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I have a T-4XC/R-4C combination that works well on all bands except 40 meters. ?I get no plate current on 40M with the T-4XC. ?Makes no difference if I select separate, transmitter or receiver on the PTO selector of the transmitter. ?My first thought was a dud 18.1 MHz crystal, so I connected the FS-4 to the transmitter using accessory crystal position 1. ?Still nothing on 40M. My brain is fried, so thought I¡¯d see if anyone has any ideas. ?THANKS!
Larry, KB9VY
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Check all of the wafers of the bandswitch.?
You could also have a shorted capacitor in one of the 40m circuits.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Mar 30, 2025 at 18:43, KB9VY via groups.io < lcoblentz3@...> wrote:
I have a T-4XC/R-4C combination that works well on all bands except 40 meters. ?I get no plate current on 40M with the T-4XC. ?Makes no difference if I select separate, transmitter or receiver on the PTO selector of the transmitter. ?My first thought was a dud 18.1 MHz crystal, so I connected the FS-4 to the transmitter using accessory crystal position 1. ?Still nothing on 40M. My brain is fried, so thought I¡¯d see if anyone has any ideas. ?THANKS!
Larry, KB9VY
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I went through the wafer switches and the seem to be good. ?I get a tiny bit of RF on the watt meter, but increasing gain does nothing. ?All other bands behave normally.
On Sun, Mar 30, 2025 at 19:03, Steve Wedge, W1ES/4 via groups.io < w1es@...> wrote:
Check all of the wafers of the bandswitch.?
You could also have a shorted capacitor in one of the 40m circuits.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Mar 30, 2025 at 18:43, KB9VY via groups.io <
lcoblentz3@...> wrote:
I have a T-4XC/R-4C combination that works well on all bands except 40 meters. ?I get no plate current on 40M with the T-4XC. ?Makes no difference if I select separate, transmitter or receiver on the PTO selector of the transmitter. ?My first thought was a dud 18.1 MHz crystal, so I connected the FS-4 to the transmitter using accessory crystal position 1. ?Still nothing on 40M. My brain is fried, so thought I¡¯d see if anyone has any ideas. ?THANKS!
Larry, KB9VY
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Do you have K4OAH¡¯s e-manual set? ?There is a bad component somewhere that will be in whatever components are unique to 40m. ?The e-manual will make it easier to find the part.
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Mar 30, 2025 at 7:57 PM, KB9VY via groups.io < lcoblentz3@...> wrote:
I went through the wafer switches and the seem to be good. ?I get a tiny bit of RF on the watt meter, but increasing gain does nothing. ?All other bands behave normally.
On Sun, Mar 30, 2025 at 19:03, Steve Wedge, W1ES/4 via groups.io <
w1es@...> wrote:
Check all of the wafers of the bandswitch.?
You could also have a shorted capacitor in one of the 40m circuits.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Mar 30, 2025 at 18:43, KB9VY via groups.io <
lcoblentz3@...> wrote:
I have a T-4XC/R-4C combination that works well on all bands except 40 meters. ?I get no plate current on 40M with the T-4XC. ?Makes no difference if I select separate, transmitter or receiver on the PTO selector of the transmitter. ?My first thought was a dud 18.1 MHz crystal, so I connected the FS-4 to the transmitter using accessory crystal position 1. ?Still nothing on 40M. My brain is fried, so thought I¡¯d see if anyone has any ideas. ?THANKS!
Larry, KB9VY
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Steve, I ordered the documentation. ?I¡¯ve been meaning to do that since the info I got from K4OAH on the Tr-4 has been invaluable. ?I¡¯m sure I¡¯ll get it figured out between the service info and some assistance from the group if needed. ?Thanks!
?
Larry, KB9VY?
