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Hi, Last week my Alpha 78 stopped working. I found the windings of the L5 was burned. I rewinded the toroid with new wires. Now, it is working. I checked the temperature after transmitting on 80 meters FT8 with approximately 1 KW output. Plate current 0.85 Amper, HV 2000 V and Grid current 25 mA. After 30 minutes the temperature readings with a digital multimeter were. L5 119 C (246 F) L4, 64 C ( 147 F) L6, 49 C (120 F) Are those temperatures right? What maybe the cause of the high temperature? Should I have to replace also el toroid? Thanks in advance for the comments. 73 de Arturo, LU6ETB
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Clipperton L Relay
Does anyone know where a replacement relay can be obtained? Or the manufacturer's name and part number? Thank you.
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DigiKey delivered my Alph 99 transformer exactly 7 weeks after ordering it for a fairly reasonable price. The new one says "Peter W. Dahl" on it and it is STOUT!. NO Hv sag at full output. Good on ya, DigiKey!! 73
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12 KW CCS ON 160-15M....USING THE 3CX-6000A7..... Part 13
Here the complex chain drive is finalized. Spur gears used on the inside of the inner front panel. The idea of the 3 x chains is to get the tune + load turns counters, and the bandswitch knob located in the correct positions on the outer panel. After some preliminary attempts, this latest version works good...and the front panel simply sides off....leaving all 3 x chains intact. On a side note, I shipped the new 397 uh plate choke today, along with a pair of .01uf @ 30 kv disc caps, used for bypassing at the cold end of the plate choke....used for the lower bands. A pair of 500 pf doorknobs will also be used at cold end of same plate choke...for bypassing at the upper bands. A pair of 100 amp supercon panel jacks also shipped. It's slowly coming together. This chain drive setup complicates things quite a bit, and required a lot of head scratching. But it's finally done...and works. The mapping has yet to be done (turns counter markings vs actual pf) for the tune + load caps. Once done, the mapping....aka .....'cheat sheets' can be made up. https://www.youtube.com/watch?v=Q3zf2PrzJs0
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Yaesu FL-2100B Key Line Polarity
6
Howdy Folks, A quick question (and maybe a stupid question... but): Can anyone see any issues in reversing the polarity on the key-line circuit (from "positive ground" to "negative ground") on the FL-2100B amp? Has anybody attempted this? Background: I'm refurbishing an FL-2100B, and have already done some upgrades and mods: New PS diodes, cap's & boards (from Harbach); Directly-grounded the grids; Performed the "Self-bias mod" (CT of filament xfmr grounded thru a 100k resistor on RX, grounded on TX thru a separate/new cube relay); Installed a new band switch (original was burned on 80m capacitor contacts), and some other general clean-up. Currently, the key line is "positive ground" (utilizing a simple, single-diode 1/2-wave rectifier and 1000uF cap). The positive side of this DC circuit goes to the chassis ("ground"), and negative side to the keying relay. Thus, when the RCA jack is shorted to "ground" by a transceiver, it is actually switching the "positive" side. I have read elsewhere that this "reversed" polarity could cause issues with some "modern" transceivers which require a "negative ground" key-line circuit (particularly those employing solid state/transistor switching), and therfore requiring the use of an external key-line "buffer" (which I have built and used succesfully). Anyway, since the bias-circuit no longer has anything to do with the keying relay circuit, any issues that anyone might be aware of, by reversing the polarity? I've studied the circuit schematic (and corrected it, as per my other changes), and I can't see anything that would prevent this from working. Since doing that bias mod, the key-line power supply only supplies power the key-line relay, and has nothing to do with bias. The key circuit currently runs at 19 volts (open circuit) and 280 mA keyed. Ultimately, this amp will be put up for sale, but I wanted to do the upgrades & mod's before I put it up for sale. Following the aforementioned modifications, I have run it, driving it with my Yaesu 101D (using my key-line buffer), and it works quite well, giving about 650-700 watts PEP (on a Telepost LP-100A). Of course... I wouldn't run it that hard in regular service, but it did work fine for the short testing done. The newer "Taylor" 572B's are in great shape. Lastly, I'm quite well aware of the many other quirks and issues with the FL-2100's, so no need to get into a discussion about all of their other problems... LOL! Thanks for the help. -- 73, ~Alan
