|
I'm not the first to have done this, just reporting this to help if anyone is on the fence.?
?
I noticed some poor performance on my T-4XC that I pulled out of mothballs this year after a long siesta.?
?
Did the heathkit shop AC-4 upgrade, no difference in output, more of a preventative thing with 48 year old caps.?
?
Started poking around the finals section and noticed that the cathode resistors were 17.2 and 19.3 ohms, pretty out of spec for 15 ohm resistors. This week I got around to looking at the rest of the circuit including screen, screen supply, and meter shunt resistors.?
- R49 2W 1.5Kohm was heat-swollen and running 1600 ohms
- R50/R51 screen resistors (68 ohm) were measuring 73/76 ohms
- R59 meter shunt resistor (3.3 ohm) was measuring 4.5 ohms
Replaced all of these with upgraded/over-spec components and WOW what a difference. Easily hits 100W output on 10M, 150W+ on lower bands.?
No, I'm not going to run this unit at those numbers but nice to see the potential. And this is with what I consider to be "soft" final tubes.?
?
Also installed a couple of binding posts on the rear panel which pigtail across the meter shunt resistor for easier bias set/checks.?
?
I could post pictures of the mods if anyone is curious.?
--
Craig/W8CS
Greenville, SC
|
Yep, those resistors are important! ?My TR-4Cw RIT has excellent cosmetics and the cathode resistors were all 17.5 to 18.5. Screen resistors were around 80. Output on 40m went from 150 to 180.?
I¡¯ll now be reviewing all of my transmitters and replacing anything out of tolerance.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 10, 2025 at 15:14, Craig W8CS via groups.io < craig_severson@...> wrote:
I'm not the first to have done this, just reporting this to help if anyone is on the fence.?
?
I noticed some poor performance on my T-4XC that I pulled out of mothballs this year after a long siesta.?
?
Did the heathkit shop AC-4 upgrade, no difference in output, more of a preventative thing with 48 year old caps.?
?
Started poking around the finals section and noticed that the cathode resistors were 17.2 and 19.3 ohms, pretty out of spec for 15 ohm resistors. This week I got around to looking at the rest of the circuit including screen, screen supply, and meter shunt resistors.?
- R49 2W 1.5Kohm was heat-swollen and running 1600 ohms
- R50/R51 screen resistors (68 ohm) were measuring 73/76 ohms
- R59 meter shunt resistor (3.3 ohm) was measuring 4.5 ohms
Replaced all of these with upgraded/over-spec components and WOW what a difference. Easily hits 100W output on 10M, 150W+ on lower bands.?
No, I'm not going to run this unit at those numbers but nice to see the potential. And this is with what I consider to be "soft" final tubes.?
?
Also installed a couple of binding posts on the rear panel which pigtail across the meter shunt resistor for easier bias set/checks.?
?
I could post pictures of the mods if anyone is curious.?
--
Craig/W8CS
Greenville, SC
|
Craig:
Congrats on the resistors already checked and replaced.? Those parts are standard checks and "replace as required" for me, which in those particular cases is often.
If you still have the T-4XC open, check the voltage on pin 1 of V-9a and pin 6 of V-9b.? If voltage is low, check resistors R-91 and R-81 (you'll need K4OAH's Service manual to find these easily) as I have found these tend to drift high as well,?especially R-91.? I have seen voltage on pin 1 as low as 68 VDC before changing R-91.
73, Peter VE7PS
On Fri, Apr 11, 2025 at 6:08?AM Steve Wedge, W1ES/4 via <w1es= [email protected]> wrote: Yep, those resistors are important!? My TR-4Cw RIT has excellent cosmetics and the cathode resistors were all 17.5 to 18.5. Screen resistors were around 80. Output on 40m went from 150 to 180.?
I¡¯ll now be reviewing all of my transmitters and replacing anything out of tolerance.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 10, 2025 at 15:14, Craig W8CS via < craig_severson@...> wrote:
I'm not the first to have done this, just reporting this to help if anyone is on the fence.?
?
I noticed some poor performance on my T-4XC that I pulled out of mothballs this year after a long siesta.?
