|
I never got that far but I have learned to avoid "off" tuning positions with the RF TUNE control. Some of the rigs are more sensitive than others.
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with Proton Mail secure email.
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On Friday, April 4th, 2025 at 2:04 PM, n4buq <n4buq@...> wrote: When there are spurious oscillations in the PA tubes, is there a particular frequency this usually occurs? In other words, does changing bands change the frequency of the oscillation? I'm just wondering what frequency I might try listening to in order to hear them.
Thanks,
Barry - N4BUQ
It is NOT normal. It is a sign that the amplifier needs to be
neutralized. Plate dip and power peak should be simultaneous. The
coincidence of these two is a very sensitive measure of neutralization.
For the T-4 and some other models Drake specifies setting the
neutralization using the coincidence but if the neutralization is not
almost correct this may be a difficult adjustment to make. A better way
to check neutralization is to measure the feed through of drive power to
the plate by disconnecting the screens of tetrodes or the plates of
triodes. Use something sensitive like a receiver or scope to see what is
coming through, then set the neutralization adjustment to null it. Once
that is adjusted you can check the neutralization via the Drake method,
that is see if the plate dip and power peak are simultaneous.
There is a great deal of information on neutralizing on the web.
You should be familiar with the theory of what is being done. The idea
is roughly to eliminate any positive feedback through the tubes by means
of a sort of bridge circuit. It is done to prevent the tubes from
oscillating. If that happens the oscillation will be uncontrolled and
destroy the tubes. In general neutralization is more critical at higher
frequencies. You can get approximate neutralization at, say 20 meters,
and then check it at 10 meters making any small adjustments necessary.
BTW, this is not a matter of the type of circuit used to match the
output to the antenna, neutralization is necessary for any type of
output pi-network or otherwise.
On 4/3/2025 6:53 AM, n4buq wrote:
I don't think I've ever owned a power meter and now I have one in my MN-2000.
Tuning up my TR-4, I notice that maximizing the output power doesn't
necessarily coincide with the "dip" in plate current but, instead, seems to
occur on the "edge" of that dip. Is this normal?
From many, many years ago, with only a plate meter, I always adjusted with the
dip at its minimum value but now I'm wondering if that wasn't yielding maximum
power output. Furthermore, I presume that getting the dip first and then
tweaking for maximum output is the most efficient way to run. Is that correct?
Is what I'm seeing normal? I presume so but after all these years, I'm
beginning to wonder.
If it matters, I'm currently only tuning into a Drake dummy load.
Thanks,
Barry - N4BUQ --
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks, Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
Yep. That¡¯s what I was trying to say.?
The reason it¡¯s done on 10 is because that¡¯s the most likely band that would give you trouble.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sat, Apr 5, 2025 at 09:05, Mike W5RKL via groups.io < mikew5rkl@...> wrote:
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks, Barry - N4BUQ
Mike, I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible. I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet. Thanks, Barry - N4BUQ Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq < n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
Steve,
I'll run through it that way.? As I said, all I did was monitor the output at the antenna jack with no dummy load.? Since the controls didn't seem to affect what I was seeing on the scope.? Perhaps it was mostly due to there not being a proper load resistance.? I'll report back - hopefully tomorrow.
Thanks so much! Barry - N4BUQ
Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq <n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
There should've been a comma:
Since the controls didn't seem to affect what I was seeing on the scope, perhaps it was mostly due to there not being a proper load resistance.
I hate it when that happens! Barry - N4BUQ
Steve, I'll run through it that way.? As I said, all I did was monitor the output at the antenna jack with no dummy load.? Since the controls didn't seem to affect what I was seeing on the scope.? Perhaps it was mostly due to there not being a proper load resistance.? I'll report back - hopefully tomorrow. Thanks so much! Barry - N4BUQ Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq <n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
We all have our moments, Barry. I pulled my TR-4Cw RIT offline because I was having power dropping off as I transmitted. I could watch the plate current and power out slowly fall and figured I had a gassy tube.?
I put it on the bench and got a rock-solid 180W out on 40 and 130W on 10. They¡¯re not new tubes but they¡¯re good enough.?
Checked everything and the neut needed touchup. Touched up the neut and Put it back on the desk. Power was falling off again.?
It turned out to be bad contact in the coax from the rig to the rig switch. I confirmed after putting it on the bench ?and using the short coax interconnect. Contact was bad. Reflowed the solder in the centre conductors and it seems okay.?
During this whole time, I decided to look at the cathode and screen resistors and they¡¯re all out of tolerance, so my work is never done!
