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

[SM6OID]

Hej !

Since quite some time I have an unused Eimac 3-1000Z waiting...
The idea is to build a PA for shortwave, I have seen some descriptions in old QST Magazines from the 60's.

So I'm looking for advice/experience from other Hams that may have some ideas!

[KD6VXI]

Bill Orr's radio handbook has a two stage amplifier, a 4CX250 driving a 3-1000Z.

Any 4-1000 GG amplifier schematic can be adapted to the 3-1000Z.

I have a commercial 3-1000Z amplifier I just put a 4-1000Z tube in, works fb, but drive went up!

The 3-1000Z is like an 8877 / 3CX1500.. Not a WHOLE lot of drive for a WHOLE lot of Pout!


--Shane

[KM1H]

There was a ARRL QST/HB article also back in the 70's I believe. Its a great tube but dont abuse it as they are very expensive to replace.

Carl
KM1H

[SM6OID]

Hej !

I have the Radio Handbook where the 4CX-250B driving the final 3-1000Z Amp is described, so I have some good ideas to use.

Then, to a possible "problem", I have a new socket for the 4-1000A, made of cast aluminium. (can't remember the  "SK" part number right now) Will a socket like this work? The pins will fit, but I'm afraid of the mechanical stess due to thermal expansion, I do not want to get any cracks in the glass base of the tube. The chimney is for a 4-1000A, hence it's a bit too tall, compared to the chimney designed for the 3-1000Z. Is this a problem?

Finding a new chimney and to have it shipped to Sweden may be a bit too exiting since glass have a nasty habit of breaking. However, the life of the tube is very important, if I need a shorter chimney I will have to find it.


 
Shane, could you please give me an idea of "operating conditions" when you had the triode in your amplifier? Plate voltage, Ip and so on!
Any "special design features"?   

[W3SLK]

Over here, they used to cut the bottoms off of large pickle jars and use them. What ever works.

[KD6VXI]

Hej !
Shane, could you please give me an idea of "operating conditions" when you had the triode in your amplifier? Plate voltage, Ip and so on!
Any "special design features"?   

The 3-1000Z is a zero bias tube at 3Kv on the plate.  That's how mine is run.

Their is not Iplate meter, so I can't tell you.  It runs a choke filter, and has EXCELLENT REGULATION.  3300 key up, 3150 key down at a kilowatt carrier (I run 8 gauge primary wire to the panel)

As someone else has said, the 3-1000 is PRICEY..  The 4-1000 can be subb'ed. 

Asking me about my amplifier is like asking a CBer about theirs (no pun intended).  Mine is switched cap on the in and output of the pI, and a roller inductor for tuning.

Any 4-1000 or 3CX1200 schematic should work.  The 1200 is the "solid state" version of the 1000Z and kinda the 1000A.

--Shane

[WA1GFZ]

The pins should float in an air system socket. It is a problem if they are tight against the insulator for thermal stress. It is not great for RF service due to long pins. Run wide copper flashing between grid pins and case ground. Also drill some holes in the sides of the air system socket to get more air flow. It takes a lot of air pressure to just rely on the hose connection. Maybe you can find a better RF socket for the tube.
The 4-1000A only had 4 1/2 inch holes to move air across the pins so it took a lot more pressure. The 3-1000Z didn't have the air restriction of the base making it have less restriction but also a weaker structure.
A fine amplifier tube. I think there was a 3-1000Z linear in the early 70s handbook or maybe the SSB handbook. It was only 1 stage.

[W2VW]

This might be of interest

http://www.google.com/imgres?imgurl=http://members.cox.net/nx7u/images/LK2000_original.jpg&imgrefurl=http://members.cox.net/nx7u/BTI.html&h=300&w=400&sz=56&tbnid=vfOsU0LiZgI0QM:&tbnh=93&tbnw=124&prev=/images%3Fq%3DLK-2000&hl=en&usg=__ydhnJNU06QBU0yS6MjdmRseTa24=&ei=LdKwS8iqLIX7lwfHt9SRAQ&sa=X&oi=image_result&resnum=7&ct=image&ved=0CBcQ9QEwBg

BTI switched from a glass chimney to that brass duct seen in the photos. It directs air across the plate cap.

Kerri KC2UFU and Ken KC2UDZ are running one of these now. I listen to them all the time.

[w3jn]

Dave wins the prize for the longest link ever posted on AMFone 

[KM1H]

That cast aluminum socket is a slug and seriously restricts air flow. The later plastic one is much better.

Many moons ago I made a chimney for a 4-400A out of a 2# peanut butter jar, it lasted about 2 months before fracturing. They are not RF and heat rated.

A big Coleman style lantern chimney may work.

Carl
KM1H

[W2VW]

Dave wins the prize for the longest link ever posted on AMFone 

It's always nice to be recognized for something 

teh tnx.

