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Author Topic: 3cx3000f7  (Read 16528 times)
NJ1K
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Posts: 3




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« Reply #30 on: July 12, 2015, 12:43:53 PM »

W8JI gave good reasons why such an amp (the 3cx3000)would be a good project for ham use.  The topic isn't about running above legal limit, it's about utilizing said tube for a ham amp.  Much good information was provided as to why it would be a good fit.

Further, no one (except you) mentioned building a ham amp that takes legal limit to drive.

With the information posted in this thread, I'm now also entertaining building around the 3cx3000 too.
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KK4RSV
Member

Posts: 78




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« Reply #31 on: July 12, 2015, 01:04:54 PM »


Barry i am not sure if you are addressing me.
Thanks for your concerns and comment.

[/quote]

Yes, I was addressing you. Sorry I put down the wrong name. So glad you are up on working with HV and RF.  I've had so many people visit here, see my home brew amps and then they say they are going to build one. Once I tell them what's involved they give  me a look like, "A deer in headlights."
I hope you go ahead with your project and wish you very good luck.

Barry, KU3X
www.ku3x.net
[/quote]


Barry I went to your website and looked at your homebrew 3cx1000  very nice  good work!!
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W1BR
Member

Posts: 4196




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« Reply #32 on: July 12, 2015, 01:06:16 PM »

W8JI gave good reasons why such an amp (the 3cx3000)would be a good project for ham use.  The topic isn't about running above legal limit, it's about utilizing said tube for a ham amp.  Much good information was provided as to why it would be a good fit.

Further, no one (except you) mentioned building a ham amp that takes legal limit to drive.

With the information posted in this thread, I'm now also entertaining building around the 3cx3000 too.

Here's you starting point:

http://www.eham.net/classifieds/detail/474141

at that price , I'd grab one.  Problem is getting them to the USA.

Pete



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NJ1K
Member

Posts: 3




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« Reply #33 on: July 12, 2015, 01:22:57 PM »

Yes Pete, I saw that machine.  While it's pretty interesting, I prefer to build from scratch on this one. 
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KK4RSV
Member

Posts: 78




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« Reply #34 on: July 12, 2015, 01:25:30 PM »

W8JI gave good reasons why such an amp (the 3cx3000)would be a good project for ham use.  The topic isn't about running above legal limit, it's about utilizing said tube for a ham amp.  Much good information was provided as to why it would be a good fit.

Further, no one (except you) mentioned building a ham amp that takes legal limit to drive.

With the information posted in this thread, I'm now also entertaining building around the 3cx3000 too.

Mr. NJ1K  I am going to build  a 3cx3000 amp.
like you said a lot of good reasons for building using this tube.
A) - Rugged and will last a lifetime
B) low IMD products ( lots of folks seem to be concerned about excessive IMD so this may be a good solution?)
C) cost less than some other tubes including 8877's and even cheaper pulls available- can also be rebuilt
D) very stable
E) easy to build around
F) still produced and available
G) no harder to cool than most other tubes
H) requires no socket

Drawbacks
A) able to exceed legal limit-- Aren't a lot of the new amplifiers using 3-500z's, 8877's etc capable of also producing more than legal limit?
B) Cost of homebrewing is expensive-- Most of us don't homebrew to save money-- I know from experience you can build cheaper than you can buy a comparable size amplifier.
C) heat and energy use for the filament (350 watts) - no work around or defense for this-it is what it is.

Sounds like a go forward project to me.
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NJ1K
Member

Posts: 3




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« Reply #35 on: July 12, 2015, 02:02:25 PM »

It looks like the advantages outweigh the disadvantages.  But the "capable of exceeding legal limit" thing just doesn't make sense to me.  If this is such a concern to everyone, why would anyone concerned drive a car that is capable of going way over the speed limit?  It's not a matter of it's capability, it's a matter of how it is used.

As for the  filament high energy consumption, most hams don't leave their amps on idle 24-7, me included.  My current amp gets a 24 hour workout on field day , then might get 5 hours a month for the rest of the year.  So, the added electrical cost over a pair of 3-500s is what, an extra 2 or 3 dollars per year?  Ok OK add in the extra air conditioning load and that's maybe another $10 a year, but deduct the reduced heating load in the winter and it offsets the added cooling load.

Anyway, the naysayers be damned, I'm plotting a budget and time commitment now just to see how and when I might be able to start.  It's likely not going to happen tomorrow, but we'll see.

Tom NJ1K

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KK4RSV
Member

Posts: 78




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« Reply #36 on: July 12, 2015, 02:24:09 PM »

It looks like the advantages outweigh the disadvantages.  But the "capable of exceeding legal limit" thing just doesn't make sense to me.  If this is such a concern to everyone, why would anyone concerned drive a car that is capable of going way over the speed limit?  It's not a matter of it's capability, it's a matter of how it is used.

As for the  filament high energy consumption, most hams don't leave their amps on idle 24-7, me included.  My current amp gets a 24 hour workout on field day , then might get 5 hours a month for the rest of the year.  So, the added electrical cost over a pair of 3-500s is what, an extra 2 or 3 dollars per year?  Ok OK add in the extra air conditioning load and that's maybe another $10 a year, but deduct the reduced heating load in the winter and it offsets the added cooling load.

Anyway, the naysayers be damned, I'm plotting a budget and time commitment now just to see how and when I might be able to start.  It's likely not going to happen tomorrow, but we'll see.

