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Author Topic: Future Projects for BIG AM SIGNAL  (Read 41524 times)
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VE3AJM
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« Reply #25 on: April 10, 2013, 08:12:29 PM »

Interesting!

Keep in mind I've still got to refurb/recap my Valiant, which is my first old style transmitter project. We're talking in a manner similar to one of the "5 year" plans. Just playing around with ideas. Note that WB4GWA has a nice design in ER mag as well. BTW, I've renewed my subscription.

Philip

The 5 year plan sounds just about right. The gaining of experience and expertise on working with and building HB tube transmitters doesn't happen overnight, let alone the accumulating of all the parts, tubes, transformers and pieces needed to undertake a HB transmitter project. It takes time.

Al VE3AJM
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KB2WIG
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« Reply #26 on: April 10, 2013, 10:47:13 PM »

" However, my edition is the 22nd and doesn't delve into plate modulation.  "


Try this....

http://www.tubebooks.org/technical_books_online.htm

Scroll down for the 15 ed.

klc
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ka4koe
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« Reply #27 on: April 10, 2013, 11:47:38 PM »

Downloading it now. Taking forever.

Philip
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« Reply #28 on: April 11, 2013, 09:29:03 AM »

A homebrew transmitter is available and I wasn't looking for it and its not that far of a drive. It has a 4-1000 modulated by a pair of 4-400s. However, I must be really cheap, as I priced replacement 4-1000s and swallowed really hard. lf the price is not crazy I may take the plunge.

Opinions? How rugged is a 4-1000? This one has the glass chimney and is ventilated via a blower.

FEELEEP
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W2ZE
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« Reply #29 on: April 11, 2013, 09:59:10 AM »

4-1000's are fairly reliable, just don't overdrive them, the grid is a bit fragile.

Personally, I prefer big triodes. RCA transmitting tube manual 4th edition has a great push pull 833a's R.F. amp my HB rig is based on. 833a's are common and easily replaced, and triodes make stable and simple amps. The biggest drawback is they need ALOT of drive. A pair of 833a's could be driven by your Valiant when the time comes, and a big PA system audio amp could drive a pair of 833a's in the modulator, no need for mic and speech amps.

Everyone has their opinions, and some people will tell you that tetrodes are better because they require less drive; which is true. It's just a matter of personal preference and situation, but give 833a's a look if your looking for QRO.

Mike
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Todd, KA1KAQ
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« Reply #30 on: April 11, 2013, 10:20:37 AM »

Oh, c'mon Mike - you're just saying that because you have oodles of NOS RCA 833s that you give away randomly to anyone who doesn't live north of Albany.  Wink

I prefer triodes myself, the biggest drawback these days being desirability of more and more 'radio' tubes by the audio crowd, driving up prices. The drive issue pales in comparison. I guess the upside is, tubes like 845s are now being reproduced to meet the demand. So availability shouldn't be an issue.

I like 810s!
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K1JJ
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« Reply #31 on: April 11, 2013, 11:33:43 AM »

4-1000's are fairly reliable, just don't overdrive them, the grid is a bit fragile.

Personally, I prefer big triodes. RCA transmitting tube manual 4th edition has a great push pull 833a's R.F. amp my HB rig is based on. 833a's are common and easily replaced, and triodes make stable and simple amps. The biggest drawback is they need ALOT of drive. A pair of 833a's could be driven by your Valiant when the time comes, and a big PA system audio amp could drive a pair of 833a's in the modulator, no need for mic and speech amps.

Everyone has their opinions, and some people will tell you that tetrodes are better because they require less drive; which is true. It's just a matter of personal preference and situation, but give 833a's a look if your looking for QRO.

Mike


Hi Mike,

For modulators, what is your opinion of running a pair of 4X1's, tetrode connected, vs: a pair of 833A's?  I'm on the fence right now and could always go wid the 833A's.  I have a solid state driver for either.

The specs show about the same power output at 3KV, but the 833A's are drawing grid current and the 4X1's are not.   I wonder mostly about which is cleaner.

T
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KA2DZT
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« Reply #32 on: April 11, 2013, 11:34:40 AM »

Philip,

That HB xmtr may be a very good way for you to get some hands-on experience with big rigs.  If it comes with the power supplies even better.  You should check it out, maybe takes some pics and post them here.