?
Did the heathkit shop AC-4 upgrade, no difference in output, more of a preventative thing with 48 year old caps.?
?
Started poking around the finals section and noticed that the cathode resistors were 17.2 and 19.3 ohms, pretty out of spec for 15 ohm resistors. This week I got around to looking at the rest of the circuit including screen, screen supply, and meter shunt resistors.?
- R49 2W 1.5Kohm was heat-swollen and running 1600 ohms
- R50/R51 screen resistors (68 ohm) were measuring 73/76 ohms
- R59 meter shunt resistor (3.3 ohm) was measuring 4.5 ohms
Replaced all of these with upgraded/over-spec components and WOW what a difference. Easily hits 100W output on 10M, 150W+ on lower bands.?
No, I'm not going to run this unit at those numbers but nice to see the potential. And this is with what I consider to be "soft" final tubes.?
?
Also installed a couple of binding posts on the rear panel which pigtail across the meter shunt resistor for easier bias set/checks.?
?
I could post pictures of the mods if anyone is curious.?
--
Craig/W8CS
Greenville, SC
|
Peter, thanks for your note. These are almost assuredly out of spec, as I noticed some odd behavior around this circuit/tube. The sidetone was starting to warble like a pubescent lad, and the gain knob has to be cranked up the entire way to get CW drive. It goes from 1 watt output to 100+W in the last 5 degrees of control of the gain knob.?
?
I'll open up the patient once again. cheers
--
Craig/W8CS
Greenville, SC
|
I just checked the cathode resistors in my TR-4 and they probably should be replaced.? They're not equal and are 20% to 40% over 15 ohms.? Is it recommended to stick with carbon comps for those or will film resistors be okay?? If I remember correctly, these should be kept at 1/4W but not 100% sure on that either.
Thanks for the reminder! Barry - N4BUQ
Craig: Congrats on the resistors already checked and replaced.? Those parts are standard checks and "replace as required" for me, which in those particular cases is often. If you still have the T-4XC open, check the voltage on pin 1 of V-9a and pin 6 of V-9b.? If voltage is low, check resistors R-91 and R-81 (you'll need K4OAH's Service manual to find these easily) as I have found these tend to drift high as well,?especially R-91.? I have seen voltage on pin 1 as low as 68 VDC before changing R-91. 73, Peter VE7PS
On Fri, Apr 11, 2025 at 6:08?AM Steve Wedge, W1ES/4 via <w1es= [email protected]> wrote: Yep, those resistors are important!? My TR-4Cw RIT has excellent cosmetics and the cathode resistors were all 17.5 to 18.5. Screen resistors were around 80. Output on 40m went from 150 to 180.?
I¡¯ll now be reviewing all of my transmitters and replacing anything out of tolerance.? Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 10, 2025 at 15:14, Craig W8CS via < craig_severson@...> wrote:
I'm not the first to have done this, just reporting this to help if anyone is on the fence.?
?
I noticed some poor performance on my T-4XC that I pulled out of mothballs this year after a long siesta.?
?
Did the heathkit shop AC-4 upgrade, no difference in output, more of a preventative thing with 48 year old caps.?
?
Started poking around the finals section and noticed that the cathode resistors were 17.2 and 19.3 ohms, pretty out of spec for 15 ohm resistors. This week I got around to looking at the rest of the circuit including screen, screen supply, and meter shunt resistors.?
- R49 2W 1.5Kohm was heat-swollen and running 1600 ohms
- R50/R51 screen resistors (68 ohm) were measuring 73/76 ohms
- R59 meter shunt resistor (3.3 ohm) was measuring 4.5 ohms
Replaced all of these with upgraded/over-spec components and WOW what a difference. Easily hits 100W output on 10M, 150W+ on lower bands.?
No, I'm not going to run this unit at those numbers but nice to see the potential. And this is with what I consider to be "soft" final tubes.?
?
Also installed a couple of binding posts on the rear panel which pigtail across the meter shunt resistor for easier bias set/checks.?
?
I could post pictures of the mods if anyone is curious.?
