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LK500 issue
Occasionally this amplifier will show no grid current with drive
present. As drive is increased the plate voltage drops in a linear manner. With no RF drive present plate voltage is normal at about 3kv. When operating in this condition the amplifier will show some output when tuned, typically about 10-20 watts and no more. Prior to further troubleshooting here does this sound like a familiar issue? The problem is intermittant in nature. K6TLA |
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Re: 4CX1500A
pentalab
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
the RF drive. ### The IMD from ur HT-33/37 is gonna be horendous as is..negating any advantage of the tetrode linear behind it. BTW... a yaesu MK- V.. properly tweaked in analog ESSB mode [not dsp mode] is an easy - 75 db of cxr suppression.... and an easy -100db od cxr suppression when in standard 300-2800 hz mode.` ### The mic gain control is NOT a power output control.. never was. ## If u want to easily drive the new tetrode amp .. use a 9:1 un un and use a 450/500 ohm termintaing resistor.[typ on a 4CX- 10,000D7. Instead of an attenuator.... just use a 50 ohm termination resistor. My buddy across town uses a 50 ohm globar on the grid of his 4CX-1500B.... 1500w pep output.. with 10-20 watts of drive. With a 200 ohm globar and a 4:1 un un.... u could drive it with next to nothing. ### IF ur Hallicrafter doesn't have a power output control... [none of those tube rigs did]... inject an adjustable dc voltage into the alc jack... then u can adjust it top any power output u want.... and zero alc overshoots... and worrying abt alc time constants in a linear... since u have already established the alc voltage from a small regulated.. adjustable outboard supply. Carrier's are okay.### Nobody can hear ur cxr.. or anybody elses cxr.... UNLESS they or u, are off freq. Which brings up another point with these older rigs.... they drift like crazy. I replaced the .5ppm tcxo in my mk- v with the .25 ppm tcxo... and at 20 mhz.... zero drift... not one hz. With a tuning rate of just 312 hz per knob revolution... and a readout in .625 hz increments... zero beating someone is a snap... unless they are drifting badly.. then u gotta chase em all over the band. me.. I just stay put.... let them do the work. Later... Jim VE7RF
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Re: 4CX1500A
On Dec 23, 2006, at 5:45 AM, David C. Hallam wrote:
Rich,Adding zeners is easy. I don't think the transformer has the outputWhat type of rectifier config.? ¨C220V will cut one off. InGood move, David. A better way of avoiding grid-I is needed. Carrier's are okay. R. L. Measures, AG6K, 805.386.3734 r@..., rlm@..., www.somis.org |
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Re: The Making of a DeForest Triode -- YouTube Video
Mike Sawyer
I saw that Steve. Very impressive. However, I think its neat what you can do
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when you have the right equipment to perform the job. I guess Phillips was pretty instrumental in providing the necessary tools and raw materials. Mod-U-Lator, Mike(y) W3SLK ----- Original Message -----
From: "Steve Cook" <vaj4378@...> To: <ham_amplifiers@...> Sent: Saturday, December 23, 2006 2:41 PM Subject: [ham_amplifiers] The Making of a DeForest Triode -- YouTube Video The making of a DeForest triode in 2006 Steve (((WG7K))) Tucson, AZ |
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Re: 4CX1500A
David C. Hallam
All boat anchors here. Either a Hallicrafters HT-32B or Johnson Invader 200
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will be used. David -----Original Message----- |
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Re: 4CX1500A
What kind of exciter are you using?
