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D&A phantom 500 12 tube

Discussion in 'Amateur Radio Amplifiers' started by 17W1517, Jun 8, 2015.

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  1. KM1H

    KM1H Ham Member QRZ Page

    The amp manufacturers couldnt do anything about it since RCA and Eimac werent producing ceramic tetrodes much better than -25 dB or so in the 60-70's. Big glass jugs such as the 4-125A, 250A, 400A, 1000A were all over -30 dB in GG .
    There were a few exceptions but those were priced thru the roof along with their sockets. Plus the 4CX350FJ and 4CX600J and JA which were low production special process tubes.

    The 4 NCL-2000's I use for 10-80 and 10-160 with vintage gear, AM only, and 6M only have all been highly modified for much better IMD performance.

    Carl
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The Dentron Clipperton-V 4CX250B 2m amp is a lousy design in all ways; Denny is a nice guy but blew it with that amp, and I think every one ever sold has required repairs. I've repaired three of them, myself (never owned one, though).

    One amazing thing omitted from the design was grid current metering! With a grid-driven tetrode having a 2W grid dissipation limit, that's almost an amazing oversight. It also didn't meter screen current, which is the most useful indicator of proper loading.

    Almost everybody just peaked for max output or maybe dipped plate current but otherwise had no idea how the amp was tuned, which led to not only crappy signals but premature failures.
     
  3. AI3V

    AI3V Ham Member QRZ Page

    I adde

    I added grid and screen and power output metering, regulated the screen.

    Had a noisy amp that made just a hair over 200 watts.

    Never could get the output tank to dip, load control was useless.

    A real craptastic amp.

    Consider you could buy a 160w ss amp that did not require lethal voltages, I look back and wonder what I was thinking.

    Rege
     
  4. AI3V

    AI3V Ham Member QRZ Page

    Sure they could.

    You add negative feedback, and the imd improves.

    But then you have a amp that requires more drive, or has less gain.

    Maybe that's what the engineers at the FCC were hoping would happen when they tried to legislate amplifier gain on 10/11 m.

    But sammy sez it's gotta be grounded grid, and take 100 watts of drive.

    Rege
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I serviced my last one several years ago, it was owned by WA3CMP (?) or something like that. Chris, from PA but last time I spoke with him he was in the Caribbean someplace.

    I ditched the HV metering and replaced that with screen current metering. Never saw any reason to "meter" anything you can't adjust.

    But, it did achieve 275W output power with about 300mA Ip and 1-2 mA Ig and 0 Ig2.

    Not too bad, but a stripline tank would have been a bit more efficient, and a better screen supply would aid linearity.

    The Gonset 903A used a silver-plated stripline tank and with only about 1700V B+ achieved 300W output power. Its screen regulation wasn't perfect, but not bad (gas tube regulators yielding 360V Eg2) and when properly loaded, Ig2 was about zero, so screen voltage wasn't changing.

    I had an old "blown up" Gonset that was badly damaged, but replaced the tube and added an outboard homebrew power supply that provided 2200V B+ and it ran 350W output power with nearly zero Ig and Ig2. Not bad, and the total cost was about $100 to get it back on the air.

    The previous owner blew the tube with excessive drive and never looked at the grid current. "Hey, I dipped the plate current, okay?":p
     
  6. KM1H

    KM1H Ham Member QRZ Page

    The last Clipperton V I had here I converted to a strip line with a GS-36B/4CX400A and SS regulated screen and bias, an easy and clean 375W out on SSB/CW. That Russian tube is amazingly clean and Ive also used them in the AM-6154/6155 at about 330W due to lower HV; on CW it will run 400W but that gets real dirty on SSB.

    Both were driven with about 3-4 W from a Microwave Modules transverter which later drove a cranked down and bias modified 160W RFC brick into the 1500W 3CX1000A7 amp; all have been just fine the past 35 years.
     
  7. N2EY

    N2EY Premium Subscriber QRZ Page

    Back in the old "maximum of 1000 watts DC/2000 watts PEP input" days, it was an FCC requirement to have plate voltage metering built-in to any transmitter capable of 900 watts or more DC input. That way the op could not feign ignorance of what the amp was actually doing.

    That's why so many pre-1984 amplifiers have B+ metering.

    The Clipperton V probably has it due to force of habit.

    No excuse for not metering the screen current, though.

    73 de Jim, N2EY
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    They not only omitted screen current metering, but also grid current metering -- using a grid-driven tube in AB1, and a tube with 2W max grid dissipation rating under ideal conditions.

    Metering Ig1/Ig2 is way more important than metering HV or even plate current. I tune up tetrode amps like this (my homebrew 4-1000A on 6m is one of them) watching output power and grid current only, then adjust LOADing to dip the screen current and I'm done. I don't care much what the plate current is and really never look at that.:p

    It would be impossible to exceed the plate dissipation rating of the tube. It is possible to exceed the 1500W PEP output limit, but not by much and who cares?:)
     
  9. N2EY

    N2EY Premium Subscriber QRZ Page

    In an amp that couldn't do anywhere near 500 W input - so why bother with HV metering at all?

    Leaving out grid and screen current meters was just dumb. Bad design, period.

    I always wondered about designs that spent lots of $$ on some things but then skimped on meters. Why?

    But, hey, there are all sorts of bad design ideas out there. Like 3-500Zs on 2 meters.

    73 de Jim, N2EY
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Funny part is:

    Denny (guy who owned/ran Dentron) also ran Amp Supply and they stocked a lot of panel meters and even sold them to home builders very inexpensively! Wish someone would still do that, but analog panel meters cost a whole lot more today than they did back then.

    Also, the Clipperton V (as one example) did have a fine panel meter. To add better "metering," all it needed was a 3-way rotary switch and two appropriate shunts, using the single meter it had.:p

    I could make a pair of 3-500Zs work on two meters: Wire each one in series with the anodes of a 5894 and let the interelectrode capacitance of the 500Z just couple the energy through it on the way to the tank circuit.:)
     
    KD2ACO and N2EY like this.

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