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Fading Away
开云体育Gents, One of the bug-a-boos about QRO tubism is the regulation and acceptability of filament voltages. ? Okay, tube manufacturers tell us “10%,” and we have to live with whatever Con Edison or Kentucky Power ends up at our QTH to ply our signals out and about. ? I know, I know Continental and all them have Buck’n’boosters, automated variacs on 3-phase mains: Just everything money can buy. ? So here’s Dave saying his filament voltage droops a bit, and I’m sure there are others out there, running 8877’s or CPX’s and other thoriated devices, and what can we as technicians offer them? ? Would it not be fabulous for QST to publish in its last edition this December, a sure-fire and affordable means to conquer filament squirrels? ? Let’s say Joe Ham has a wonderful $6K to $10K linear running tubes that are in need of regulation. Would it not be remiss to afford 10% more for a regulation gizmo?? ? I know how much a good set of finals cost, and frankly, I don’t know if I can ante up for a new set if I pop the ones I got right now.? ? So like owning a car that’s beginning to use a bit more oil, I keep the drive down a bit on my inputs, and just hope the beast can gently grow old like the old man. ? Hal W4HBM |
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John W Cress
Years ago there was a company that produced a regulating 1:1 or 2:1 transformer with a ferro-resonant winding. hTeret had a capacitor across to hold the voltage steady. I don't know the specifics of it's performance; and don't? remember the name of the company nor the name of the product, but they were quite prevalent in industry and remember them?being in demand by hams back then. It's probably been 30 or 40 years since hearing the name. John K0GCJ On Mon, Oct 16, 2023 at 2:08?PM HaL Mandel <hmandel@...> wrote:
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John W Cress
I just remembered the company, it was Sola and the product is/was the Constant Voltage Transformer. Looked on ebay and there's quite a few listed with a wide range of characteristics. On Mon, Oct 16, 2023 at 4:10?PM John W Cress via <johnk0gcj=[email protected]> wrote:
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开云体育I just calculated the percentages of Mains and Filament Voltage drop from idle power to 1.3 KW. The Mains dropped 2.4 Volts from 242 VAC, that is a 1% drop. The Filament Voltage dropped 0.29 VAC, that is a 5.3% drop. ? That says to me the significant Voltage drop is in the Alpha transformer and filament wiring, not in the Utility company service.? ? While I was at it, I opened the amp’s power switch box and measured the AC current draw.? With 1.3 KW out of the Alpha I am drawing 9.3 amps of current.? But, the AC mains Voltage is now 240 dropping to 238 AC volts at 1.3 KW output from the Alpha.? That is 2213.4 Watts of input power for 1,300 Watts of output power.? For 58.4% overall efficiency of the entire amplifier.? Subtract the idle power [240 VAC @ 0.57 Amps] and then the PA (tube and plate circuit) efficiency percentage rises to 62.3% efficiency.? For a class AB2 linear amplifier that is right in the ballpark for an expected efficiency (65%). ? That says to me the significant Voltage drop is in the Alpha transformer and filament wiring, not in the Utility company service.? ? I’m in a rural area and due to the 1-acre lot size here, there is a distribution service transformer between my lot and my closest neighbor on one side.? The real Utility company problem is they vary the line voltage during the seasons.? During the high demand season the up the line voltage to over 250 Volts.? My solar power controller throws an error code each summer complaining about over voltage. ? The Utility company isn’t the problem with the Voltage drop.? However, the utility company is responsible for the initial line Voltage. ?And the mains droop I experienced today is most likely a result of the 150 feet of service wiring between the Service panel at the house and my separate structure shop.? When built the shop I only asked for a 60 Amp service to the shop.? So that 1% droop is most likely my doing. ? Regards, Dave, w6de ? From: [email protected] <[email protected]>
