Re: TR7 - 40 meter oscillation
Here is another somewhat obscure point regarding the 2nd Mixer. I also saw it inked in to a paper service manual that I came across so I know there are at least two people have done this. :) Also don't overlook the grounding of the ALC board. The two screws are a mechanical ground connection to the HPF module. 73 -Jim NU0C On Sun, 21 Apr 2024 23:15:44 -0700 "Raoul Meunier via groups.io" <rmeunier@...> wrote: Thanks Jim, Kam and Gary for your comments and pictures, very explanatory!?I definitely need to do more work after looking at those ferrite beads over several wires.
Today I added a ground strap to the rear HPF board with good results. I was able to increase the pre-driver pot to get 60 watts on 10 meters and no oscillation on 40 meters, loading the 4-band Yagi antenna. However, when I went through the tuner to reduce the SWR, the scary oscillation immediately started, so I reduced the pre-driver pot to get 50 Watts on 10 meters. I can go through the tuner with no problems now, on 40m.
For some other reason, I can't get more than 60 Watts on 10 meters (using the Dummy Load).
I'll look for those ferrite beads and install them.
Thanks again!
73 de Raoul CE3RY
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Re: L7 makes alot of smoke
Bob,
Thank you for keeping us informed of your progress and success.
73,
Evan, K9SQG
On Sunday, April 21, 2024 at 07:05:45 PM EDT, K6OXN Bob <bobk6oxn@...> wrote:
RF Parts and Fedex came thru. Received the replacement Parasitic Choke resistors.? Ordered a spare set also and also 2 door knob capacitors 500 pf 7.5kv plate capacitors. Built up a small 2 strip copper attachement to hold the capacitors and rebuilt the chokes.? Also I forgot of course the .82 ohm fuse resistor in the PS went pop also. Replaced it and after a tenative slow power up checking things the L7 is back amongst the living.? Drake sure built an Armour plated PS and Amp. Is working just fine now on 40 meters my preferred band with 60-70 watts in from a TR7 I get a nominial 1 kw out of the L7.? Thanks for all the info and the help from our files and photo sections are also helpful.? Now to see if Karma has forgiven me.
73? Bob
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When it was serviced, did they replace the can capacitor? ?I have had similar failures due to this cap opening.?
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 21, 2024 at 21:24, Lyndon VE7TFX < lyndon@...> wrote: > Check your VOX again.
Already tried that, but I want back and tried again. Worked through
pretty much every permutation of gain and anti-vox possible. No joy.
--lyndon
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Re: L7 makes alot of smoke
The oem Drake plate block caps in the L7 are failure prone. They went cheap, and used a pair of disc ceramic caps.? When they fail, they typ fail shorted.... which will take out the .82 ohm HV fuse.?
You might want to also check the safety choke across the load cap as well. It could have easily failed open during a HV fault condition.?
?The pair of 500 pf @ 7.5 kv rated HEC ceramic doorknob caps you installed is the correct component for the plate block cap assy.??
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Re: TR7 - 40 meter oscillation
Did you also add a ground strap at the other corner where there is an empty screw hole in the inner chassis wall? 73 -Jim NU0C On Sun, 21 Apr 2024 23:15:44 -0700 "Raoul Meunier via groups.io" <rmeunier@...> wrote: Thanks Jim, Kam and Gary for your comments and pictures, very explanatory!?I definitely need to do more work after looking at those ferrite beads over several wires.
Today I added a ground strap to the rear HPF board with good results. I was able to increase the pre-driver pot to get 60 watts on 10 meters and no oscillation on 40 meters, loading the 4-band Yagi antenna. However, when I went through the tuner to reduce the SWR, the scary oscillation immediately started, so I reduced the pre-driver pot to get 50 Watts on 10 meters. I can go through the tuner with no problems now, on 40m.
For some other reason, I can't get more than 60 Watts on 10 meters (using the Dummy Load).
I'll look for those ferrite beads and install them.
Thanks again!
