The AM Forum

Jen and I enjoyed a visit from Steve 'HX this past weekend. He arrived Friday night and was here through Sunday afternoon helping me out with a number of transmitter projects. We had great success on more levels than we first realized.

The first rig we decided to tackle was the KW-1 since it would only require a "quick" transformer swap. After losing the modulation transformer again last fall, I decided to try to substitute a nice old Thordarson CHT Multi-Match 500w unit in its place. I'd picked up this iron maybe 15-20 years ago at the Milton, VT hamfest, for a whopping $10. The guy said it was good, it was in really nice condition, so the time was at hand to try it out.

This particular transformer uses little push-pin type plugs for the connections. Pretty slick and fast, provided you have the pins. They're a bit...scarce these days? Fortunately a list member (Chuck, WA2ONK) came through and sent me a dozen that were a perfect fit (Thanks again, Chuck!). So the next chore was to make jumpers to combine terminals as needed along with hooking up the primary and secondary connections. Steve had figured out the likely combinations from the Multi-Match info he has posted on the AM Window site.

I had though the push pins would be a good fit for the existing harness ring lug connectors, simply by sliding them over the pins to be pressed between the plug and terminals. Unfortunately, the rings were too large, resulting in enough twisting pressure to force the pins back out of the terminals for a very loose fit - not good for 2500V. Steve had already made 5 jumpers for the necessary connections, so he went back to work adding HV pig tails with a ring lug on the end to tie to the original harness. This worked MUCH better, and we were off to the races!

First contact was Rock Cave Dave, N8LGU in WVa. Good audio reports from Dave, so we took a break to grill some steaks and relax a bit. Our "quick" job had taken all afternoon. A few hours later we came back to work WA2PJP for a while, followed by a call from Gene WA4PGI before he called it a day at midnight. While talking with Gene we had a station break in saying "Good Morning, good morning". Steve said "That's Jean". Sure enough, we paused on the next break and were called by F6AQK, Jean in France! Guess the rig was working okay.

After signing with Gene and Jean, we decided to try tuning and operating the transmitter up in the 75m portion where it had been arcing badly. Steve was able to tune up and work Brandon K5IIA, Mark AB9MP, and Ralphie W3GL who moved down to 80m with us to finish up the night.

Day one: success. Below are some shots of the transformer swap, including a good shot of the CHT replacement.

A few more shots of the transmitter in operation, including a shot of the modulation waveforms on the 'scope. The shot that looks like I'm pecking bird seed off the table, sleeping, or praying, is actually a result of using a D-104 clipleaded to a footswitch temporarily to avoid that nasty spike caused by the grip to talk stand. And a shot of the 4-250s blushing away.

Day 2 saw work on the 32V-2 that had lost audio last fall, and the "wedding gift" T-368 that had exhibited a hard HV short the one time I tried to fire it up several years ago. Steve actually had the 32V apart while I was still in the shower and had the T-368 moved out & ready to look over. We yanked the PS deck and did a visual as well as electrical inspection with a DVM for obvious shorts. Nothing found, so we reinstalled in with the HV cable & rectifiers removed and tested it. On came the lights, no shorts. Out with deck again to reinstall the 3B28s. Still no problems. So we reinstalled the HV cable to the back connector and moved on to the RF deck.

Long story short: we found no HV problems at all, despite what had happened the first time I plugged it in and blew the house breaker along with the transmitter breaker. The issue now appeared to be a lack of excitation. Looking over the RF deck for obvious problems revealed nothing, until I got to the exciter itself and found several cold tubes. A quick check with the B&K showed the tubes to be good. Out with the exciter and in with a spare. Still no luck. Before calling it a day, I decided to swap the original exciter back in along with a new 6000 tube recently sent to me by Jim W5JO (thanks Jim!). Voila - excitation appearing on the meter! Turns out the original 6000 tube had a broken alignment key and had been installed wrong.

Steve was able to tune the transmitter up fine and after a few more setbacks, he had it making RF and weak audio. Turns out a former owner had installed an additional audio jack which worked much better than the mic jack.

Now it has plenty of audio but some issues with frequency stability (to the tune of 5-10 kc up or down), still a lot better than going BANG when it's turned on. Still a few bugs to work out, but much closer to being online.

While I was swapping out exciters and tubes in the T-3, Steve went back to troubleshooting the 32V and was able to find a 470K resistor that measures essentially open, despite looking brand new. With my resistors still stored up north for a couple more weeks, it will have to wait, but at least it's been tracked down.