On Behalf Of John W Cress via groups.io
Sent: 16 October, 2023 21:10 To: [email protected] Subject: Re: [ham-amplifiers] Fading Away ? ? Years ago there was a company that produced a regulating 1:1 or 2:1 transformer with a ferro-resonant winding. hTeret had a capacitor across to hold the voltage steady. I don't know the specifics of it's performance; and don't? remember the name of the company nor the name of the product, but they were quite prevalent in industry and remember them?being in demand by hams back then. It's probably been 30 or 40 years since hearing the name. ? John K0GCJ ? ? ? ? On Mon, Oct 16, 2023 at 2:08?PM HaL Mandel <hmandel@...> wrote:
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On 17 Oct 2023, at 3:08 am, HaL Mandel <hmandel@...> wrote:
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开云体育In the book by Eimac called “The Care and Feeding of Power Grid Tubes”, ?in para 6.11.1 Maximum Tube Ratings;? it states that:? “At some point in filament voltage [reduction] there will be a noticeable reduction in plate current, or power output, or an increase in distortion.? Safe operation may be at a filament voltage slightly higher than that point at which performance appeared to deteriorate.? A recheck should be made in 12 to 14 hours to make certain the emission is stable.” ? “A 3% increase in filament voltage will result in a 20 deg Kelvin increase in temperature, a 20% increase in peak emission, and a 50% decrease in life due to carbon loss.”? ? NOTE:? Peak emission as meant here is the emission obtained in the test for emission described in the Test Spec.? This is normally many times the peak emission required in communication service. ? I do recall an article many many years ago where the filament voltage was reduced I believe in a TL 922 to extend tube life.? ? Jim – KR9U ? ? ? On Mon, Oct 16, 2023 at 2:08?PM HaL Mandel <hmandel@...> wrote:
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An 8877 is NOT a thoriated tungsten fil !? ? ? ?On the 8877, and other OXIDE tubes, you CAN'T? run the heater at reduced voltage and increase tube life.? ?You can only do that on? directly heated thoriated tungsten tubes, like 3-500Z, 3CX-3000 / 6000A7 tubes etc..... 'instant on'? tubes.? ? From the other thread.? 5.3 VAC at initial power on. 5.45 VAC after 180 Second warm up remains at 5.45 during subsequent Standby (not Transmitting). 5.16 VAC on Key Down 1.3 KW. ? Since his loaded fil voltage is 5.16 vac @ 1.3 kw cxr....(and probably a little less IF a good tube was used, and a full? 1.5 kw out) , he does not? have a loaded fil V issue.? ?However, on RX, he does have 5.45 vac...which is exactly 9% on the high side...which IMO, is a bit too high.? He will spend more time on RX than he will on TX.? ?Those oxide tubes are supposed to be +/- 5% of rated fil V. ...... or? ?4.75 vac to? 5.25 vac.? ? Considering his incoming line V is a bit on the high side (242.0 vac), myself,? I would add a small drop resistor in one leg of the fil xfmr primary.? Size it such that on RX, the fil V is 5.1 vac.? ?Then on TX, it will be 4.81 vac.? Considering the fil is only 5.0 vac @ 50 watts, that's only 208 ma drawn from the 240 vac fil xfmr pri.? A 75 ohm resistor would do the trick.....and only consume? 3.25 watts.? ?A 0-100 ohm rheostat would also work.? This would be the? 'easy fix'.? ? Plan B,? use a regulated 5.0 vdc supply...either linear or switching.? The tube only sucks 50 watts of fil power, so this is a? simple task.? ?Then it's 5.0 vdc on the fil, regardless of incoming line Voltage or if on? RX? or? TX..... or if incoming line V varies.? The switching version has soft start built into it.? ?Watch out, even with the soft start built into em, the tube will? suck stupid amounts of inrush current.? Typ the cold resistance is only? 1/10 the hot resistance.? You may well have to use a switching supply that is rated for a LOT more than 50 watts.? Buddy had to do just that when using a switching supply on his? GS35B fils.? ? In my own case. my line V USED? to be 247.7 in spring + summer....... and 239.9 vac in fall + winter.? It was like that for years.? ?No more.? Now it's all over the map, and changes by the hr and the day.? ?Typ it's 234.4 vac? and as low as 232.1 vac? ? I use a 750 va SOLA? constant V xfmr which provides a constant 234 /117 vac output.? Weighs? 