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Author Topic: Alpha Delta DX-EE Replacement help  (Read 689 times)
W1DY
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Posts: 29




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« on: January 19, 2008, 07:38:38 PM »

I have been using my Alpha Delta DX-EE for @ 4 years now...
While this antenna is rated up to full legal power...I have had this same issue happen twice already.

Now Normally I run my Yaesu FT-990 barefoot up to 100 watts and never have a problem...

However..I also own an Ameritron AL-80B, and whenever I use it..I usually end up damaging my antenna!

The Alpha Delta utilizes 2 coils wraped around what appears to be PVC tubing.

While Using @ 600 Watts..I have evidently heated up those coils enough to melt the PVC..as they are now obviously distorted!

THis weekend...I could not use the amp at all as any power over @200 Watts was most definately arcing and driving my tuner and Amp crazy!

This antenna fits PERFECTLY in my back yard...and I hate to scrap it...

I need to either find a way to make a coil that fills the bill but can actually handle the power, or I need to replace the antenna completely!


This will be the second time I have had to rebuild those 2 coils....so I need a better solution than varnished Copper wire wound around plastic tubes!~

Thanks!!!!

Wendy

W1DY
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KA5N
Member

Posts: 4380




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« Reply #1 on: January 20, 2008, 03:39:14 AM »

First off there is different kinds of insulation for copper wire: enamel and formvar (and of course others). The formvar is much tougher. Also you can buy Teflon tubing to put over the wire and it provides much more insulation (while being very thing) and can withstand a great deal of heat. Amidon sells wire in small quantities at reasonable prices and motor rewinding shops can be often be talked out of fag ends of wire.
Then there is differences in PVC. One test is to put a sample in a microwave and see if it heats up. I have some old Melimine (sp ?) plates that have been in the microwave a few hundred times without harm, but some plastics melt with RF.
My question with just about all advertising: who designed this, an engineer or a copywriter?
Good Luck
Allen
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K3JVB
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Posts: 837


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« Reply #2 on: January 20, 2008, 06:12:58 AM »

I used a DX-cc

No issues with the coils at up to legal limit. But I did fry the end insulators. I only had the problem operating the antenna "off resonance" with power.
The SWR was about 2 to 1, and It loaded fine, with my Swan gear. I was on 75 meters. It sipmly melted the insulators, and one was on fire. Sure got my attention...and my dog's.

Changed to ceramic, no issues since. I think off resonace, the voltage at the ends of the 75-80 meter wire were very , very high. Too high !
73
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WB2WIK
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Posts: 20537




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« Reply #3 on: January 20, 2008, 09:56:40 AM »

Wow, I'm surprised this happened.

I've used A-D loaded antennas many times at 1kW+ and this has never happened to any of them, although I have had the "end insulator fire" experience a couple of times, until I changed end insulators.

Don W8AD tells me they now ship fireproof end insulators to resolve that problem!  I'm not sure when they cut in that change.

Why not contact A-D about sending them your "melted" loading coil assemblies and asking them to replace them?  They probably would -- and possibly the "new" ones are made of better material.  Again, I've never actually seen this happen, but whatever they were using 4 years ago may not be as good as what they're using now.

WB2WIK/6
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W1DY
Member

Posts: 29




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« Reply #4 on: January 20, 2008, 12:52:56 PM »

I have phoned A-D asking to buy a new set of coils...

THe original pair melted, and I had to re-wind around a new core myself once already..so asking A-D to replace these would not be the right thing to do.

Let me tell you what I am seeing...maybe I may have trouble elsewhere as well..

Since the coils have obviously distorted and melted...I'm starting my trouble shooting there...
But here is the root of my problem...

When I tune up my Ameritron AL-80B amp...I can only get to @ 400 watts..when it all of a sudden drops load and plate readings to the bottom of the scale

Grid @50 Plate @ 75...

Everything seems fine as I tune up power...but once it tunes up to @400 watts ..the grid and plate drop right off...

Backing off brings load and plate back up!!

It seems that something is Giving out as the power climbs...

Again..since the coils have been obviously melted..I'm starting there...but I suppose the problem could also Lie in the Feadline/Connectors or the Balun at the center feedpoint of the AD-DX-ee...

This is my only antenna..so I can't test it

Everything works perfectly...and tunes well barefoot!

Hit it with more power...and something isn't happy!

Oh...and there isn't any arching in my amp that I can detect..

band is 20 Meters...easily tuned...

Thanks

Wendy
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WB2WIK
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Posts: 20537




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« Reply #5 on: January 20, 2008, 04:28:35 PM »

"Grid @ 50, plate @ 75?"

I guess you mean 50mA for Ig and 750mA for Ip.  The 750mA for Ip is *very* high, and way beyond what a single 3-500Z can safely do, so something there isn't quite right.

Normally, an AL-80B will have Ig = 100-150mA and Ip = 500-600mA for full output power.  Anything beyond 500mA is "intermittant duty" only, as the tube is rated 400-500mA maximum, depending on the tube.  In SSB or CW service, it can safely be higher.