Sum total for both days: 3 transmitters repaired or troubleshot for repair. Also success in getting the KW-1 to work on 75m again, and a DX AM call from France to round it all out.

I can't thank Steve enough for his help, including the photos of our progress. As well, Chuck, Jim, and others who have helped me out with parts for these projects. Time and Life in general have finally allowed for some work to be done, resulting in getting back on the air here at KAQ Radio again. And this time, I'll have some back up transmitters ready if(when) one craps out.

Hope to work some of you folks soon. Will be on the road again some over the next month, but should have the 40m aerial back up in the air sometime in May if not sooner. Look for me on 80 for now.

Below are photos of the T-368. Note meters and lights. Yes, it works!

Todd, very good and congratulations on getting the KW-1 going again.   Always wonderful to have knowledgable help and tremendously satisfying to get things accomplished.   A few questions:  The iron seems to be working okay but I have wondered about resting my old Thordarson plate transformer on flat ceramic floor tiles to insulate it from the rack.  Of course the transformer would just sit there but the darn thing weighs so much, around 200 lbs.,  I figure it won't move around.  However this might be questionable.   But the idea is to not stress the winding resistance.  Of course putting it on ceramic floor tiles might be easier said than done.   the other thing is I notice that your oil caps are on their sides.  Is that okay?  I had some idea they had to be kept vertical but evidently not.  

tnx

rob

p.s. looking forwart to working you on 75!  I think I may have some half-way decent RF by this weekend. 

Hey Rob -

You're absolutely right about having a talented, experienced friend like Steve around at times like this. I would've never gotten as much done alone, too much self-doubt in my abilities. ;) Something that I'd look at and wonder over even if I recognized the problem Steve can just look at and say 'yup' or 'nope, because..' and move on.

I agree that it's a good idea to insulate the transformer from the chassis in the case of these old units with original insulation. We had actually planned to do so with this one using a heavy but thin plastic cutting board, but the overhang of the feet and minimal top clearance made it impossible. I'm going to come up with something else later this week before using the transmitter more. It needs to last me for a while. The original is going back to Gary at NEAR-Fest for a tear down and postmortem before rebuilding.

As far as the caps, that's the way it came from the factory so I'm guessing it must be okay. Those Collins techs were no dummies. None of these caps show any sign of leaking or other problems, while one of the caps mounted vertically in the T-368 was oily on top. Go figure!

Will be looking for you this weekend, good luck with your project(s).

Todd, that's great!

You need to let the T-3 warm up a good half hour or it'll drift.  The PTO has a oven, and it needs a while to stabilize.  If after a half hour or so it's still gyrating, perhaps the thermostat is bad in which case I'd just disconnect the oven.

What was wrong with the 32V?

Next in the barrel room is the 30K, I hope  ;D

Yes Todd, nothing like having a friend drop over to help a body get motivated.

I have a mod transformer exactly like the one your using in the KW-1. I wonder if it is wired in series for your set up or are some of the windings paralleled?

I used it in a BC-610 for years and people said it sounded great. I once saw a mod reactor made by the same company and it looked exactly like the mod transformer. I think it was about 50 Henry's. I missed out on it in an auction :'( :'( :'( 

Good show, Todd.  Steve was telling me it was an action-packed weekend... ;)    

Now with the good WX OM, and you're on a roll, time to get outside and raise that antenna. When you drop your new mawls, you want the alligators down there to stay at bay in the neighboring swamps.


Let me know when you're getting on and I'll meet ya.  75 or 160M is FB.

T

So, Todd, you blew that re-built mod transformer?  The one that caused you so much grief with the gorillas at Fedups and the cracked end bell casting?

If you haven't already done so, I suggest disconnecting all the components in that splatter filter circuit (splatter choke, caps and all) IMMEDIATELY, before this one blows too.

I used a similar splatter filter circuit in my homebrew rig back in the late 60s and early 70s, and blew no less than a half dozen KW size modulation transformers before I wised up and removed it, and haven't lost a mod transformer since. Don't stay as far behind the learning curve as I did.

I did exactly that, Don. Not sure how, but suspect it could be related to a spike from the grip to talk stand whacking the transformer on a fast key up.

The splatter filter is disconnected and has been since I first put it on the air some 20 years ago. Uncle Ed/WA3PUN filled me in on the potential for damage as well as bypassing the clipper and using the 12,000 ohm P to P taps on the transformer for better fidelity. I'll be adding a limiter/compressor later this week to keep things even more in line with the audio as well as allowing me to finally use the RCA 77D mic given to me by Joe/WA2PJP.


