Re: TR-4 Decreased Sensitivity on High Bands
Hi Gary,
I checked this morning and I'm getting the following:
80M : 70W, XMTR GAIN saturation point is at 9:30 o'clock 20M : 50W, XMTR GAIN saturation point is at 9:30 o'clock
These are both into a dummy load.
I've started to notice that if I hold the key down for more than a couple of seconds, the output begins to drop very slightly.? If I hold the key down for about 5 seconds, the output continues to drop.? It's a very slow drop but is there nonetheless.? I wonder if my tubes are actually going soft.
As a bit of a side note, I mentioned that I replaced the original 12.5pF padding capacitor across the neutralizing variable capacitor with two 12pF in series to obtain 6pF across the variable capacitor.? With only 10pF across it, I could approach a null but the rotor was fully unmeshed at that point.? With 6pF, the null is at approximately half-mesh.? I was reading Drake's paper regarding replacing the PA tubes and how they had switch to G.E. branded tubes and how those would likely need an additional few pF across the neutralizing variable capacitor.? I have G.E. tubes and find it odd that instead of more capacitance, I need way less and that made me think something else is not quite right (maybe the tubes after all).? Anyway, just thought I'd mention that in light of what I read about it last night.
Thanks again, Barry - N4BUQ
The reason I ask the questions about 80 vs 20 output is that, on these two bands, the injection coupling coils do not matter at all since they are out of the circuit altogether on those two bands. The fact that 80 meters produces good output suggests that the PTO level is good, as well as the drive level from the carrier generator. What¡¯s more, since the receive path for the 9 MHz signals is different for TX and RX, it is not likely that any problems are present in those IF amplifiers since it is unlikely that both paths would be defective.
The fact that 40 meters produces good output suggests that the premier for the crystal oscillator, and the crystal oscillator itself are OK.
That leaves the RF coils as suspect. While I generally do not recommend aligning a radio that once worked and now does not work, in this case you can pick a band that produces some measurable output and adjust the RF coils just a little, keeping track of how much you moved them. Any properly aligned coil should show a drop in output either side of the starting position.?
If you have a piece of brass and a piece of ferrite that will?fit into the adjustment holes, you can insert these into the coils without moving the coil slugs themselves. Inserting the brass will rise the tuned circuit frequency, inserting ferrite will lower that resonant frequency, performing the same test without physically moving the coil slugs¡ Insertion of either should reduce output of the radio if it is properly aligned already.
I have a tool for this purpose but that does you little good, sorry.
Gary
W0DVN On Apr 29, 2025, at 10:33?AM, n4buq <n4buq@...> wrote:
Two minor clarifications: The cap across the neutralizing variable cap allows me to set a proper null so that the variable cap can swing through that at about the point where the rotor is meshed approximately half-way (it wouldn't do that with the original cap). The loading equipment for the injection coupler alignment is called an "alignment load", not necessarily a "dummy load" as I referred to it and I didn't want to cause confusion with the antenna dummy load (and I still wonder about the etymology of that phrase). Gary, This morning, as I tuned up (into a dummy load) across all bands and I noticed that the XMTR GAIN seems to saturate at about the same point for all bands.? I seem to recall that a few weeks ago (before I started touching up the alignment points), I could get a LOT more gain out of the lower bands. The only component work I've done is to replace the cap across the PA neutralizing cap and have that so I can minimize the spurious oscillations with the appropriate power peak at the valley (dip) of the plate tuning cap rotation.? I also replaced the cathode resistors with new 15R 1W metal film caps as the originals were out of spec and were not well-matched. Maybe I've botched the alignment(s) and, perhaps, I need to revisit those.? Disappointing as I'd hoped to make things better and apparently that's not the case but I don't yet know what I might have done wrong (yes, I did use the designated dummy load when tweaking the injection couplers which I know is essential to getting those correct). Thanks again,
Barry - N4BUQ
From: "Gary Follett via groups.io" <xntrick1948@...>
One test I have found to be useful is to plot output power on a given band versus position of the TX gain pot on the different bands. If you find that ?the saturation point of output (the point at which increasing the gain position produces no increase in output) versus position of the pot does not change as you go up in bands, then likely you have an alignment issue or a drive issue before the final mixer, because these earlier stages should produce more output than needed on the low bands to make up for poorer efficiency on the higher bands. In other words, you should be able to drive the heck out of the radio on 80 meters well before the saturation point of the TX gain pot.? Receiver gain issues track TX gain issues religiously. If TX gain is weak, receiver gain will be weak too. Gary W0DVN On Apr 28, 2025, at 7:44?PM, Ham Radio via groups.io <bernard.murphy@...> wrote:
Steve: I assume you meant AGC. ? I have a TR-4 that has the same issue. ? Fine on TX but low on RX. ? See attached file.