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 20:46, n4buq < n4buq@...> wrote:
There should've been a comma:
Since the controls didn't seem to affect what I was seeing on the scope, perhaps it was mostly due to there not being a proper load resistance.
I hate it when that happens!
Barry - N4BUQ
Steve,
I'll run through it that way.? As I said, all I did was monitor the output at the antenna jack with no dummy load.? Since the controls didn't seem to affect what I was seeing on the scope.? Perhaps it was mostly due to there not being a proper load resistance.? I'll report back - hopefully tomorrow.
Thanks so much!
Barry - N4BUQ
Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq <
n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
I should do a voltage/resistance check at all the tubes but I'm afraid of what I'd find!? I think my next target is the 60/20/10 can cap.? I restuffed the cans in the AC-4 but haven't replaced the can caps in my 2-B, R-4B, or this TR-4.? The 2-B and R-4B seem operatively fine but I'm beginning to distrust this TR-4 just a bit mostly due to its age and condition.? The chassis isn't the prettiest of the three.? Not horrible but not all that good either.? Time to get the old ukumpucky removal process back in action.
Good luck with those cathode and screen resistors.? If they're still like the TR-4's design (and I presume so) then they're probably not terrible to access.
73, Barry - N4BUQ
We all have our moments, Barry. I pulled my TR-4Cw RIT offline because I was having power dropping off as I transmitted. I could watch the plate current and power out slowly fall and figured I had a gassy tube.?
I put it on the bench and got a rock-solid 180W out on 40 and 130W on 10. They¡¯re not new tubes but they¡¯re good enough.?
Checked everything and the neut needed touchup. Touched up the neut and Put it back on the desk. Power was falling off again.?
It turned out to be bad contact in the coax from the rig to the rig switch. I confirmed after putting it on the bench ?and using the short coax interconnect. Contact was bad. Reflowed the solder in the centre conductors and it seems okay.?
During this whole time, I decided to look at the cathode and screen resistors and they¡¯re all out of tolerance, so my work is never done!
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 20:46, n4buq <n4buq@...> wrote:
There should've been a comma:
Since the controls didn't seem to affect what I was seeing on the scope, perhaps it was mostly due to there not being a proper load resistance.
I hate it when that happens!
Barry - N4BUQ
Steve,
I'll run through it that way.? As I said, all I did was monitor the output at the antenna jack with no dummy load.? Since the controls didn't seem to affect what I was seeing on the scope.? Perhaps it was mostly due to there not being a proper load resistance.? I'll report back - hopefully tomorrow.
Thanks so much!
Barry - N4BUQ
Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq <
n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
Regardless of how I go about it, with C77 in place, C76 minimizes the output at fully open and with C77 disconnected, C76 minimizes the output at fully closed.
With one leg of C77 disconnected, I started checking its value and I kept getting very weird values: either several microfarads (yes with a "micro") or somewhere around 140 picofarads.? I decided to de-solder the other end and checked it again and it went complete to "Unknown or damaged part" on my T7 component checker.? Apparently it was on the verge of completely bad and de-soldering finished it off (short lead on one end).
I don't have a proper replacement yet but I do have a 27pF 500V SM that I might throw in there just to see if changes things much the same way the original cap did.? I presume it will still be too much extra capacitance but it might be interesting to see, with it in circuit and even though it's about double the original capacitance, whether C76 gets the output closer to a full null when it's at or nearly fully open.
I presume a disk ceramic is still the appropriate cap to use for C76?
Thanks, Barry - N4bUQ
Steve, I'll run through it that way.? As I said, all I did was monitor the output at the antenna jack with no dummy load.? Since the controls didn't seem to affect what I was seeing on the scope.? Perhaps it was mostly due to there not being a proper load resistance.? I'll report back - hopefully tomorrow. Thanks so much! Barry - N4BUQ Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq <n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
Yes, it needs to be the value shown in the schematic, in parallel with the variable. Substantially higher values are not recommended and the original values should be used if you¡¯re not using RCA tubes.?
I¡¯m just getting up and so don¡¯t have the manual in front of me and can¡¯t remember the exact values.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, Apr 7, 2025 at 19:53, n4buq < n4buq@...> wrote:
Regardless of how I go about it, with C77 in place, C76 minimizes the output at fully open and with C77 disconnected, C76 minimizes the output at fully closed.
With one leg of C77 disconnected, I started checking its value and I kept getting very weird values: either several microfarads (yes with a "micro") or somewhere around 140 picofarads.? I decided to de-solder the other end and checked it again and it went complete to "Unknown or damaged part" on my T7 component checker.? Apparently it was on the verge of completely bad and de-soldering finished it off (short lead on one end).