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It's going to take some time to find it.? I would first attach an ohmmeter lead to the common of each wafer and check for contact at the 40m position.? Probe at the solder points and not the delicate switch contacts.? You should see continuity at each, of course.? While you are at each one, check resistance to the chassis.? Some continuities may be okay but base your actions on the schematic.? Likewise, you should have continuity from the switch common to whatever circuit is being switched-in.
The observation that you have a small signal at the output suggests either an open or short that shouldn't exist.? I'd be more inclined to believe a short.
The band oscillator has its output on the common connection of its wafer switch.? You should see a robust signal there.
You can also make absolutely sure it isn't the crystal by swapping the 18.1 in the tx with the one in the rx.
Good luck!
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Monday, March 31st, 2025 at 8:54 AM, KB9VY via groups.io <lcoblentz3@...> wrote:
Steve, I ordered the documentation. ?I¡¯ve been meaning to do that since the info I got from K4OAH on the Tr-4 has been invaluable. ?I¡¯m sure I¡¯ll get it figured out between the service info and some assistance from the group if needed. ?Thanks!
?
Larry, KB9VY?
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Well, here¡¯s the latest update. ?I swapped the 18.1 MHz crystal in from the receiver. ?Still no drive on 40M. ?So, crystal is good. ?Went through all of the wafers on the band switch. ?Need to visit one of them again since there was some funky stuff going on. ?Decided to go ahead and do the resistance measurements on all of the vacuum tubes for future reference. ?Very strange measurements around V4 and V8. ?Back to checking a few resistors tomorrow, but more importantly looking for a bad capacitor somewhere in the 40M circuit. ?The service data from K4OAH is quite useful! ?I already knew it would be since I have the TR-4C files from a few years back. ?
Enough for today, my back hurts and I can¡¯t see straight after leaning over schematics and radios hi hi.
?
Larry, KB9VY?
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Just keep in mind that you now have more ideas on what it NOT causing the problem.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, Mar 31, 2025 at 17:27, KB9VY via groups.io < lcoblentz3@...> wrote:
Well, here¡¯s the latest update. ?I swapped the 18.1 MHz crystal in from the receiver. ?Still no drive on 40M. ?So, crystal is good. ?Went through all of the wafers on the band switch. ?Need to visit one of them again since there was some funky stuff going on. ?Decided to go ahead and do the resistance measurements on all of the vacuum tubes for future reference. ?Very strange measurements around V4 and V8. ?Back to checking a few resistors tomorrow, but more importantly looking for a bad capacitor somewhere in the 40M circuit. ?The service data from K4OAH is quite useful! ?I already knew it would be since I have the TR-4C files from a few years back. ?
Enough for today, my back hurts and I can¡¯t see straight after leaning over schematics and radios hi hi.
?
Larry, KB9VY?
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Yessir. ?Always look at the positive!
On Mon, Mar 31, 2025 at 19:07, Steve Wedge, W1ES/4 via groups.io < w1es@...> wrote:
Just keep in mind that you now have more ideas on what it NOT causing the problem.?
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, Mar 31, 2025 at 17:27, KB9VY via groups.io <
lcoblentz3@...> wrote:
Well, here¡¯s the latest update. ?I swapped the 18.1 MHz crystal in from the receiver. ?Still no drive on 40M. ?So, crystal is good. ?Went through all of the wafers on the band switch. ?Need to visit one of them again since there was some funky stuff going on. ?Decided to go ahead and do the resistance measurements on all of the vacuum tubes for future reference. ?Very strange measurements around V4 and V8. ?Back to checking a few resistors tomorrow, but more importantly looking for a bad capacitor somewhere in the 40M circuit. ?The service data from K4OAH is quite useful! ?I already knew it would be since I have the TR-4C files from a few years back. ?
Enough for today, my back hurts and I can¡¯t see straight after leaning over schematics and radios hi hi.
?
Larry, KB9VY?
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Do you have an oscilloscope?
