

Its not perfect but it worked!

I was actually thinking ahead when I was planing on placing the fuse holder in its location.  I thought about the outer case and how it might not clear the fuse holder.  I looked at the mounting holes on the chassie and assumed the fuse holder would clear.  Well we all know what the word "Assume" can do!!!  As I was drilling the holes, the drill and the file had slipped a few times revealing a couple of scratches.  I thought I could clean them up with Steel Wool.  Well I did some what but it also took off the gray like paint covering that revealed with the outer case would fit.  If I didn't use the steel wool I would had noticed up front that the fuse holder wouldn't had cleared.  That's what I get for trying to hide my mistakes!

Anyway so I had to grind and file a half circle to accommodate the new installed fuse holder.  I didn't what to do a hack job, but it looks like I did anyway.  Well live and learn, but sometimes we never do!

I want to thank everyone here who had participated in helping me to getting the is DX-100 back on line.

I may have not commented back to everyone who posted, but I did take everyone's advice in and thought about what was said.

So a Big Thank You to All.

Ken

I will have to post again to add more pics....
 

More pics....

and more pics...

Last pic... :)

Ken,

Nice work. Thanks for posting the photos. Have fun with that DX 100B.

Brad

Hello Brad, how's going?

Thank you.  Thanks for your help.  If you and everyone else didn't chime in, I am not sure where I would be?  So again Thank You.

I powered it up today and it seemed to be working okay from 15 meter on down, or is up?  To 160 meter anyway.

The strange thing is I thought this was a 100 watt PEP transmitter? 

I tuned it up on 75 meter in the "CW" mode the way the manual instructed and then switched to the "AM" mode.  I was getting around 150 watt carrier.  When I turned up the Audio up, and begin to talk into the Mic, it was modulating roughly to 320 watts.

It seem the same from 15 meter to 160 meter.  When going to 10 meter I could not peak the Grid meter to 5 MA's, which also met that I could not get the plate current to 250 MA's.  But on 10 meter I was able to get the transmitter to transmit about 30 watts and with modulation the watt meter was peaking 120 watts.

So I am not sure what is what!  Or is that What is What Watts!!!

Is the DX-100 a 100 watt carrier rig or is it a 100 watt peak rig?

I am wondering what I should really be seeing on the output?

Again, Thank you Brad.

Ken

Ken,

With two 6146 tubes in the PA, it's a 100W +/- carrier (unmodulated) rig.  Generally, modulating the carrier results in peaks up to four times the unmodulated carrier power.  So, the peaks of between 300-400W you are seeing would seem about right.  You seem to be seeing the same results on 10M (30W carrier x 4 = 120W). I can't address the low power output on 10M. Perhaps low drive.  Someone else here will surely have some advice.

Brad

Hi Ken,

Good work on your DX-100B project. I did up my DX-100 (non B) about 10 years ago. I did quite a few mods plus repairs and updates.
With low power on 10 I would first (if you haven't already) sub in a fresh set of 6146's. 6146 or 6146A - not B.  Maybe same with driver tube.

As was already said - A 100 watt carrier output plate modulated rig if fully 100 % modulated and with a stiff power supply and all else optimum will put out about 400 watts PEP as measured on a peak reading meter. Do a search on average vs pep power and see the power distribution. The reason SSB has more talk power for any given power output is mostly due to fact that all of the power is concentrated in the one sideband. With AM, the intelligence (sound, voice) is usually only received one one of the sidebands and the carrier doesn't add anything to the "punch".....but is sure sounds good when it "thumps" on.

Good luck, Dave - W3NP

Try adjusting that plate coil for the driver tube.  Spread the turns or compress them for max grid current in the finals.  That little coil is for 15 and 10 meters.  Sounds as if the 15 meter section is ok.

Okay, so it is a 100 watt rig unmodulated...that explains it.  :) 

I do understand the 4:1 ratio meaning 4 times the carrier equals PEP.  I had someone set me straight on this when I was first getting into "AM".  For some reason I was believing the DX-100 was like a 25 watt carrier with 100 watts PEP???