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Jim SM2EKM ------------- David C. Hallam wrote: 3. I could reduce the drive by turning down the audio gain but really don't |
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Re: 4CX1500A
David C. Hallam
Rich,
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In regard to your suggestions of increasing the screen voltage to 750V or turning down the drive, these are my problems. 1. The screen, bias, and HV supplies are already built. The screen supply is 550V zener shunt regulated. I don't think the transformer has the output to increase the voltage by any significant amount, i.e., more than 50V or so. I could run some tests and see. 2. The bias supply would operate at -170V, but I don't think it has enough head room to supply the necessary voltage to bias the tube to cut off in stand by with 750V on the screen. In stand by it puts out about -220V. In addition to supplying the grid bias, I use it to hold in a relay that operates the relay for HV and screen primary power. That way if the bias fails for any reason, HV and screen voltage are removed from the tube. 3. I could reduce the drive by turning down the audio gain but really don't want to operate that way. 4. The exciter's carrier suppression is degraded if I turn down the RF drive. David -----Original Message----- |
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Re: 4CX1500A
On Dec 22, 2006, at 7:50 AM, David C. Hallam wrote:
Rich,Correct, but since it takes 170v peak RF V to drive the grid from ¨C 170v up to 0v, the higher the grid terminating R, the leas RF power will be needed to reach 0v. It takes +105v-pk of RF drive to overcome ¨C105V of grid bias. Why not use more screen V ? Why not turn down the power output, David ? R. L. Measures, AG6K, 805.386.3734 r@..., rlm@..., www.somis.org |
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Re: VE7RF amp
Garry
Ditto Jan,
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Couldn't agree more! And he takes nice, detailed pictures too! Merry Christmas & Happy New Year to you and to all!! Garry - WR4R Jan Erik Holm wrote: Since I have forgot/lost my Yahoo password/ID and the |
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Re: 4CX1500A
David C. Hallam
I would really like to keep the exciter looking at 50 ohm so the amp could
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be switched in and out without retuning. David -----Original Message----- |
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Re: 4CX1500A
"Robert B. Bonner
Use ALC that would control exciter power. BOB DD
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Sent From Mobile Device -----Original Message-----
From: "David C. Hallam" <dhallam@...> Date: Fri, 22 Dec 2006 10:50:18 To:<ham_amplifiers@...> Subject: RE: [ham_amplifiers] 4CX1500A Rich, So what you are saying is that it really doesn't matter from the tube's input impedance stand point what value of resistor I use. I am running 3KV on the anode and 550V on the screen. According to the constant current curve, -105V should give me 250 mA ZSAC or 50% of the max dissipation, so I need about 95V of drive across the resistor. Jerry Sevick's W2FMI has a trifilar wound 2:1 transformer supposedly good for 150W continuous. However, it is only flat up to 25MHz. The same transformer with a slightly different tap position for 2.25:1 is supposed to be good up to 30MHz. If I go to the 4:1 and use a 200 ohm resistor, I have to look at an attenuator for the exciter to keep from overdriving the amp. David -----Original Message----- Yahoo! Groups Links |
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Re: 4CX1500A
David C. Hallam
Rich,
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So what you are saying is that it really doesn't matter from the tube's input impedance stand point what value of resistor I use. I am running 3KV on the anode and 550V on the screen. According to the constant current curve, -105V should give me 250 mA ZSAC or 50% of the max dissipation, so I need about 95V of drive across the resistor. Jerry Sevick's W2FMI has a trifilar wound 2:1 transformer supposedly good for 150W continuous. However, it is only flat up to 25MHz. The same transformer with a slightly different tap position for 2.25:1 is supposed to be good up to 30MHz. If I go to the 4:1 and use a 200 ohm resistor, I have to look at an attenuator for the exciter to keep from overdriving the amp. David -----Original Message----- |
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Re: 4CX1500A
On Dec 22, 2006, at 5:11 AM, David C. Hallam wrote:
Does anyone have information as to the approximate input impedanceD. -- The resistive component of the grid input Z is well over 1,000,000-ohms in AB1, and the reactive component is 78pF. With 750V on the screen, it takes c. ¨C170 grid V to establish a ZSAC of 200mA. If the grid is terminated in 200-ohms, 73w-pep is needed to drive a 4CX1500A. With a 50-ohm termination, 289w is needed. I50 to 200 ohm un-uns are a piece of cake, but a 50 to 100 ohm un-un probably isn't very easy to make. cheerz R. L. Measures, AG6K, 805.386.3734 r@..., rlm@..., www.somis.org |
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4CX1500A
David C. Hallam
Does anyone have information as to the approximate input impedance of a
4CX1500A for the proper value of a passive grid resistor for this tube? I need about 100 ohm to get sufficient grid drive, i.e., 95 volts, so will have to use a balun to maintain 50 ohm for the exciter. I just wondered how close a 100 ohm resistor would be. David KC2JD |
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Re: Tube rebuilder
ad4hk2004
Well, Santa brought me an $800 xmas present... I removed the HV lead
from the 3CX1200D7 and cooked the filament at 7.26 volts for 6 minutes... Eimac had suggested 7.5 volts for 5 minutes but 7.26 was all I could get without going looking for the 220 Variac and unsoldering a bunch of wires inside the Henry... For a moment I started to pull the tube out on the bench and cobble up a test jig, then basic laziness caught up with me <I had already put in a 12 hour day, so cut me some slack> Anyway, post toasty, the tube puts out 1700 watts for 74 watts of drive and the grid current right on 200 mils.. Before the toasting it put out 1100 watts with 48 watts of drive hitting 200 mils on the grid... So for the moment all is well... Who knows how long the tube will work... I have reset the filament to 6.6 volts for running, which is right at the upper limit per Eimac... I did try it at 6.3 volts and saw a 120 watt drop on output... So the filament emission current is sagging... At full output I am seeing the input swr at 1.6:1 through the input transformer... I was going to calculate the grid dissipation then realized I don't know the Grid to cathode voltage under load... We tried taking a DC measurement off the filament to ground under load, but with the AC superimposed on the cathode current I don't trust the numbers I see, especially since there is a half volt, or more, difference from one side of the filament compared to the other... So I don't know how to calculate the dissipation unless I just assume that voltage from the Eimac tube curves... Anyone? denny / k8do |
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VE7RF amp
Since I have forgot/lost my Yahoo password/ID and the
lot for my ordinary email address I havent been able to sign in and view the pictures. Finaly I signed in with a new Yahoo ID and it was nice to be able to see the pictures. I must say that VE7RF sure built a very nice amplifier!! Sure would have been nice if my junk amps was that nice. Maybe I should post some pictures just to show that some stuff isnt nice looking? But it works just fine. Merry Christmas and Happy New Year to you all Jim SM2EKM |
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Re: Tube rebuilder
ad4hk2004
I know what I paid for my 3KU brand new... When I look at the quality
of the materials, the hand made switching solenoids in the tank circuit, the silver plated 1/4" tubing roller inductor the size of your thigh, the thick aluminum cabinets, the milspec connectors and the cable to the control head, etc., they had to have been barely breaking even given their obvious material and labor costs... The amp is built hell for stout... I suspect that losing their lease gave them a graceful way to staunch the bleeding... I understand where you are coming from Rich on the untuned input, yet the amp always gets compliments on the rare occasions I get into a roundtable on phone with the guys... And even Eimac during my phone call to them complimented Henry for doing innovative things that no one else in the industry did... I have been through several Henry amps, 3K and 4K, and the last few years they were in business when I called to talk to the techs no one there spoke english anymore... And the answers I got made me suspect they were winging it, rather than really knowing the amp... LA is a ferociously expensive place to live and to do business - and California taxation will spin your hat... Any tech who had electronic skills could demand $25 or $30 an hour, and get it... Henry's overhead had to be eating them... Had I been running the company I would have moved it to Laramie Wyoming, or Depuke Ioway, in a heart beat... The remaining 3K Classic I have, with 3-500's, will sit there and pump out 1500 watts of CW all day long... Of course, the plates glow like a xmas tree doing it, but they seem to hang in there... denny / k8do |
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