66 lbs.? It's ferro resonant and also has oil caps...which make it 'harmonically neutralized'.? ?IE: it will take...'dirty power from the street and turn it into clean, pure sinewave power.? The problem with that is....with NO load at all on the output of the SOLA, the load on the input side is 50% of it's total VA rating....which is why they run hot...when unloaded.? ?That's caused by the oil caps.? I'm gonna ask Sola if the caps can be removed.? I want the V regulation,? but I don't want the? clean power...not for directly heated cathode tubes.? ? The above 750 va sola uses aluminum windings.... it's old.? It has primary taps at? 117 / 208 /? 234 vac.? ?Output is 234 / 117 vac. The new version is also 66 lbs, but is rated at 1 kva? CCS....and uses copper windings.? New version has pri taps at? 120 / 208 / 240 / 470.? Output is 240 / 120 vac.? ? I take the constant 234 vac? and feed that into the input of the small 0-240 vac variac ( 5 amp rated) ...and output of variac feeds the input of the? fil xfmr.? Output of the fil xfmr feeds the cold end of the fil choke on either the 3x3 tube or the 3x6 tube.? I don't use conventional step? start on either tube.? ?I just bring up the variac slowly, and watch both the 0-75 amp (or 0-100 amp) AC panel ammeter...and also the 0-15 vac panel meter ( and also the fluke DVM) until desired vac is reached on the fluke 87.? Done that way, there is NO surge on the cold tube.? When finished for the night, variac slowly turned down to zero, then? 240 vac? supply? vac shut off.? ?Blower runs for another 10 mins.? ? Another method is to use? conventional step start? + the variac, + sola.? Variac tweaked, and left alone.? Sola makes constant V xfmrs? in 125 /? 250/500/1000 / 2000 va types.? ?Typ a variac is all that's needed,? BUT in my case,? with line V all over the map, PLUS a big V drop from the street on? TX? (when sucking 50-100 amps from the 240 vac line) ... like a whopping 8-9 vac...it just doesn't work? without the sola.? ? IE: with no sola, and the? variac set for correct fil V on RX, it's then too low on? TX.? ?Set correct on TX, it's too high on? RX.? ? Other schemes I have seen used, is the use of 2 x variacs, one for RX, the other for TX, switched by vac relays.....and tied into the TR relays.? That sorta works, but fil V ends up too high when sucking just idle current.? And it only works IF the line V is not all over the map each night.?? ? Jim? ?VE7RF ? ? ? ? ? |
开云体育This whole thing comes up from time to time. Meanwhile this is a completely useless thing to try in a ham radio setting. This information was Intended for broadcast use where they try to stretch life out of the tube. No ham is ever going to
benefit in any way.
On Oct 17, 2023 6:03 AM, "Jim VE7RF via groups.io" <jim.thom@...> wrote:
An 8877 is NOT a thoriated tungsten fil !? ? ? ?On the 8877, and other OXIDE tubes, you CAN'T? run the heater at reduced voltage and increase tube life.? ?You can only do that on? directly heated thoriated tungsten tubes, like 3-500Z, 3CX-3000 / 6000A7 tubes etc..... 'instant on'? tubes.? ? From the other thread.? 5.3 VAC at initial power on. 5.45 VAC after 180 Second warm up remains at 5.45 during subsequent Standby (not Transmitting). 5.16 VAC on Key Down 1.3 KW. ? Since his loaded fil voltage is 5.16 vac @ 1.3 kw cxr....