Linear Power Amp, 3-1000Z --Any Suggestions?--

[KM1H]

Back in my 4x1 building days I used one or two in either grid drive or GG, depending on the customer requirements.

The PS started at 4200V but soon went to 5200VDC key down as the standard. A local company wound the iron.

With sufficient drive the output was 2500W per tube at least thru 20M with good pulls from local stations.

Carl
KM1H

[SM6OID]

Hej !

Thank you all for all comments!

So, to some conclusions(?) regarding the socket.
I have a new SK-500 (this is the aluminium socket).

1) I understand by looking at it, and this is also in line with comments in the thread, it will cause high backpressure for the cooling fan. Possibly this can be improved by making some extra holes in the socket.

2) Is there a possible problem for the 3-1000Z to use a SK-500? Will it cause mechanical stress for the pin to glass seal. I'm not sure that I fully understood the previous comments about that.

3) Or should I start looking for the plastic SK-510 socket?

4) Any suggestions/comments regarding Power Supply? 

As you all can understand, I want to get things at correct as possible from the beginning, things can go wrong in a big way with a high power amplifier...

[W3RSW]

After you've read all the notes and if your still wanting to use a 3x1 then the aluminum SK500 socket should be fine at the 3x1's 'lower' plate voltages and "somewhat lesser" cooling restrictions.  I thnk it'd be elegant to use the 3x1; who else will ever use them for something more than a shelf queen in a (gasp) collection  ?

I have a SK500 in hand and just want you to know that the pins can be aligned accurately simply by very slightly enlarging 4 out of 5 holes in the base, loosely installing the pin connecting hardware, inserting the tube and then tightening the nuts to the new spacing requirements.  This will set up the cold alignment.

Since your very slightly flexible GG copper strap and braid will "nail down" permanent spacing between three of these pins permanently to the rim of the socket and float as a unit that satisfies the bulk of thermnal stress for those three pins. Double nut the GG connections, leaving the three holes slightly loose to the base phenolic if you want 'maximum' flexability.

The other two pins for filament can be left floating as far as the sockets base phenolic goes as long as the tube pins are tight to the clamps and the double nutted hardware from pins to filament supply leads are tight.   

Sounds complicated but simple in practice.
Also even if everything is stock tight, keep in mind that the phenolic in the socket insulator also expands radially with increased heat.  Don't have the exact figures but I'll bet it's not too different than pyrex glass.

[ke7trp]

My 4-1000 amp had 6200 volts on the plate under load.  Big PDahl Iron.  With a 100watt SSB radio on 80 meters if I wispered it would SLAP the Bird 2500 slug HARD in the corner.  I have no idea how much that amp actualy made.  I could run it at 800 to 900 watts AM Carrier it it did not seem to care. The blower was VERY loud and the room would shoot up 30 degrees in 10 minutes of use. I sold it off. 

It was a 4PR-1000 tube though.

C

[SM6OID]

Hej !

OK, I now have the situation under control, checked the procedure "align socket with pins", everything is now clear. 

My plan is to run the tube at "quite low" power, or in other words following the Eimac Data Sheet for linear SSB service.

Here in Sweden we have an advatage when it comes to feeding the power supply, our mains voltage (that you will find in every room) is 230 V / 10 A (50 Hz) or possibly in newer installations 16 A.
Every (almost) house is feed with three phase 400/230 V 16 A at least. To find 400/230 V 20 or 25 A is not uncommon, and even 32 A! Actually my apartment is feed with 400/230 V 16 A. So, for QRO operators, power usually is not a problem.   

[Opcom]

The metal socket was made for use with a high pressure blower. An airflow switch should be used with the system. The metal socket is perfectly OK if you have a good enough blower. "No" fans or low speed blowers, but something like a 3-4" diameter squirrel cage, 2-3" wide, running at 3450 RPM or more. The higher the rotational speed of the blower the better it will serve if you have the metal socket. The big xmtr here has a 4-1000A and the metal socket, and a good size 3750? RPM blower. It can run for hours with rated dissipation and no problems. The construction is such that the "hose inlet" of the socket is open to a pressurized compartment. I cant' stand it when people, and even manufacturers, use fans for cooling a tube like that. I don't know how much 3-1000's cost, but they are still made by "Amperex" IIRC - I have some spares for RF generators used in semiconductor manufacturing.