[K5UJ]

That cast aluminum socket is a slug and seriously restricts air flow. The later plastic one is much better.

Many moons ago I made a chimney for a 4-400A out of a 2# peanut butter jar, it lasted about 2 months before fracturing. They are not RF and heat rated.

A big Coleman style lantern chimney may work.

Carl
KM1H

Carl, what is ur opinion of eimac SK500 socket for 4x1?

tnx
rob

[KM1H]

The aluminum is a slug, the plastic is fine.  I dont know model # without going downstairs and Im too lazy right now. The aluminum can be modified as well as cutting out alternate sections in the tube base to reduce back pressure when using the aluminum one.

Carl
KM1H

[K5UJ]

The aluminum is a slug, the plastic is fine.  I dont know model # without going downstairs and Im too lazy right now. The aluminum can be modified as well as cutting out alternate sections in the tube base to reduce back pressure when using the aluminum one.

Carl
KM1H

Okay tnx i'll look for plastic. you just saved me a few shekels

R.

[ka1tdq]

When I built my amplifier I wanted to use a 3-1000 but had second thoughts when I found out each tube is $1100 new.  That's awfully expensive when you're beating the p*ss out of them during the testing stage.  I decided to go with a pair of 3-500's and it works just as well.  I ended up with 1200 watts.

[K5UJ]

When I built my amplifier I wanted to use a 3-1000 but had second thoughts when I found out each tube is $1100 new.  That's awfully expensive when you're beating the p*ss out of them during the testing stage.  I decided to go with a pair of 3-500's and it works just as well.  I ended up with 1200 watts.

That's NOS too, not really new.   Don't know how long they have not been in production but yes, when planning an amp from scratch or halfway from that if you have a choice, 3x1 not the best way to go.  It is a great tube, but risky.  You gamble buying used; and vendor/auction prices are sky high.  If I had a pair 3x1 amp already, and a good set I'd stick with them because if you treat them right they'll last and really put out but I don't.  I considered quad 3-500 then decided that was too iffy and too much work, next came 3cx3K for contemplation but then a hb gg 4x1 project sort of fell into my lap, one with enough oomph to make it a pair 4x1, so that sort of decided the issue for me 

[WA1GFZ]

You could always pick up a 4-1000a and build a rig. once you get it working right install the 3-1000. A good tube will last a long time.

[The Slab Bacon]

4x1 is a good, rugged, hard to kill tube. The one in my big homebrew rig was used when I built it, and I've beat the pants off of it for 10 years now. Still using the same tube!!

And it sure looks purty with the plate glowing red!!

[KD6VXI]

You could always pick up a 4-1000a and build a rig. once you get it working right install the 3-1000. A good tube will last a long time.

Have you done this before, Frank?

My Harris wants about 200 watts of drive with the 4-1000 in it, to produce legal limit.

Before, approximately 100 watts of drive pushed it to legal limit, I'm told. 

The difference is a 3-1000 vs 4-1000 at app 3Kv.

--Shane

[WA1GFZ]

I ran a 4-1000A GG for years and today it sits in my buddy's shack about 5 miles east. 160 through 10.
I could have dropped a 3-1000Z right in because I had a string of Zeners for variable bias. Resting current will go up.

[W2VW]

You could always pick up a 4-1000a and build a rig. once you get it working right install the 3-1000. A good tube will last a long time.

Have you done this before, Frank?

My Harris wants about 200 watts of drive with the 4-1000 in it, to produce legal limit.

Before, approximately 100 watts of drive pushed it to legal limit, I'm told. 

The difference is a 3-1000 vs 4-1000 at app 3Kv.

--Shane

A good 3-1000 cathode driven with 3200 volts on it under load will make legal limit with 60-80 watts under carrier conditions.

A good 4-1000 in the same exact situation with all the grids strapped will need 110 - 130 watts drive for 1500 watts carrier.

[WA1GFZ]

That's what I measured in the 4-1000A
So if you have a clean layout the 3-1000Z will give you a bit more gain.

[Fred k2dx]

The 4-1000 in GG likes plate voltage - 5 to 6 kV makes it much easier to drive than at 3 kV. Max rating per Eimac is 6 kV. A small globar resistor should be used in the plate parasitic suppressor at this voltage. The plastic socket is much better than the older cast aluminum one.

[W2VW]

The 4-1000 in GG likes plate voltage -

That's for sure.

No reason the 3-1000 can't be run at that voltage too with zener bias.

[WA1GFZ]

I put 5500 on my amp once. Made real power but blower wasn't rated for the air flow required. I ran a pair of BC610 transformers across a 240 volt line.
It ran just over 3000 volts and makes 1500 out with just over 100 watts drive.