73 de Raoul CE3RY
-- 73 -Jim NU0C
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Re: TR7 - 40 meter oscillation
Thanks Jim, Kam and Gary for your comments and pictures, very explanatory!?I definitely need to do more work after looking at those ferrite beads over several wires. Today I added a ground strap to the rear HPF board with good results. I was able to increase the pre-driver pot to get 60 watts on 10 meters and no oscillation on 40 meters, loading the 4-band Yagi antenna. However, when I went through the tuner to reduce the SWR, the scary oscillation immediately started, so I reduced the pre-driver pot to get 50 Watts on 10 meters. I can go through the tuner with no problems now, on 40m.? For some other reason, I can't get more than 60 Watts on 10 meters (using the Dummy Load). I'll look for those ferrite beads and install them. Thanks again! 73 de Raoul CE3RY 
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Re: TR7 - 40 meter oscillation
Collins had the same issues originating from the use of tube socket mounting screws as grounds for critical RF circuits, especially in KWM-2¡¯s and S Lines. A lot of problems were repaired by simply loosening these screws a bit and retightening them.
Gary
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On Apr 21, 2024, at 7:57?PM, Kam VA6CA <cwopqrp@...> wrote:
Hi Raoul,
This happened to my TR7 last year. The oscillation was fixed by tightening every single chassis screw. They came quite loose over time.
Good luck and 73....
Kam, VA6CA?
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Check your VOX again. Already tried that, but I want back and tried again. Worked through pretty much every permutation of gain and anti-vox possible. No joy. --lyndon
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Re: TR7 - 40 meter oscillation
Hi Raoul,
This happened to my TR7 last year. The oscillation was fixed by tightening every single chassis screw. They came quite loose over time.
Good luck and 73....
Kam, VA6CA?
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Check your VOX again.?
Steve Wedge, W1ES/4
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 21, 2024 at 18:59, Lyndon VE7TFX < lyndon@...> wrote: That's the best explanation I have for what's going on around
here :-P
The T-4XB was tuning up okay (100W out), but only putting out about
15 watts on CW. I swapped V1, and all that did was drop the power
output on tune to 60W. So I hauled it off to the bench for a closer
look.
Meanwhile I dragged the T-4/R-4 off the shelf and set those up.
The T-4 tunes up fine on 15 (100W out), but on CW, while it sends
dits just fine, when I send a dash it drops back into receive mode
after about 1.5xdot time. I thought it might be the keyer, so I
plugged in the bug, and sure enough, hold down the dash paddle and
I get maybe a couple of hundred milliseconds of transmit, then the
T-4 goes back to receive mode.
For the brief moments when it does transmit, the waveform looks
perfectly normal.
Will somebody please tell me W.T.F. is going on here? Because I
don't have even the beginnings of a glimmer of a clue.
BTW, the T-4 got the full WB4HFN treatment right before it came to
me, which makes this even more baffling.
Also, I haven't tested SSB because my 90-degree microphone plug
collides with the bottom lip of the cabinet. A very expensive
S830 is now on its way, so I'll be able to solve that with a
pigtail in a couple of days.
--dazed and confused
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Re: L7 makes alot of smoke
RF Parts and Fedex came thru. Received the replacement Parasitic Choke resistors.? Ordered a spare set also and also 2 door knob capacitors 500 pf 7.5kv plate capacitors. Built up a small 2 strip copper attachement to hold the capacitors and rebuilt the chokes.? Also I forgot of course the .82 ohm fuse resistor in the PS went pop also. Replaced it and after a tenative slow power up checking things the L7 is back amongst the living.? Drake sure built an Armour plated PS and Amp. Is working just fine now on 40 meters my preferred band with 60-70 watts in from a TR7 I get a nominial 1 kw out of the L7.? Thanks for all the info and the help from our files and photo sections are also helpful.? Now to see if Karma has forgiven me.