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12 KW CCS ON 160-15M....USING THE 3CX-6000A7..... Part 12
Here, some updates. This is the beginnings of the elaborate chain drive assy. 2 x more chains, yet to be installed, plus tensioner's....( for the vac tune + load caps). Note on the big model 90 switch, there is a tall, rhombus shaped black end plate....at both ends of the switch assy....(oriented vertically). In the normal configuration, the black end plate, at the FRONT of the switch is mounted on the INSIDE of the panel (along with the spring detent / nylon assy). In normal configuration, only the 1/4" steel shaft sticks out the front of the panel....through a panel bearing. In this amplifier, the switch was taken apart, and the FRONT end plate was mounted on the OUTSIDE of the front (inner) panel....( along with the spring detent assy). Done like this so the switch wafer assy doesn't stick as far back on the inside of the RF deck. There is severe space constraints on the inside of the RF deck. Ferrite loaded plate choke finally fabricated...(and tweaked)....and tested on the VNA. It will be shipped out to Scott later this week. I had to make new, narrower copper straps ( 1/2" vs 3/4") so I could get an extra 8 turns onto the assy. The winding is now 5.5" long (vs 5.0") . Final choke config is now 405 uh. This dropped the 1st series resonance freq down to where I want it. (1st series resonance now at 17. 125 mhz...midway between top of 20m..and bottom of 15m..so choke won't work on 17m). The amp only works on 160-80-40-20-15m. NO 17/12/10m on this amp. It only has a 5 position bandswitch...with 4 x sequential rotors.... to make it into a shorting style bandswitch. And no, we can't re-use the 15M tap on 17m. Reason is, with the L coil inserted between the plate block cap assy, and the C1 vac tune cap, it's designed to lower the loaded tank on 15M. In software, if 15m tap re-used on 17m, the loaded tank Q skyrockets to an unacceptable value. Without the extra '"L" coil installed, the Q is too high on 15M..... BUT if re-used on 17M, would only increase the tank Q by another 17%. So L coil installed, low Q on 15m, and no 17m operation. Since no 17m operation, having the plate choke resonate near 17m band is a non issue. The model 90 switch is a 10 position, 36 deg switch. The max you can do with that switch is a 5 pole sequential rotor...which results in a 6 position bandswitch. Scott is re-using an old model 90 switch, and it only came with a 4 pole sequential rotor...so only 5 x bands. Original loaded plate choke with it's 5" winding, was 305 uh, and resonated at 19.750 mhz....(and also 33 mhz). Interestingly enough, as an experiment, I removed 3/4" of turns so 12.5 turns removed...and winding was now only 4.25" long. Inductance dropped to 249 uh....and 1st series resonance shifted up to 23.3 mhz.... ( and 2nd series resonance shifted up to 39.990 mhz). Ok, winding completely removed....and new, narrower straps installed. This time, winding length increased to 5.5". Choke is now 405 uh. 1st series resonance is now 17.125 mhz.... ( and 2nd series resonance is now 29 mhz). I believe this latest, and last config will work good. It will also minimize the residual RF current through the choke on 160m. Stay tuned for more. https://www.youtube.com/watch?v=exY4_UBmhsI
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Identifying some rare tubes... 2nd
Even located in the adjacent room I can still hear an arc if were to occur. The 3x6 I’m building now will have a spark gap on the c1 and c2 , grid overload , plate overload , cathode return fuse , grid current fuse , plate b+ fuse , series glitch plate b+, fuse in series with one side of the plate secondary , blower pressure interlock. Should be pretty bullet proof.