(and probably a little less IF a good tube was used, and a full? 1.5 kw out) , he does not? have a loaded fil V issue.? ?However, on RX, he does have 5.45 vac...which is exactly 9% on the high side...which IMO, is a bit too high.? He will spend more time on RX than he will on TX.? ?Those oxide tubes are supposed to be +/- 5% of rated fil V. ...... or? ?4.75 vac to? 5.25 vac.? ? Considering his incoming line V is a bit on the high side (242.0 vac), myself,? I would add a small drop resistor in one leg of the fil xfmr primary.? Size it such that on RX, the fil V is 5.1 vac.? ?Then on TX, it will be 4.81 vac.? Considering the fil is only 5.0 vac @ 50 watts, that's only 208 ma drawn from the 240 vac fil xfmr pri.? A 75 ohm resistor would do the trick.....and only consume? 3.25 watts.? ?A 0-100 ohm rheostat would also work.? This would be the? 'easy fix'.? ? Plan B,? use a regulated 5.0 vdc supply...either linear or switching.? The tube only sucks 50 watts of fil power, so this is a? simple task.? ?Then it's 5.0 vdc on the fil, regardless of incoming line Voltage
or if on? RX? or? TX..... or if incoming line V varies.? The switching version has soft start built into it.? ?Watch out, even with the soft start built into em, the tube will? suck stupid amounts of inrush current.? Typ the cold resistance is only? 1/10 the
hot resistance.? You may well have to use a switching supply that is rated for a LOT more than 50 watts.? Buddy had to do just that when using a switching supply on his? GS35B fils.? ? In my own case. my line V USED? to be 247.7 in spring + summer....... and 239.9 vac in fall + winter.? It was like that for years.? ?No more.? Now it's all over the map, and changes by the hr and the day.? ?Typ it's 234.4 vac? and as low as 232.1 vac? ? I use a 750 va SOLA? constant V xfmr which provides a constant 234 /117 vac output.? Weighs? 66 lbs.? It's ferro resonant and also has oil caps...which make it 'harmonically neutralized'.? ?IE: it will take...'dirty power from the street and turn it into clean, pure sinewave power.? The problem with that is....with NO load at all on the output of the SOLA, the load on the input side is 50% of it's total VA rating....which is why they run hot...when unloaded.? ?That's caused by the oil caps.? I'm gonna ask Sola if the caps can be removed.? I want the V regulation,? but I don't want the? clean power...not for directly heated cathode tubes.? ? The above 750 va sola uses aluminum windings.... it's old.? It has primary taps at? 117 / 208 /? 234 vac.? ?Output is 234 / 117 vac. The new version is also 66 lbs, but is rated at 1 kva? CCS....and uses copper windings.? New version has pri taps at? 120 / 208 / 240 / 470.? Output is 240 / 120 vac.? ? I take the constant 234 vac? and feed that into the input of the small 0-240 vac variac ( 5 amp rated) ...and output of variac feeds the input of the? fil xfmr.? Output of the fil xfmr feeds the cold end of the
fil choke on either the 3x3 tube or the 3x6 tube.? I don't use conventional step? start on either tube.? ?I just bring up the variac slowly, and watch both the 0-75 amp (or 0-100 amp) AC panel ammeter...and also the 0-15 vac panel meter ( and also the fluke
DVM) until desired vac is reached on the fluke 87.? Done that way, there is NO surge on the cold tube.? When finished for the night, variac slowly turned down to zero, then? 240 vac? supply? vac shut off.? ?Blower runs for another 10 mins.? ? Another method
is to use? conventional step start? + the variac, + sola.? Variac tweaked, and left alone.? Sola makes constant V xfmrs? in 125 /? 250/500/1000 / 2000 va types.? ?Typ a variac is all that's needed,? BUT in my case,? with line V all over the map, PLUS a big V drop from the street on? TX? (when sucking 50-100 amps from the 240 vac line) ... like a whopping 8-9 vac...it just doesn't work? without the sola.? ? IE: with no sola, and the? variac set for correct fil V on RX, it's then too low on? TX.? ?Set correct on TX, it's too high on? RX.? ? Other schemes I have seen used, is the use of 2 x variacs, one for RX, the other for TX, switched by vac relays.....and tied into the TR relays.? That sorta works, but fil V ends up too high when sucking just idle current.? And it only works IF the line V is not all over the map each night.?? ? Jim? ?VE7RF ? ? ? ? ? |
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Hold on a minute there Jim, thanks for quoting the book I edited at one point in my career.