--
73, Bernie. VE3FWF
Real?radios glow in the dark
<TR-4-tubes-sensitivity.xls>
|
Try RF Parts.com. They have tons of Mitsubishi modules. Terry- WB0VQP
Hi Ron,
I thought I would pop in my 2 cents worth on this subject.? I have repaired a few of these modules in the past, and I have also ordered replacements from Aliexpress without any issues but one.
If you have power coming out and drawing 10A, which seems high, I would suggest removing the drive to the module and looking to see if the current drops significantly.? If the module is working, it should drop.? If it does, pull the top off the module and carefully inspect the traces on the output side of the module.? You will likely see a crack in a trace.? You can repair this with a very hot soldering iron and a bit of solder, but you will have to remove the module from the heat sink to accomplish this.? You might even see a burned out component which is also replaceable.
It takes a bit of time to do this but can save a ton of money and you'll also feel proud of yourself.
I have ordered several module from Aliexpress over the years and had great luck with them.? I had one arrive that was definitely bogus as it had pins in the wrong location but sending them a photo of it solved the problem and another was sent to me, no return of the bogus part was required.
Your chances of getting bogus parts are there even if you order from Icom or one of the other manufacturers.? They get their parts from the same places these days, especially if the radio hasn't been manufactured for a long time.
73,
Clint, VE3CMQ
|
Hi Ron,
I thought I would pop in my 2 cents worth on this subject. I have repaired a few of these modules in the past, and I have also ordered replacements from Aliexpress without any issues but one.
If you have power coming out and drawing 10A, which seems high, I would suggest removing the drive to the module and looking to see if the current drops significantly. If the module is working, it should drop. If it does, pull the top off the module and carefully inspect the traces on the output side of the module. You will likely see a crack in a trace. You can repair this with a very hot soldering iron and a bit of solder, but you will have to remove the module from the heat sink to accomplish this. You might even see a burned out component which is also replaceable.
It takes a bit of time to do this but can save a ton of money and you'll also feel proud of yourself.
I have ordered several module from Aliexpress over the years and had great luck with them. I had one arrive that was definitely bogus as it had pins in the wrong location but sending them a photo of it solved the problem and another was sent to me, no return of the bogus part was required.
Your chances of getting bogus parts are there even if you order from Icom or one of the other manufacturers. They get their parts from the same places these days, especially if the radio hasn't been manufactured for a long time.
73,
Clint, VE3CMQ
|
GM, for a module replacement work I acquired an "original" part, "guaranteed", from a local seller, the end result was it was indeed an "original" part but refurbished ..
So bad done also (I took apart the cover to see a monkey would have done a better soldering job) that when I installed it I got roughly a watt (25 intended).
Fortunately the seller returned the money, and I mailed (no cost) "the thing" back. But time lost ...
I guess they got this "things" in bulk, named "every spare parts for radio" combos.
If you can get the original Icom, go for it.
Regards
Guillermo - LU5WE.
toggle quoted message
Show quoted text
El 30/4/25 a las 02:37, Ron Magnus via groups.io escribi¨®: This is a bit off topic in some ways, in others it's something we have tossed around recently.
I have an Icom repeater that appears to have a failed PA module, it draws 10 amps and has an output of 1 watt.? It's a Mitsubishi RA55H4047M.? I have talked to Icom, they have the part in stock for about $120.? I have looked on line and I find this unit listed in many places other than Digikey, Mauser or Newark (They don't carry it).? The images of the units all look identical including 'Japan" printed on the units as compared to the unit in the repeater but all sources that I can find seem to be coming from Asia, specifically China at price points between $38 and $66.
The $64,000 question of course is do I risk one of these alleged "Genuine Mitsubishi" units or bite the bullet with Icom?
73, Ron
wa7gfe
|
See:??
Seems it's now the?$97.91 question.
73 de Andrew/N5ASE
This is a bit off topic in some ways, in others it's something we have tossed around recently.
?