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I've been offered this job lot from a SK sale... I recognise 3CX15k, 4CX5k, Gu81m, ITL9-1, BR1106, Vac-Vars (10-200, 25kV) any idea's for the rest? There are some kanji characters on the big glass bulbs, so Japanese maybe ?
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Ameritron Plate Chokes
23
Does anyone know if Ameritron have resolved the issues with their spare parts plate chokes? I would be interested in purchasing a couple if they are not going to burn up. 73, Alek VK6APK.
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PA tube testing, Interesting findings.
4
I recently acquired a few Alpha amplifiers that needed repair. Along the way I decided to test all 10 tubes I had on hand. I put each 3cx400A7 in one at a time, let the filament run for a while to burn in. I Applied 1500 volts for 10 minutes or so.. then Keyed up While monitoring Grid and Plate current for 5 minutes. I noted idle current and then applied 15w RTTY drive on 20 meters and noted output power. Out of the 10, Two where bad, one had open filament and the other a grid short. The other eight where all good. Output power for those eight tubes: 175 w 175 w 175 w 150 w 140 w 120 W 100 w 75 w I let them run each tube keyed for 5 minutes or so and power was stable, and no tuning would produce more. All tubes ended up at pretty much exactly the same tune and load. ONE of the new tubes made 50W but after a cycle of key OFF and Key ON power rose up. 75, then 100, then 120. It ended up at 175 over about a 10 to 15 minute period. Interesting to see it rise up like that. Something was coming back to life. ALL other tubes made power instantly. What is interesting is that even the tubes that have lower output power and gain at 15w, make FULL power in the amplifier. I can take the two weak tubes, 75 and 100, and put them in the amp and make 1500w out with a woodpecker. I can put the best three in the other map and make 1800w. I can remove them and put the weakest three in the amp and make 1800w. Is there a better way to test power tubes? Or do you really need to just test them to full output? I had reservations about applying 2700 volts to them right away, that's why I used 1500v and low drive. Some of the tubes where new and marked 1980 so some run time is probably advisable at low voltage. I guess the drive and or added B plus is overcoming the loss of gain? C
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I've built many EHT supplies over decades but have always used capacitive only, ripple-filtering. Sitting below my desk for many years, is an inductor rated 7,500V, 0.85A CCS, 10 Henries. It came from an industrial RF heater. I've never seen one used in an EHT ham amplifier supply...has anyone experience of this? 10H, even with just 1uF after it, has a -3dB frequency of 50Hz, so it would be pretty effective at 300Hz (3-phase, full-wave ripple). But how would the inductive ripple filter respond with an SSB load? What happens if the tube flashes over? Are some extra protections required? Thanks Tim
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8410/9500 Wattmeter Failure
9
I have an 8410; however, according to the schematic(s), it appears as if it probly uses the same wattmeter as the 9500. The other day, I encountered intermittent flashover in my external antenna tuner while running around 1100 watts on 160; it would cause all the reflected power LEDs on my 8410 to light up. I managed to finish working someone, let the amp cool down for five mins, then shut it down. All front panel indicators appeared to work properly at that time (although I've never, ever, seen a grid current LED light up, nor the FAULT LED even though I once did have a real fault where I thought that LED SHOULD light... but it didn't). The output power and reflected power indicators have always been very accurate and worked fine. Later that day, I fired it up again... and was chagrined to find NO output power indicated on the front panel LEDs... neither forward nor reverse. But the amp was still amplifying normally; output power on an external wattmeter indicated full power out. I fired up the AE9K Alpha Monitor program and it, too, shows no output power. But the amp does still have full output power; so something common to both forward and reverse power that drives the front panel display failed in my amp. When the tuner flashed over, my external LP-100A power meter usually indicated something really high like over 2500 watts momentarily.. once, I think I saw 2932 watts indicated ===8-O Since then, I've fixed the tuner problem... but have no output power indication on either the amplifier front panel, nor with the AE9K Alpha Monitor program, even though the amp is actually still correctly putting out full power. I'm now printing out all 19 pages of the schematics, but an eyeball perusal in Acrobat hasn't yet identified exactly which connector carries the output of the tube deck to the TR system and what it plugs into on another schematic page. Meanwhile, I thought I'd ask here, in case someone else has already "invented the wheel" and fixed this kind of problem. Any help? TNX, Steve K0XP
