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Plate current is a fixed meter shunt. What is adjustable is the grid current metering. And the high voltage meter, but you don't want to mess with that unless you have a real HV probe. It's not critical anyway. Grid metering is. On Fri, 03 May 2024 19:52:31 -0700 "K6OXN Bob via groups.io" <bobk6oxn@...> wrote: I do know I have to readjust the Plate current meter reading -- 73 -Jim NU0C
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It appears that now, my older Eimac 3-500Z tubes are the cause of the parasitic oscillations. I replaced the tubes with a newer set of 3-500ZG's and it seems to be working much better.? It seems the tubes were a problem under load I also replaced the parasitic chokes resistors with some 100 ohm 5 watt, MOF resistors.? Can't see any appreciable lowering of power out or tuning problems. I do know I have to readjust the Plate current meter reading, so will be taking it apart again. Will keep my fingers and toes crossed hoping for the best now. Thanks for all the hints and advice.
73? Bob
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Reducing the HV can be done with a variac, lightbulb, heater elements, ?etc. but the filament primary needs to be isolated from the HV transformer primary.
On Friday, May 3, 2024 at 02:45:34 PM EDT, John W4BFS <blivetbell@...> wrote:
Sounds to me like big vhf parasitic oscillation ¡ to start with you need to get the hv supply power reduced for testing without destruction ¡. A very handy thing to have is a high power series ballast ¡. What is needed are something like floor heater cones or large incandescent bulbs with switching arrangement ,,, do you feel this?
Well, I am at my wits end. I replaced the 47 ohm carbon resistors with 47 ohm 5 watt metal oxide film resistors and now the same thing is happening. Got the indication that there was an arc and then lost the amp. Have it on the bench and the resistors show high heat and cracked ceramic coating.? I have spares so can replace, but now I am wondering where and how to find if there is a parasitic oscillation.? I don't know where to look or how. I cannot see anything when tuning up and cannot see any other indications.? I can use some help or suggestions.
73? Bob
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Bob,
Just so I understand fully,
When you "key" the amp (no driving power) the plate current "goes to max"??
On my L-4B the plate current max is? 1A !? If it is indeed MAX (1A) the power supply transformer will likely be "groaning and the circuit breakers would likely open!!
Does this happen with the coaxial cable from the IC-7610 not connected? and? "keying" it ?
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On Fri, May 3, 2024 at 02:22 PM, K6OXN Bob wrote:
Just got it back together after a full inspection.? Burnished the TR relay contacts, dirty but not arced. Now notice on low power CW mode, the Plate Current goes to max when I keyup and then takes awhile to reset back to 0 after releasing the key. This is with my 7610 and it releases when I unkey.? Studying the schematics to see where this hangup might be. Its as if something is setting and then not releasing when I unkey.? Also when the plate current is at max the audio on the SDR is garbled. Without the amp and keying with about 20 Watts of drive from the 7610 it seems ok.? Will keep looking at suspect items.
73? Bob
? --
73/Rick
W4XA
*Every post is created using Linux
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Just throwing spaghetti against the wall here... Maybe your 7610 does not like the input circuit of the amp and is breaking into oscillation? Maybe you still have a relay issue. Hot switching can cause bad things to happen. Check for damaged plate choke or bypass capacitors. Excessive plate current can be a symptom of way too much drive and/or severe mis-tuning. What is happening with the grid current when this happens? Always start tune up with low drive and overcoupled Load. You might also check the input tuning adjustments per the manual procedure. You haven't said if you checked the grid current calibration. Do it. 73 -Jim NU0C On Fri, 03 May 2024 14:22:51 -0700 "K6OXN Bob via groups.io" <bobk6oxn@...> wrote: Just got it back together after a full inspection.? Burnished the TR relay contacts, dirty but not arced. Now notice on low power CW mode, the Plate Current goes to max when I keyup and then takes awhile to reset back to 0 after releasing the key. This is with my 7610 and it releases when I unkey.? Studying the schematics to see where this hangup might be. Its as if something is setting and then not releasing when I unkey.? Also when the plate current is at max the audio on the SDR is garbled. Without the amp and keying with about 20 Watts of drive from the 7610 it seems ok.? Will keep looking at suspect items.
73? Bob
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Bob,
I know you probably
don't want to hear this, but have you considered 'exorcism'?
Keep plugging away at
it and I'm sure you'll figure it out.
73 de Steve, NR4M
On 5/3/2024 5:22 PM, K6OXN Bob wrote:
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Just got it back together after a full inspection.? Burnished the
TR relay contacts, dirty but not arced. Now notice on low power CW
mode, the Plate Current goes to max when I keyup and then takes
awhile to reset back to 0 after releasing the key. This is with my
7610 and it releases when I unkey.? Studying the schematics to see
where this hangup might be. Its as if something is setting and
then not releasing when I unkey.? Also when the plate current is
at max the audio on the SDR is garbled. Without the amp and keying
with about 20 Watts of drive from the 7610 it seems ok.? Will keep
looking at suspect items.
73? Bob
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Just got it back together after a full inspection.? Burnished the TR relay contacts, dirty but not arced. Now notice on low power CW mode, the Plate Current goes to max when I keyup and then takes awhile to reset back to 0 after releasing the key. This is with my 7610 and it releases when I unkey.? Studying the schematics to see where this hangup might be. Its as if something is setting and then not releasing when I unkey.? Also when the plate current is at max the audio on the SDR is garbled. Without the amp and keying with about 20 Watts of drive from the 7610 it seems ok.? Will keep looking at suspect items.