I have an Icom repeater that appears to have a failed PA module, it draws 10 amps and has an output of 1 watt.? It's a Mitsubishi RA55H4047M.? I have talked to Icom, they have the part in stock for about $120.? I have looked on line and I find this unit listed in many places other than Digikey, Mauser or Newark (They don't carry it).? The images of the units all look identical including 'Japan" printed on the units as compared to the unit in the repeater but all sources that I can find seem to be coming from Asia, specifically China at price points between $38 and $66.
?
The $64,000 question of course is do I risk one of these alleged "Genuine Mitsubishi" units or bite the bullet with Icom?
?
73, Ron
wa7gfe
|
Ron,
I don't have an answer for you, just a related thought:
I have an Icom IC-2100H that has effectively zero RF output, I got it as a parts radio for another IC-2100H that had a scratchy volume knob. Well, it turns out the IC-2100H has a a similar RF Power Module that is available from several sources, and researching it led me to believe forged power modules are really a thing. The SC-1091 is the specific part for the IC-2100H.
I don't know if Icom still carries/offers the part, but I've seen online prices range from around $25 to $130... in my case, I can't justify $130 for a 20+ year-old FM radio, but I could see $25 or so...
If it's important, and Icom stocks the correct part, I'd suggest buying it from Icom and being sure the part is real.
Just my $0.02,
toggle quoted message
Show quoted text
On Apr 30, 2025, at 00:37, Ron Magnus via groups.io <ron.magnus@...> wrote:
? This is a bit off topic in some ways, in others it's something we have tossed around recently.
?
I have an Icom repeater that appears to have a failed PA module, it draws 10 amps and has an output of 1 watt.? It's a Mitsubishi RA55H4047M.? I have talked to Icom, they have the part in stock for about $120.? I have looked on line and I find this unit listed in many places other than Digikey, Mauser or Newark (They don't carry it).? The images of the units all look identical including 'Japan" printed on the units as compared to the unit in the repeater but all sources that I can find seem to be coming from Asia, specifically China at price points between $38 and $66.
?
The $64,000 question of course is do I risk one of these alleged "Genuine Mitsubishi" units or bite the bullet with Icom?
?
73, Ron
wa7gfe
|
This is a bit off topic in some ways, in others it's something we have tossed around recently.
?
I have an Icom repeater that appears to have a failed PA module, it draws 10 amps and has an output of 1 watt.? It's a Mitsubishi RA55H4047M.? I have talked to Icom, they have the part in stock for about $120.? I have looked on line and I find this unit listed in many places other than Digikey, Mauser or Newark (They don't carry it).? The images of the units all look identical including 'Japan" printed on the units as compared to the unit in the repeater but all sources that I can find seem to be coming from Asia, specifically China at price points between $38 and $66.
?
The $64,000 question of course is do I risk one of these alleged "Genuine Mitsubishi" units or bite the bullet with Icom?
?
73, Ron
wa7gfe
|
Re: Another TR7 Journey begins
It¡¯s 40 meters but yes I¡¯m guessing there¡¯s a problem with the switch section. ?
|
Re: TR-4 Decreased Sensitivity on High Bands
The reason I ask the questions about 80 vs 20 output is that, on these two bands, the injection coupling coils do not matter at all since they are out of the circuit altogether on those two bands.
The fact that 80 meters produces good output suggests that the PTO level is good, as well as the drive level from the carrier generator. What¡¯s more, since the receive path for the 9 MHz signals is different for TX and RX, it is not likely that any problems are present in those IF amplifiers since it is unlikely that both paths would be defective.
The fact that 40 meters produces good output suggests that the premier for the crystal oscillator, and the crystal oscillator itself are OK.
That leaves the RF coils as suspect. While I generally do not recommend aligning a radio that once worked and now does not work, in this case you can pick a band that produces some measurable output and adjust the RF coils just a little, keeping track of how much you moved them. Any properly aligned coil should show a drop in output either side of the starting position.?
If you have a piece of brass and a piece of ferrite that will?fit into the adjustment holes, you can insert these into the coils without moving the coil slugs themselves. Inserting the brass will rise the tuned circuit frequency, inserting ferrite will lower that resonant frequency, performing the same test without physically moving the coil slugs¡ Insertion of either should reduce output of the radio if it is properly aligned already.
I have a tool for this purpose but that does you little good, sorry.