--
Craig/W8CS
Greenville, SC
|
Barry:
On the PA cathode resistors, note they are 1 watt resistors in all the 4-line gear.? I've been using?film resistors for years without issue.??
73 PS
I just checked the cathode resistors in my TR-4 and they probably should be replaced.? They're not equal and are 20% to 40% over 15 ohms.? Is it recommended to stick with carbon comps for those or will film resistors be okay?? If I remember correctly, these should be kept at 1/4W but not 100% sure on that either.
Thanks for the reminder! Barry - N4BUQ Craig: Congrats on the resistors already checked and replaced.? Those parts are standard checks and "replace as required" for me, which in those particular cases is often. If you still have the T-4XC open, check the voltage on pin 1 of V-9a and pin 6 of V-9b.? If voltage is low, check resistors R-91 and R-81 (you'll need K4OAH's Service manual to find these easily) as I have found these tend to drift high as well,?especially R-91.? I have seen voltage on pin 1 as low as 68 VDC before changing R-91. 73, Peter VE7PS
On Fri, Apr 11, 2025 at 6:08?AM Steve Wedge, W1ES/4 via <w1es= [email protected]> wrote: Yep, those resistors are important!? My TR-4Cw RIT has excellent cosmetics and the cathode resistors were all 17.5 to 18.5. Screen resistors were around 80. Output on 40m went from 150 to 180.?
I¡¯ll now be reviewing all of my transmitters and replacing anything out of tolerance.? Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 10, 2025 at 15:14, Craig W8CS via < craig_severson@...> wrote:
I'm not the first to have done this, just reporting this to help if anyone is on the fence.?
?
I noticed some poor performance on my T-4XC that I pulled out of mothballs this year after a long siesta.?
?
Did the heathkit shop AC-4 upgrade, no difference in output, more of a preventative thing with 48 year old caps.?
?
Started poking around the finals section and noticed that the cathode resistors were 17.2 and 19.3 ohms, pretty out of spec for 15 ohm resistors. This week I got around to looking at the rest of the circuit including screen, screen supply, and meter shunt resistors.?
- R49 2W 1.5Kohm was heat-swollen and running 1600 ohms
- R50/R51 screen resistors (68 ohm) were measuring 73/76 ohms
- R59 meter shunt resistor (3.3 ohm) was measuring 4.5 ohms
Replaced all of these with upgraded/over-spec components and WOW what a difference. Easily hits 100W output on 10M, 150W+ on lower bands.?
No, I'm not going to run this unit at those numbers but nice to see the potential. And this is with what I consider to be "soft" final tubes.?
?
Also installed a couple of binding posts on the rear panel which pigtail across the meter shunt resistor for easier bias set/checks.?
?
I could post pictures of the mods if anyone is curious.?
--
Craig/W8CS
Greenville, SC
|
For whatever reason, I was thinking the "standard, basic" carbon composition resistors that are everywhere in vintage gear were 1/4W but instead I think they're 1/2W.? The typical schematic would read "unless otherwise stated, resistors are 1/2W", etc., and I was thinking those were stated as 1/4W which would have been pretty atypical back then.? Anyway, I got my 1/4W and 1/2W sizes confused in my head.
Apparently the ones in my TR-4 are 1/2W (measured at 0.135" diameter x 0.4" long) and I wonder why Drake did that if they're supposed to be 1W.? These appear to be factory originals.
Thanks, Barry - N4BUQ
Barry: On the PA cathode resistors, note they are 1 watt resistors in all the 4-line gear.? I've been using?film resistors for years without issue.?? 73 PS
I just checked the cathode resistors in my TR-4 and they probably should be replaced.? They're not equal and are 20% to 40% over 15 ohms.? Is it recommended to stick with carbon comps for those or will film resistors be okay?? If I remember correctly, these should be kept at 1/4W but not 100% sure on that either. Thanks for the reminder! Barry - N4BUQ Craig: Congrats on the resistors already checked and replaced.? Those parts are standard checks and "replace as required" for me, which in those particular cases is often. If you still have the T-4XC open, check the voltage on pin 1 of V-9a and pin 6 of V-9b.? If voltage is low, check resistors R-91 and R-81 (you'll need K4OAH's Service manual to find these easily) as I have found these tend to drift high as well,?especially R-91.? I have seen voltage on pin 1 as low as 68 VDC before changing R-91. 73, Peter VE7PS
On Fri, Apr 11, 2025 at 6:08?AM Steve Wedge, W1ES/4 via <w1es= [email protected]> wrote: Yep, those resistors are important!? My TR-4Cw RIT has excellent cosmetics and the cathode resistors were all 17.5 to 18.5. Screen resistors were around 80. Output on 40m went from 150 to 180.?