The text in C&F?refers to Thoriated Tungsten filaments, it has no relationship to oxide cathode tubes such as the 8877. That said, it is possible to reduce heater voltage on an 8877 with a good cathode and slow the loss of oxide material from the cathode if done without any testing or other distortion measurements (in rf amplifers as used with ham service, other use such as MRI doesn't allow reduction. And yes, a 3-500Z can benefit from a say 5% lower filament voltage (below nominal) especially if you have high line voltage. These are two completely different scenarios, oxide tubes do not behave like thoriated tungsten filament tubes and vice versa.? 73,? Reid still W6MTF |
开云体育Thanks Reid and Jim for the clarification. ? Does the same procedure apply to the Oxide Cathode tube when setting filament voltage? ? Jim – KR9U ? _________________ Hold on a minute there Jim, thanks for quoting the book I edited at one point in my career. |
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A new? Eimac? 8877? is now a whopping $4250.00? USD,? as of last week, from? MFJ / Ameritron.? (which is gonna be a helluva lot more than that anywhere outside the USA,? like 36% more in Canada =? $5780.00....and? 57% more in VK land =$6672.50 ).? ?Then adding shipping + insurance, also in USD, and you had better have deep pockets.? Reid sez you can run the 8877 fil? at reduced voltage (assuming a new tube, or at least a known good tube).? For the meager cost (chump change)? of a 5.0 vdc regulated supply, it would be dirt cheap insurance.? ? Jim? VE7RF |
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On Tue, Oct 17, 2023 at 05:52 PM, W7WRX wrote:
<This whole thing comes up from time to time. Meanwhile this is a completely useless thing to try in a ham radio setting. This information was Intended for broadcast use where they try to stretch life out of the tube. No ham is ever going to <benefit in any way. ## For directly heated, thoriated tungsten tubes like? expensive 3CX-3000 / 6000 / 10,000? triodes, or 4CX-5000 / 10,000 / 15,000? tetrodes,? ?I'm 90% convinced that the grid to cathode shorts are caused by the high inrush current, when no form of step start is used.? Measure the peak current when T=0. You will gag.? ?The fil xfmrs that Henry Radio used are Z limited, such that the max inrush current is no? more than double the tube's rated current....(which is still too much imo).? ?Everybody else's fil xfmr are capable of a lot more than that.? The problem gets worse when the fil xfmr used has a higher current rating than required.? ?Larry,? W7IUV? used a 5 vac @ 30 amp fil xfmr on a single 4-400? amp.? With no inrush protection, that resulted in numerous grid to cathode shorts.? ? ? ##? Scott,? KB1SEL? modified a 5.0 vdc @ 200 amp? CCS? server supply, so it outputs 6.3 vdc? @ 160 amps.? ?He's been using that on his 4x15 tube for the last 20 years.? ? ##? In the OP's? case, if no room for a 5.0 vdc regulated supply, the? 75 ohm @ 5-10 watt? resistor in one leg of the 240 vac primary will work (or a 0-100 ohm, 25 watt rheostat).? That will not only reduce the fil V on his 8877 to an acceptable level, it will also? provide for step start, and eliminate any inrush. The beauty is.... the resistor stays in the primary at all times.? ? ## Some broadcast PA's have used a rheostat in the fil pri..... instead of a variac.? ?The rheostat, once dialed in correctly, provided for the correct heater / fil voltage...and also provided for step start / current limiting on turn on.? Broadcasting is different in that the PA is run 24/7/365? and down for periodic maintenance.?? ? ##? IF a variac is used on the bigger, directly heated tubes, it still needs the step start circuit / resistor / relay.? Variac is set, then left alone.? Plan B is what I do, and just dial the variac up each night to desired voltage.? Then the fil current rises slowly from zero? to normal current. ( I have fil V panel meters, and also? a set of jacks for the fluke 87..and also a fil current panel meter.? Fil current meters uses an external 75:1? or? 100:1? xfmr.? ? ##? At the cost of these tubes,? I'm not about to be using fil V that's? too high / too low, nor slamming on a ton of inrush current each night.? ? ##? between my incoming? 234? vac sagging 8-9 vac on? TX.....and not knowing what it is from hr to hr, or day to day,? ?I had to go the sola route.? On the small? Drake L4B amps,? it's a non issue.? The drake amps get the entire B+? and fil xfmr step started with a 20 ohm resistor in one leg of the mains....that's it.? Done externally.? And the step start relay is manually activated.? ? ##? I used a pair of DPST-30 amp relays in a 8x8x4 box...on the floor.? 