Gary
toggle quoted message
Show quoted text
On Apr 29, 2025, at 10:33?AM, n4buq <n4buq@...> wrote:
Two minor clarifications:
The cap across the neutralizing variable cap allows me to set a proper null so that the variable cap can swing through that at about the point where the rotor is meshed approximately half-way (it wouldn't do that with the original cap).
The loading equipment for the injection coupler alignment is called an "alignment load", not necessarily a "dummy load" as I referred to it and I didn't want to cause confusion with the antenna dummy load (and I still wonder about the etymology of that phrase).
Gary, This morning, as I tuned up (into a dummy load) across all bands and I noticed that the XMTR GAIN seems to saturate at about the same point for all bands.? I seem to recall that a few weeks ago (before I started touching up the alignment points), I could get a LOT more gain out of the lower bands. The only component work I've done is to replace the cap across the PA neutralizing cap and have that so I can minimize the spurious oscillations with the appropriate power peak at the valley (dip) of the plate tuning cap rotation.? I also replaced the cathode resistors with new 15R 1W metal film caps as the originals were out of spec and were not well-matched. Maybe I've botched the alignment(s) and, perhaps, I need to revisit those.? Disappointing as I'd hoped to make things better and apparently that's not the case but I don't yet know what I might have done wrong (yes, I did use the designated dummy load when tweaking the injection couplers which I know is essential to getting those correct). Thanks again,
Barry - N4BUQ
From: "Gary Follett via groups.io" <xntrick1948@...>
One test I have found to be useful is to plot output power on a given band versus position of the TX gain pot on the different bands. If you find that ?the saturation point of output (the point at which increasing the gain position produces no increase in output) versus position of the pot does not change as you go up in bands, then likely you have an alignment issue or a drive issue before the final mixer, because these earlier stages should produce more output than needed on the low bands to make up for poorer efficiency on the higher bands. In other words, you should be able to drive the heck out of the radio on 80 meters well before the saturation point of the TX gain pot.? Receiver gain issues track TX gain issues religiously. If TX gain is weak, receiver gain will be weak too. Gary W0DVN On Apr 28, 2025, at 7:44?PM, Ham Radio via groups.io <bernard.murphy@...> wrote:
Steve: I assume you meant AGC. ? I have a TR-4 that has the same issue. ? Fine on TX but low on RX. ? See attached file.
--
73, Bernie. VE3FWF
Real?radios glow in the dark
<TR-4-tubes-sensitivity.xls>
|
Re: Another TR7 Journey begins
You may be making contact with the 5 MHz section and hearing stuff through it. My guess is you either have a fault in the 40M section or one of the switch contacts for 40M needs attention. If you have a nanoVNA you can do an S21 sweep of the filter sections to check them. For future reference you did not really need to unsolder the high current PA feed. All that is needed to run everything except the PA is to clip-lead an external source of 13V to ground and the low current pin on the big 4-pin power connector. On Tue, 29 Apr 2025 11:24:48 -0700 "Bill NZ0T via groups.io" <nz0tham@...> wrote: Wiring is fine.? I discovered if I turned the bandswitch knob in between the detents for 7 and 5 MHz which is even with the yellow 7 on the inside ring that 40 meters works OK.? ?All other bands work as they should in the proper dentent.? Any ideas? -- 73 -Jim NU0C
|
Re: TR-4 Decreased Sensitivity on High Bands
How much weaker is output on 20 meters compared with 80 meters?
Gary
W0DVN
toggle quoted message
Show quoted text
On Apr 29, 2025, at 10:33?AM, n4buq <n4buq@...> wrote:
Two minor clarifications:
The cap across the neutralizing variable cap allows me to set a proper null so that the variable cap can swing through that at about the point where the rotor is meshed approximately half-way (it wouldn't do that with the original cap).
The loading equipment for the injection coupler alignment is called an "alignment load", not necessarily a "dummy load" as I referred to it and I didn't want to cause confusion with the antenna dummy load (and I still wonder about the etymology of that phrase).