"Something's rotten in Denmark"
-Wm. Shakespeare

WB2WIK/6



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W1DY
Member

Posts: 29




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« Reply #6 on: January 20, 2008, 06:13:59 PM »

No...I really mean once it hits @400 watts....all of a sudden it drops to Plate 50 Grid 75!!!!!!

Seriously the meters drop.....!!!!

That's what I'm trying to explain!!!!

Meters all look good....as power comes up..@400 watts..Bang something happens and I see 50 plate 75 Grid!

It's like something just gives out!

HELP!!!!!

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WB2WIK
Member

Posts: 20537




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« Reply #7 on: January 20, 2008, 07:07:46 PM »

RE: Alpha Delta DX-EE Replacement help  Reply  
>by W1DY on January 20, 2008  Mail this to a friend!  
No...I really mean once it hits @400 watts....all of a sudden it drops to Plate 50 Grid 75!!!!!!

Seriously the meters drop.....!!!!

That's what I'm trying to explain!!!!

Meters all look good....as power comes up..@400 watts..Bang something happens and I see 50 plate 75 Grid!

It's like something just gives out!

HELP!!!!! <

::I hate to say this but it sounds like you have no idea what you're talking about.  "I see 50 plate 75 grid?"  That's not what you first posted.  50 plate - 500 mA.  75 grid - 75 mA.  Big difference.

I'd strongly suggest you find a local "Elmer" who knows about amplifiers and is close enough to drop by and see what's going on to help you out.

BTW it's not uncommon for light-duty amateur radio amps (like the AL-80B and many others) to simply melt their internal connections and start behaving in an unusual manner.  My own AL-80B melted its plate connections, and I had to solder them to correct the problem: Which had nothing at all to do with SWR, mismatch, operator error, or anything else.  

WB2WIK/6
 
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W1DY
Member

Posts: 29




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« Reply #8 on: January 20, 2008, 07:46:29 PM »

Umm....Now where did you see me post 750 Plate??


It has been 75 since I posted my original....


I do want to thank you for your statement that I have no idea what I am talking about!

That was very mature and Constuctive ....Kudos!

BRAhhhh..VooHhhhh.

Do you treat everyone that way...or just YL's???

Whiskey Tango Foxtrot....


Anyway...I found that I have a bad Primary tube....
replaced it and everything loads properly.....

I still need to change out those Antenna Coils..

Wendy




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WB2WIK
Member

Posts: 20537




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« Reply #9 on: January 21, 2008, 08:17:36 AM »

Sorry, Wendy.  I didn't notice your name or that you're a YL, it just sounded like you were contradicting yourself.  In reality, I just didn't understand what you were saying.

So, the problem was the 3-500Z tube itself?  Please let us know, because that's an interesting tidbit of info.  I've seen 3-500Z's fail in many different amps over many years but I never saw the kind of failure you describe, where it's okay up to a certain power level and then "poof," it's not.  That's a new one on me.

In my experience, normally the tube just shorts out and that's that.

73

Steve WB2WIK/6
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W1DY
Member

Posts: 29




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« Reply #10 on: January 21, 2008, 12:55:07 PM »

It was really driving me up a wall...

The tube I had in there was an RF parts 3-500ZG.


I remembered that I had a spare 3-500 Eimac tube sitting on the shelf, and just decided to swap tubes in an effort to eliminate the Amp...and/Or add to the odds that the problem was in the feedline/Connectors/Antenna Balun, as I had originally suspected.

Imagine my suprise when the Eimac tuned up 600 Watts no problem!

So I pulled the Eimac and re-installed the RF Parts 3-500ZG and the problem returned!

With the RF Parts tube..I could start tuning the amp, and as soon as I hit @400 Watts the Plate and Grid meters would drop!
If I backed off on Driver power to lower the output below 400 Watts the Meters would jump back up to their normal levels!

Oh Well....
I ordered a new tube from RF parts today...



My Husband called Alpha Delta today to discuss the coil melting issue, and told me that A-D has confirmed that this situation was likely caused by something called a Carona Effect on the antenna ends.

That's a new one on me.....but what really shocked me was that A-D is sending me a NEW ANTENNA FREE OF CHARGE!!!

They said that this has happened before under certain conditions, and they have made changes to the design to combat this issue!

Since my Antenna is an older version, they thought the best solution was to replace the antenna completely!

This is WAY MORE than I expected!!

I was hoping that, at best, they would let me BUY a new set of coils!

A-D has made a customer for life!

Wendy




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WB2WIK
Member

Posts: 20537




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« Reply #11 on: January 21, 2008, 03:57:17 PM »

Told ya (about Alpha Delta)...that's why I recommended you contact them.  They own up to problems very well and in a mature manner, and I'm not surprised about your experience.

The "tube is good to 400W and then not!" is absolutely a new one on me, too.  I've never seen that happen.  Maybe the guys who build hundreds of amps have.

Now if only we'd get some sunspots....

WB2WIK/6
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