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Hi, I am looking for Bandswitch Rear Wafer E4C-N18 for my Alpha 78. Anybody in the group either has one for sale or know where to buy it? Thanks 73 de Arturo, LU6ETB
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I'm currently fabricating several versions of ferrite bead loaded plate chokeS. I used 1" OD, hollow teflon tubing (.145" wall thickness) (.710" ID). Each of the .687" OD beads (type 61) was shimmed with tape, so they make a snug fit, when stuffed into the hollow teflon tube. A 1" electrolytic capacitor bracket is used to hold the base of the choke to the chassis. 1/2" copper straps wrapped around the hollow teflon tube, and machine screwed with a single brass 8-32 machine screw etc. A 1/4" to 3/8" hole is drilled into the amplifier chassis, to allow compressed air in the plenum, to flow up though the .374" ID of all the beads. Easy way of air cooling. Actual top temps will be taken with a fluke 62 IR. The actual winding is made from 22 ga, silver plated, stranded teflon wire. Insulation is pretty thick, and the OD of the wire is exactly .060". ( wire inside is only .028" OD) Upper + lower winding terminated on the upper / lower straps, then soldered. Lower strap is 1" from the top of the electrolytic bracket. That provides 1" of exposed teflon. On paper, should be good for 10 kv of...'surface creep'. After measuring the inductance with my LCR meter, it was time to see where the 2 x series resonance freqs are located. I used the S11 output, then a single provided coax cable to a (SMA female / BNC female adaptor)....then the BNC plugged into a dual binding post fitting, with it's BNC male connector built into the bottom end. Then 1 SHORT test lead to top of choke...and the other test lead to bottom o f choke. Test leads have an alligator clip at one end...and other end is a banana plug. Did the usual open / short / 50 ohm calibration. Ok, found the 2 x series resonance freqs asap...on both HB chokes. ( I also compared to a new Ameritron choke, since I know where the 2 x series resonant freqs are on the Ameritron choke). I had the chokes being tested, laying on top of my bed mattress...along with vna etc. I then placed the choke on Styrofoam, so only the extreme ends of the choke were supported, in the horz plane. 90% of the choke, and all of the winding was in mid air. Well that was a surprise. The series resonant freqs INCREASED in freq by a bunch. Instead of 19.002 mhz laying on the bed, it was 19.750 mhz, when in mid air. Same deal with the upper series resonant freq (aprx 32 mhz...which also increased). I also stood the chokes vertical on the bed, and supported the very top of the choke with the handle of a wooden spoon...same deal. Resonant freq increased by 748 khz. I can see getting any plate choke near an aluminum sidewall, or large metal triode tube, can easily lower the resonant freq, but not laying on a bed mattress. I also held my hand parallel to the choke, and once 2.5" away, resonant freq decreased, and decreased more, the closer the palm of my hand got to the choke. W8JI warned about getting plate chokes too close to any dielectric or insulator. He is correct...I shoulda listened. Next up, knowing all this, is to replace the 3/4" wide copper straps with 1/2" wide copper straps...and rewind the choke. That will allow for an extra (.5" / .060") 8.33 turns. The idea here is to lower the 1st series resonance point, (19.750 mhz) so it's midway between 21.000 mhz....and 14.350 mhz. (midpoint is 17.675 mhz). The new 3x6 linear amplifier is not used on the 17m band (18.068 mhz to 18.168 mhz) nor is it used on 12 + 10m bands. We have height constraints, so the completed choke is exactly 8.25" tall. (Top lid is exactly 9.25" above the chassis). The existing 5" winding will be increased to 5.5"..... by fabricating the new 1/2" narrower straps. Wish me luck. Existing choke measures 315 uh....which will increase a bit once the extra 8 turns are added. On choke #2, it's a full 12" tall, and uses a 8.75" winding. Measures 750 uh. Resonates at 9.7 mhz...and also 17.8 mhz. I will try the narrower 1/2" wide straps...so I can get another 8.33 turns on it. (Then the new winding will be 9.25" and uh will increase a bit). The idea here is to lower both series resonant freqs a bit. Midpoint between 14.350 mhz and 18.068 mhz is 1