Not sure what the price is, but, it may prove to be cheaper then trying to obtain every part needed to complete a xmtr starting from nothing.  I'm assuming that you don't have much in spare parts.

Even if the rig doesn't work perfect, most of the folks on the forum can trouble-shoot the xmtr just from pictures.

Fred
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KA2DZT
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« Reply #33 on: April 11, 2013, 11:42:23 AM »

"I wonder mostly about which is cleaner"

Tom,  it depends on which dishwasher rack you place them on, top or bottom.


Another solid helpful comment from,

KA2DZT
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W2ZE
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« Reply #34 on: April 11, 2013, 12:58:15 PM »

I dunno, 6 to 1 , half dozen to the other. There are going to be non linearities using a mod xfmr. The 4-1000 tetrode connected are fine if you don't have a lot audio drive, but you will either need a choke or dropping resistor on the unmodulated B puss for modding the screen. the 833a's are a lower Mu, and are class B so each tube conducts on opposite cycles, but needs a lot of voltage for audio drive, hence a large audio amp and line to voice coil xfmr. I think you already know where I stand with tetrodes, but I have always kicked around the idea of a 4-1000 modded by 833a's.

I would be interested to see how the numbers crunch (THD) 1 vs. the other. The SS driver, is that GFzed's design? I never got around to building it. How does work?
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K1JJ
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« Reply #35 on: April 11, 2013, 02:15:58 PM »

Well, the 4X1 modulators, tetrode-connected,  will need a very well regulated screen supply. I use a shunt electronic regulator type that drops maybe 1 volt under load.The data suggests 1KV screen voltage when run in AB1. That's how I did it with Fabio I and it tested very FB.   I think you were refering to the RF final with the choke, etc.  Yes, I have a choke in there for the screens.


The GFZ solid state MOSFET driver works very well. I was able to get negative feedback from the sec of the mod xfmr back to the low level 1 volt audio input. I had maybe 10dB, so it reallly helped clean it up even further in AB1.  This can be done with ONLY one transformer in line, the mod xfmr. If a driver xfmr is used, forget tapping the sec of the mod xfmr.

I think Steve/ QIX has a direct-coupled ss MOSFET version that I may look at too. I don't know if he has a board made for it. I sent him an email axing.

The only problem I've had wid 833A's is when I make a mistake, I usually burn a hole in the plate. I then change over to 4X1 modulators and they can take anything.  But the 833A is simpler and kinda cool - and LESS air noise, if any.

I can see why you like the 833A's by 833A's rig.  Have you had it on 40M and above?  I plan for 160 - 40M.   I can always use my linears above that.

T
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There's nothing like an old dog.
W2ZE
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« Reply #36 on: April 11, 2013, 02:54:38 PM »

Yes, I was referring to the RF section. Modulator screens need to be well regulated like you said. Just more parts to worry about was my point.

Any tube off resonance will crap out after a while. The carbon plate chinese jobs seem to be better at taking a beating. They work fairly well and are cheap, more watts per dollar...

Like I said, personal preference. A 4-1000 may be more forgiving, but when she lets go, its a costly lesson learned these days; except for Tom Vu, leal estate mogul and pletty ladies extradonaire Wink

I think I have the schiz-matic for the SS driver around here somewhere. I might just have to re-visit things and get my sorry ass back on the air. I really like the idea of eliminating as much iron as possible, especially the non linearities of driving push pull grids.
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K1JJ
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« Reply #37 on: April 11, 2013, 04:49:34 PM »

I think one of the biggest advantages of the ss driver is to permit heavy NFB without more phase shift introduced by a driver transformer(s).   I am still amazed to be able to include the secondary of the mod transformer into the loop and still get 10 dB of NFB.  Ever try it  with a tube driver?

I've never blown a 4X1 after years of running many, many homebrew rigs with them. I've used them in linears up to four tubes, modulators, RF finals, etc.  They are truely amazing tubes.  The only problem I've made for myself is once running the air too slowly and seeing the red paint turn brown from excessive heat. Still, the tube runs FB and I use it today.   Now I have a digital temp gauge sampling air coming out of all my amps.. with alarms.

Well, guess I'll stick with the tetrode-connected 4X1's for modulators. I was hoping you'd sway me but it really is a toss up, as you said.    I have run them triode-connected, which is easier, but found they run a little cleaner as designed in tetrode service.   