I¡¯ll now be reviewing all of my transmitters and replacing anything out of tolerance.? Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 10, 2025 at 15:14, Craig W8CS via < craig_severson@...> wrote:
I'm not the first to have done this, just reporting this to help if anyone is on the fence.?
?
I noticed some poor performance on my T-4XC that I pulled out of mothballs this year after a long siesta.?
?
Did the heathkit shop AC-4 upgrade, no difference in output, more of a preventative thing with 48 year old caps.?
?
Started poking around the finals section and noticed that the cathode resistors were 17.2 and 19.3 ohms, pretty out of spec for 15 ohm resistors. This week I got around to looking at the rest of the circuit including screen, screen supply, and meter shunt resistors.?
- R49 2W 1.5Kohm was heat-swollen and running 1600 ohms
- R50/R51 screen resistors (68 ohm) were measuring 73/76 ohms
- R59 meter shunt resistor (3.3 ohm) was measuring 4.5 ohms
Replaced all of these with upgraded/over-spec components and WOW what a difference. Easily hits 100W output on 10M, 150W+ on lower bands.?
No, I'm not going to run this unit at those numbers but nice to see the potential. And this is with what I consider to be "soft" final tubes.?
?
Also installed a couple of binding posts on the rear panel which pigtail across the meter shunt resistor for easier bias set/checks.?
?
I could post pictures of the mods if anyone is curious.?
--
Craig/W8CS
Greenville, SC
|
I have never had reason to dig into the ancillary PCBs in the bottom of the T4 chassis before. Honestly don't know how you extract anything from the bottom of those boards! Will try again tomorrow once I restore some patience.?
--
Craig/W8CS
Greenville, SC
|
I sometimes remove the screws holding the board to the chassis. I can move the board enough to replace components.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Fri, Apr 11, 2025 at 21:34, Craig W8CS via groups.io < craig_severson@...> wrote:
I have never had reason to dig into the ancillary PCBs in the bottom of the T4 chassis before. Honestly don't know how you extract anything from the bottom of those boards! Will try again tomorrow once I restore some patience.?
--
Craig/W8CS
Greenville, SC
|
I received my TR-4 manual from K4OAH last night and the cathode resistors are clearly marked as 1W in the schematic as well as the parts list.? The schematic I found on line did not show that "1W" so I wasn't sure.
I'll definitely be getting 1W resistors.? Thanks for the info!
Barry - N4BUQ
For whatever reason, I was thinking the "standard, basic" carbon composition resistors that are everywhere in vintage gear were 1/4W but instead I think they're 1/2W.? The typical schematic would read "unless otherwise stated, resistors are 1/2W", etc., and I was thinking those were stated as 1/4W which would have been pretty atypical back then.? Anyway, I got my 1/4W and 1/2W sizes confused in my head. Apparently the ones in my TR-4 are 1/2W (measured at 0.135" diameter x 0.4" long) and I wonder why Drake did that if they're supposed to be 1W.? These appear to be factory originals. Thanks, Barry - N4BUQ Barry: On the PA cathode resistors, note they are 1 watt resistors in all the 4-line gear.? I've been using?film resistors for years without issue.?? 73 PS
I just checked the cathode resistors in my TR-4 and they probably should be replaced.? They're not equal and are 20% to 40% over 15 ohms.? Is it recommended to stick with carbon comps for those or will film resistors be okay?? If I remember correctly, these should be kept at 1/4W but not 100% sure on that either. Thanks for the reminder! Barry - N4BUQ Craig: Congrats on the resistors already checked and replaced.? Those parts are standard checks and "replace as required" for me, which in those particular cases is often. If you still have the T-4XC open, check the voltage on pin 1 of V-9a and pin 6 of V-9b.? If voltage is low, check resistors R-91 and R-81 (you'll need K4OAH's Service manual to find these easily) as I have found these tend to drift high as well,?especially R-91.? I have seen voltage on pin 1 as low as 68 VDC before changing R-91. 73, Peter VE7PS
On Fri, Apr 11, 2025 at 6:08?AM Steve Wedge, W1ES/4 via <w1es= [email protected]> wrote: Yep, those resistors are important!? My TR-4Cw RIT has excellent cosmetics and the cathode resistors were all 17.5 to 18.5. Screen resistors were around 80. Output on 40m went from 150 to 180.?