Gary
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On Mar 30, 2025, at 5:43?PM, KB9VY via groups.io <lcoblentz3@...> wrote:
I have a T-4XC/R-4C combination that works well on all bands except 40 meters. ?I get no plate current on 40M with the T-4XC. ?Makes no difference if I select separate, transmitter or receiver on the PTO selector of the transmitter. ?My first thought was a dud 18.1 MHz crystal, so I connected the FS-4 to the transmitter using accessory crystal position 1. ?Still nothing on 40M. My brain is fried, so thought I¡¯d see if anyone has any ideas. ?THANKS!
Larry, KB9VY
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Show quoted text
On Mon, Mar 31, 2025 at 19:22, Gary Follett via groups.io < xntrick1948@...> wrote: Do you have an oscilloscope?
Gary
W0DVN
On Mar 30, 2025, at 5:43?PM, KB9VY via groups.io <lcoblentz3@...> wrote:
I have a T-4XC/R-4C combination that works well on all bands except 40 meters. ?I get no plate current on 40M with the T-4XC. ?Makes no difference if I select separate, transmitter or receiver on the PTO selector of the transmitter. ?My first thought was a dud 18.1 MHz crystal, so I connected the FS-4 to the transmitter using accessory crystal position 1. ?Still nothing on 40M. My brain is fried, so thought I¡¯d see if anyone has any ideas. ?THANKS!
Larry, KB9VY
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If the switch,crystal and the other bands are ok, the only thing left is 2 fixed caps and 2 trimmer caps,? or a bad connection.
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Have you tried adjusting the trimmers?
?
It is painful watching threads like this.. everyone needs a scope, would probably make this fix take only a few minutes.
73,
Gary
WB6OGD
?
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Then start looking at the grid of the finals, then the grid of the driver and work your way back until you get a signal.?
Look at the wiper of the crystal selector section of the band switch to see if the signal strength there is roughly on par with the output on 80 and 20 meters.
These tests will tell you all you need to know.
The signals should all bee strong enough to see with the scope.
Gary
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On Mar 31, 2025, at 6:25?PM, KB9VY via groups.io <lcoblentz3@...> wrote:
Yes.
On Mon, Mar 31, 2025 at 19:22, Gary Follett via??<xntrick1948@...> wrote:Do you have an oscilloscope?
Gary
W0DVN On Mar 30, 2025, at 5:43?PM, KB9VY via groups.io <lcoblentz3@...> wrote:
I have a T-4XC/R-4C combination that works well on all bands except 40 meters. ?I get no plate current on 40M with the T-4XC. ?Makes no difference if I select separate, transmitter or receiver on the PTO selector of the transmitter. ?My first thought was a dud 18.1 MHz crystal, so I connected the FS-4 to the transmitter using accessory crystal position 1. ?Still nothing on 40M. My brain is fried, so thought I¡¯d see if anyone has any ideas. ?THANKS!
Larry, KB9VY
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I¡¯m sorry you think this is painful. I¡¯ve read this group for several years and decided to jump in with a ¡°project¡±. ?
No, I have not diddled any trimmers, yet. ?All bands other than 40 work well. ?I¡¯m fairly certain that 40 meters loaded into a dummy load with no issues a couple of months ago. ?
I only started chasing this problem today. ?I¡¯m certain I will find the issue eventually.
KB9VY
On Mon, Mar 31, 2025 at 19:28, Gary WB6OGD via groups.io < winbladgary@...> wrote:
If the switch,crystal and the other bands are ok, the only thing left is 2 fixed caps and 2 trimmer caps,? or a bad connection.
?
Have you tried adjusting the trimmers?
?
It is painful watching threads like this.. everyone needs a scope, would probably make this fix take only a few minutes.
73,
Gary
WB6OGD
?
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By the way, you should see SAOME plate current on all bands, even if there is no output, as you should see the idle plate current and that should change with the bias pot adjustment.
The fact that you are getting some RF output (small) but that it does not change with setting of the Gain pot suggests that one of the oscillators is not supplying signal, which suggests where to state with the oscilloscope.