If 3-1000Z cost is a factor, you might be able to trade what you have for a set of 3-500Z hardware and the tubes will be more like $150 each new Chinese. I use them in a modulator and in 40+ hours of tests, never have had a failure.

[SM6OID]

Hej !

Thank's for the input! A pressure sensor connected to the socket has been included in the plan, actually it is a MAP (Manifold Absolute Sensor) from an automotive application. 

Since I already have the Eimac 3-1000Z I will keep it, I did not pay that much for it, and it is new. However, my concern is that IF it breaks it will not be pleasant to find a replacement.

[KD6VXI]

I thnk it'd be elegant to use the 3x1; who else will ever use them for something more than a shelf queen in a (gasp) collection  ?

ME!!!  I'd LOVE to find one that I could trade for or something to put in my Harris.  The 3x1 is about vaporized now.

I also have a 3CX1000 I'd stuff in if I could find a bayonet socket for it that cost less than my Harris


--Shane

[KD6VXI]

Hej !

Thank's for the input! A pressure sensor connected to the socket has been included in the plan, actually it is a MAP (Manifold Absolute Sensor) from an automotive application. 

Since I already have the Eimac 3-1000Z I will keep it, I did not pay that much for it, and it is new. However, my concern is that IF it breaks it will not be pleasant to find a replacement.

The 3-1000Z can be replaced by a 4-1000Z.  Just make sure you GROUND pins 2,3 and 4.

It's a seckzi tube....  SOMEDAY I'll find one to return my amp to stock.  I LOVE the drive requirements.  I'd also consider doing grid driven on my 4-1000 that's in the 3-1000 RF deck now.

--Shane

[KM1H]

I thnk it'd be elegant to use the 3x1; who else will ever use them for something more than a shelf queen in a (gasp) collection  ?

ME!!!  I'd LOVE to find one that I could trade for or something to put in my Harris.  The 3x1 is about vaporized now.

I also have a 3CX1000 I'd stuff in if I could find a bayonet socket for it that cost less than my Harris


--Shane

How about modifying the erector set Chinese 4CX-1000A socket? Start by removing one layer and see what needs to be changed. The original 3CX1000A7 socket was for grid drive and I modified mine for GG.

Carl
KM1H

[WA1GFZ]

I found the 4CX1000 socked is a source of spare parts for the 4CX3000A socket so I bet it was a standard sice contact.
6200 on a 4-1000A Oh MY...

[Fred k2dx]

From my experience running the 4-1000 at 6 kV pay attention to your plate parasitic suppressor. Mine was made of about two or three windings over 3 paralleled two watt carbon resistors, I forget the value but I guess 50 or 100 ohms each. (As in the published Eimac design intended for lower B+). When they failed - obviously by overheating - the results were dramatic to say the least! I was told (by Rich Measures I think) that the tube has a tendency for a VHF parasitic. I guess the elevated B+ increased the load the on the supressor. But the amp sure did play VERY well - for a while untill the great explosion, which was about like discharging a shotgun in the room.   The 3  two watt carbon resistors were replaced by a small globar resistor, nichrome wire, a new plate choke, another 4-1000, and all was fine.

The power supply survived just fine, 50 ufd oil cap and K2AW rectumfryers.

[KD6VXI]

How about modifying the erector set Chinese 4CX-1000A socket? Start by removing one layer and see what needs to be changed. The original 3CX1000A7 socket was for grid drive and I modified mine for GG.

Carl
KM1H

I have a 4CX1000 socket here.  In the current config, the cathode end is floating (on the 3CX1000) and the end of the fils that DOESN'T have the cathode connected is grounded.  That was the only problem I had with modifying the socket.  I'd have to elevate the tube above the base of the socket by 1 'pin' to get it to ground the cathode.  To drive the cathode, I'd have a HELL of a time, as the tube would have to drop so far into the socket the anode sits on top of the socket

I'm trying to use the Eimac socket, it's what I had on hand.  Once I disassembled it, I found that a couple of the (I assume) BeO insulators where cracked and split.  So, that project was shelved until I can source another socket.  In the meantime, I've come into some 4-1000s, so it's on hold.

I'd LOVE to get a low drive tube in it instead.  65-80 for full output would be nice!

--Shane