I don't have a proper replacement yet but I do have a 27pF 500V SM that I might throw in there just to see if changes things much the same way the original cap did.? I presume it will still be too much extra capacitance but it might be interesting to see, with it in circuit and even though it's about double the original capacitance, whether C76 gets the output closer to a full null when it's at or nearly fully open.
I presume a disk ceramic is still the appropriate cap to use for C76?
Thanks,
Barry - N4bUQ
Steve,
I'll run through it that way.? As I said, all I did was monitor the output at the antenna jack with no dummy load.? Since the controls didn't seem to affect what I was seeing on the scope.? Perhaps it was mostly due to there not being a proper load resistance.? I'll report back - hopefully tomorrow.
Thanks so much!
Barry - N4BUQ
Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq <
n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
The schematic I have shows 12.5pF.? I'm not looking at it at the moment, but I think the one that was in there is (was) a 12pF so I presume a 12pF or 13pF should do fine. I'll need to get one ordered.
My tubes are GE.
Thanks,
Barry - N4BUQ
Yes, it needs to be the value shown in the schematic, in parallel with the variable. Substantially higher values are not recommended and the original values should be used if you¡¯re not using RCA tubes.?
I¡¯m just getting up and so don¡¯t have the manual in front of me and can¡¯t remember the exact values.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, Apr 7, 2025 at 19:53, n4buq <n4buq@...> wrote:
Regardless of how I go about it, with C77 in place, C76 minimizes the output at fully open and with C77 disconnected, C76 minimizes the output at fully closed.
With one leg of C77 disconnected, I started checking its value and I kept getting very weird values: either several microfarads (yes with a "micro") or somewhere around 140 picofarads.? I decided to de-solder the other end and checked it again and it went complete to "Unknown or damaged part" on my T7 component checker.? Apparently it was on the verge of completely bad and de-soldering finished it off (short lead on one end).
I don't have a proper replacement yet but I do have a 27pF 500V SM that I might throw in there just to see if changes things much the same way the original cap did.? I presume it will still be too much extra capacitance but it might be interesting to see, with it in circuit and even though it's about double the original capacitance, whether C76 gets the output closer to a full null when it's at or nearly fully open.
I presume a disk ceramic is still the appropriate cap to use for C76?
Thanks,
Barry - N4bUQ
Steve,
I'll run through it that way.? As I said, all I did was monitor the output at the antenna jack with no dummy load.? Since the controls didn't seem to affect what I was seeing on the scope.? Perhaps it was mostly due to there not being a proper load resistance.? I'll report back - hopefully tomorrow.
Thanks so much!
Barry - N4BUQ
Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq <
n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
GE tubes should work fine with the ¡°stock¡± cap setup.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Tue, Apr 8, 2025 at 08:39, n4buq < n4buq@...> wrote:
The schematic I have shows 12.5pF.? I'm not looking at it at the moment, but I think the one that was in there is (was) a 12pF so I presume a 12pF or 13pF should do fine. I'll need to get one ordered.
My tubes are GE.
Thanks,
Barry - N4BUQ
Yes, it needs to be the value shown in the schematic, in parallel with the variable. Substantially higher values are not recommended and the original values should be used if you¡¯re not using RCA tubes.?
I¡¯m just getting up and so don¡¯t have the manual in front of me and can¡¯t remember the exact values.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, Apr 7, 2025 at 19:53, n4buq <
n4buq@...> wrote:
Regardless of how I go about it, with C77 in place, C76 minimizes the output at fully open and with C77 disconnected, C76 minimizes the output at fully closed.
With one leg of C77 disconnected, I started checking its value and I kept getting very weird values: either several microfarads (yes with a "micro") or somewhere around 140 picofarads.? I decided to de-solder the other end and checked it again and it went complete to "Unknown or damaged part" on my T7 component checker.? Apparently it was on the verge of completely bad and de-soldering finished it off (short lead on one end).
I don't have a proper replacement yet but I do have a 27pF 500V SM that I might throw in there just to see if changes things much the same way the original cap did.? I presume it will still be too much extra capacitance but it might be interesting to see, with it in circuit and even though it's about double the original capacitance, whether C76 gets the output closer to a full null when it's at or nearly fully open.
I presume a disk ceramic is still the appropriate cap to use for C76?
Thanks,
Barry - N4bUQ
Steve,
I'll run through it that way.? As I said, all I did was monitor the output at the antenna jack with no dummy load.? Since the controls didn't seem to affect what I was seeing on the scope.? Perhaps it was mostly due to there not being a proper load resistance.? I'll report back - hopefully tomorrow.