Steve and I discussed this very topic on Sunday. The center of the big grin dipole is maybe 20 feet or so off the ground, which makes it amazing that F6AQK heard and called us Saturday night/Sunday morning. Maybe I'm onto a new design, a Beverage Dipole!  :D

The problem with getting it up higher is my ability, or lack thereof, to get higher up in the trees tan it is already. The fused vertebrae in my neck make it impossible to crank my head around in Linda Blair style up in those close branches to see what I'm doing. That'll definitely be a job for Steve.


I'll send you along the hook up we used for the 810s, Terry. Steve has the info for this series of transformers on the AM Window site, he simply checked out an early Handbook, did the math, and came up with the proper choice. We double checked with a calculator on Saturday just to be sure. There might be a better choice as the highs seem to be attenuated a bit, but for now it's close enough. They are indeed beautiful transformers, makes me wish there was a viewing window to see those nickel plated acorn nuts and all that black wrinkle.


There was indeed some drift as it warmed up Johnny, but this was more of a jumping up or down the band on key up or whenever Steve touched anything on the set. It acts like a dirty connection or something as you say. Very flaky, but at least it's all working now! I really had Steve believing it was out to kill me, but it gave him no trouble. Zero HV zorches beyond voice peaks when testing.

32V has an open resistor in one of the first audio stages. That appears to be all. Ten minutes of soldering to replace it should do the trick. Turns out it still had audio, just very little. So the peanut whistler will be back online soon.

30K-5 will indeed be the next to undergo surgery. You know how close it is to working, we just need to figure out where or why the 807 driver grid current is missing, or if it's something else. I was just concerned it would become a time sink preventing us from getting other problems solved with the other transmitters. Only 3 left now - the Mod-5, 300G, and 21E which just needs an electrical drop and reassembly.

Will be giving you a call sometime this week to pick your brain on the T-368 and tell you about our successes. Easier than trying to spell it all out here.  ;)

Todd,

Do you have spark gaps on the mod iron and Heising reactor?  It's not hard to make your own, if not. Gaps have many times saved my mod iron from mistakes.

No need to climb the trees. Get a bow and arrow with a spinning rod. EZ to do.

T

Mr. Todd,
Music to my ears (sorry for the pun!)!  Wonderful that Steve was able to get down you way and lend you a very skillful hand.  The zorching on the KW-1 may have been an internal problem in the original mod transformer. I forget all the details but the fact that its solid now is a good think.  I realize that you don't have that audio transient caused by the choke to key with the D-104, but a lot of KW-1's use that same choke the chicken D-104. 
All in all, I know your thrilled over the successful weekend.  Now, I can't wait to work you.  40M in the mid mornings would work great.
Oh, those steaks, I remember those well...
Joe, W3GMS 

Todd,
I just landed one of those transformers in a trade about two weeks ago.
Almost broke my toe tripping over it so moved it to the bunker yesterday.
Toe still red but it stopped hurting. I assume you have it connected series pri parallel sec.
Do you have any voltage specs on it? I can't find anything except wattage and current rating. Does it need to be heising connected?

The 6000 tube can be replaced by a 25AV5 with little or no retuning required. That's what I used for a spare in my T-368.

With best regards,


Kevin, WB4AIO.

Hey if Steve gets that much done he's always welcome over here.

It must really be satisfying to finally get a handle on the busted radios laying around.

I've got a list and every time I go out there it's like, ugh, so I just get on the air and don't do any of them.

Ive always understood that the filter caps have to be completely immersed in oil which doesnt happen on their sides?? There is an expansion air gap between the top of the cap and top of the case.

Glad you guys made some progress.

Dunno what to tell ya, Carl. I've got a broadcast rig that has some mounted horizontally too, so I'm guessing it's okay to do so. Maybe they had specially rated caps for such service?

It's been a case of chasing my tail since moving here. First the KW-1 and 32V both worked, then one would crap out and I'd use the other, but it would eventually crap out too. Chased HV gremlins in the KW-1 until they appeared to be cured, then the mod iron died again. Changed the same oil filled cap twice in the 32V, eventually its audio died. They're old radios, they sometimes crap out when used regularly I guess. After  while, you start to scratch your head and doubt your abilities. This is when someone with more experience and knowledge is a big help. Along with Steve, I've pestered Johnny and Joe/PJP and Joe/GMS via email and phone. Another set of eyes, or in this case - another, sharper mind thinking about it seems to help.

