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Author Topic: 4-1000A Dual Tube Amplifier  (Read 5595 times)

Posts: 15

« on: December 12, 2005, 11:02:19 AM »

Do you now own, or have you owned, or perhaps dreamed of owning a 4-1000A amplifier? Maybe one with two (2) tubes?

Well I'm trying to collect schematics for the once popular, still sought after 4-1000A amplifer. I myself own three single tube versions and in the near future intend on building a two lunger but I still need that last vaccume variable output cap.

If you have a schematics for a 4-1000A or better yet one for a pair of 4-1000A's I would love to receive a copy as I plan to store them electronically and make them available to all who need or looking for them.

Here is a schematics I found searching the net just to wet your whisle:


Posts: 20834

« Reply #1 on: December 12, 2005, 04:08:08 PM »

I've only used them grid-driven, not GG.  Never needed "two," since one will run >1500W output power w/4400V Ep.

My homebrew six meter 4-1000A graced the cover of the February 1985 "CQ" magazine, archived here:

I have another that looks almost identical except for the input/output tank components, it's a single bander for 160m built out of desparation in 1984 when I wanted to go 160 and my Henry HF amps only covered 80-10.

They share a common 4.4 kV/1.0A CCS power supply and have clucked along since '84 with zero problems.  Original tubes, which were broadcast pulls when I got them.

Nice to have a tube that makes enough room light so you can read by it.



Posts: 430

« Reply #2 on: December 13, 2005, 05:31:49 AM »

Looks like you'd have to add some parts to get 160m coverage.

Posts: 20834

« Reply #3 on: December 13, 2005, 02:36:16 PM »

As mentioned above:

"I have another that looks almost identical except for the input/output tank components, it's a single bander for 160m built out of desparation in 1984 when I wanted to go 160 and my Henry HF amps only covered 80-10."

...the 160m deck has different input and output tank components.  

Instead of using a toroid like most for 160 coverage, I used a rather large air-wound (Air Dux) inductor made of #14 gauge wire, 2" diameter, that runs most of the width of the 17" chassis.  Just seemed the thing to do at the time, and I had the Air Dux inductor.

For the 160 model, I did not use a vacuum variable for the TUNE cap -- too many turns.  

It runs 1500W out with ~12W drive (grid driven) and thus has this large Globar padder resistor across its input!

Would be fun to see more homebrew 4-1000 amps; not the schematics, but the end products.


Posts: 1134

« Reply #4 on: December 14, 2005, 08:40:43 AM »

I like the $2 price on the cover of CQ Magazine of Steve's web site.

Posts: 26

« Reply #5 on: January 02, 2006, 08:47:12 PM »

I do not have a complete schematic of my 4-1000A amp.  It was built by W7LFA who was at that time one of the engineers at KING-TV in Seattle and it is built very well indeed.  I  rebuilt the control circuitry and power supply and converted it to grid driven Class AB2 by adding a control grid and screen grid supply.  The control grid operates at -63 VDC and the screen operates at 500 VDC, both with shunt regulation.  The control grid is bias switched by using a reed relay to the bias supply with cutoff at about -90 VDC.  High voltage in 4000 VDC.  Naturally the cathode is at rf ground.

The input is fed through a 4:1 balun terminated by non-inductive resistance of 200 ohms and then through a blocking cap to the grid.  The grid voltage is fed through an rf choke bypassed on the supply side.

The control circuitry is step start.  The main power is through a key switch which arms the filament, fan and control circuitry switch.  That switch, in addition to turning on the filaments, fan and control circuitry, also arms the high voltage supply switch.  The high voltage switch turns on a 7 second timer relay  and a power relay at the same time.  The power relay starts powering up the plate voltage with the plate power transformer connected on the primary side through a surge resistor.  A second power relay actuates after 7 seconds to shunt out the primary resistor and connect the screen supply to the screen.  When the High Voltage switch is turned off both power relays are deactivated and the screen is immediately disconnected from the tube and the plate transformer is cut off letting the plate voltage power down.  Restarting the high voltage starts the process all over again.

Finally the high voltage switch arms the T/R switch. A second switch is placed on the back chassis to switch between external QSK and an internal T/R relay.  With the QSK switch in the external position, activating the front panel T/R switch activates the internal relay so that any rf coming from the exciter is fed to the 4-1000A.  Idle cutoff is handled through a reed switch that is connected to the relay line coming from the exciter.  Input and output of the amp are connected to a dual trace scope with the exciter t/r relay connected to the external sweep input of the scope.  Envelope delay of approximately 5 ms is incorporated to assure that that all t/r relays have settled.  This is based on the swithching characterstics of the Ameritron external QSK switch.

I really love my 4-1000A but I use it pertty much only on 20 meters these days. (I use my AL-800 on the other bands).

I hope you are successful wtih yours.


Posts: 9597


« Reply #6 on: January 04, 2006, 03:37:29 AM »

Sounds like a nice 4-1000 amp, and grid driven is definitely the way to go! Sounds like you were careful with the design, using a shunt regulator on both grids.

The 4-1000A in grounded grid simply does not have enough gain to fully use the tube. A 100 watt exciter, even with 4000-5000 volts on the anode, will only develop 1000-1200 watts output when the 4-1000A is cathode driven. A pair of tubes will barely do better.

The reason for that is the cathode impedance of the 4-1000 is too high, and since the ratio of cathode to anode operating impedance primarily determines gain in a GG amp...the 4-1000A has significantly less gain than a zero bias triode.

In the 70's, I had a pair of 4-1000A's (for a while) that started out being cathode driven, but was later converted to grid driven with system similar to yours. Back then I use vacuum tube regulators, a 6146 and 6AG7 combo forming the screen regulator circuit.

I soon swapped over to GG triodes, and never regretted the change. The only tetrodes I've used since then have been specifically for high gain applications, when the tubes were grid driven. All of my amateur stuff since the 70's has been cathode driven triodes, because they are cleaner for IM distortion and easy to operate.

I still have fond memories of those big glowing jugs, but I also remember the performance versus size baggage that came along with them. Kind of like having a warm hearted but high maintenance girlfriend, hi hi.


Posts: 4

« Reply #7 on: July 04, 2006, 12:09:44 PM »

Here is my dual 4-1000a amp.

ken, wa4mnt

Posts: 32

« Reply #8 on: October 08, 2006, 02:05:04 AM »

Ken, Your amp is a work of art!
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