Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: Prev 1 [2] 3 4 Next   Go Down
  Print  
Author Topic: 3cx3000f7  (Read 16515 times)
K8AXW
Member

Posts: 7042




Ignore
« Reply #15 on: July 10, 2015, 11:22:19 AM »

RSV:  First of all, how much drive does this tube require for full output?  If it can be driven to full output with a 100w exciter.....then by all means build it!  However, I suggest building it so it can be run at full output.

Not that you would ever use it but whenever an amp is built, you build it proportionally.....big tube, big transformer, etc.  Any time you build dis-proportionally you open yourself to potential problems, rather it's dropping a full-house engine in a VW or a big ass tube into an amp that doesn't have components to make the tube happy.

But, build it!  You'll find it a hoot!

BTW, I know a guy who build a big amp which requires an amp to drive it.  To my way of thinking, this is nothing more than a construction exercise.  The practical use is compromised.
Logged

A Pessimist is Never Disappointed!
KK4RSV
Member

Posts: 78




Ignore
« Reply #16 on: July 10, 2015, 11:58:29 AM »

RSV:  First of all, how much drive does this tube require for full output?  If it can be driven to full output with a 100w exciter.....then by all means build it!  However, I suggest building it so it can be run at full output.

Not that you would ever use it but whenever an amp is built, you build it proportionally.....big tube, big transformer, etc.  Any time you build dis-proportionally you open yourself to potential problems, rather it's dropping a full-house engine in a VW or a big ass tube into an amp that doesn't have components to make the tube happy.

But, build it!  You'll find it a hoot!

BTW, I know a guy who build a big amp which requires an amp to drive it.  To my way of thinking, this is nothing more than a construction exercise.  The practical use is compromised.
Oh Mr. K8AXW I like your advice and comment and your way of thinking!! My plans exactly!

Logged
WB2WIK
Member

Posts: 21837




Ignore
« Reply #17 on: July 10, 2015, 01:34:29 PM »

There are lots of reasons to use a 3CX3000 type tube on HF in amateur service.

The best ones are: I already have one; and they actually cost less than a 3CX1500A7/8877.

That's the main reason ASI here locally to me uses them in amateur amps.  Charlie buys them in bulk and they cost him less (each) than an 8877, so he uses them.

Yes, they require a lot of heater power.  But they loaf along at legal-limit power, have excellent IMD when run below a few kilowatts, are almost impossible to overdrive with any kind of amateur equipment...and did I mention they cost less? Cheesy
Logged
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #18 on: July 10, 2015, 04:46:33 PM »

The 3cx3000*7 family of tubes are exceptionally clean tubes. They are reliable, have long life, have very low IMD, are completely stable with the grid grounded properly.

They do not have inrush issues when used with a proper size transformers, and the flying lead tube actually has LESS of a problem at 30 MHz than a socketed A7 tube unless you completely rework the socket. The primary issue is most socket designs have hundreds of pF capacitance shunting the filament to ground. The flying leads add very little capacitance compared to a socket, and actually can be made to look like a ~40-60 ohm transmission line to the chassis. I've used them on 70-100 MHz that way.

They are not exceptionally high gain, so if you keep anode voltage down around 4kV or so they will have a gain of about 20-30. That means somewhere around 50 watts or so will typically give 1500 out.

There is NO LAW that you have to blast the cooler with air to dissipate 4kW, the anode dissipation limit. You can run the air down around 1/2 inch SP (less than 45 cfm) and it will be quiet and cool enough for Ham use, even on RTTY.  If you know what you are doing, you can reduce the filament voltage for Ham use.  300 watts or 350 watts of filament power is not that bad, or even if you run full voltage it is 370 watts.  It's just silly to worry about that when the tube is free and when the tube will last over 30 years.

Of course you could help all the worry warts and busy bodies feel better and run a Chinese 3-500Z, and have ten times the IMD levels of the 3CX3000 series. That would make things better.

Logged
KK4RSV
Member

Posts: 78




Ignore
« Reply #19 on: July 10, 2015, 05:53:32 PM »

OH Mr. WB2WIK and Mr. W8JI  You boys are some silver tongued Devils!  Grin  I like the things you say. And Just for the record I have the 3cx3000F7, filament transformer. Vacuum cap for plate and load. I also have several plate transformers from 2750 vac to 5000 vac I think I can make this work. Yehaa
KK4RSV Smiley

What are you guys thoughts on using a heavy roller inductor in the PI network?
« Last Edit: July 10, 2015, 06:12:14 PM by KK4RSV » Logged
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #20 on: July 10, 2015, 06:57:29 PM »

OH Mr. WB2WIK and Mr. W8JI  You boys are some silver tongued Devils!  Grin  I like the things you say. And Just for the record I have the 3cx3000F7, filament transformer. Vacuum cap for plate and load. I also have several plate transformers from 2750 vac to 5000 vac I think I can make this work. Yehaa
KK4RSV Smiley

What are you guys thoughts on using a heavy roller inductor in the PI network?


Rollers suck in tank circuits, unless they are narrow frequency range tank systems or the tank does not require much inductance delta from lowest band to highest.