Thanks so much!
Barry - N4BUQ
Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq <
n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
BTW, I bought 1kV NP0 caps.? Apparently the original is 2kV.? Does that really need to be a 2kV cap?
I see that it connects between +650V and +250V so nominally it's only seeing 400V; however, is it the case that modulation peaks would require higher than a 1kV part - at least to be on the safe[r] side?
I half-way wondered that Drake may have had these on hand for other rigs and used what they had instead of stocking multiple voltage values.
Thanks, Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Tuesday, April 8, 2025 8:08:13 AM
Subject: Re: [DRAKE-RADIO] Tuning a pi-Network Output
GE tubes should work fine with the ¡°stock¡± cap setup.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Tue, Apr 8, 2025 at 08:39, n4buq <n4buq@...> wrote:
The schematic I have shows 12.5pF.? I'm not looking at it at the moment, but I think the one that was in there is (was) a 12pF so I presume a 12pF or 13pF should do fine. I'll need to get one ordered.
My tubes are GE.
Thanks,
Barry - N4BUQ
Yes, it needs to be the value shown in the schematic, in parallel with the variable. Substantially higher values are not recommended and the original values should be used if you¡¯re not using RCA tubes.?
I¡¯m just getting up and so don¡¯t have the manual in front of me and can¡¯t remember the exact values.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, Apr 7, 2025 at 19:53, n4buq <
n4buq@...> wrote:
Regardless of how I go about it, with C77 in place, C76 minimizes the output at fully open and with C77 disconnected, C76 minimizes the output at fully closed.
With one leg of C77 disconnected, I started checking its value and I kept getting very weird values: either several microfarads (yes with a "micro") or somewhere around 140 picofarads.? I decided to de-solder the other end and checked it again and it went complete to "Unknown or damaged part" on my T7 component checker.? Apparently it was on the verge of completely bad and de-soldering finished it off (short lead on one end).
I don't have a proper replacement yet but I do have a 27pF 500V SM that I might throw in there just to see if changes things much the same way the original cap did.? I presume it will still be too much extra capacitance but it might be interesting to see, with it in circuit and even though it's about double the original capacitance, whether C76 gets the output closer to a full null when it's at or nearly fully open.
I presume a disk ceramic is still the appropriate cap to use for C76?
Thanks,
Barry - N4bUQ
Steve,
I'll run through it that way.? As I said, all I did was monitor the output at the antenna jack with no dummy load.? Since the controls didn't seem to affect what I was seeing on the scope.? Perhaps it was mostly due to there not being a proper load resistance.? I'll report back - hopefully tomorrow.
Thanks so much!
Barry - N4BUQ
Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq <
n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
|
If the original was 2KV that is the minimum that I would replace it with. On Tue, 8 Apr 2025 11:12:59 -0400 (EDT) "n4buq via groups.io" <n4buq@...> wrote: BTW, I bought 1kV NP0 caps. Apparently the original is 2kV. Does that really need to be a 2kV cap? -- 73 -Jim NU0C
|
I think the original was an C0G/NP0 because it has "C0" labeled on it. I don't see >1kV in C0G/NP0 and, given the hot environment it's in, I'm concerned something else may vary too widely with the heat. Of course, it's not an exact value for all bands anyway but I wanted to try to minimize that effect. I'll keep looking.
Thanks,
Barry - N4BUQ
toggle quoted message
Show quoted text
If the original was 2KV that is the minimum that I would replace it with.
On Tue, 8 Apr 2025 11:12:59 -0400 (EDT)
"n4buq via groups.io" <n4buq@...> wrote:
BTW, I bought 1kV NP0 caps. Apparently the original is 2kV. Does that really
need to be a 2kV cap?
--
73
-Jim
NU0C
|
Here's a picture of the old cap.
Barry - N4BUQ
toggle quoted message
Show quoted text
I think the original was an C0G/NP0 because it has "C0" labeled on it. I don't
see >1kV in C0G/NP0 and, given the hot environment it's in, I'm concerned
something else may vary too widely with the heat. Of course, it's not an exact
value for all bands anyway but I wanted to try to minimize that effect. I'll
keep looking.
Thanks,
Barry - N4BUQ
If the original was 2KV that is the minimum that I would replace it with.
On Tue, 8 Apr 2025 11:12:59 -0400 (EDT)
"n4buq via groups.io" <n4buq@...> wrote:
BTW, I bought 1kV NP0 caps. Apparently the original is 2kV. Does that really
need to be a 2kV cap?
--
73
-Jim
NU0C
|
Jim Shorney