1st relay applies the 240 vac.? ?Pole #1 of the 2nd relay? shunts the 20 ohm resistor.? ?Pole #2 of 2nd relay? is wired to a pair of RCA jacks...with keyline run in /out? of them.? A small control cable is run from the 8x8x4 electrical box (with loads of knock outs, home depot)....? to a small mini box on the desk.? Mini box has 2 x mini toggle switches. Toggle #1 turns on relay #1.? ?Toggle #2? turns on relay #2.? ?Amp can not be keyed until? relay #2 is activated. Dead simple mech interlock.? Normal deal is to activate toggle? #1..... then a few secs later, activate toggle? #2.? B+ comes up to 90%..and fils of? 3-500Z's come up to 70% of normal brilliance with the 20 ohms inline. ##? When done for the night,? reverse? sequence is used.? With the 20 ohms back inline, prior to shut down, it kills the back emf 100%.? ? Due to the high C filter caps I used,? I also put the resistor back inline, when switching from CW? (1900 vdc)? to? SSB? (2650 vdc).? I cant afford a tube failure.? ?As is, the On / OFF? switch on one of my drake amps is fried.? Below the rocker is just a cheap 10 amp rated on / off slide switch. ? Jim? ?VE7RF ? |
开云体育Jim, you comment: ##? In the OP's? case, if no room for a 5.0 vdc regulated supply, the? 75 ohm @ 5-10 watt? resistor in one leg of the 240 vac primary will work (or a 0-100 ohm, 25 watt rheostat).? That will not only reduce the fil V on his 8877 to an acceptable level, it will also? provide for step start, and eliminate any inrush. The beauty is.... the resistor stays in the primary at all times.? ? I will consider this, but first, I need to address the fluctuating Mains voltage from my Electric Service Utility.? Just during the day of the testing, the Mains voltage dropped from 242 Volts to 240 Volts.? And I have measured the Mains Voltage in the Summertime at 250 Volts.? I need to address this problem first. A variac could handle this with manual checking and setting.? A Constant Voltage Transformer could work too but they are bulky, heavy and several times the price of a 240 Volt variac.? Too many variables to be sure now, but maybe, just maybe a variac on the Main’s supply could be used to set the filament voltage lower too. ? That is all for now. 73, Dave, w6de ? From: [email protected] <[email protected]>
On Behalf Of Jim VE7RF via groups.io
Sent: 18 October, 2023 07:45 To: [email protected] Subject: Re: [ham-amplifiers] Fading Away ? On Tue, Oct 17, 2023 at 05:52 PM, W7WRX wrote:
## For directly heated, thoriated tungsten tubes like? expensive 3CX-3000 / 6000 / 10,000? triodes, or 4CX-5000 / 10,000 / 15,000? tetrodes,? ?I'm 90% convinced that the grid to cathode shorts are caused by the high inrush current, when no form of step start is used.? Measure the peak current when T=0. You will gag.? ?The fil xfmrs that Henry Radio used are Z limited, such that the max inrush current is no? more than double the tube's rated current....(which is still too much imo).? ?Everybody else's fil xfmr are capable of a lot more than that.? The problem gets worse when the fil xfmr used has a higher current rating than required.? ?Larry,? W7IUV? used a 5 vac @ 30 amp fil xfmr on a single 4-400? amp.? With no inrush protection, that resulted in numerous grid to cathode shorts.? ? ? ##? Scott,? KB1SEL? modified a 5.0 vdc @ 200 amp? CCS? server supply, so it outputs 6.3 vdc? @ 160 amps.? ?He's been using that on his 4x15 tube for the last 20 years.? ? ##? In the OP's? case, if no room for a 5.0 vdc regulated supply, the? 75 ohm @ 5-10 watt? resistor in one leg of the 240 vac primary will work (or a 0-100 ohm, 25 watt rheostat).? That will not only reduce the fil V on his 8877 to an acceptable level, it will also? provide for step start, and eliminate any inrush. The beauty is.... the resistor stays in the primary at all times.? ? ## Some broadcast PA's have used a rheostat in the fil pri..... instead of a variac.? ?The rheostat, once dialed in correctly, provided for the correct heater / fil voltage...and also provided for step start / current limiting on turn on.? Broadcasting is different in that the PA is run 24/7/365? and down for periodic maintenance.?? ? ##? IF a variac is used on the bigger, directly heated tubes, it still needs the step start circuit / resistor / relay.? Variac is set, then left alone.? Plan B is what I do, and just dial the variac up each night to desired voltage.? Then the fil current rises slowly from zero? to normal current. ( I have fil V panel meters, and also? a set of jacks for the fluke 87..and also a fil current panel meter.? Fil current meters uses an external 75:1? or? 100:1? xfmr.? ? ##? At the cost of these tubes,? I'm not about to be using fil V that's? too high / too low, nor slamming on a ton of inrush current each night.? ? ##? between my incoming? 