The AM Forum
March 29, 2024, 05:12:57 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Turned on T3 and R390 today and RX noise is rising and falling  (Read 7451 times)
0 Members and 1 Guest are viewing this topic.
ke7trp
Contributing
Member
*
Offline Offline

Posts: 3659



« on: January 10, 2011, 01:27:27 PM »

RX noise on any band is rising and falling in a cyclic motion.  S0 to 20 up and down.  Carrier from Icom across the room shows the same thing.. 40db up to full scale, Then back down.  Worked all switches, Poked around for loose tubes ect.. 

Cant get it to stop. Does this on all bands.   Any idea where to start?  It seems that if you use this gear every day, Its fine for years. If you let it sit for even a month, Its then broken and needs repair.

This is an R390. NOT an A model.  Worked perfectly since recaped, Retubed, Cleaned, Aligned and painted last year.

I was thinking an AGC issue, However, This happens with the AGC off or on.  If you turn it off into MGC, Then turn the gain down, You still have a cyclic up and down S meter and noise reading.  Any ideas?

C
Logged
Todd, KA1KAQ
Administrator
Member

Offline Offline

Posts: 4310


AMbassador


« Reply #1 on: January 10, 2011, 01:32:53 PM »

I'm a bit confused, Clark. If I read your question correctly, you're receiving the same effect on other equipment as well? If so, that would seem to indicate to me that it's not your R-390 specifically. I'd be looking at the power line or aerial. I've seen this in high wind conditions before, just not to the extreme you're experiencing. Also not regular to a 'cyclic' nature, tracking instead with wind gusts.

Logged

known as The Voice of Vermont in a previous life
ke7trp
Contributing
Member
*
Offline Offline

Posts: 3659



« Reply #2 on: January 10, 2011, 01:35:54 PM »

No. Its just this R390.  Any band. Antenna, No antenna, I have now put a sig gen straight into the R390, The Gain of the RXer is rising and failling.

AGC on or OFF.
Any switch turned rocked.. Does not matter
Any RF gain level.
Voltage is steady at the wall.

Maybe an IF tube?Huh  I guess my next step is to lug out the TV7 and start checking tubes in the IF. 

C
Logged
ke7trp
Contributing
Member
*
Offline Offline

Posts: 3659



« Reply #3 on: January 10, 2011, 01:42:41 PM »

http://qik.com/ke7trp

Click on the R390 video.

C
Logged
flintstone mop
Contributing
Member
*
Offline Offline

Posts: 5055


« Reply #4 on: January 10, 2011, 10:03:53 PM »

C
You have a lot of strange things going on there these past few months.
You can break the R390 down and shoot an I.F. freq from a sig gen. If the R390 still displays this up and down, then it is something in the I.F. taking off and getting ready to motorboat.
And any RF gain level means RF gain fully counter clock wise and you still have this 60-80 carrier swinging back and forth?Huh Full CCW 1st I.f. is cut off. and any swinging carrier meter might be the I.F. oscillating or the Filters have a problem or leaking DC volts. Why Collins runs D.C. through them, I'll never know. The D.C. I'm talking about is AGC!!! AGC voltage goes through the filters. I isolated my filters with a .01 cap before and after the precious filters and jumpered the D.C. around them. I had a helluva time finding an AGC problem in my R390A. When it got warm the 11 volts of AGC on a strong BC station would dribble down to 1 volt and the meter would be pegged and any reception of radio signal was overload to the I.F.
So waz happenin'?
Fred
Logged

Fred KC4MOP
ke7trp
Contributing
Member
*
Offline Offline

Posts: 3659



« Reply #5 on: January 10, 2011, 10:13:52 PM »

No idea...  I guess I will have to yank it out of the rack and start working on it tomorrow or the next day Fred. Really annoying. 

The RF gain works. but even at a low level, I can hear the RX going up and down. 


C
Logged
ke7trp
Contributing
Member
*
Offline Offline

Posts: 3659



« Reply #6 on: January 10, 2011, 10:53:41 PM »

Got the damn thing out of the rack and on the bench and it was normal.  No more problem.. Great..  Put it back in the rack ontop of the T3 real fast and its working as normal. I have no idea what the heck was going on but the act of moving the R390 and fixed it. For now anyways.. I will report back if this condition comes back.

C
Logged
W7TFO
WTF-OVER in 7 land Dennis
Contributing
Member
*
Offline Offline

Posts: 2521


IN A TRIODE NO ONE CAN HEAR YOUR SCREEN


WWW
« Reply #7 on: January 10, 2011, 11:03:22 PM »

I keep a rubber mallet handy just for such gremlins.   Doesn't leave a mark but gets results.

73DG
Logged

Just pacing the Farady cage...
w3jn
Johnny Novice
Administrator
Member

Offline Offline

Posts: 4620



« Reply #8 on: January 10, 2011, 11:26:40 PM »

I'm betting one of the 6082 regulator toobs is loose in its socket.  Or something else associated with the regulator, perhaps the voltage ref tube, it seems to be oscillating at a very low rate.  Those 6082s are brutal on the sockets with all their heat rising upward.

Obviously the B+ is drifting around, hence the change in frequency.  The B+ drifting around is also manifesting itself in the guess-meter drifting up and down.
Logged

FCC:  "The record is devoid of a demonstrated nexus between Morse code proficiency and on-the-air conduct."
flintstone mop
Contributing
Member
*
Offline Offline

Posts: 5055


« Reply #9 on: January 11, 2011, 05:34:19 AM »

C
I had a not so similar problem when I had to tear into mine for the AGC problem.
The dam I.F. module was not tightened down completely. One screw was loose in a corner. I was able to get it to happen again by lossening one of the mounting screws.

