I’ve always subscribed to the notion that if it ain’t broke, don’t fix it.

Wholesale replacement of capacitors always makes me break out in a cold sweat.

Mike WB8VGE

The Heathkit shop

On Apr 7, 2025, at 9:51 AM, Steven KW4H via <reedsteve@...> wrote:

The issue was found this morning, and it's one of those things that suddenly hits you across the head.? A previous owner had recapped this 2-C and installed C-53, which is on the AVC voltage line, in reverse.? I'm pulling Board 1 to fix that, and will also check everything else on that board -- and upgrade the rectifiers.

?

73 - Steve, KW4H

I’ve always subscribed to the notion that if it ain’t broke, don’t fix it.

Wholesale replacement of capacitors always makes me break out in a cold sweat.

Mike WB8VGE

The Heathkit shop

On Apr 7, 2025, at 9:51 AM, Steven KW4H via <reedsteve@...> wrote:

The issue was found this morning, and it's one of those things that suddenly hits you across the head.? A previous owner had recapped this 2-C and installed C-53, which is on the AVC voltage line, in reverse.? I'm pulling Board 1 to fix that, and will also check everything else on that board -- and upgrade the rectifiers.

?

73 - Steve, KW4H

On Apr 7, 2025, at 9:51 AM, Steven KW4H via <reedsteve@...> wrote:

The issue was found this morning, and it's one of those things that suddenly hits you across the head.? A previous owner had recapped this 2-C and installed C-53, which is on the AVC voltage line, in reverse.? I'm pulling Board 1 to fix that, and will also check everything else on that board -- and upgrade the rectifiers.

?

73 - Steve, KW4H

The issue was found this morning, and it's one of those things that suddenly hits you across the head.? A previous owner had recapped this 2-C and installed C-53, which is on the AVC voltage line, in reverse.? I'm pulling Board 1 to fix that, and will also check everything else on that board -- and upgrade the rectifiers.

?

73 - Steve, KW4H

On Apr 6, 2025, at 3:42?PM, atlasstuff via groups.io <g4fph@...> wrote:

?

Ed,

?

My suggestion would be to pair your TR5 with a Datong ASP, if you can find one for sensible money over there.

?

I acquired a Drake SP75 some while back and was curious as to how it sounded / performed in absolute terms and when compared with the Datong, when connected to my TR4310 and TR7 transceivers. My conclusion after some A/B testing and listening to my transmitted signal on a WebSDR (so over a real, noisy radio channel, not just monitoring clean / locally) was that the SP75 was quite good, but the Datong had the edge.

?

Both the Drake and Datong units are proper RF clippers. The Drake makes it's SSB using the filter method at 459 kHz, while the Datong makes it's SSB at 60 kHz using the phasing method. Both units feature audio compressors in front of the clipping stages to reduce the dynamic range of the audio baseband and thereby make the clipping process more effective.

?

To my ears, the SP75 sounded most useful / at it's best with next to no clipping action, i.e. just benefitting from the effect of the audio compressor. Adding clipping, I thought it started to sound less good at even quite modest levels (of clipping). By contrast, the Datong sounds at it's best with low to medium levels of clipping. Even at high levels of clipping, the Datong does not sound terrible, just over-processed / like a one man pile-up!

?

The Datong has been my go-to clipper for many years. With a Shure 444 driving it, it seems to pair well with any of my vintage SSB radio. It's quite a 'clever' design that uses unbuffered CMOS logic IC as analogue amplifiers in some parts of the circuitry. If needs be, it's still very mendable circa 40 years after it was first introduced. There's an article (linked below) where a chap was having trouble with the carrier oscillator / resonator and filters in an SP75.

Replacements for those parts are certainly hard to come by over here (so I hope mine never go faulty)!

?

Regards,

?

Mark, G4FPH.

?

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.

Sent from for iOS

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.

Sent from for iOS

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.

Sent from for iOS

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.

Sent from for iOS

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

?

?

?

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.

Sent from for iOS

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

?

?

?

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

?

?

?

On Apr 6, 2025, at 4:48?PM, Mark N2DMI via groups.io <markkiziuk1@...> wrote:

?

I am writing this as a new topic instead of staying on the scraping sound topic.

?

After I tuned up the TR-4CW on 80 the S meter slowly went to the right and stayed there and now I have about hardly any volume even with the RF gain and volume knobs

fully clockwise.

Also by adjusting the RF gain (the little metal finger piece) the volume and the S meter do NOT change. Its as if the RF gain now does nothing.

Any ideas? I don't want to spend alot of time on this because with my work schedule there is hardly any time.

Mark