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Author Topic: sb200 running 3-500  (Read 1927 times)
AC2RY
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Posts: 283




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« Reply #15 on: November 06, 2017, 04:17:11 PM »

I should have written it down..... Darn.....
I was talking with a fellow ham quite a while ago and he converted a sb200 to use single 3-500 tube..
since I know it is possible does anybody know of or who they know that has tried this???
getting sick of 572's issues.... never seem to be able to match quality of the Cetrons with the Chinese
replacements..
Hope to hear of 3-500 possibility...

                                                                                  Thanks,
                                                                                  Mike (KD2DYY)

If you are not satisfied with reliability of this amp, and want long term DIY project - start filling up this amplifier with sensors of all kind of conditions. Use that data to build self protection system. Along with that you can add full auto-tune feature. Over this project you will learn a lot of useful things about all kinds of measurement, modern components, digital interfaces. Also you will likely need to learn how to develop logic and program it in FPGA. At least all this knowledge you will be able to use down the line, unlike fruitless effort to squeeze tube that was not meant in that box.
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KM1H
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Posts: 2502




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« Reply #16 on: November 06, 2017, 05:12:16 PM »

A pair of 813's would be more interesting than some IMD POS Ruskie tubes.

I havent measured but a pair of 4-125A's might be another choice. Both work well at 2400V and have the Pd to handle an easy 600W out. Hang a filament transformer somewhere and scrap the bias circuit and redo the relay control.

Both tubes have their clones in Europe and all are pretty common NOS and used.

Keep it American powered over here Grin

Carl
« Last Edit: November 06, 2017, 05:20:27 PM by KM1H » Logged
N2EY
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Posts: 4441




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« Reply #17 on: November 07, 2017, 06:51:56 AM »

I'd have to have a better reason than just being tired of Chinese tubes to try this.  Like having a junker SB-200 and nothing better to do!

There's lots of people that decide to do stupid stuff, "because they have nothing better to do."   They make a simple project way more complicated than it should be, end up over their heads, ignore advice from experts, end up blowing stuff up (and seem to be proud of it), and in the end, either it "sorta works," (if they are lucky), or the project never works, and a perfectly good piece of equipment is tossed aside never to work again.  



In other words:

"Just because you can, doesn't mean you should".

There is probably a way to convert an SB-200 to use a 3-500Z. Let's see....

1) Tear out the 572Bs, sockets, etc.

2) Replace the front and back panels with new ones so there is more vertical height to accommodate the 3-500Z (which must be mounted vertically)

3) Extend the sides to match the front and back panels.

4) Make up a subchassis to hold the tube socket, chimney, etc.

5) Modify the cooling system for the 3-500Z.

6) Replace the filament transformer and choke with ones suitable for the 3-500Z

7) Modify the input and output networks, metering, etc., as needed.

And there you are. Of course a 3-500Z works better at 3000+ volts, rather than the 2000 or so in the SB-200, but you can't have everything - unless you replace the power supply....

It all starts to become a bit like this classic sketch:

https://www.youtube.com/watch?v=v3Q2HZRjHHQ

73 de Jim, N2EY

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K8AXW
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Posts: 6312




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« Reply #18 on: November 07, 2017, 10:17:23 AM »

Good point..... a guy wants to convert an SB-200 to use a 3-500Z because he has nothing better to do.

Since I have nothing better to do, I'd love to watch that modification!  I think him "lighting it off" would even be more fun!

The last time I had that kind of enjoyment was about 30 years ago when I ran into a guy at a hamfest.  He had his mobile workshop with him which was a stripped out hearse.

Inside he had a work bench (Homebrew of course) and the floor was littered with unidentifiable junk (?).

The dash board had all (copy ALL) of the instrumentation hanging out of the mounting holes and were hanging by the connecting wires.  The hearse was painted orange and black. The owner said he used to work for the CIA but was now in "service." 

What kind I couldn't ask because I was in a borderline state of hysterical laughter.  Nice guy but ...............
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KM1H
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Posts: 2502




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« Reply #19 on: November 07, 2017, 10:22:44 AM »

Sorta reminds me of Timtron, WA1HLR at hamfests.

Carl
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K1ZJH
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Posts: 3308




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« Reply #20 on: November 07, 2017, 11:52:53 AM »

If I had a junker SB-200 it would be converted to a pair of 4CX300A tubes using a salvaged RF tube sub-chassis from an old HT-33 that was parted out eons ago. That box has the input circuits, sockets and mounting for the small squirrel fan. The original fan, tube assembly and input circuitry would drop right into the existing cabinet space with only perhaps some modifications on the rear apron for the fan, if needed. The Heath PA tank would work with little changes.  A regulated solid state screen would need to be added.  you'd end up with an amp capable of 650 watts output, and with the ability to be driven from any power level above two watts, depending on the grid load resistor.  The original supply would be well matched for this application, with some changes for the screen and AB1 bias.  After completing my SB-220 project, I'd be game to play with a SB-200 in a similar manner. I'm tempted to start searching for a cheap junker that is mostly complete just to have a winter project.

As an aside, Hallicrafters also used fixed loading that monster, beast of an amp, just like Heathkit did in the minuscule HA-14.