Forgot about that
Fred
Logged

Fred KC4MOP
ke7trp
Contributing
Member
*
Offline Offline

Posts: 3659



« Reply #10 on: January 15, 2011, 01:52:19 PM »

Turned on the T3 and R390 a few moments ago and the trouble is back.  40 meters is rising to 30 DB down to 10 over and over.  Banged all over that radio with no change. Opened top lid and poked all around.  Its stuck rising and falling.

What a heck of a problem.. You get the radio on the bench and its fine.. THen you put it back in the case and a few days later, The trouble is back

C

Logged
Pete, WA2CWA
Moderator
Member

Offline Offline

Posts: 8154


CQ CQ CONTEST


WWW
« Reply #11 on: January 15, 2011, 04:59:09 PM »

Quote
THen you put it back in the case...
Roll Eyes
Logged

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
K1JJ
Contributing
Member
*
Offline Offline

Posts: 8893


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


« Reply #12 on: January 15, 2011, 08:39:36 PM »

Clark,

That's a strange problem about the cabinet making it die. Maybe the cabinet is holding in the heat just enough to cause this problem.     Are there any screws that may be touching a circuit when in the cabinet?

OK, here's what ya do...   Put the RX on the bench with the same sig gen and S meter reading as shown on the video. Take a hair dryer gun and blow some hot air onto all parts and see if the S-meter starts swinging. If it does, then use a can of that Radio Shack component cooler to spray individual parts to make it stop. This may zero you in to a bad part. (Don't spray the hot tube glass, of course)

The next thing to do is start taking voltage measurements. Johnny may be right about it being a swinging B+ or regulated + voltage cuz of the VFO or LO drift.  Check that regulated + voltage first and then all other voltages. 

If you can get it to fail with the heat, the VOM and cool spray will zero you in.  Maybe even clean some tube sockets with spray and move the tubes around in the scockets.

Let us know what you find and we'll go from there.  From the symptoms, this shud be an easy one to fix IF you can get it to die on the bench..

T
Logged

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.
ke7trp
Contributing
Member
*
Offline Offline

Posts: 3659



« Reply #13 on: January 15, 2011, 09:13:42 PM »

ITs just a bud case. Nothing is touching anything that I can see.  Really frusterated with this one. I put it back on the bench, Its rock solid for hours and hours and now its working again.  Thanks for the advice. I think I will get the heat gun out and start blasting parts with heat... although I dont think its temp related.  It starts this the second I turn it on cold.

C
Logged
K1JJ
Contributing
Member
*
Offline Offline

Posts: 8893


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


« Reply #14 on: January 15, 2011, 09:58:14 PM »

Be careful not to melt anything with that gun, like xfmr wax, etc.

Another idea came to me.  If you have no luck finding the problem on the bench, put it back in the cabinet with a clip lead hanging out attached to the regulated voltage that goes to the VFO/LO and another for the AGC/S-meter in case they are separate.   Hook it to the VOM and see if it swings around whe the problem occurs.  Sometimes ya gotta play its own game to win.

When on the bench, look for even SLIGHT voltage wavering. This may give a clue.

T
Logged

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.
ke7trp
Contributing
Member
*
Offline Offline

Posts: 3659



« Reply #15 on: January 15, 2011, 10:49:02 PM »

THats a good idea.. I am going to try that first.  I see a 2 volt Swing at the wall outlet.  That cant possibly do this right?  I am not using the balast tube. I am using some resistors.

C
Logged
w3jn
Johnny Novice
Administrator
Member

Offline Offline

Posts: 4620



« Reply #16 on: January 16, 2011, 08:00:41 AM »

Did you check the regulated voltages as I suggested above?
Logged

FCC:  "The record is devoid of a demonstrated nexus between Morse code proficiency and on-the-air conduct."
k4kyv
Contributing Member
Don
Member

Offline Offline

Posts: 10057



« Reply #17 on: January 16, 2011, 10:14:57 AM »

Sounds like 95% of my  radio problems.  I rarely have a textbook case of a straight-forward malfunction with a straight-forward solution.  It's nearly always intermittent and usually something I wouldn't have suspected in an entire lifetime.

The most outstanding, but typical, example in my memory occurred back in the 60's with a homebrew exciter.  The input stage went into self-oscillation and produced a very stable, clean carrier right in the middle of the 160m band on receive, even though in receive mode the entire HV plate supply was turned off by breaking the primary of the transformer with a relay.  No, it was not the relay.

I agree that the only way to fix the problem is to hang probes all over the receiver to allow you to measure vital signs while the receiver is in the cabinet and hope to catch the problem in the act.  Sometimes, even the presence of a VTVM or DVM probe  can affect whether the problem occurs. 

Besides the black hole swallowing up tools and parts while I am working on something, this has to be the most frustrating aspect of radio work.
Logged

Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

- - -
This message was typed using the DVORAK keyboard layout.
http://www.mwbrooks.com/dvorak
WQ9E
Member

Offline Offline

Posts: 3282



« Reply #18 on: January 16, 2011, 10:46:17 AM »

Clark,

Even something as solidly built as an R-390 is going to be affected by the mechanical stress of the support and fastening provided by a case.  My guess is a capacitor or other component is failing and being mechanically stressed by the case mounting.

With the receiver on the bench try lightly lifting the rear corners of the chassis and see if this makes it take off.  If this doesn't do it try slightly twisting the chassis and the front panel.  Depending upon the case used the chassis will be supported by the case while the front panel is exposed to other forces by the panel mounting screws.
Logged

Rodger WQ9E
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.055 seconds with 19 queries.