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Re: Added photo album DRAKE TR-7 DIGITAL VFO
#photo-notice
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Hi Paul,
I just added a close in SA plot of the output of my TR-7 digital VFO which uses the Si5351A device.
Regards,
Dale W4OP
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Photo Si5351A CLOSE IN.png uploaded
#photo-notice
Group Notification
The following photos have been uploaded to the DRAKE TR-7 DIGITAL VFO photo album of the [email protected] group. By: Dale Parfitt <PARINC1@...> |
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Re: Photo Notifications
#photo-notice
Paul,
I'm curious as to the RF output voltage you're obtaining from your Si5351A VFO.? I suspect you're amplifying for use into the Drake 2NT?? I'm using the same Si board with a homebrew RF voltage amp (images below).? With a bifilar output transformer, it produces 30Vp-p from a +12V source.? That's enough to drive most boatanchor transmitters. My only issue from these PLL and DDS VFOs is close-in spurs next to the carrier frequency.? They're not nearly as clean as a classic PTO circuit.? I typically see worst-case spurs at -35 dBc.? They're down quite a bit, but it's possible to detect the spurs from stations when propagation is good.? Paul, W9AC ? |
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Photo Notifications
#photo-notice
Group Notification
Paul Lukosius <plukosius@...> added the photo album Drake 2-NT Digital VFO : An EU station complained about my HA-5 drifting on 10M so I decided to put together a digital VFO. This is the QRP Labs VFO kit that uses the Si5351A synthesizer. Added a 5V reed relay to switch the output ON/OFF and use a 1N4007 blocking diode so it can be keyed by the 2-NT VFO Key line. Powered by a cell phone charger, it drives the 2-NT to full output on all bands. The following photos have been uploaded to the Drake 2-NT Digital VFO photo album of the [email protected] group. By: Paul Lukosius <plukosius@...> |
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Re: TR7 PTO
On 2024-04-14 13:02, jerry-KF6VB wrote:
OK - I swapped PTO's. Had to do a little mix & match. Put it all*** OK, I pulled it apart again. Recleaned the plastic gears, and cleaned and lubed everything that was metal-to-metal sliding contact. Put it back together, and all is well. The tuning dials turn like they should. The reason for the "fast & strange tuning" was that my lab supply was not delivering quite enough current to run the rig. I arranged for more current, and the tuning cleaned right up. UNFORTUNATELY, I put it together with the clear disk backwards. So the numbers are all mirror image. Gotta take it all apart again. Sometimes, it don't pay to get up in the morning. Today was the local ham swap. It was a little smaller than usual because rain was forecast. Didn't see anything Drake. There was a guy with a KWM-2A project for $300. I was tempted... I did find fuses for my frequency counter. Of course, if I put them in, it'll just blow them again. Gotta actually troubleshoot it. I suspect that the main switching transistor is shorted - leading to overvoltage, which is then "corrected" by the crowbar circuit. - Jerry, KF6VB |
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Re: TR7 PTO
I have a TR7 PTO, total;y disassembled where it could be, ultrasonic cleaned to remove old lubricant, relayed and reassembled. This one its as good as factory new. $50 shipped in CONUSA.
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Gary W0DVN On Apr 14, 2024, at 3:02?PM, jerry-KF6VB <jerry@...> wrote: |
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Re: TR7 PTO
Jerry,
I had the same problem (PTO output dropping) in my T-4XB when I bought it. It turned out to be the ground connection was via a lug under the PTO mounting stud.? Probably was loose from the factory. I finally found it by poking around.? I poked it enough that the buffer transistor inside failed, I figured the PTO had found ground through that transistor somehow. Maybe your problem? 73, Gary WB6OGD |
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TR7 PTO
Hello All,
You may remember my TR7 that loses lock. But only when it's in the right mood. Tap on the big tuning knob and *poof* - no lock. Hit the "FIX" button a couple times, and lock comes back. I had traced it down to the output of the PTO. Tap the big tuning knob, the output of the PTO goes down to 1/10th of what it should be. I even traced it down to the low pass filter at the output of the PTO. When the fault occurred, the voltage at the output was low, and the AC voltage at the buffer transistor was HIGH. So it pretty much had to be one of those three parts, or their connections. I resoldered all the connections, including the feedthrough at the ceramic front plate, and the problem went away. Yay! I put the radio back together and used it...for a while...until the problem came back :(. So now, I have the TR7 back on the bench. Flipped down the front panel, popped the can off the PTO - ready to fix it once & for all. Only thing is, it's not doing it now. Damn I hate that. I just know it will misbehave if I just put it back together. Maybe I should just replace the whole LPF? I do have a second PTO; might just swap them. Only thing is - that second PTO doesn't have its gear train together. Somebody ( not me! ) had tried to clean the frequency display disks with some sort of powerful solvent and they'd gone all blotchy-milky. And it doesn't come off. So I would have to move the gear train from the intermittant PTO to the other one. Is that a big deal? One complication - my good HP frequency counter has died. Blows its fuse. So I would have to set up this thing without a counter. Or set the TR7 - all apart - aside, and troubleshoot the counter. I'd really rather not do that. I don't like having stuff laying around all apart. OK - I swapped PTO's. Had to do a little mix & match. Put it all together, it works. HOWEVER - the gear train is not working correctly. Both indicator wheels are turning in unison, and the frequency change is way too swift. Something need lubrication? - Jerry, KF6VB |
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Photo Notifications
#photo-notice
Group Notification
The following photos have been uploaded to the DRAKE TR-7 DIGITAL VFO photo album of the [email protected] group. By: Dale Parfitt <PARINC1@...> The following photos have been uploaded to the DRAKE TR-7 DIGITAL VFO photo album of the [email protected] group. By: Dale Parfitt <PARINC1@...> |
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Added photo album DRAKE TR-7 DIGITAL VFO
#photo-notice
Group Notification
Dale Parfitt <PARINC1@...> added the photo album DRAKE TR-7 DIGITAL VFO : The VFO is from QRP Labs and employs the Si5351A CMOS clock generator and a TCXO time base. A PIC controls the clock and LCD readout: https://www.qrp-labs.com/vfo.html |
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Re: So Why Do Those TR-4C Can Caps Fail?
Interestingly, the original AC-3 was designed to run the TR-3, in ¡®63-64, so they did add capacitance in the transceivers. The transmitters really did not have extra filtering, as their cans were for the CW oscillator and cathode bypass.? I would like to have been a fly on the wall at their engineering meetings when they decided to use 250 WV capacitors. The cost differential can¡¯t have been very much.? The earlier rigs used a different can. I¡¯m thinking that those capacitors were underrated in their time. Regardless, they have definitely held up better! Of course, a 60+ year lifespan was probably not planned for.? 73, Steve Wedge, W1ES/4 Time flies like an arrow. Fruit flies like a banana. Sent from for iOS On Sat, Apr 13, 2024 at 17:50, Michael Smith via groups.io <tw8kcabpilot@...> wrote:
I checked the TR-4C, S/N 37k: Mallory, 250, 250, 250, 25 VDC. ?I cannot see the date codes clearly, but I do see 85 degrees C, clearly. ?That one looks original, too. ?I have one Hayseed cap for replacement I can use. ?It looks like Drake decided they needed more smoothing for the TR series, than the AC-4 was originally designed to produce. ?It is interesting they used a 350 VDC 80 uF electrolytic for smoothing in the AC-4, did not use that WDCV for the cap(s) in the TR-4C. ?I¡¯m going to work on this AC-4 now: it does not have an upgrade installed, but I conditioned the 400 WVDC voltage doubler caps for 650 VDC and the 150 VDC caps for Bias, before. ?Works great. ?I just need to replace R3 and condition the 350 WVDC cap for 250 VDC as I have a better-than-original wire-wound replacement from Mouser. ?Giving lots of time to allow the ions to form and move is important: the electrolyte is viscous-pasty making the process slow. |
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Re: So Why Do Those TR-4C Can Caps Fail?
I'm surprised Drake didn't design more headroom in the application.? That's cutting it close Electrolytic caps that run anywhere near their rated temperature have a remarkably short lifetime in their purchase spec. ? Looking at? Nichicon I see anywhere from 2000 hours to 20000 hours, depending on the size of the part (the bigger the part for the same voltage and capacitance, the longer the lifetime) . I used 47 uF at 450 volt as an example.? While that's remarkably short , that's typically at rated temp (usually 85 C, though the 105C? parts are significantly better and more expensive). As hot as the Drake transceivers run, the can caps will run very quite warm too,? even though Drake typically put them in the front corner IIRC which is likely one of the cooler parts of the chassis. Will parts run longer than that in the application? Yep, but reliability engineers are the actuaries of the electronics world and they're usually pretty good at determining how long it takes for an item to fail. Just another possibility. John K5MO On Sat, Apr 13, 2024 at 5:37?PM Steve Johnston via <sbjohnston=[email protected]> wrote:
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Re: So Why Do Those TR-4C Can Caps Fail?