234? vac sagging 8-9 vac on? TX.....and not knowing what it is from hr to hr, or day to day,? ?I had to go the sola route.? On the small? Drake L4B amps,? it's a non issue.? The drake amps get the entire B+? and fil xfmr step started with a 20 ohm resistor in one leg of the mains....that's it.? Done externally.? And the step start relay is manually activated.? ? ##? I used a pair of DPST-30 amp relays in a 8x8x4 box...on the floor.? 1st relay applies the 240 vac.? ?Pole #1 of the 2nd relay? shunts the 20 ohm resistor.? ?Pole #2 of 2nd relay? is wired to a pair of RCA jacks...with keyline run in /out? of them.? A small control cable is run from the 8x8x4 electrical box (with loads of knock outs, home depot)....? to a small mini box on the desk.? Mini box has 2 x mini toggle switches. Toggle #1 turns on relay #1.? ?Toggle #2? turns on relay #2.? ?Amp can not be keyed until? relay #2 is activated. Dead simple mech interlock.? Normal deal is to activate toggle? #1..... then a few secs later, activate toggle? #2.? B+ comes up to 90%..and fils of? 3-500Z's come up to 70% of normal brilliance with the 20 ohms inline. ##? When done for the night,? reverse? sequence is used.? With the 20 ohms back inline, prior to shut down, it kills the back emf 100%.? ? Due to the high C filter caps I used,? I also put the resistor back inline, when switching from CW? (1900 vdc)? to? SSB? (2650 vdc).? I cant afford a tube failure.? ?As is, the On / OFF? switch on one of my drake amps is fried.? Below the rocker is just a cheap 10 amp rated on / off slide switch. ? Jim? ?VE7RF ? |
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I would not recommend? using a BIG? 240 vac variac to run the entire amplifier.? You will end up with poorer V regulation.? ?The peak current on the 240 line, every 8.3 msecs will make you gag.? W8JI measured 60 amps every 8.3 msecs on an AL-1500 running 1.5 kw? CCS? CXR.? ?However, I have seen? BIG variacs used on 1-2 kw output amps.? But they gotta be big, in order to not get sag on peaks.? ? I have seen? constant V xfmrs? (Sola and other brands)? that were as high as 10-50 kva.? ?To run just the 5V @ 10 amp fil on the 8877, a small, OUTBOARD? 125 va? ?sola could be used.? ? The alpha 9500? only has taps for 220 vac...and also 240 vac.? ?They say not to use > 250 vac.? Below is from their manual. 250 vac is probably not going to damage anything.... except for perhaps the higher than normal fil V.? ?Sure, the B+ will be on the high side of normal, but that's really a non issue.? Myself, I would be inclined to use a 5 vdc outboard supply..... and modify the rear apron, to? feed the external 5 vdc into the amp.? But that's just me.? ? I doubt you will get anywhere with the local power company.....you might, would not hurt to ask.? ? Another possible option (instead of using an external 4 kva rated 250 to 240 xfmr)..... is to use a buck - boost xfmr.....in buck mode.? ? IE:? 240-250 vac primary, and a 10 vac (@ 50 amp)? secondary.? ?The 10 vac sec is wired in? series with one leg of the incoming 250 vac.? ?Then you end up with 240 vac? going into the amplifier.? This method has been used before with excellent results.? BUT,? you have to know when to use it, and when to remove it from the line.? IE: keep track of seasonal? ?incoming V changes.? ? I know several folks? who have 253 vac....and in some cases, even a bit higher..... in summertime.? ? (? AZ, Ga? etc).? |
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In regard to seasonal line voltage changes, this is a very real issue ?in areas where houses are fed with unground utilities, like?developments.??Several houses?will be connected to pad mounted transformers. ?During the AC season many people will be drawing constant power to run big and multiple AC units! ?Your Line?voltage will most likely vary. ?Same goes for overhead wiring in an area where houses are close together. ?Many houses?connected to one transformer. ?In my case I’m lucky, I am the only house on my transformer! ?My line voltage doesn’t vary much at all because of that! ? ?You would probably have an easier time convincing ?the power company to add a smaller transformer just for you on the pole closest to your house if you pay for the cost. ?Trying to regulate the power on a varying basis due to an overloaded transformer by other users ?would be more difficult than just having your own. ?