Thanks for setting me straight on the DX-100.  It's nice when you know what is going on and what to expect!


Thanks Dave. I guess the DX-100 will be a work in progress.  I have another DX-100 B and I think 3 standard DX-100's along with 2 Apaches and 2 Mohawks, so I should be able to find some tubes to compare.  I picked up this DX-100B hoping I wouldn't have to do any work on it due to working on my house.  Time is what I need more of!

The transmitters and such are stored away, so I guess I will have a look to see what I can find.

I'll let you know Thanks.


Hello Jim,

I guess this might be something to try first, before trying to locate the other gear for spare parts.
If doing so will this effect the 15 meter band or some of the others as well?

Like I mentioned 15 on down are okay.

Thanks Jim,

Ken

The coil is the one near the divider between the final and driver, I believe it is mounted on a wafer of the bandswitch.  It has been a while but I believe it is about 3/4" in diameter and is one long coil with a tap.  The long part up to the tap is for 15, the shorter part is for 10.  Since 15 is working so well, try not to disturb that part, just move the part from the tap to the end with fewer number of turns.  If it is already wide spaced, push it together just a bit and see what happens.  If that does not help, move the turns apart.

Every DX 100 radio I have had would, after adjusting that coil, have more than adequate grid current to drive it to about 70-90 watts.  That part of the coil does not affect any other band.

Even if you move the 15 meter, you can always readjust it.

Very nice job Jim.  It's good that you documented it with these pics.  Great resource for someone who might be going to the same experience.  I looked at the wiring and the job overall and I consider it a thread I would recommend to anyone without reservation,

Thanks, Al

Thank you Al,

I take it you met to say Ken?  I like good forums like this one.  For one there are so many here to learn from.  And of course if someone has an issue or even a question, there are many who jumps in! 

Plus for everyone who documents their procedures and such they're always here for everyone including the the original "Author" who may want or even need to come back to see what he or she has done for what ever future reasons!

So I am happy too!  But most of all I am thankful for all of those who help.

Well I have to get back to spreading and leveling stone in my driveway!  (Not That I Want To!)  I was on my break.

Thanks again Al,

Ken

Hello Jim,

Thanks for the suggestion.  It did increase the power on 10 meter, but it only brought it up to 60 watts.  With that being said, I found 15 meter on down in frequency the wattage was lacking more then before.  So I decided to place the coil back as before.

One question I have if the carrier let say is 100 watts, and with audio the PEP is only let say 300 watts, and the PEP is suppose to be 400 watts, is this due to a weak component in the modulation circuit / weak audio tube perhaps?

I would think (my lack of knowledge) that the final output tubes generate the 100 watt carrier, and the modulation transformer combine with the audio output tubes would generate the PEP wattage?   

Just trying to figure all this out...

Thank you.
Ken
 

B+ supply sag?

Hi Ken,

Looks like your having fun! 

I would strongly suggest looking at the percentage of modulation with a scope.  That way you can see whats happening.  Not saying anything wrong with your PEP wattmeter, but I would measure percentage of modulation with a scope or the REA modulation monitor that I believe you have.   You need to see what things look like. 

Joe

Hello Joe!

My scope was borrowed from someone down the road.  They're finished with it, I just need to go there to pick it up.

I did take the REA Monitor out of storage a while.  Your right I need to connect it so I can see what's going on.  I am still having issues with the output of the DX100.  I think when I find time I will hunt for the other transmitters and borrow some tubes from them.

But I am having some fun! :)

Thanks Joe,

Ken
 

Again a late post is better than no post I suppose. Having a repair and modification business on the side, whenever I encountered one of those boat anchors I did almost the very same things. The almost was instead of installing fuses I installed push button resettable circuit breakers of the same rating as the original fuses including the internal LV transformer fuse. Obliviously this saved digging inside replacing fuses and the easy part was my "day job" supplied them and plenty of goodies for my various projects. (;->)