I¡¯ll now be reviewing all of my transmitters and replacing anything out of tolerance.? Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 10, 2025 at 15:14, Craig W8CS via < craig_severson@...> wrote:
I'm not the first to have done this, just reporting this to help if anyone is on the fence.?
?
I noticed some poor performance on my T-4XC that I pulled out of mothballs this year after a long siesta.?
?
Did the heathkit shop AC-4 upgrade, no difference in output, more of a preventative thing with 48 year old caps.?
?
Started poking around the finals section and noticed that the cathode resistors were 17.2 and 19.3 ohms, pretty out of spec for 15 ohm resistors. This week I got around to looking at the rest of the circuit including screen, screen supply, and meter shunt resistors.?
- R49 2W 1.5Kohm was heat-swollen and running 1600 ohms
- R50/R51 screen resistors (68 ohm) were measuring 73/76 ohms
- R59 meter shunt resistor (3.3 ohm) was measuring 4.5 ohms
Replaced all of these with upgraded/over-spec components and WOW what a difference. Easily hits 100W output on 10M, 150W+ on lower bands.?
No, I'm not going to run this unit at those numbers but nice to see the potential. And this is with what I consider to be "soft" final tubes.?
?
Also installed a couple of binding posts on the rear panel which pigtail across the meter shunt resistor for easier bias set/checks.?
?
I could post pictures of the mods if anyone is curious.?
--
Craig/W8CS
Greenville, SC
|
Barry, be aware that modern metal film resistors are quite a bit smaller, physically.? They are well capable of their 1W rating but they look almost as small as 1/2W CC resistors.
I've replaced the cathode resistors in several rigs already with the new metal film and they work great.
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Saturday, April 12th, 2025 at 11:15 AM, n4buq <n4buq@...> wrote:
I received my TR-4 manual from K4OAH last night and the cathode resistors are clearly marked as 1W in the schematic as well as the parts list.? The schematic I found on line did not show that "1W" so I wasn't sure.
I'll definitely be getting 1W resistors.? Thanks for the info!
Barry - N4BUQ For whatever reason, I was thinking the "standard, basic" carbon composition resistors that are everywhere in vintage gear were 1/4W but instead I think they're 1/2W.? The typical schematic would read "unless otherwise stated, resistors are 1/2W", etc., and I was thinking those were stated as 1/4W which would have been pretty atypical back then.? Anyway, I got my 1/4W and 1/2W sizes confused in my head. Apparently the ones in my TR-4 are 1/2W (measured at 0.135" diameter x 0.4" long) and I wonder why Drake did that if they're supposed to be 1W.? These appear to be factory originals. Thanks, Barry - N4BUQ Barry: On the PA cathode resistors, note they are 1 watt resistors in all the 4-line gear.? I've been using?film resistors for years without issue.?? 73 PS
I just checked the cathode resistors in my TR-4 and they probably should be replaced.? They're not equal and are 20% to 40% over 15 ohms.? Is it recommended to stick with carbon comps for those or will film resistors be okay?? If I remember correctly, these should be kept at 1/4W but not 100% sure on that either. Thanks for the reminder! Barry - N4BUQ Craig: Congrats on the resistors already checked and replaced.? Those parts are standard checks and "replace as required" for me, which in those particular cases is often. If you still have the T-4XC open, check the voltage on pin 1 of V-9a and pin 6 of V-9b.? If voltage is low, check resistors R-91 and R-81 (you'll need K4OAH's Service manual to find these easily) as I have found these tend to drift high as well,?especially R-91.? I have seen voltage on pin 1 as low as 68 VDC before changing R-91. 73, Peter VE7PS
On Fri, Apr 11, 2025 at 6:08?AM Steve Wedge, W1ES/4 via <w1es= [email protected]> wrote: Yep, those resistors are important!? My TR-4Cw RIT has excellent cosmetics and the cathode resistors were all 17.5 to 18.5. Screen resistors were around 80. Output on 40m went from 150 to 180.?