Gary, This morning, as I tuned up (into a dummy load) across all bands and I noticed that the XMTR GAIN seems to saturate at about the same point for all bands.? I seem to recall that a few weeks ago (before I started touching up the alignment points), I could get a LOT more gain out of the lower bands. The only component work I've done is to replace the cap across the PA neutralizing cap and have that so I can minimize the spurious oscillations with the appropriate power peak at the valley (dip) of the plate tuning cap rotation.? I also replaced the cathode resistors with new 15R 1W metal film caps as the originals were out of spec and were not well-matched. Maybe I've botched the alignment(s) and, perhaps, I need to revisit those.? Disappointing as I'd hoped to make things better and apparently that's not the case but I don't yet know what I might have done wrong (yes, I did use the designated dummy load when tweaking the injection couplers which I know is essential to getting those correct). Thanks again,
Barry - N4BUQ
From: "Gary Follett via groups.io" <xntrick1948@...>
One test I have found to be useful is to plot output power on a given band versus position of the TX gain pot on the different bands. If you find that ?the saturation point of output (the point at which increasing the gain position produces no increase in output) versus position of the pot does not change as you go up in bands, then likely you have an alignment issue or a drive issue before the final mixer, because these earlier stages should produce more output than needed on the low bands to make up for poorer efficiency on the higher bands. In other words, you should be able to drive the heck out of the radio on 80 meters well before the saturation point of the TX gain pot.? Receiver gain issues track TX gain issues religiously. If TX gain is weak, receiver gain will be weak too. Gary W0DVN On Apr 28, 2025, at 7:44?PM, Ham Radio via groups.io <bernard.murphy@...> wrote:
Steve: I assume you meant AGC. ? I have a TR-4 that has the same issue. ? Fine on TX but low on RX. ? See attached file.
--
73, Bernie. VE3FWF
Real?radios glow in the dark
<TR-4-tubes-sensitivity.xls>
|
Re: Another TR7 Journey begins
Wiring is fine.? I discovered if I turned the bandswitch knob in between the detents for 7 and 5 MHz which is even with the yellow 7 on the inside ring that 40 meters works OK.? ?All other bands work as they should in the proper dentent.? Any ideas?
?
73, Bill NZ0T
|
Re: Another TR7 Journey begins
Update:? I unsoldered the high current PA load wire so I could work on the receiver without the transmitter issue.? I have managed to get the 40 MHz, 13.695 MHz and? 8.05 MHz oscillators set correctly and the fixed passband adjustments are also correct.? RX is working great except for 40 meters which is dead.? The CAL signal is fine on 40 which leads me to believe there's an issue with band 4 in the LPF module which I had taken out to correct the weird "mods" that someone had done in the past.? So I'll look for a wiring mistake or bad solder connection in that circuit which I am certainly capable of doing!? If I can get that resolved then it's on to figuring out what is wrong with the power amplifier module.
?
But progress!
?
73, Bill NZ0T
|
Re: TR-4 Decreased Sensitivity on High Bands
Two minor clarifications:
The cap across the neutralizing variable cap allows me to set a proper null so that the variable cap can swing through that at about the point where the rotor is meshed approximately half-way (it wouldn't do that with the original cap).
The loading equipment for the injection coupler alignment is called an "alignment load", not necessarily a "dummy load" as I referred to it and I didn't want to cause confusion with the antenna dummy load (and I still wonder about the etymology of that phrase).
Gary, This morning, as I tuned up (into a dummy load) across all bands and I noticed that the XMTR GAIN seems to saturate at about the same point for all bands.? I seem to recall that a few weeks ago (before I started touching up the alignment points), I could get a LOT more gain out of the lower bands. The only component work I've done is to replace the cap across the PA neutralizing cap and have that so I can minimize the spurious oscillations with the appropriate power peak at the valley (dip) of the plate tuning cap rotation.? I also replaced the cathode resistors with new 15R 1W metal film caps as the originals were out of spec and were not well-matched. Maybe I've botched the alignment(s) and, perhaps, I need to revisit those.? Disappointing as I'd hoped to make things better and apparently that's not the case but I don't yet know what I might have done wrong (yes, I did use the designated dummy load when tweaking the injection couplers which I know is essential to getting those correct). Thanks again,
Barry - N4BUQ
From: "Gary Follett via groups.io" <xntrick1948@...>
One test I have found to be useful is to plot output power on a given band versus position of the TX gain pot on the different bands. If you find that ?the saturation point of output (the point at which increasing the gain position produces no increase in output) versus position of the pot does not change as you go up in bands, then likely you have an alignment issue or a drive issue before the final mixer, because these earlier stages should produce more output than needed on the low bands to make up for poorer efficiency on the higher bands. In other words, you should be able to drive the heck out of the radio on 80 meters well before the saturation point of the TX gain pot.? Receiver gain issues track TX gain issues religiously. If TX gain is weak, receiver gain will be weak too. Gary W0DVN On Apr 28, 2025, at 7:44?PM, Ham Radio via groups.io <bernard.murphy@...> wrote:
Steve: I assume you meant AGC. ? I have a TR-4 that has the same issue. ? Fine on TX but low on RX. ? See attached file.