Frank, that Thordarson is a nice transformer. It looks a lot like the Tru-Fidelity series used in BC gear. Pretty sure that was the biggest one they offered in the CHT series. Check the AM Window site, that's where I found the dope on the Multi-Match CHT series. If it's just like mine, it's a T11M78:

http://www.amwindow.org/tech/htm/modtran/thordarson/thordarson1.htm

Tom, the design of the transformer doesn't work well with spark gaps. The HV cables are held into the ceramic insulators by push-in pins, so there's no way to mount, muchless adjust and lock into place a spark gap. That's the only thing I don't like about it. I actually have a bunch of nice ball gaps yanked from the Raytheon iron at WGAI in Elizabeth City that I couldn't haul back with me. Would work great on the primary if I could screw them down tight, provided the cables were in line and not on opposite corners.


The steak tradition goes back quite a few years, Joe. It started during the days of Hosstraders at Hopkinton, NH. Joe/PJP used to come up early and stay over so we could head out Friday to the 'fest. Over time it grew into more of a group BBQ prior to NEAR-Fest with others like Gary/'INR, Steve, Johnny, and others making the trip. Even Howie W1CL made it down to the last one along with JP K4OZY and Nick K4NYW who came up from NC.

As much fun as the stuff is, it's really the people that make it all worthwhile. A chance to spend time with good friends who share a common passion for radio as well as good food and twisted humor.  ;)

Will be picking up/building the new 40m aerial the next time I'm back up in New England on business. Going to get there a few days early to see friends and take care of some other items. Will also be hauling the rest of my parts and radio stuff back here, finally! Until then I'll be on 80m only.

"  Tom, the design of the transformer doesn't work well with spark gaps. The HV cables are held into the ceramic insulators by push-in pins, so there's no way to mount, muchless adjust and lock into place a spark gap. "

Ya don't have to mount them at the transformerr, du ya? Can't ya mount them on the other side of the wire??

klc

If I'm remembering right, the other ends are considerably further apart, so they'd have to be some might big/long gaps.

I'd come to believe that the T-368 was out to kill me from the very first (and only) mega-zorch it made on first power up after I got it in 2006. The following picture shows that I was able to convince others of its evil intentions.... ;)

Todd,

Here's three pictures of remote mounted spark gaps. They will work FB that way. My leads are about 6 inches long on the 1KW BC mod xfmr..


Look half way down the page:
http://amfone.net/Amforum/index.php?topic=22073.50

Your original mod iron would probably still be working if you used spark gaps.

T

Pictured below is a combo mod xfmr and Heising reactor gap protector. The mod xfmr primary also has a set. (not pictured)

Todd,

Now we know Steve's secret!  Carry a big stick and where those rubber gloves!

Hi voltage is the safest thing in the world as long as you don't get across it.  He who get complacent with it, usually does not live very long.  It bit me real hard at 14 years old and fortunately I survived.  From that point on, no chances are taken.  Assume its on even when the switch is off.  There are rules to go by.
   
Joe, W3GMS

And don't have the dummy load connect (take a close look at the photo)!! Good thing the exciter didn't work on the first try!

Sounds like the handle there is "Frank" and everything is homebrew.

T

Rare wi-fi option for the dummy load.

(you have to keep it pretty close to stay within range at this power level)

It is a dummy load after all.

u got newpaged!

Fortunately we were just testing the circuit continuity prior to testing RF outpoot or anything else. Of course, after my dire warnings of a killer T-368 on the loose, it exhibited no HV problems whatsoever.

That didn't stop me from keeping my distance. Those who have been here will recognize that the photo of Steve was taken from the garage door. Outside, even. *brawk* <:=

Todd,
I saw the T11M78 and wondered if it was the same thing. I found some paper work on the iron but no voltage rating. I want to build a modulator with a pair of 813s. The full primary will do 20Kohms so think it will work. I saw a current rating of 320/640ma.

There should be a small plate attached to the side of the laminations, Frank. Even if the paint has worn off, the model should be stamped into it. I'm running a pair of 810s with mine and aside from a little talk back, it seems to be taking it all in stride. So far. ;)

I've got some Thordarson paper here, I'll see if it's listed.

No plate on my transformer. The number stamped on one end bell, with power rating.

Interesting. They must've decide to cut costs a bit by deleting the tag and its associated screws. It's a decent piece of iron from what I can report so far. Adding the Joemeek threeQ for using the 77D mic brought the highs up nicely, so it certainly isn't attenuating any frequencies.

If it doesn't work out for the 813s and you get sick of stubbing your toes on it, keep me in mind.  ;)