I¡¯ll now be reviewing all of my transmitters and replacing anything out of tolerance.? Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 10, 2025 at 15:14, Craig W8CS via < craig_severson@...> wrote:
I'm not the first to have done this, just reporting this to help if anyone is on the fence.?
?
I noticed some poor performance on my T-4XC that I pulled out of mothballs this year after a long siesta.?
?
Did the heathkit shop AC-4 upgrade, no difference in output, more of a preventative thing with 48 year old caps.?
?
Started poking around the finals section and noticed that the cathode resistors were 17.2 and 19.3 ohms, pretty out of spec for 15 ohm resistors. This week I got around to looking at the rest of the circuit including screen, screen supply, and meter shunt resistors.?
- R49 2W 1.5Kohm was heat-swollen and running 1600 ohms
- R50/R51 screen resistors (68 ohm) were measuring 73/76 ohms
- R59 meter shunt resistor (3.3 ohm) was measuring 4.5 ohms
Replaced all of these with upgraded/over-spec components and WOW what a difference. Easily hits 100W output on 10M, 150W+ on lower bands.?
No, I'm not going to run this unit at those numbers but nice to see the potential. And this is with what I consider to be "soft" final tubes.?
?
Also installed a couple of binding posts on the rear panel which pigtail across the meter shunt resistor for easier bias set/checks.?
?
I could post pictures of the mods if anyone is curious.?
--
Craig/W8CS
Greenville, SC
|
Steve wrote "I sometimes remove the screws holding the board to the chassis. I can move the board enough to replace components. "
?
That's what I had to do. All I had on hand were 1/2W resistors and the leads were too fat to fit in the holes, so I had to hit Harbor Freight to get a set of dental picks with 90 degree hooks that I could use to ream out the holes. So tedious. Transmitter actually does work better now as I have access to the entire range of the gain control vs. the final 5 degrees as before. All the resistors (and more) that Peter had called out were all way out of spec.?
?
Someone wrote in overnight and requested pictures of the resistor mods in the final stage that I did. I hesitate to do this as I did these mods for me and my own OCD about over-engineering, versus some of the accepted best practices that I've read on this site.?
Here is the mod that I did for the meter shunt resistor R59. Not only could I not accurately set my bias due to the "non-zero" meter on the T-4XC, but the resistor was reading way out of spec (again!) and therefore giving inaccurate iP readings. I decided to ridiculously over-spec it to 25W, mostly so I could get a quality 1% resistor? on there that I could branch off leads to binding posts. That way I could measure the drop across the 3.3 ohm resistor externally, and accurately set bias. I fabricated a little copper clip to hold the resistor. At full plate current this resistor should only dissipate .4W so heat should not be an issue, but I'm covered.?
?
I also didn't like the fact that the cathode resistors were being used as "fuses" and seemed vulnerable to heat stress. So I set up some 5W units to heat-sink against the chassis.?
?
So far, so good. TX a lot more stable and the output difference is noticeable. Again, mods are very personal and not everyone's cup of tea.?
?
Thanks Steve & Peter for your suggestions & advice.?
--
Craig/W8CS
Greenville, SC
|
Yes, I've run into that with other things.? A 2W from some manufacturers looks like a grain of rice.? I don't like it but it's pretty much what we have now.? At least they're not as drifty as carbon comps.