--
73, Bernie. VE3FWF
Real?radios glow in the dark
<TR-4-tubes-sensitivity.xls>
|
Re: TR-4 Decreased Sensitivity on High Bands
Gary,
This morning, as I tuned up (into a dummy load) across all bands and I noticed that the XMTR GAIN seems to saturate at about the same point for all bands.? I seem to recall that a few weeks ago (before I started touching up the alignment points), I could get a LOT more gain out of the lower bands.
The only component work I've done is to replace the cap across the PA neutralizing cap and have that so I can minimize the spurious oscillations with the appropriate power peak at the valley (dip) of the plate tuning cap rotation.? I also replaced the cathode resistors with new 15R 1W metal film caps as the originals were out of spec and were not well-matched.
Maybe I've botched the alignment(s) and, perhaps, I need to revisit those.? Disappointing as I'd hoped to make things better and apparently that's not the case but I don't yet know what I might have done wrong (yes, I did use the designated dummy load when tweaking the injection couplers which I know is essential to getting those correct).
Thanks again,
Barry - N4BUQ
From: "Gary Follett via groups.io" <xntrick1948@...>
One test I have found to be useful is to plot output power on a given band versus position of the TX gain pot on the different bands. If you find that ?the saturation point of output (the point at which increasing the gain position produces no increase in output) versus position of the pot does not change as you go up in bands, then likely you have an alignment issue or a drive issue before the final mixer, because these earlier stages should produce more output than needed on the low bands to make up for poorer efficiency on the higher bands. In other words, you should be able to drive the heck out of the radio on 80 meters well before the saturation point of the TX gain pot.? Receiver gain issues track TX gain issues religiously. If TX gain is weak, receiver gain will be weak too. Gary W0DVN On Apr 28, 2025, at 7:44?PM, Ham Radio via groups.io <bernard.murphy@...> wrote:
Steve: I assume you meant AGC. ? I have a TR-4 that has the same issue. ? Fine on TX but low on RX. ? See attached file.
--
73, Bernie. VE3FWF
Real?radios glow in the dark
<TR-4-tubes-sensitivity.xls>
|
Re: R7 parent board pin out
Thanks....? I missed your answer about board compatibility. Sorry, I don't mean to be a pest.
Thanks for all your help.
73, Dan (W3DF)
One again, yes. The two boards are interchangeable. However as I have already stated you will want to change all the small electrolytics from the output of the TDA2002 to the output of the rectifier/voltage multiplier. See attached photo of mine. That is not a gray cap in the front left. It was the same color as the others before it saw several years of continuous service. While you are at it you might want to put a 10uF from pin 1 of the LM317 to ground. It is recommended on the data sheets to improve ripple rejection and I have learned over the years that it is wise to follow such recommendations.
You may want to consider running the R7 from external DC. It will take a lot of heat out of the box.
On Mon, 28 Apr 2025 23:38:24 -0400
"Daniel W3DF via " <danflan49=[email protected]> wrote:
> And a newer version power supply board.? My R7 has the older one.? Will the
> new one work in an older R7?
> I don't want to destroy anything by trying to use this newer PS board.
--
73
-Jim
NU0C
|
DRAKE USERS NET 7.238 MHZ.
Evan, K9SQG was our NCS for the Sunday Users net. There were 22 people checking into the net, and the users were using the following radios:?
?
A line: ?1
B line: ?1
C line: ?3
TR-4: ?4
TR-5: ?1
TR-7: ?5
Others: ?7
?
Next week's NCS will be Ron, WB4HFN.?
?
73'S,
Mark, WB0IQK
|
Re: TR-4 Decreased Sensitivity on High Bands
Both, actually.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, Apr 28, 2025 at 22:32, n4buq < n4buq@...> wrote:
Which relay did you clean?
Barry - N4BUQ
The one I¡¯m working on goes intermittent all bands but 15 and 10 are both weak, transmit and receive.?
Cleaned the relay but long term that hasn¡¯t helped. Replaced 4 dodgy tubes.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, Apr 28, 2025 at 20:44, Ham Radio via groups.io <
bernard.murphy@...> wrote:
Steve: I assume you meant AGC. ? I have a TR-4 that has the same issue. ? Fine on TX but low on RX. ? See attached file.