I checked the TR-4C, S/N 37k: Mallory, 250, 250, 250, 25 VDC. ?I cannot see the date codes clearly, but I do see 85 degrees C, clearly. ?That one looks original, too. ?I have one Hayseed cap for replacement I can use. ?It looks like Drake decided they needed more smoothing for the TR series, than the AC-4 was originally designed to produce. ?It is interesting they used a 350 VDC 80 uF electrolytic for smoothing in the AC-4, did not use that WDCV for the cap(s) in the TR-4C. ?I¡¯m going to work on this AC-4 now: it does not have an upgrade installed, but I conditioned the 400 WVDC voltage doubler caps for 650 VDC and the 150 VDC caps for Bias, before. ?Works great. ?I just need to replace R3 and condition the 350 WVDC cap for 250 VDC as I have a better-than-original wire-wound replacement from Mouser. ?Giving lots of time to allow the ions to form and move is important: the electrolyte is viscous-pasty making the process slow.
Michael Smith, N4KZO |
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Re: So Why Do Those TR-4C Can Caps Fail?
I've also heard the story that one should operate electrolytic capacitors near their marked voltage.? The rationale was always been theoretical rather than practical (based on experience over time).? I suspect there may be an element of caring more about initial performance than about long-term reliability.? Maybe the capacitor provides more capacitance for its size/cost under those circumstances (just a guess) but that might explain the interest in promoting this approach (best $ value to the manufacturer). From a reliability perspective this has always seemed wrong to me.? As I accumulated years of repair and restoration experience on all sorts of electronics, it has been my increasing observation that it seems to be better to operate electrolytic capacitors with some headroom between their marked voltage and the operating voltage.? I am just going on a sense of how often I replace failed or failing capacitors that were running near their rating versus how often I done so for those that had some headroom. My mind visualizes that this provides some room for peaks as opposed to average voltage, as well as the variation in how hard the capacitors have to work (how much ripple being smoothed) but I don't have any controlled experiments to back it up. The oldest electrolytic caps I've encountered are sometimes marked for "working voltage".? That concept seems like it might enter into this story as well. 73?? Steve? WD8DAS |
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Shimming PTOs
I'm working on a TR-4C (yep -- the same one that had the bad can) that was built in September, 1972, so a very early example. I noticed that there were small flat brass washers between the PTO and the chassis in the two front holes. Of course, I forgot to put them back and was met with all sorts of grief getting the PTO to rotate without scraping.? So I have two take-aways here.? First, if there are washers used for mounting the PTO, it's probably best to keep them and second, if you forget, you can still gain enough clearance to drop the PTO and drop the washers onto the two front mounting studs. Yes, those little washers made a huge amount of difference!? Have any of you seen this on any of your sets?? This is the first time that I've seen this after working on probably 100 sets. Steve Wedge, W1ES/4 Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
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Re: So Why Do Those TR-4C Can Caps Fail?
Interestingly, the cap I removed from this TR-4C (built in September, 1973) has no branding on it.? Date code of 7326, so around the end of June.? One of the high-voltage sections failed leakage test with my TO-6m which is not surprising given that it was too hot for me to touch and sounded like bacon frying when I cut the power. My TR-4Cw RIT came with a Hayseed cap already installed.? This set may have been done by Ron but I have no paperwork.? It's also a later one: 44138.? I bought and sold another one to a friend that's 44444.? Wish I had kept that one, instead, as it's a cool serial number to have... Steve Wedge, W1ES/4 Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Saturday, April 13th, 2024 at 3:04 PM, Michael Smith via groups.io <tw8kcabpilot@...> wrote:
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Re: So Why Do Those TR-4C Can Caps Fail?
The TR-4CWRIT multi-cap can manufacturer is Mallory ¡ª looks original. ?The four VDC markings are 250, 250, 250, 25. ?The transceiver serial number is 44K. ?I have a TR-4C I¡¯ll check for as soon as I can. ?The serial number for that is, of course, less than the CWRIT. ?I have a late model AC-4, with transformer switch, that I found R3 to be open. ?I haven¡¯t had an opportunity to replace that wire wound resistor yet to give you a DC voltage reading today; I¡¯ll need to perform a slow cap conditioning after repair which takes several hours, so it may be a little bit before I get back to you on that. ?My line voltage in VA is 122 VAC today, the highest I¡¯ve seen. ?I¡¯ll check the DC voltage with the available AC line input voltage present, when possible. ?I have an auto-transformer to set the line to the nominal input voltage for the equipment I¡¯m using, which can vary. ?Because I have a 117 AC input scope-monitor, I don¡¯t like to get far away from 120 VAC, which is usually what I see ¡ª a little high today. |
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Re: So Why Do Those TR-4C Can Caps Fail?
The interesting bit is that the +250 is already filtered in the AC-4. This buss is then filtered again in the TR3/4, so there¡¯s not much ripple there to begin with.? Steve Wedge, W1ES/4 Time flies like an arrow. Fruit flies like a banana. Sent from for iOS On Sat, Apr 13, 2024 at 11:40, Bill Leonard N0CU <billincolo73@...> wrote:
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Greg W?GUS
Paul Christensen
Gary WB6OGD
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