73? Bob
|
That's the best explanation I have for what's going on around
here :-P
The T-4XB was tuning up okay (100W out), but only putting out about
15 watts on CW. I swapped V1, and all that did was drop the power
output on tune to 60W. So I hauled it off to the bench for a closer
look.
Meanwhile I dragged the T-4/R-4 off the shelf and set those up.
The T-4 tunes up fine on 15 (100W out), but on CW, while it sends
dits just fine, when I send a dash it drops back into receive mode
after about 1.5xdot time. I thought it might be the keyer, so I
plugged in the bug, and sure enough, hold down the dash paddle and
I get maybe a couple of hundred milliseconds of transmit, then the
T-4 goes back to receive mode.
For the brief moments when it does transmit, the waveform looks
perfectly normal.
Will somebody please tell me W.T.F. is going on here? Because I
don't have even the beginnings of a glimmer of a clue.
BTW, the T-4 got the full WB4HFN treatment right before it came to
me, which makes this even more baffling.
Also, I haven't tested SSB because my 90-degree microphone plug
collides with the bottom lip of the cabinet. A very expensive
S830 is now on its way, so I'll be able to solve that with a
pigtail in a couple of days.
--dazed and confused
|
Re: TR7 - 40 meter oscillation
I don't know if this will be helpful or not but I noticed that in later version Drake shortened the wires between the HPF and LPF modules and added several ferrite beads. I have attached some internet pics with examples. Beads have also been found on one of the wires connecting to the ALC board but I need to look at one to tell you which. There were also several changes to the 2nd Mixer board which I think has been discussed here recently that seem to be at least in part stability related. One of my rigs was demonstrating some bat-feces crazy instability because of leaky driver transistors. *Very carefully* measure the base voltage of the drivers and finals in RX. It should be very close to zero volts. 73 -Jim NU0C On Sat, 20 Apr 2024 14:57:57 -0700 "Raoul Meunier via groups.io" <rmeunier@...> wrote: Jim, thanks very much for the explanation on the value of the capacitors. I don't have Tantalums at home but I'll try electrolytics.
Regarding the oscillation, I ended up installing a ground strap at the point you mention in the HPF. You gave me this tip in the past and it worked for me in that case. After that, I got more "room" to increase the pre-driver pot but it's still oscillating past that. I'm getting some 30 Watts on 10 meters now.
It's strange that this problem occurs in some rigs, not all of them. I believe it's due to the sum of many little factors that contribute to get the oscillation and one needs to cure all of them to get to a happy end. I'll keep on searching.
I'll come back with more info.
Thanks again!
73, Raoul
-- 73 -Jim NU0C
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Re: L7 makes alot of smoke
On Sat, Apr 20, 2024 at 05:52 PM, K6OXN Bob wrote:
I think I now know what caused my major fault.? I was trying to tune up on 15 meters because the Easter Island Dx station was so strong. Problem was it was on 21.262 which is not in the proper part of the band for a General Class license. Sometimes karma does get you.
73? Bob
Pretty sure the radio doesn't really know what frequency you're on!! But that Karma can come in other forms as well, --
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Re: L7 makes alot of smoke
Bob,
Glad you found the issue which was along the line of a parasitic, self-oscillation, or frequency multiplying. ? Some of the newer amps have circuitry to prevent incorrect bandswitch positions which is almost a requirement for solid state amps. ?Good luck with the repairs and informing us of the causative factor.
73,
Evan, K9SQG
On Saturday, April 20, 2024 at 08:52:40 PM EDT, K6OXN Bob <bobk6oxn@...> wrote:
I think I now know what caused my major fault.? I was trying to tune up on 15 meters because the Easter Island Dx station was so strong. Problem was it was on 21.262 which is not in the proper part of the band for a General Class license. Sometimes karma does get you.
73? Bob
|
Re: L7 makes alot of smoke
I think I now know what caused my major fault.? I was trying to tune up on 15 meters because the Easter Island Dx station was so strong. Problem was it was on 21.262 which is not in the proper part of the band for a General Class license. Sometimes karma does get you.