Hope you get back on OM.  My goal is to have the new 4X1 AM rig running before Deerfield. That's about three weeks away.

T
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There's nothing like an old dog.
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« Reply #38 on: April 12, 2013, 01:26:17 AM »

I have to say, I prefer triodes as modulators.  The biggest reason is more plate swing without distortion.

Using a self-modulating screen is OK if the choke is sufficiently large to allow full modulation at very low frequencies, and also not to introduce a phase shift as the modulating frequency gets lower and lower.

My last big tube rig was a pair of 450TLs modulated by a single 4-1000 pulse width modulator.  I like triodes in the RF amp as well  Grin
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K1JJ
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« Reply #39 on: April 12, 2013, 01:56:13 AM »

I have to say, I prefer triodes as modulators.  The biggest reason is more plate swing without distortion.

Yes, I just remembered that the plate voltage cannot swing below the screen voltage, thus there is 1000 V (of screen voltage) that would be subtracted from the swing, right? 

Maybe I shud try triode-connected 4X1's again.   

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?

I know 813's work very well triode-connected and so do 4X1's. But I didn't have the testing setup like I do now to measure THD and IMD.  The last time I went from triode-connected to tetrode-connected 4X1's I based my results on hearing and reports from guys on the air who thought the tetrode-connected sounded better.

I wud go with the good old 833A triodes, but don't trust them to hold up under full strap.

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 #40 on: April 12, 2013, 07:43:04 AM »

Tom,
You could always use (4) 833A's in Push Pull Parallel!  I did that with 810's and it worked excellent.  That shoudl give you plenty of strap.
Joe, GMS 
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« Reply #41 on: April 12, 2013, 08:43:22 AM »

I would think 4 833As would be just as good as a pair of 4X1s, and the 833s would very likely produce better audio, and be easier to drive.

That's the way I would go for sure, if I had the tubes.  They are are also, I believe, easier to cool.
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W2ZE
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« Reply #42 on: April 12, 2013, 09:14:44 AM »

No blower noize....

Come to light tom, come to the light.....
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K1JJ
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« Reply #43 on: April 12, 2013, 11:48:51 AM »

No blower noize....

Come to light tom, come to the light.....


I'm thinking, I'm thinking.    Four 833A's would require about 80 watts more filament power than a pair of 4X1's.

But maybe I can make it up by saving money on HV wire -  like this guy did:   Grin


(Note the Romex on the secondary of the pole pig)


* Save on HV wire (2).jpg (306.22 KB, 860x1152 - viewed 555 times.)
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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 #44 on: April 12, 2013, 12:24:47 PM »

Some folks should be forced to turn in their license.
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KM1H
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« Reply #45 on: April 12, 2013, 08:51:39 PM »

Seems that the BCB boys used 4 833's in QRP rigs and 4 4X1's in a mans rig and both had low enough distortion to fit inside their channel and sound fine.

Triode vs Tetrode is strictly a personal choice and not a clean signal one if built properly.

Carl
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w3jn
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« Reply #46 on: April 12, 2013, 09:36:37 PM »

Pair o' 4X1s?  Sho 'nuff.



* death1.jpg (105.72 KB, 960x635 - viewed 1485 times.)

* death3.jpg (89.1 KB, 797x601 - viewed 543 times.)

* death7.jpg (71.91 KB, 589x785 - viewed 544 times.)
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« Reply #47 on: April 12, 2013, 09:38:25 PM »

.


* death2.jpg (108.56 KB, 960x798 - viewed 549 times.)

* death4.jpg (95.2 KB, 594x794 - viewed 568 times.)

* death6.jpg (70.48 KB, 587x787 - viewed 565 times.)
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« Reply #48 on: April 13, 2013, 05:32:46 AM »

Pair o' 4X1s?  Sho 'nuff.



OK John,

Now we need for you to channel the late Paul Harvey because we must hear "The rest of the story"  Smiley

With the "death" naming of the JPGs one might assume you are building a suitably creepy rig in order to get  Stephen King to join us on AM.
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« Reply #49 on: April 13, 2013, 05:45:09 AM »

I think it is more like JN covertly photo-ed a defunct Bayou CB blaster... Cool

73DG
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