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Author Topic: 'Dream Amplifier': Solid State vs Tube  (Read 2575 times)
VK3BL
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« on: August 15, 2018, 01:35:22 AM »

Ok, so one of my 'bucket list' items is to build 'the big one'.  Not because I want to use it on air in a CB Competition, but because of the engineering challenge; after all that is the attraction to some of us in the hobby.

Now, here is the deal.

I've got the perfect enclosure; beautiful steel and on wheels etc already.  I also just came into possession of 3x 16v 90 Amp "Class H 180 degree" transformers.

So, thats 240v in for ~50V out @ 90 Amps.  Nothing to sneeze at given thats about 4500VA (~4500W) worth of power, before rectifiers and a nice big filter cap.  The amp itself would in all likelihood be capable of in excess of 5000W PEP.  I can obtain more of these transformers pretty easily, so if I wanted to go 'really hard' I could just get more or go switch mode....

So the question is, do I build a 5Kw Solid State amp, the bear minimum would be 2x 2 LDMOS pallets with splitters and combiners, but that probably wouldn't achieve the linearity I'm chasing so perhaps 5x 1 LDMOS pallets would be more realistic, or even 5x 2....

If I wanted to hit 10K, we're talking at least a 5x2 and after the associated splitting etc I can't imagine linearity would be much better than -30dBc...

Or, do I bite the bullet and 'go hard or go home' with a proper tube.  Something like a 3CX3000A7 or a 3CPX5000A7 (the 'MRI Pull' tube with handles').

The problem is, transformers for such tubes just don't come about often in VK; I'm almost certain I'd have to have one made up, and that could get expensive very fast.

The plus side would be a much simpler amp, capable of much greater output and/or much better linearity.

What would you use for your 'ultimate amp challenge'... Bear in mind 75% of the goal is to learn/build a 'broadcast quality' product, not something to make a Bird 43 with a '25k' slug 'swing'.  What power level would you go to?  I don't see any point building less than 5Kw when today's market is full of proven 2kW SS designs for all bands, and even proven 4kW tube designs for all bands.

Remember, this is for fun; a project spanning years and a dream.  What would you dream?  As for bands, if I went tube I'd probably only bother building for 80, 40 & 20 with the possibility of 160 also.
« Last Edit: August 15, 2018, 01:38:21 AM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
VK4BG
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« Reply #1 on: August 15, 2018, 02:50:38 AM »

Well Jarrad, I have just what you want....New 4CX10,000 / 4CX5000 socket, filament transformer ( new ), screen transformer and bias transformer...all new. I have one Econco refurbished 4CX10,000 tube, with zero hours since rebuild, and a Econco 4CX5000, also a zero hours rebuild, and if you are really fussy, a hand picked 4CX5000 ( YC108 ?? )for MRI use...more linear apparently.

So...if you want to get really serious...I'll do you an excellent deal on the lot. Why...I'm happy with my SPE 2K.

This is a serious offer...so email me if you are interested at  glenn4655mcneil@gmail.com

73
Glenn
VK4BG
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KK4RSV
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« Reply #2 on: August 15, 2018, 07:05:04 AM »

Hi Jarrad, I am not an expert on amplifiers. There are a lot of members on here that are. However I have built a good many amplifiers.
   I have built a 2 x blf188 6m-160m and it works well. I have also built 2 x 3cx3000a7 amps and they work well also. I have built a few with Russian tubes, 3cx1500a7's and 3-500z's.
  I love old school stuff. I actually enjoy tuning tube amps. Twisting knobs. hahahaha. the Solid state amp just sits there I turn it on and switch to the band I want and just use it. Of course with the tube amps, sometimes you have warm up time then change to your band, then tune.
  I prefer the old tube amp and if I were going to do what you are after, I would build a 3cx5000a7. Its a high gain tube, higher than the 3cx3000. Tubes are much more forgiving. And I would get a kick out of tuning it. Also, it would not be that difficult to make it run 10m-160m .
The things I would consider are:
   Any large amp like you are talking about is going to require a lot of cooling=air=fan and air noise.
   The solid state will be somewhat safer to work on verses the high voltage of a tube (4000-7000VDC) which is deadly.
  If you build the tube amp, it will last several lifetimes with out worry if you use good components.
  An EM pulse will not kill your tube amp, but will kill your solid state.
  I would probably stay away from tetrode tubes (4cx series) as the power supplies become more complicated and costly.
  You are probably going to get a cleaner signal with a tube.
  The ultimate in reliability is a single tube amplifier.

  These are just a few of my thoughts based on my experiences and personal feelings Like I said, I am not an expert.

Darrell
KK4RSV

 
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K6AER
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« Reply #3 on: August 15, 2018, 07:33:45 AM »

MRI's stopped using large tubes 20 years ago.  You might find a tube sitting on someone's trophy shelf but a  proper tube socket might be harder to find. Today's MRI run under 200 watts. They don't even have you taking metal out of your pocket anymore during the scan.

Three KW solid state amp will be hard to dissipate the heat. Amplifying stages, filters and power supply will require at least 3 KW of heat transfer.

Ten meters will not be easy with a high power amp. Stray capacitance in large components will be your enemy.
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KM1H
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« Reply #4 on: August 15, 2018, 08:48:47 AM »

Jarrad, are there any BCB or SW stations over there that have gone SS and the old hollow state TX is still there?