The critical thing in any GG triode is the grid to chassis impedance. Build a flange plate to tie the grid directly to the chassis, and (unless you have a poor layout) the tube will be unconditionally stable without any other suppression. It is a cleaner tube than most other Ham tubes by far, it is stable, they have a good life history, and they are very easy to cool at the 2kW dissipation level. You will actually need less pressure than an 8877 needs, and you would have ten times the tube life.

I typically would see in the -40's dB single tone of two equal tones for third order, and rapidly falling off at higher order, when the setup is right. The IMD will be exciter quality limited.
Logged
QRP4U2
Member

Posts: 262




Ignore
« Reply #21 on: July 10, 2015, 07:24:07 PM »

Driving the cathode should be simple since the input impedance is around 47 ohms.

I would bias it for a zero signal plate current of 125 mA.

I say go for it and publish your circuit

Phil - AC0OB
« Last Edit: July 10, 2015, 07:39:58 PM by QRP4U2 » Logged

AC0OB - A Place Where Thermionic Emitters Rule!
--------------------------------------------------------------------
Besides, when you're a Ham, you experiment with and improve boat anchors - that's what you do!. Smiley
K8AXW
Member

Posts: 7042




Ignore
« Reply #22 on: July 10, 2015, 08:16:18 PM »

Something else to consider.  My friend who built his BIG amp used a small roller inductor and variable caps in the INPUT circuit.  He's able to tune the input to a 1:1 SWR on all bands. 

The beauty of this concept is that the input is IN the amp....not external.  While the typical input circuit is broadbanded....it still requires two caps and an inductor for each band as well as a switch to change bands.

When I built my amp I had to use a right angle drive to simultaneously switch the tank circuit as well as the input circuit.  This was necessary because of the layout and the whole desire to use one bandswitch instead of two.  The whole thing became a royal PITA but I got it right on the first try.

As I said, "something to consider."
Logged

A Pessimist is Never Disappointed!
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #23 on: July 11, 2015, 04:22:33 AM »

Driving the cathode should be simple since the input impedance is around 47 ohms.

I would bias it for a zero signal plate current of 125 mA.

I say go for it and publish your circuit

Phil - AC0OB

The input impedance is higher with less drive and lower power.

It is also is around 50 ohms or so in parallel with ~100pF without a socket. With some sockets, it is around 50 ohms in parallel with 250-400 pF.

100 pF is about 50 ohms on ten meters, so with a 300 pF socket (which is accidentally caused by socket construction) it would be about 50 ohms in parallel with a 15-20 ohm reactance capacitor, which is a terrible SWR on 10 meters.

This is why the flying lead tube can be better, if the grid is directly grounded.
Logged
WB8PFZ
Member

Posts: 310




Ignore
« Reply #24 on: July 12, 2015, 06:30:29 AM »

I bought a 14 mhz amp real cheap at the last hamfest. I would like to put on 6. Any feedback, hopefully positive. Not looking for 3000 out just reliable 1000. Thanks Mike
Logged
AD4U
Member

Posts: 2543




Ignore
« Reply #25 on: July 12, 2015, 07:35:14 AM »

Many on this site, myself included, have the knowledge and ability to build an amp running a 3XC20,000A7 in grounded grid which is capable of running at least 25-30KW when driven by 1500 watts from any of the current ham amps. There are many reasons why we have not done so. Legality is one. Cost is another.

Dick AD4U
Logged
DL8OV
Member

Posts: 1057




Ignore
« Reply #26 on: July 12, 2015, 08:07:56 AM »

I wonder if the FCC would issue an experimental licence for amateur operation at 30 KW output power? The technical article in QEX should be interesting reading if only for the insane power supply requirements.

Peter DL8OV
Logged
NJ1K
Member

Posts: 3




Ignore
« Reply #27 on: July 12, 2015, 08:26:08 AM »

Many on this site, myself included, have the knowledge and ability to build an amp running a 3XC20,000A7 in grounded grid which is capable of running at least 25-30KW when driven by 1500 watts from any of the current ham amps. There are many reasons why we have not done so. Legality is one. Cost is another.

Dick AD4U

I'm not seeing what this has to do with the discussion at hand.  Please enlighten me.
Logged
KD0REQ
Member

Posts: 2402




Ignore
« Reply #28 on: July 12, 2015, 09:06:01 AM »

PFZ, depending on the tube and internal layout of the amp, such a conversion could be a real challenge to the laws of physics.  need more info
Logged
AD4U
Member

Posts: 2543




Ignore
« Reply #29 on: July 12, 2015, 12:33:21 PM »

Many on this site, myself included, have the knowledge and ability to build an amp running a 3XC20,000A7 in grounded grid which is capable of running at least 25-30KW when driven by 1500 watts from any of the current ham amps. There are many reasons why we have not done so. Legality is one. Cost is another.

Dick AD4U

I'm not seeing what this has to do with the discussion at hand.  Please enlighten me.

Sir the discussion at hand is regarding an amp running a 3CX3000F7 which is capable of running significantly more than the US legal limit of 1500 watts. Many of the original replies are why someone would want or use such an amp when the US legal limit is 1500 watts. My point if you missed it is that many hams run a lot more power than what a 3CX3000 can deliver and many more of us could build sand use much an amp if we wanted to do so.

Dick AD4U
Logged
Pages: Prev 1 [2] 3 4 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!