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Author Topic: Future Projects for BIG AM SIGNAL  (Read 41527 times)
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KE6DF
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« Reply #50 on: April 13, 2013, 09:57:34 AM »

triodes such as the 25T/25TG/3C24 are plentiful and provide sufficient drive.

NOS USA 2A3's are out of sight and Id suggest triode connected 6V6/6F6/6L6 (all are 30's tubes) And 203's are mostly gone to air. The 812A is a direct zero bias sub.

Carl



Another tube that the audiophools use as a sub for 2A3s is a 1619 triode connected.

It's a directly heated tube, which the audio types like, and it uses a 2.5v filament like the 2A3.

There is even a guy out there that makes an adaptor socket for it so it can plug into the 4 pin 2A3 socket.

1619s are cheap and plentiful.
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Steve - K4HX
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« Reply #51 on: April 13, 2013, 11:17:15 AM »

Quote
Something that I don't understand....  in modulator service, if the screen voltage in AB1 is so critical and must be regulated precisely, how is it that we can actually connect the screen to the grid and let it swing all over the place with the signal?   How can both cases be linear and do justice to the transfer curves?

The grid is directly varying with the input signal (well, almost). The screen is not.
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w3jn
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« Reply #52 on: April 13, 2013, 12:09:04 PM »

I stole those pictures from an ebay auction some years ago.

Just looking at the pictures in that auction scared the hell out of me.
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K1JJ
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« Reply #53 on: April 13, 2013, 12:09:58 PM »

Quote
Something that I don't understand....  in modulator service, if the screen voltage in AB1 is so critical and must be regulated precisely, how is it that we can actually connect the screen to the grid and let it swing all over the place with the signal?   How can both cases be linear and do justice to the transfer curves?

The grid is directly varying with the input signal (well, almost). The screen is not.


OK, thinking more, here's my take:

When the screen is fixed, there is higher gain and still linear. (tetrode config)

When the screen is tied to the grid, the tube is still linear but has lower gain. This is because it approximates a triode.

So, we are really only changing the "type" of tube - from tetrode to triode and both modes operate linearly.  


In contrast, in tetrode config, if we had a badly sagging screen supply and the screen voltage dropped with signal, this would cause severe non-linearity.  The same holds true if we had a sagging grid supply in triode config.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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There's nothing like an old dog.
Steve - K4HX
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« Reply #54 on: April 13, 2013, 05:54:18 PM »

No it didn't. I'm willing to bet you have a lot more hell left in you.   Wink


I stole those pictures from an ebay auction some years ago.

Just looking at the pictures in that auction scared the hell out of me.
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KM1H
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« Reply #55 on: April 14, 2013, 09:49:14 PM »

Looks more like a ham 20M amp by the looks of the coil and the B&W butterfly cap.
A Cber wouldnt have the iron in a galvanized bucket Roll Eyes

A real ham uses chimneys, a CBer uses a pair of table fans. Grin
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w3jn
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« Reply #56 on: April 15, 2013, 09:01:58 PM »

The bucket is great to immerse the tranny in oil when you run it 100% over its rated current.
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Todd, KA1KAQ
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« Reply #57 on: April 15, 2013, 10:30:45 PM »

The key to using 833s successfully is proper ventilation and plenty of it, as demonstrated here.

Makes you wanna just reeeach over and tweak that big bread slicer, dunnit?

No it didn't. I'm willing to bet you have a lot more hell left in you.   Wink

This should clean out the rest. Wink


* K4UXK.JPG (406.47 KB, 1600x1200 - viewed 697 times.)
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KA2DZT
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« Reply #58 on: April 15, 2013, 10:35:44 PM »

The key to using 833s successfully is proper ventilation and plenty of it, as demonstrated here.

Makes you wanna just reeeach over and tweak that big bread slicer, dunnit?

Some folks should not be allowed to have electricity.
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« Reply #59 on: April 16, 2013, 01:34:43 AM »

With 833 pics like that, someone's going to dig out the one of that South American 833 station.
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« Reply #60 on: April 16, 2013, 07:20:44 AM »

The key to using 833s successfully is proper ventilation and plenty of it, as demonstrated here.

Makes you wanna just reeeach over and tweak that big bread slicer, dunnit?