--
73, Bernie. VE3FWF
Real?radios glow in the dark
|
Re: R7 parent board pin out
One again, yes. The two boards are interchangeable. However as I have already stated you will want to change all the small electrolytics from the output of the TDA2002 to the output of the rectifier/voltage multiplier. See attached photo of mine. That is not a gray cap in the front left. It was the same color as the others before it saw several years of continuous service. While you are at it you might want to put a 10uF from pin 1 of the LM317 to ground. It is recommended on the data sheets to improve ripple rejection and I have learned over the years that it is wise to follow such recommendations. You may want to consider running the R7 from external DC. It will take a lot of heat out of the box. On Mon, 28 Apr 2025 23:38:24 -0400 "Daniel W3DF via groups.io" <danflan49@...> wrote: And a newer version power supply board. My R7 has the older one. Will the
new one work in an older R7?
I don't want to destroy anything by trying to use this newer PS board. -- 73 -Jim NU0C
|
Re: R7 parent board pin out
Many thanks for the info Jim.? I have a spare Regulator Board, which currently does not work in my R7....? And a newer version power supply board.? My R7 has the older one.? Will the new one work in an older R7?? I don't want to destroy?anything by trying to use this newer PS board.
BTW, today I replaced the regulator board's 4700 uf cap and now my voltages are closer to correct.? Over 12v? out of the regulator board and 10.3v on the 10V rail on the PS board.? I think this R7 has had PS problems in it's past.? Four of the pins on the regulator board have been very hot because the molex connector has turned brown there.
Thanks again for your help.
73, Dan (W3DF)
On Mon, 28 Apr 2025 00:58:03 -0400
"Daniel W3DF via " <danflan49=[email protected]> wrote:
> Yes... I replaced the 220 uf on both the regulator board and the power
> supply board today.? I am also going to replace the 4700 uf capacitor.
> Changing the 220s did not change any of the voltages... still 11.8v instead
> of 13.8v and 11v instead of 10v.? The caps run warm, especially the 220 uf
> on the power supply board, it gets a little hot. I cannot get the voltages
> right with the adjustment pots.? I checked the resistors on the regulator
> board and they are OK and I think the pot is OK too.? I turn it fully
> clockwise to get 11.8v.? Does line voltage affect this much?? I'm running
> it on 115vac? Since I cannot get the power supply board out I cannot get to
> the resistors.
The 220uF on the PS board will run warm because it is essentially filtering square wave ripple from the mutltivibrator oscillator. That's why I recommend a high quality 105C cap. Harder to find in axial, but possible. I would use a 35V part.
It almost sounds like something is drawing too much current. Do you have a scope? If so, check for excessive ripple at the output of the bridge rectifier. The variable regulators on both boards are bog standard 723 circuits which are mature technology. Barring component value drift you should be able to dial in the voltages with no trouble. As has been said, check your Molex connectors thoroughly. Unplug the Power Supply board and see if you can adjust the Regulator to spec. You can also try running the rig from external DC and see if you can net the +10v.
> Are the old and new version power supply boards plug-in compatible?
Yes.
> The R7 works fine the way it is, but there is one strange problem... on the
> BC band switch positions I hear this randomly wandering heterodyne on
> several spots on the dial that interferes with weaker BC signals.
> Sometimes it will wander off to another frequency.
That could be spurs from the 23 KHz multivibrator oscillator on the PS board. Usually they are about 23 KHz apart and will wander a bit.
I am attaching the PS board BOM per your request. I did notice one thing I had not seen before. My R7A has the late version board so I had not looked at the early board much. There is an added capacitor on the schematic that is not present on the TR7 version of this board, C1919. It is shown as a 1000uF from the primary center tap of the transformer to ground. It is NOT listed on the BOM on shown in the pictorial. Which makes me want to open up another R7 so see what is there. If you do have that capacitor it should he replaced as well by the same logic as C1908, as it has been worked hard. If you don't have it, don't worry about it at this point. It is either a late addition or an artifact of a part that was removed from the build. We don't know which at this point and TR7 boards seem to work fine without it.
It is also worth noting that the PS board has two independent ground circuits which connect to the parent board. You have one ground for +10/+5, and another for the +24/-5. Check both.
--
73
-Jim
NU0C
|
Ron Magnus
Jim Shorney