The nice thing is that you can easily compare levels between 80 meters and 40 meters to compare.
Gary
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On Mar 31, 2025, at 6:25?PM, KB9VY via groups.io <lcoblentz3@...> wrote:
Yes.
On Mon, Mar 31, 2025 at 19:22, Gary Follett via groups.io < xntrick1948@...> wrote: Do you have an oscilloscope?
Gary
W0DVN
On Mar 30, 2025, at 5:43?PM, KB9VY via groups.io <lcoblentz3@...> wrote:
I have a T-4XC/R-4C combination that works well on all bands except 40 meters. ?I get no plate current on 40M with the T-4XC. ?Makes no difference if I select separate, transmitter or receiver on the PTO selector of the transmitter. ?My first thought was a dud 18.1 MHz crystal, so I connected the FS-4 to the transmitter using accessory crystal position 1. ?Still nothing on 40M. My brain is fried, so thought I¡¯d see if anyone has any ideas. ?THANKS!
Larry, KB9VY
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Did this radio ever work for you on 40 meters? If not, then, after determining that the 18.1 MHz oscillator is running and producing roughly the same output as the 14.6 MHz crystal on 80 meters, adjusting the trimmers might be of value. If, however, the 40 meter band once worked and now does not, then do not, under any circumstances, adjust any trimmers until the reason for the failure is determined.
Gary
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Show quoted text
On Mar 31, 2025, at 6:35?PM, Gary Follett via groups.io <xntrick1948@...> wrote:
By the way, you should see SAOME plate current on all bands, even if there is no output, as you should see the idle plate current and that should change with the bias pot adjustment.
The fact that you are getting some RF output (small) but that it does not change with setting of the Gain pot suggests that one of the oscillators is not supplying signal, which suggests where to state with the oscilloscope.
The nice thing is that you can easily compare levels between 80 meters and 40 meters to compare.
Gary
W0DVN On Mar 31, 2025, at 6:25?PM, KB9VY via groups.io <lcoblentz3@...> wrote:
Yes.
On Mon, Mar 31, 2025 at 19:22, Gary Follett via groups.io < xntrick1948@...> wrote: Do you have an oscilloscope?
Gary
W0DVN On Mar 30, 2025, at 5:43?PM, KB9VY via groups.io <lcoblentz3@...> wrote:
I have a T-4XC/R-4C combination that works well on all bands except 40 meters. ?I get no plate current on 40M with the T-4XC. ?Makes no difference if I select separate, transmitter or receiver on the PTO selector of the transmitter. ?My first thought was a dud 18.1 MHz crystal, so I connected the FS-4 to the transmitter using accessory crystal position 1. ?Still nothing on 40M. My brain is fried, so thought I¡¯d see if anyone has any ideas. ?THANKS!?
Larry, KB9VY
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Yes, I see only idle current on 40M. All other bands provide a bit under 100 watts output. ?I really suspect a band switching issue, either a short somewhere or a faulty switch. ?As stated, I need to revisit one wafer on the band switch. ?I was interrupted during my troubleshooting today, and need to backtrack a bit,
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>I¡¯m sorry you think this is painful. I¡¯ve read this group for several years and decided to jump in with a ¡°project¡±.
?
I am sorry Larry, that didn't come out right, didn't mean to be snarky and didn't realize you only started this yesterday.
I just wanted to say, with a scope, it should be so easy to find.
Good luck with the repair.
73,
Gary
WB6OGD
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Update. ?It appears C137, 3.3pF tubular ceramic capacitor, is shorted. ?I have continuity to ground on either side of the capacitor. ?This capacitor is in the 40 meter band oscillator around T11. ?Anyone feel like looking at a T-4XC schematic and giving me a sanity check? ?Now to hunt down a replacement.
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Sorry, that's not it.
C137 has one end grounded and the other end connects to ground through T11 and T5.
73,
Gary
WB6OGD
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Gary WB6OGD