Tom NJ1K




Me too Tom  I have the tube, Vacuum cap, filament transformer, filament choke, plate transformer or hv power supply, vacuum relay, band switch, tuned input assembly and blower. Need a cabinet and plate choke to get started. Need to also inventory my meters to see what I may need for that. Its going to be slow going as my shop has no AC and we are in the high 90's right now. So first things first.
kk4rsv
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NJ1K
Member

Posts: 3




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« Reply #37 on: July 12, 2015, 02:47:11 PM »

What's that??  No air conditioning in the shop??  The Hal you say!!!

I couldn't survive without it.  Of course since I'm a career HVAC company, mine always comes first... Hah!!
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W1BR
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Posts: 4196




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« Reply #38 on: July 12, 2015, 02:58:55 PM »

We just had two Mitshubishi multizone  heat pump systems installed, and I made sure a cassette unit went into the shop.  So far no RFI problems.  And, it is nice and comfy cold.
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NJ1K
Member

Posts: 3




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« Reply #39 on: July 12, 2015, 03:09:27 PM »

Air Conditioning is the main reason  I operate class D on Field day....


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ZL1BBW
Member

Posts: 1375




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« Reply #40 on: July 13, 2015, 12:04:50 AM »

Is there any supply of 3cx3000f7's that are pulls from equipment?  Have nearly everything here, just need the tube and a kick in the backside to get going on building it.
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ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.
KM1H
Member

Posts: 5562




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« Reply #41 on: July 13, 2015, 05:53:14 AM »

Quote
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

The 3CW20000A7 is quieter  Roll Eyes

The 3CX3000A/F7 has been acknowledged for several decades as the ultimate ham amp tube. At 1500W the cooling requirements are very low and the 225W grid can be used as a dummy load, parasitic free, very forgiving of tuning errors.....the only amp you will ever need to build. The FCC may even raise the power to 5KW and if you want to build to that level then go for it, the tube will easily run 8KW.

If you want to really get carried away look at the Henry 8K, complete with remote tuning so the blower noise and heat is in another room. An above average builder could duplicate while keeping the cost down and improve on the reliability.....the motor driven rotary inductor is a weak link; Ive had my share in for service.

Carl

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WB2WIK
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Posts: 21837




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« Reply #42 on: July 13, 2015, 09:28:44 AM »

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?


Vacuum cap for the load adjustment?  That sounds like a bad idea to me.

Shouldn't be so much voltage there that you'd need a vacuum cap, and a really BIG cap as required on the lower bands will be time consuming to crank.  Even a vaccum cap for the plate tuning, while more justified IMO, can be a hassle unless you use a motor drive on it or something.

Henry used some very big edge-wound, silver-plated roller inductors in their high-end amps and they manufactured those.  Still a bit of a nuisance when switching from 80m to 10m (example), lots of cranking and not so easy.  To avoid stressing a plate tank bandswitch, those models used cam-actuated plunger switches with very large contacts and a lot of space around them (the input circuits used a conventional switch, driven by the same shaft with a sprocket and chain).  Not a bad idea, as there was nothing to fail there unless the chain broke. Cheesy
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KM1H
Member

Posts: 5562




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« Reply #43 on: July 13, 2015, 10:07:21 AM »

Quote
Vacuum cap for the load adjustment?  That sounds like a bad idea to me.

Why?  Even at 1500W many new and used air variables have a poor ground wiper plus RF integrity of the stator. It doesnt take much RF current to create hot spots.
At RTTY and higher power a vacuum is an easy way to go as Ive had to replace many of the cheap OEP 800pf Load caps over the decades, the amp manufacturers seem to prefer the cheapest of the 3 they offer in the same value and size; the difference is in the wipers.

Quote
Shouldn't be so much voltage there that you'd need a vacuum cap, and a really BIG cap as required on the lower bands will be time consuming to crank.  Even a vaccum cap for the plate tuning, while more justified IMO, can be a hassle unless you use a motor drive on it or something.

The voltage is only low when there is a complete path from amp to antenna, relays are known to hot switch, or antenna and feedline integrity go to hell. Some ops insist in loading full power into an antenna with a heavy ice load on elements and wires.

Why use a big cap? Those old style glass 1500-2500pf vacuums are fine for a 160-80M amp but very old fashioned for new all band construction. Besides many are defective from arcing and seal leakage. Ceramic caps are physically much smaller and require less torque and are easier to mount.

Since a vacuums voltage rating is only for fully open chose one that you dont go much beyond 50% capacity or so, look up the spec sheets for the derating curves from Jennings, Comet, etc; some are as low as 1500-2000V fully meshed for a 5KV rated cap.
As an example use a 500 pf cap and switch in high current RF rated fixed C for 160 and 80; the lowest band is easy as it doesnt require an extra switch section. Several older commercial amps had a separate high current switch just for fixed load C; the WW2 BC-375 tuning unit switches are still cheap even NOS, and will handle well beyond 1500W

With a turns counter its easy to return to a chart when QSY or changing bands. A vacuum isnt on a contesters list much anymore if he expects to win an all band entry.

Another good point about the 3X3's is that you can run full power as an AM linear if the PS can support it.

Carl
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G3RZP
Member

Posts: 1326




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« Reply #44 on: July 14, 2015, 12:33:26 AM »

Carl

Quote
the WW2 BC-375 tuning unit switches are still cheap even NOS, and will handle well beyond 1500W

Although they are only a single 1 pole 6 way non-progressively shorting wafer, there was an article in CQ (probably back in the late 80s or early 90s) on ganging two of the wafers: it could probably be expanded to 3 wafers if needed.

For QRO manual switching, I figure them as a bargain. Fair Radio has them at $5.95 each, 10 for $52.50 and 40 for $198. From which I figure they have a reasonable amount of stock!
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