Thanks,
Barry - N4BUQ
From: "Steve Wedge, W1ES/4 via groups.io" <w1es@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Saturday, April 12, 2025 12:08:11 PM
Subject: Re: [DRAKE-RADIO] Replaced T-4 Finals Resistors, Big Difference
Barry, be aware that modern metal film resistors are quite a bit smaller, physically.? They are well capable of their 1W rating but they look almost as small as 1/2W CC resistors.
I've replaced the cathode resistors in several rigs already with the new metal film and they work great.
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Saturday, April 12th, 2025 at 11:15 AM, n4buq <n4buq@...> wrote:
I received my TR-4 manual from K4OAH last night and the cathode resistors are clearly marked as 1W in the schematic as well as the parts list.? The schematic I found on line did not show that "1W" so I wasn't sure. I'll definitely be getting 1W resistors.? Thanks for the info! Barry - N4BUQ For whatever reason, I was thinking the "standard, basic" carbon composition resistors that are everywhere in vintage gear were 1/4W but instead I think they're 1/2W.? The typical schematic would read "unless otherwise stated, resistors are 1/2W", etc., and I was thinking those were stated as 1/4W which would have been pretty atypical back then.? Anyway, I got my 1/4W and 1/2W sizes confused in my head. Apparently the ones in my TR-4 are 1/2W (measured at 0.135" diameter x 0.4" long) and I wonder why Drake did that if they're supposed to be 1W.? These appear to be factory originals. Thanks, Barry - N4BUQ Barry: On the PA cathode resistors, note they are 1 watt resistors in all the 4-line gear.? I've been using?film resistors for years without issue.?? 73 PS
I just checked the cathode resistors in my TR-4 and they probably should be replaced.? They're not equal and are 20% to 40% over 15 ohms.? Is it recommended to stick with carbon comps for those or will film resistors be okay?? If I remember correctly, these should be kept at 1/4W but not 100% sure on that either. Thanks for the reminder! Barry - N4BUQ Craig: Congrats on the resistors already checked and replaced.? Those parts are standard checks and "replace as required" for me, which in those particular cases is often. If you still have the T-4XC open, check the voltage on pin 1 of V-9a and pin 6 of V-9b.? If voltage is low, check resistors R-91 and R-81 (you'll need K4OAH's Service manual to find these easily) as I have found these tend to drift high as well,?especially R-91.? I have seen voltage on pin 1 as low as 68 VDC before changing R-91. 73, Peter VE7PS
On Fri, Apr 11, 2025 at 6:08?AM Steve Wedge, W1ES/4 via <w1es= [email protected]> wrote: Yep, those resistors are important!? My TR-4Cw RIT has excellent cosmetics and the cathode resistors were all 17.5 to 18.5. Screen resistors were around 80. Output on 40m went from 150 to 180.?
I¡¯ll now be reviewing all of my transmitters and replacing anything out of tolerance.? Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Thu, Apr 10, 2025 at 15:14, Craig W8CS via < craig_severson@...> wrote:
I'm not the first to have done this, just reporting this to help if anyone is on the fence.?
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I noticed some poor performance on my T-4XC that I pulled out of mothballs this year after a long siesta.?
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Did the heathkit shop AC-4 upgrade, no difference in output, more of a preventative thing with 48 year old caps.?
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Started poking around the finals section and noticed that the cathode resistors were 17.2 and 19.3 ohms, pretty out of spec for 15 ohm resistors. This week I got around to looking at the rest of the circuit including screen, screen supply, and meter shunt resistors.?
- R49 2W 1.5Kohm was heat-swollen and running 1600 ohms
- R50/R51 screen resistors (68 ohm) were measuring 73/76 ohms
- R59 meter shunt resistor (3.3 ohm) was measuring 4.5 ohms
Replaced all of these with upgraded/over-spec components and WOW what a difference. Easily hits 100W output on 10M, 150W+ on lower bands.?
No, I'm not going to run this unit at those numbers but nice to see the potential. And this is with what I consider to be "soft" final tubes.?
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Also installed a couple of binding posts on the rear panel which pigtail across the meter shunt resistor for easier bias set/checks.?
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I could post pictures of the mods if anyone is curious.?
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Craig/W8CS
Greenville, SC
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Craig W8CS