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On Wednesday, October 18, 2023, 11:02 PM, Jim VE7RF <jim.thom@...> wrote:
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开云体育You know, this discussion of filament voltage and tube life just prompted me to why I originally joined the AMPS group and then consequently leading up to this group. The pieces finally fell into place. About 20 years ago I purchased a well-used, (but still very operational) RCA Radiomarine SB-1K amplifier. It uses a pair of 3-400Z’s at 2800VDC for a solid 1KW out. When I connected it to my electrical system, I was only getting ~~500W? out. I had 5.2 VAC at the transformer but 3.8 VAC (IIRC) at the tube socket! The short answer was the previous owner used a piece of lamp cord (gauge escapes me now but I wouldn’t run a filament with it!), to the filament. Replaced it with some stouter wire and I had 5.0 on the filaments again and a solid 1K out. I scratched my bohunkous many times wondering why somebody would do that. This recent discussion gave me the answer I believe. ? Mod-U-Lator, Mike(y)/W3SLK ? ? |
开云体育Dear Mike, ? Some years ago on the Amps @ Cont…Com forum, mention was made on methods of limiting thew inrush current to transmitting tubes and I believe to remember someone suggesting to run a lighter diameter piece of wire in the filament circuit to limit the 颈苍谤耻蝉丑…. ? Hal Mandel W4HBM |
开云体育That would have been it Hal! ? Mod-U-Lator, Mike(y)/W3SLK ? ? ? From: [email protected] [mailto:[email protected]] On Behalf Of HaL Mandel
Sent: Thursday, October 19, 2023 10:04 AM To: [email protected] Subject: Re: [ham-amplifiers] Fading Away ? Dear Mike, ? Some years ago on the Amps @ Cont…Com forum, mention was made on methods of limiting thew inrush current to transmitting tubes and I believe to remember someone suggesting to run a lighter diameter piece of wire in the filament circuit to limit the 颈苍谤耻蝉丑…. ? Hal Mandel W4HBM |
开云体育Somewhere is all the messages my question spawned; Adria Fewster posted a link to a Richard Measures, AG6K (SK), article about modifications to a Kenwood TL-922 amplifier. In this article Richard Measures AG6K (SK) suggested using a smaller wire to feed the 3-500Z tube to knock down the filament voltage. ? 73, Dave, w6de ? From: [email protected] <[email protected]>
On Behalf Of HaL Mandel via groups.io
Sent: 19 October, 2023 14:04 To: [email protected] Subject: Re: [ham-amplifiers] Fading Away ? Dear Mike, ? Some years ago on the Amps @ Cont…Com forum, mention was made on methods of limiting thew inrush current to transmitting tubes and I believe to remember someone suggesting to run a lighter diameter piece of wire in the filament circuit to limit the 颈苍谤耻蝉丑…. ? Hal Mandel W4HBM |
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A Chinese tube never does from filament issues no matter??what amp they are in and what the filament voltage is. ?It will die from a G-F short or some other issue long before it dies from any filament issue of tenths of a volt. ?When operating tubes 24/7 key down in commercial service you could extend filament life in a 3-500 by watching the filament voltage.
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On Thursday, October 19, 2023, 3:02 PM, Adrian Fewster <vk4tux@...> wrote:
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HaL Mandel
Brandon DX