73? Bob
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Re: L7 makes alot of smoke
After a serious full inspection it seems that the only damage was the parasitic plate chokes and the coupling capacitors C39 and 40. I have spare parts coming from RF Parts so should have the amp up and running early next week.? Will keep everyone apprised as to final results.? Lots of careful inspection and cleaning of all areas have been accomplished.
73? Bob
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Re: TR7 - 40 meter oscillation
Jim, thanks very much for the explanation on the value of the capacitors. I don't have Tantalums at home but I'll try electrolytics.
Regarding the oscillation, I ended up installing a ground strap at the point you mention in the HPF. You gave me this tip in the past and it worked for me in that case. After that, I got more "room" to increase the pre-driver pot but it's still oscillating past that. I'm getting some 30 Watts on 10 meters now.?
It's strange that this problem occurs in some rigs, not all of them. I believe it's due to the sum of many little factors that contribute to get the oscillation and one needs to cure all of them to get to a happy end. I'll keep on searching.
I'll come back with more info.
Thanks again!
73, Raoul
|
Re: TR7 - 40 meter oscillation
Hi Raoul, I'm thinking the caps essentially follow the resistor color code. Brown-black-blue = 106, or 10000000 pF, 10uF. I could maybe measure one later to confirm. Try this: Slide the cover back on slowly until you reach the point where the oscillation recurred. This will give you a hint to the sensitive area. In my case I found it to be the rear board of the HPF module. This is where I placed the ground strap at the upper rear corner which finally cured it in two of my rigs. This seems to me to be a problematic area because the HPF module (including the ALC board) has SIX coaxial cables connected to it that run to various points in the radio and only one chassis ground at the opposite corner near the speaker. 73 -Jim NU0C On Sat, 20 Apr 2024 08:11:07 -0700 "Raoul Meunier via groups.io" <rmeunier@...> wrote: Hi All,
I'm working in my spare TR7 for I found a severe oscillation on 40 meters when using the Yagi antenna. It does not happen with the dummy load and it goes off if I reduce the pre-driver pot in the PA (pre-driver V2). Unfortunately, if I do that, the power on 10 meters goes down to about 20 Watts, so I need to fix this condition. I read every thread about the subject and proceeded with everything I found, installing grounding straps, cleaning contacts, cleaning Molex, changing star washers (corrosion), et cetera. Now I can reach about 50 Watts on 10 meters... with the cover off. With the cover on, the oscillation starts again.
I noticed this TR7 (#2901) does not have the Tantalum capacitors on the 10V and 5V lines on the bottom of the Parent Board and are shown in Figure 2-3 of the Service Manual. However, I can't find the value of these caps in the parts list. I would like to try this.
My other TR7 has those caps... but I found hard to interpret the colors on them.
Your comments, suggestions are always welcome.
Thanks.
73 de Raoul, CE3RY
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TR7 - 40 meter oscillation
Hi All,
I'm working in my spare TR7 for I found a severe oscillation on 40 meters when using the Yagi antenna. It does not happen with the dummy load and it goes off if I reduce the pre-driver pot in the PA (pre-driver V2). Unfortunately, if I do that, the power on 10 meters goes down to about 20 Watts, so I need to fix this condition. I read every thread about the subject and proceeded with everything I found, installing grounding straps, cleaning contacts, cleaning Molex, changing star washers (corrosion), et cetera. Now I can reach about 50 Watts on 10 meters... with the cover off. With the cover on, the oscillation starts again.
I noticed this TR7 (#2901) does not have the Tantalum capacitors on the 10V and 5V lines on the bottom of the Parent Board and are shown in Figure 2-3 of the Service Manual. However, I can't find the value of these caps in the parts list. I would like to try this.
My other TR7 has those caps... but I found hard to interpret the colors on them.?
Your comments, suggestions are always welcome.
Thanks.
73 de Raoul, CE3RY
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Jim Shorney