If so they may be there for the asking as many are over here

The 3CX3000A7 is still one of the best tubes built for exceptional IMD and aftermarket sockets often show up at reasonable cost. The 4CX5000A is another old BC tube that can be quite clean with attention to PS details. Ive built a few of the 3x3's for ham use and both are still popular with the CB crowd.

I would stay away from the 3CX5000A7 as it is an indirectly heated cathode tube that is easily stripped with high drive and is a reason its YC-156 cousin (3CX15000B7 internals, 5000 external) has become about obsolete for a good one on the pulls market.  I have a full output one sitting here for about 25 years I'll never get around to using along with the filament transformer. The grid direct bolts to chassis and when run as a conservative 5000 the IMD is pushing -50dB.

Now if you really want to get serious ask me about the 3CW20000A7 here that was used in a tech college only as a demo of water cooling and never had HV applied. Complete with socket, 240V filament transformer and blower, bypass caps, and all mounted on an aluminum plate.

Carl
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N9AOP
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« Reply #5 on: August 15, 2018, 09:15:18 AM »

Don't forget that some AM stations are using 50,000 watt solid state amps.
Art
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KK4RSV
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« Reply #6 on: August 15, 2018, 11:28:53 AM »

oh one other thing, the 3cx3000a7or f7 does not need a socket. It can be clamped directly to the chassis. Which makes if less expensive.
darrell
kk4rsv
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KM1H
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« Reply #7 on: August 15, 2018, 11:51:55 AM »

Don't forget that some AM stations are using 50,000 watt solid state amps.
Art

Of course but I wasnt going to go to the CBers upper end here Grin
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KB2FCV
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« Reply #8 on: August 15, 2018, 02:36:12 PM »

Don't forget that some AM stations are using 50,000 watt solid state amps.
Art

I was at a tour for a pretty large NY based AM broadcast station located in NJ and they had a 50kw Harris solid state amp. The amp had 1kw modular slide-in sections (not sure if they were hot-swappable?)... each around 1kw. They had two amps.. one being a stand-by for the other. Cool setup!
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VK3BL
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« Reply #9 on: August 15, 2018, 06:57:36 PM »

Don't forget that some AM stations are using 50,000 watt solid state amps.
Art

I was at a tour for a pretty large NY based AM broadcast station located in NJ and they had a 50kw Harris solid state amp. The amp had 1kw modular slide-in sections (not sure if they were hot-swappable?)... each around 1kw. They had two amps.. one being a stand-by for the other. Cool setup!

Thats my dilemma.  To achieve power levels worth the effort with acceptable IMD and cooling, I'd need to use a reasonable quantity of pallets and a splitter / combiner network, not to mention one heck of a filter setup.

The simplicity of single large tube; especially a tetrode if grid driven, really does make a lot of sense for a Ham.

The downside of course is that the skills learnt really only apply to fixing up old broadcast gear, and of course mastering a small section of the past.

On the other side, pursuing the solid state route would likely result in marketable skills.  Its a real catch 22; either way my enclosure (an ex large UPS second battery box) is up to the task. 

The reality is a SS amp would likely top out at 5kw PEP with multiple pallets depending on power supply design (I could acquire some switch modes), where as a single tube amp, despite the weight and pain in transformers, would easily surpass such levels with more than respectable IMD Performance.

Its a hard one really... Its a pity Glenn who posted earlier doesn't have the plate transformer, though I will need to email him as the 4CX10000D7 has my interest Wink. Looks nice and easy to cool without a screamer blower.

Cheers for the ideas guys!  Either way, I'll use my current transformers to create a nice 48v linear supply for the shack.

73, Jarrad VK3BL
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
N8CBX
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« Reply #10 on: August 15, 2018, 07:56:16 PM »

I'm confused. What is the point of this? Don't you have a power limit in Australia?
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
VK3BL
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« Reply #11 on: August 15, 2018, 08:36:21 PM »

I'm confused. What is the point of this? Don't you have a power limit in Australia?
Jan N8CBX

Of course we do, like every country.

That said, if I want to self educate in the construction of a broadcast quality transmitter thats not a problem, so long as I use it within our power limits and/or run it into a dummy load when testing beyond that.

The point is simple; producing 2Kw is a commodity item now for Ham Amplifiers.  If I am going to build and maintain something, why not stretch myself to a commercial level?

It is a technical hobby with the specific purpose of self education after all, and if people like myself don't dream big, there will be no one left in VK who has the skills to service or put a SW station on the air in 20 years time.

We've cut national funding to SW like crazy in VK, and the engineers who built and and even maintain the current stations are ageing.

So the point is education; for the sake of the art of radio, and for the sake of my country if needed.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
G3RZP
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« Reply #12 on: August 16, 2018, 12:25:41 AM »

Quote
So the point is education

which really meets the criteria on which the amateur service is justified - 

ITU Radio Regulation 1.56      amateur service:  A radiocommunication service for the purpose of self-training, intercommunication and technical investigations carried out by amateurs, that is, by duly authorized persons interested in radio technique solely with a personal aim and without pecuniary interest.
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KD8MJR
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« Reply #13 on: August 16, 2018, 01:41:17 AM »

I would go with what I am more comfortable in designing.
Seems like a you are more comfortable going solid state.

Rob
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“A lie can travel half way around the world while the truth is putting on its shoes.”  (Mark Twain)
AF6LJ
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« Reply #14 on: August 16, 2018, 04:48:45 AM »

I would go solid state, I would also avoid using digital control for my protection circuits. Use analogue circuits for your protection, they respond faster, and don't require software experience to write a program to run protection circuitry.

In order to keep the size and weight down I would go with liquid cooling.


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