73? Bob
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I have tried 2 different sets of tubes. Both were matched sets and seem to work perfect in my friends L4B..
Bob
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This has been going on for a while, so please excuse me if I ask if you have tried different tubes.
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Friday, May 3rd, 2024 at 2:59 PM, K6OXN Bob <bobk6oxn@...> wrote:
I have looked very closely at the tuning caps and cannot find any areas of arcing. It now seems that the problem is the TR relay is hanging up with some contact not releasing. I am going to remove it and look at burnishing the contacts, and if not possible, I do have a NOS replacement relay.? I don't have high power series ballast or a bunch of incandescent bulbs.? So I will keep looking.? Thanks
73? Bob
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I have looked very closely at the tuning caps and cannot find any areas of arcing. It now seems that the problem is the TR relay is hanging up with some contact not releasing. I am going to remove it and look at burnishing the contacts, and if not possible, I do have a NOS replacement relay.? I don't have high power series ballast or a bunch of incandescent bulbs.? So I will keep looking.? Thanks
73? Bob
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Sounds to me like big vhf parasitic oscillation ¡ to start with you need to get the hv supply power reduced for testing without destruction ¡. A very handy thing to have is a high power series ballast ¡. What is needed are something like floor heater cones or large incandescent bulbs with switching arrangement ,,, do you feel this?
toggle quoted message
Show quoted text
Well, I am at my wits end. I replaced the 47 ohm carbon resistors with 47 ohm 5 watt metal oxide film resistors and now the same thing is happening. Got the indication that there was an arc and then lost the amp. Have it on the bench and the resistors show high heat and cracked ceramic coating.? I have spares so can replace, but now I am wondering where and how to find if there is a parasitic oscillation.? I don't know where to look or how. I cannot see anything when tuning up and cannot see any other indications.? I can use some help or suggestions.
73? Bob
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I don't recall the symptoms you are having, but have you checked the plate tuning cap for any signs of arcing? Bill N0CU
Well, I am at my wits end. I replaced the 47 ohm carbon resistors with 47 ohm 5 watt metal oxide film resistors and now the same thing is happening. Got the indication that there was an arc and then lost the amp. Have it on the bench and the resistors show high heat and cracked ceramic coating.? I have spares so can replace, but now I am wondering where and how to find if there is a parasitic oscillation.? I don't know where to look or how. I cannot see anything when tuning up and cannot see any other indications.? I can use some help or suggestions.
73? Bob
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Well, I am at my wits end. I replaced the 47 ohm carbon resistors with 47 ohm 5 watt metal oxide film resistors and now the same thing is happening. Got the indication that there was an arc and then lost the amp. Have it on the bench and the resistors show high heat and cracked ceramic coating.? I have spares so can replace, but now I am wondering where and how to find if there is a parasitic oscillation.? I don't know where to look or how. I cannot see anything when tuning up and cannot see any other indications.? I can use some help or suggestions.
73? Bob
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The plate chokes in my L7 are copper with a coating of some type but can be soldered well. I have not put the Metal Oxide resistors on them yet and still using amp at a lower power level that is working great.?
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Not so sure of this. I think aluminum can be soldered using aluminum solder and a flux like borax. A problem with aluminum is that pure aluminum develops a layer of oxide almost immediately. The layer is only about a molecule thick but prevents further oxidation and gives trouble with soldering. The oxide is also a very poor conductor.
I used to repair RCA ribbon microphones. The ribbons are made of 100% pure aluminum foil (made originally for capacitors). It is soldered onto the pole piece clamps after stretching using aluminum solder and a very hot (1000F) iron. I was taught how to do this by a VP of engineering at RCA acoustical products.
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On 4/30/2024 5:27 AM, Jim VE7RF wrote: You can't solder aluminum anyway.
_._,_._,_
------------------------------------------------------------------------
Groups.io Links:
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
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You can't solder aluminum anyway.?
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Message /g/DRAKE-RADIO/message/77423 . On Sun, 28 Apr 2024 20:26:30 -0700 "K6OXN Bob via groups.io" <bobk6oxn@...> wrote: I did not see the referral for that articl -- 73 -Jim NU0C
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I did not see the referral for that article but have now studied it and think I might use the MOF resistors I have. I have several 100 ohm 5 watt resistors, I think I will place in my L7 and see how it goes. I did find some old stock 47 ohm 2 watt carbon resistors, but they are hard to solder. I have to use some emory cloth on the leads so I can pre-tin them.? Still have to use some extra wattage to solder to the copper plated chokes that Drake placed in the L7.
73? Bob
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Did you read this link that I posted previously? On Sun, 28 Apr 2024 13:37:37 -0700 "K6OXN Bob via groups.io" <bobk6oxn@...> wrote: would the newer metal oxide film resistors rated at 5 watts be a better replacement for the old carbon resistors?? I am looking at replacing the 47 ohm carbon 2 watt resistors in my L7 with 47 ohm 5 watt mof resistors. -- 73 -Jim NU0C
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would the newer metal oxide film resistors rated at 5 watts be a better replacement for the old carbon resistors?? I am looking at replacing the 47 ohm carbon 2 watt resistors in my L7 with 47 ohm 5 watt mof resistors.
73? Bob
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Jim Shorney