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Author Topic: Valiant with fuzzy carrier  (Read 6488 times)
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KB5MD
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« on: February 25, 2012, 01:01:20 AM »

My Valiant has a fuzzy carrier appearance on the scope when operating with vfo but has good sharp carrier indication when on crystal .  All voltages and resistances check okay on the vfo tube.  Anyone have any ideas as to what will cause this or has anyone had a similar problem with a valiant.  It does this on all bands.
I hate like the dickens to pull that VFO out as it looks almost impossible.  HELP!
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WQ9E
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« Reply #1 on: February 25, 2012, 08:10:36 AM »

Has the VR tube dropping resistor been replaced with a higher wattage unit?  Even if this isn't the cause of the current problem it should be done before there are additional issues.  This replacement can be done through the left side (your left looking from the front) without removal of the entire VFO unit, only the top and left cover need to come off.

If the dropping resistor has been replaced first try a new keyer tube, a little heater to cathode leakage in this tube will hum modulate the VFO.  A bad VR tube or a problem with the 6AU6 VFO tube could also be the issue and these can be replaced through the  top of the VFO without removal of anything but the cover.
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Rodger WQ9E
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WD5JKO


« Reply #2 on: February 25, 2012, 08:39:22 AM »

My Valiant has a fuzzy carrier appearance on the scope when operating with vfo but has good sharp carrier indication when on crystal . 

  I wonder if the "fuzzy" is hum (60 or 120 hz), or possibly if the carrier wave has an off frequency component? For example, I use a Knight V44 VFO with my Gonset G76. This VFO runs on 80m when the G-76 is on 40-10m, so for 10m output the VFO is multiplied 8X. So on 10m, the carrier on the scope has two levels; the one at 29 Mhz, and another somewhere else. The scope shows a highlighting at the lower level. If I switch to a 7.250 crystal, this effect goes away. When on a VFO, if I open up the oscilloscope sweep to see the 29 Mhz waveform, I notice that it is not a pure sine wave. Switch to a crystal and the wave is pure.

Jim
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w1vtp
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« Reply #3 on: February 25, 2012, 07:24:45 PM »

My Valiant has a fuzzy carrier appearance on the scope when operating with vfo but has good sharp carrier indication when on crystal . 

  I wonder if the "fuzzy" is hum (60 or 120 hz),

<SNIP>
Jim
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Hum on a carrier is easy enough to figure out.  Put the scope on line sync or if you have a calibrated scope you can set the trace speed to either 16.7 ms (60 Hz time period) or 8.3 ms (120 Hz time period) If one or the other matches then it's 60 Hz or 120 Hz. 

A
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KB5MD
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« Reply #4 on: February 25, 2012, 09:45:42 PM »

Worked on the Valiant most of the afternoon, never found the problem, but it just stopped.  Hope it stays that way.  I hate intermittents.  Tnx for the help anyway.  Grin
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flintstone mop
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« Reply #5 on: February 26, 2012, 07:23:47 AM »

Might be a shielding or grounding inside the TX.
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Fred KC4MOP
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« Reply #6 on: February 26, 2012, 11:26:43 AM »

If it suddenly went away it sounds like an intermittent ground creating either hum or a parasitic.
Replace with a 6AH6 the next time youre in it; better stability and rugged.

Carl
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Rob K2CU
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« Reply #7 on: February 28, 2012, 12:45:13 PM »

It the rig was a kit build, then the next time you have its pants down, recycle/tighten all the screws, especially the tube sockets, even in the VFO.
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The Slab Bacon
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« Reply #8 on: February 28, 2012, 02:57:52 PM »

One of the things that I have always hated with Valiants and Rangers was the horrible lack of shielding between the RF and audio sections. I so many times wondered how they didn't become noise and hum generators.

Most of the ones I have ever done, have a few extra "dams" shielding the low level audio sections better and seperating the loading caps totally from the audio sections. One mod that I have never regretted doing!

The lack of shielding in both of them makes proper bypassing very important, I even add a few extra in different spots just for good luck. It has always payed off!! Also the long mic inpoot cable that goes from the front of the chassis to the rear mounted mic connector is just an abomination. If you run a real tall grid inpoot resistor, it leaves you wide open for high-impedance hummage and niose pick-up.
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"No is not an answer and failure is not an option!"
w1vtp
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« Reply #9 on: February 28, 2012, 03:47:54 PM »

Roy

Where the problem was there and then went away, I have a couple of observations: 

1) Did you receive a problem report while on the air as you were getting the strange display on the scope? 

2) If you did, then you can consider that the scope picked up on a problem.  If you did not, then consider that you might have had a temporary setup problem with your scope connection.

What kind of connection are you making with the scope, just for edification.

Al
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