Looks like a good subject for studying the cumulative effects of RF exposure...Assuming the subject isn't electrocuted before the data can be collected Smiley

That photo reminds me of a story told to me by some well drilling friends about a customer who was using various pieces of garden hose and garden hose connectors to bring natural gas into his house through his attached garage from his backyard well.  He and his neighbors were both lucky he didn't blow his house into the next township.  Some people DO need a keeper.
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« Reply #61 on: April 16, 2013, 08:55:00 AM »

YIKES!

I wonder if that plywood is fire rated?
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KM1H
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« Reply #62 on: April 17, 2013, 12:33:57 PM »

Now if he had added a few more studs plus horizontal reinforcements he could have nailed up a sheet of galvanized metal salvaged from the dump or recycler.

Then screwed/soldered on some more tin to support the tubes and other stuff.

Some people just dont think these things out beforehand  Grin Roll Eyes

Carl
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Steve - K4HX
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« Reply #63 on: April 17, 2013, 06:37:34 PM »

I wonder if foil-backed drywall would work?
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K1JJ
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« Reply #64 on: April 17, 2013, 11:19:20 PM »

Is it my imagination or is that little green RF choke across the 50 ohm output?

This may be documented scientific proof that the builder puts his safety first.


T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
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« Reply #65 on: April 17, 2013, 11:30:17 PM »

 Grin good one T!
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ke7trp
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« Reply #66 on: April 18, 2013, 11:38:27 AM »

How about 304TL's Tom.

You can run them in B, ab1 or ab2. They will have much less distortion in AB1 as the Grid is 0.  You are allowed to run up to an amp per tube in plate current where the 833 is 500ma each. A pair makes 750watts ab1 and 1800 in AB2.  AB2, Just needs more drive... Even at 1000 watts carrier and 125% positive its not even in Ab2. They are pyrex and just need a simple fan across the raised socket pins.  No blower motors. 

Robert built a transmitter with 304tls with one 4-1000. It had a strong voice.

Both the 833 and the 304 Tl sure look cool and I would be happy with either but the 304 will be cleaner.


C
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K1JJ
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« Reply #67 on: April 18, 2013, 12:38:32 PM »

Yes, a lot to be said about using 833A or 304TL triodes. I almost went with the 833A's but opted for the tetrode-connected 4-1000A's.  Just finished wiring them. Now adding an electronically regulated screen supply.

To compare power, according to Eimac's datasheet,  a pair of 4X1 modulators in AB1 push-pull will put out between  2300 to 3800 watts of audio depending on voltage.   In AB2, they will put out even more.

Since I like to run my modulators and linears at less than 1/2 to 1/3 of rated power in class AB1 with heavy NFB, the 4X1's in AB1 will give plenty of conservative headroom for cleanliness. That's why I went that route. We'll see what the THD tests look like in a coupla of weeks.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
ke7trp
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« Reply #68 on: April 18, 2013, 12:46:40 PM »

Yes. That is a much larger tube. I have a new one here in the box if you need it.

I thought you had this transmitter running before?  I seem to remember you putting 30 DB over the top of Steve out here in AZ.  HEHEHE

C
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K1JJ
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« Reply #69 on: April 18, 2013, 01:37:13 PM »

Thanks for the tube offer, OM.  Though, I already have six 4X1's and five chimneys.  This makes two spares, so all set for now.  They never seem to wear out. Been using a few of these same used/pulls  4X1's for 20-30 years now.


You are probably thinking of Fabio I, the 4X1 Plexiglass rig. When I built the class A linear project last year, I ran out of room, so tore Fabio I down.  I'm using some of the same parts to build Fabio II and doing a much better job. Better layout, bigger parts and higher voltage ratings this time.  And, all aluminum construction, no Plexi... Wink

I have my workbench, office desk and shack all crammed into one room, so if a rig isn't actively used, I get rid of it.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
ke7trp
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« Reply #70 on: April 18, 2013, 01:46:39 PM »

Yeah. Thats it.  Same config though right?  4-1000 by a pair triode connected?

C
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« Reply #71 on: April 18, 2013, 09:29:06 PM »

I am simply amazed at the length of this thread after posting my 5 year plan!

Philip
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« Reply #72 on: April 18, 2013, 10:10:18 PM »

It's easier for some then starting a new thread. Six months from now no one will remember under what title all this information was post. And then, regurgitation will start somewhere else. It's not uncommon.
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« Reply #73 on: April 18, 2013, 10:42:48 PM »

way to much qso'ing in the technical area. come on people get with the program.  Grin
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« Reply #74 on: April 19, 2013, 05:39:35 AM »

We have to conserve the internet.
No QSOs unless the content is important, never repeats, and is in the right category.
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