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Retrofit for remote operation of tube amplifiers
Does anyone make a retrofit module for tube amplifiers that can monitor key parameters remotely, ideally via Ethernet. I could build something but if something is available ready-made, I would rather save the time. For now, I could use an IP camera for the metering, but they are noisy and not ideal for an EMEr such as I. A long shot I know. 73 Conrad PA5Y
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572's
5
I've got a friend who needs 572B's for his SB200. He's ready to buy the PSVANE tubes on Amazon for $149.99/pair. I see that RF parts is selling Svetlana's for $200/ea. He's a SSB rag chewer so no heavy digital use. Money is tight for him. What's the story with 572's now? Jim - KR9U
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Does anyone know of an after market plate current meter for the Kenwood TL-922? Any leads appreciated. 73, Alek VK6APK.
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Transformer "burn-in"
7
Hello all. I have a brand-new Peter Dahl clone transformer from Hammond coming for my Alpha 99. I am wondering if I need to condition it or burn it in prior to using it at full power. I don't want to fry a $1000 transformer due to ignorance. 73 Warren / NI5L
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Hi, Hoping someone can look at the pictures of my amp and suggest why it is oscillating? It's a PA3CSG design for 432MHz. I thought I had built it quite well, but on power up, as soon as the EHT appears it oscillates with about 500W RF showing on the meter into the load. I've checked (cold) with the VNA and dummy resitors that both cathode and aode circuits tune perfectly on 432MHz. EHT is 4kV Bias 27V Thanks G4LOH
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Palstar 2500 repair
4
Hello everyone New to this list. I'm trying to repair a Palstar 2500 ( non export 2 tube ) dated 2009. I bought the amp in non-working condition. When I first opened up the amp I noticed the plate block caps were blown. I have since replaced them with equivalent to what was in there but have heard that HEC caps would be a good choice. In checking around in the amp I also see some diodes shorted..SM84A diodes which are rather large for SM components. IN5408 were recommended but these are fairly large so may look for another alternative...I can't find the SM84A anywhere For now , I am just trying to get the amp running and it's taking some time. I'm not an expert with amplifiers and am being careful but am learning. Right now the tubes are removed and the HV transformer is unplugged. I think there are some issues deriving from the control board. I'm trying to learn from the schematics and there are some voltages that are supposed to be present that I'm not seeing, or voltages that are on different pins ( where the connectors attach ) that go to the tuned input board as well as back to the PS board. One is 30VDC that I can't find on the connector and am not too sure what it is for...from the schematic...it seems to be pointing to the TR relays on the input but these are 12V ..I have the control board, meter board and PS board removed and am trying to learn the amp from the schematics while comparing it to the boards. There is no component listing or board layout in the manual and it's a layered board. There are some notes on the schematic and the PO also changed some wiring around on the IDC connectors, this is also making things rather confusing. I have bought some new IDC connectors but need to trace out the wiring and make sure the correct control voltages are getting were they should be Is anyone on here familiar with this amp?...I understand it was a redesigned Commander 2500..I know this message likely does not contain all the pertinent info , but I just thought to reach out to see if anyone is familiar with it for a start 73 Brian
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