Pete
« Last Edit: November 07, 2017, 12:06:16 PM by K1ZJH » Logged
G3RZP
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Posts: 8125




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« Reply #21 on: November 07, 2017, 01:06:58 PM »

As a project, it sounds to me to at least as major as the Denver and Rio Grande Western Railroad conversion of a standard gauge (4 foot 8 and one half inch) inside framed 2-8-0 steam locomotive to an outside framed 3 foot gauge 2-8-2 (The K37 class).
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K1ZJH
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Posts: 3308




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« Reply #22 on: November 07, 2017, 01:37:01 PM »

It would be a piece of cake; I don't think it would take much.  Short of the tetrode control board, which I don't have.
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AF6LJ
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Posts: 366




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« Reply #23 on: November 07, 2017, 01:50:28 PM »

If I had a spare 3-500Z and nothing better to do I know what I would do. Smiley
Posted this before on the Zed and got some rather interesting reactions.
As for what to do with an SB-200 when you have nothing to do, how about a pair of 3CX800s and an external supply built into an SB-600 enclosure???
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Take Care
Sue,
AF6LJ
KM1H
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Posts: 2502




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« Reply #24 on: November 07, 2017, 02:04:53 PM »

Quote
It would be a piece of cake; I don't think it would take much.  Short of the tetrode control board, which I don't have.

Those tubes really need that board as all they are is shock resistant, IMD poor, 4CX250B's. The HT-33 was a real pig since it had minimal IMD design as did most tetrodes back then. Running them Super Cathode driven is far cleaner to start with.

One of my NCL-2000's was a Beta test for Ians board and made a 5-6dB IMD improvement. The NCL-2006 was similarly modified and both are still in use, plus Ive converted numerous HF and VHF T'Bolts.

Carl
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N2EY
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« Reply #25 on: November 07, 2017, 02:40:27 PM »

Good point..... a guy wants to convert an SB-200 to use a 3-500Z because he has nothing better to do.

I think it's more a question of wanting to get away from 572Bs.

On the surface, it might seem to be a practical conversion, at least to those who don't do engineering.

But when you get into the details, the problems show up fast.

First, the SB-200 cabinet is only 6-1/2 inches high on the inside. A 3-500Z is 6 inches high - and that's just the tube - and it has to be mounted vertically. So right away there's a bunch of sheet metal work to do, to increase the cabinet height.

Second, the 3-500Z needs forced air on the pins to avoid overheating the seals. So there's cooling work to do.

Third, the SB-200 power supply only delivers about 2000 volts under load. Maybe a little more - 2200 volts - with today's higher line voltages and the removal of the filament and bias loads. Maybe. That's really not enough to get the most out of a 3-500Z - at 2000 volts, 400 mA is the recommended max plate current - 800 watts input, and maybe 500 out. (Eimac tube data sheet). With 572Bs, you can run more power at 2000 volts.

https://frank.pocnet.net/sheets/140/3/3-500Z.pdf

Fourth, you need to add a filament transformer (5 volts at ~14.5 amps) and replace the filament choke (the Heath one is good for 8 amps, but 14.5 is another story entirely). Might need to work on the input network too.

When all those factors are considered, it becomes clear that the whole idea is more trouble than it's worth.

----

I've seen project after project where somebody takes an idea and runs with it, without doing real research, figuring out all the issues, calculating the various values needed ("Math is HARD!!"), etc. Often they focus on the wrong things and ignore the essentials. IOW, they don't do the needed engineering.

Paper is cheaper than parts.

Then, when the project problems, they pour money and snake-oil "fixes" into it, trying to FORCE it to work. Sometimes they succeed, sort-of; sometimes they wind up turning what was a good piece of gear into a piece of junk.

What's even more interesting is how some folks will latch onto a bad idea and INSIST on doing it, even when those who have much more experience and understanding clearly and calmly tell them why it's a bad idea. Then when it doesn't "turn out" well, they say it was "bad luck". Worse, they often destroy hard-to-obtain parts and equipment in the process.

IMHO, if 572Bs are the issue, and what's wanted is a single-3-500Z amp, the best path is to sell the SB-200 and put the money into an SB-1000 or AL-80. Or homebrew a single-3-500Z amplifier from a GOOD design - they're out there.

73 de Jim, N2EY

 
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KM1H
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« Reply #26 on: November 07, 2017, 05:33:08 PM »

Quote
Second, the 3-500Z needs forced air on the pins to avoid overheating the seals. So there's cooling work to do.

No forced air is required on the filament pins, just an adequate fan flow.
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KD2DYY
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Posts: 65




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« Reply #27 on: November 11, 2017, 07:35:34 AM »

Again. thanks to all for thier comments and opinions....This question started as I have been waiting 2 months for an order of new set of Chinese tubes for my amp..(Something about caught in customs).. I'm thinking now that I really SHOULD just put the SB200 on the block and get one of them- there AL80b's or possibly an SB1000....Kind of stuck with the same issues of availability of 3-500's....Still only new ones are Chinese made... Correct?
Let's close this post out..... I think we could all use a breather and ,again, thanks for all the interest.

                                                                                                              Mike (KD2DYY)
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KM1H
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Posts: 2502




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« Reply #28 on: November 11, 2017, 08:36:34 AM »

.
Quote
Kind of stuck with the same issues of availability of 3-500's....Still only new ones are Chinese made... Correct?

Correct but they are in ready supply.....for now

Stuck in customs where? Who did you buy the 572B's from? RF Parts has them in stock.

Carl
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KD2DYY
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Posts: 65




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« Reply #29 on: November 11, 2017, 08:40:29 AM »

I'd rather not name names but the owner DOES provide one year warranty and very good to work with....
NO, not RF parts....I'm happy with my source......Thanks

                                                                                                  Mike (KD2DYY)
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