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Author Topic: Hum in DX-100  (Read 9815 times)
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W1UJR
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« on: April 18, 2005, 07:26:58 AM »

Quick question to perhaps save me from lugging this beast out to the office. Most of my test gear and stash of spare parts is at the office.

My trusty and crusty DX-100 seems to have developed a very pronounced hum on the carrier. Happens in both fone and CW, so that should cross out the modulator section. In fact I pulled the 1625s and the hum was still present.

For a quick bench test I swapped out the VFO and driver tubes, also swapped out the 6146s, still present. Swapped out the rectifer tubes as well, still there.

I was hoping for a easy tube fix so I did not have to move the beast.
The one thing I have not tried is running it on a XTAL, did not have one on hand but can grab one from the office today.

Any suggestions of where to look, thinking someone may have run into this before.

Tnx guys!


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K1JJ
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"Let's go kayaking, Tommy!" - Yaz


« Reply #1 on: April 18, 2005, 11:22:00 AM »

Hi Bruce,

Well, looks like you're trying to fix it w/o test gear for now. So, I would get a few HV electrolytic caps with clip leads and put them across various power supplies looking for the hum reduction. Maybe a bad filter cap somewhere?

Otherwise, lug in a scope and put the rig into a dummy load and probe around until you see the hum.   Hum is about the easiest thing to find vs: a problem like distortion, etc, so you'll dig it out soon.

73,
T
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W1UJR
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« Reply #2 on: April 18, 2005, 10:08:26 PM »

Hi Tom,

Like the new avatar!!!!!!!!!

Yes, you were correct, one of the electrolytics in the B+ opened up.
I jumped another cap across it and like magic the hum was gone.

I did have to drag it out to the shop, too little light in the barn and for safety sake I felt better seeing what I was doing.

So, need to order up some caps.

I did get DX-100 #2 on the air this evening.
This one is bone stock, no mods, bought it from the builder about 5 years ago.
This guy did a great job, it was a pleasure to clean up, not even going to do the PTT mod on this one, staying stock.

I did hi-fi the audio amp section as per Timmy, so expect to have on air tomorrow.

73 Bruce W1UJR



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K1JJ
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"Let's go kayaking, Tommy!" - Yaz


« Reply #3 on: April 18, 2005, 11:03:50 PM »

Good going, OM.

Ahhhhh, wish the whirl were that EZ all the time, Bruce.

To have found it that quickly, you must be a CIE grad, no?

T

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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
w3jn
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« Reply #4 on: April 19, 2005, 07:08:49 AM »

So Bruce, how many different D-104s do you have, and are you going to run every different permutation of DX-100/D-104 on the air?

Tom Vu - isn't that "Bob", the founder of the Church of the Subgenious?
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K1JJ
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« Reply #5 on: April 19, 2005, 12:45:28 PM »

Yep, that's right, John -

I've got a few more coming later on that I liked.

I was looking over some of the "Mungus" posts and was surprised to see your Rifleman's woody on that forum too.   :lol:

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
W1UJR
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« Reply #6 on: April 19, 2005, 12:56:18 PM »

Quote from: w3jn
So Bruce, how many different D-104s do you have, and are you going to run every different permutation of DX-100/D-104 on the air?

Tom Vu - isn't that "Bob", the founder of the Church of the Subgenious?


Hi John,

Only two DX-100 and two D-104s at the moment.
I like the DX-100s, a fine, simple transmitter that covers 160.
This one is soon to be the "barn transmitter" while I keep the really good stuff safe and secure at office.

Just redid the audio section, it had a leaky cap in the grid input to the 12BY7, make it sound very "yellowie".
This is a nice clean unit, no mods at all, so I did a nice job with the audio upgrades.
I should have it on the air this evening, if my cold/flu goes away.

Of course, I have yet to work the most famous "JN" station for he is rare DX.

-Bruce


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w3jn
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« Reply #7 on: April 19, 2005, 02:02:00 PM »

I know it, Bruce.  I'm going thru agony with my station... things started out innocently enough with the purchase of a mike mixer at Timonium (I was using an old hissette deck as a mike preamp).  Gave me the chance to go balanced audio - an advantage, so I'm told, for RF immunity.  

OK FINE.  I now have horrendous RF feedback, not from the mixer but from the EQ which, up to now, had no problems (ran it unbalanced).  I even had Deutch Welle interposed on my signal (that came from the mixer til I used a few ferrite snapons).

Thought I had it licked Saturday with a bunch of snapon ferrites, revised lead dress, etc.,  then Sunday I fired the rig up and it was worse than ever.  QTF.  That's disheartening to re-do the whole shebang only to have it much WORSE than it was.

Oh well, I'll get it sorted out.

Tom Vu - have you seen the Cole V2.0 episode on thescambaiter.com?  Dumb mugu paid over $5 grand to have a busted dryer to be shipped to Lagos.

73 John
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WA1GFZ
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« Reply #8 on: April 20, 2005, 11:14:55 AM »

Bruce,
You were good and loud last night but must have crapped out before
your call. We were on until 10:15.  fc
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WA1GFZ
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« Reply #9 on: April 20, 2005, 11:18:52 AM »

Those snap on beads you have saved the day during an EMI qualification test I was running a while back. I was running 200 V/M and trashing a reference supply outside the chamber. I remember I had a handful of the snap on beads in my truck. 3 in series did the trick.
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