Future Projects for BIG AM SIGNAL

[ka4koe]

I found this excerpt online for the 1940's Radio Handbook, by Orr. See the attachment. Aside from the older tube types, is it a good, workable design?

Philip
KA4KOE

[ka4koe]

More pages

[ka4koe]

And Page 6.

Philip

[WQ9E]

Seriously consider the price for the tubes (and spares) you will need.  That is an interesting design but a lot of the tubes used are going to be quite expensive now.  There is nothing wrong with plug-in coils but they are very inconvenient if you plan to change bands often and you need to consider the safety factor of either designing in safety interlocks or being very careful to always power down and short HV to ground when reaching inside to change coils.

I would seriously consider looking towards the mid to late 50s designs with more recent finals (like 813 or 4- series), a Pi type output network and more recent modulators (811A, triode connected 813, etc) unless your focus is more upon building a period specific rig than a big signal plate modulated transmitter.

The modulation transformer (and even more so a modulation reactor choke if you want to use one) are going to be some of the most difficult components to find.  You can take a dual path of choosing a design and looking for a suitable transformer while also keeping an eye out for mod transformers and if you see one that looks interesting consider looking for a circuit to match.

There are a lot of user friendly designs in the 1950s handbooks (both Orr and ARRL), QST and CQ of the era, and other magazines like Radio and TV News.

[W7TFO]

With a little diligent sleuthing, all the tubes in that design are available.

The 203Z's are the most difficult, easily subbed with 838's.

You will find it more difficult to source the rest of it, than the tubes.  It would be a great transmitter if done properly with period parts for looks and newer iron for longevity.

73DG

[KM1H]

The 35T's are pricey lately and HK254's very scarce but the various 25W WW2 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.

That circuit is easily capable of 500-600W input with a single PS of 1500V for the 3C24/100TH/812A

Carl

[W7TFO]

Carl sure likes to rain on other peoples' parades...

203Z= 838 available <$75

2A3= 6B4G available  <$100 pr.

I'll GIVE you a pair of 35T's if you promise to finish the project...

Here is a power supply, only one week old...everything there was sourced within the last year.

73DG

[ka4koe]

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

[KA2DZT]

You should be able to build a xmtr from scratch without looking at anyone else's design.

Fred.

[W7TFO]

More itch than scratch with me, Fred, but I know what you mean.

73DG

[K5UJ]

That's a nice power supply Dennis.  First time seeing 866s conducting.

Phil, I do not want to discourage you but you're probably better off at first getting an existing rig and going through it and breaking/fixing/modifying it.  Something like a Globe King 500 or better, a BC610.  However, if you want to build from scratch FB.  I'd start going to every hamfest especially dayton with a lot of cash and start looking for and collecting parts.  Be on the lookout for chassis/rack panel assemblies.  They are getting hard to find.  I don't even know if new ones are being made.  How is your machine shop?  If you are like me, you are going to have to start learning about metal working and getting tools and learning how to use them.  I advise building the rig into two short 5 foot racks.  Easier to move and get into places like a basement.  If you are patient building a big rig is wonderful and a great retirement plan.  You will really get an appreciation of homebrew gear.  Most of the time what you don't see on a nicely laid out chassis is more important.  You don't see all the different ways parts could have been laid out wrong, botched holes, and other boo boos avoided by years of practice.

[steve_qix]

Whether to build the project as documented, or do something more modern (and it wouldn't take much in this case  ) depends on whether you want a higher power transmitter that will work and sound better, or a nostalgic higher power transmitter that's true to a time period, but won't perform as well, and probably be more complex and expensive to build.

You could accomplish a better result, and still stay in the tube domain by using more modern tubes like 813s.  A pair modulated by either another pair or perhaps by 572Bs or 810s is a reasonably sane choice.  PI section output networks are easier to configure and require few special parts.

A much better modulator design could be had by eliminating all driver transformers and using some type of direct coupled driver, either tube based or solid-state (easier than a tube driver and works better).

If you're willing to move into the 21st century    and are primarily looking at 160-40 meters, Wayne WA1SSJ brought Al W1VTP's class E rig over to my place the other day, and we hooked it up and ran a nice cool 400 watts output with DC coupled audio and 175% positive peaks.  I can lift the entire transmitter by myself.

The design depends on your ultimate goal 

Regards,

Steve

[ka4koe]

"You should be able to build a xmtr from scratch without looking at anyone else's design.

Fred"

Fred, likely the answer is yes. However, designing a high power transmitter from scratch with zero experience and only a textbook with formulae is a risky proposition. Why reinvent the wheel?

My idea of a successful project entails the following criteria:

1. The operator is not distilled into a smoking, stinking, and steaming pile of carbonized fat.
2. The transmitter outputs a clean signal at rated output and modulation.
3. The various components do not self-destruct from any variety of failure modes.

Given the cost of the components involved in a high power, plate modulated transmitter, I'd rather not see a ton of invested money become "one with the snows of yesteryear".

I think the biggest lesson here is not to work in a vacuum and obtain help and advice from those more learned in these things than I. This rationale is the primary reason we have this jam up forum with which to exchange ideas.

I have already started on my "5 year plan". I recently obtained a rather nice 6' rack on casters. Just needs a little wire brushing and a coat of paint to look new.

PHILIP
KA4KOE

"FEELEEP"

[W2VW]

And 203's are mostly gone to air. The 812A is a direct zero bias sub.

Carl

Not even close. Maybe a typo? 811?

http://www.r-type.org/pdfs/812a.pdf

[flintstone mop]

And 203's are mostly gone to air. The 812A is a direct zero bias sub.

Carl

Not even close. Maybe a typo? 811?

http://www.r-type.org/pdfs/812a.pdf

WOW Carl
You are taking a beating in this thread.

But I agree about vintage special period transmitter designs. Limitations to what was available, and accepting performance for that time period. Not today's 125% pos peak TX and hi-fi audio.

[ke7trp]

Thats a neat transmitter. The parts are out there if you look hard enough.  I like the old design and old tubes. Its different and different is cool.

More Modern designs will be easier and might work better in some respects, but are common.  "813s here"  Blah... Heard it a hundred times on the air.  I always wanted a 450 TL or 450 TH for final.  Maybe 304TLs for modulators. 

I would never expect you to build something like this with no plans or help.  Maybe try to find an old home brew transmitter somewhere on a classified add.  Then, Fix it, Mod it, update it and get it working.

C

[W3GMS]

You should be able to build a xmtr from scratch without looking at anyone else's design.

Fred.

When you have never built a big rig before that is a tall order. 

Phil, I agree with you on your approach.  Look for the parts first and then you will have a feel for what your going to build.  With every rig you built, you will definitely learn something.  At all cost, don't let those with attacking personalities bother you.  If some of these people are as good as they think they are, they would have far less to beat their chest about! The true innovators will help you and you may want to do that on a one on one basis since here you will get some good advice and some bad advice.  Pick someone you respect and work the design issues through them.  I would certainly be willing to donate parts if I have anything you can use once you determine what you want to build! 

Joe, W3GMS   

[ka4koe]

Well, I've got power fever and want the lights in the house to dim when I key and hear that ominous KERCHUNK!! Most amps I've seen aren't really designed for this duty cycle. I could find a T368 a lot cheaper than a legal limit rated amp.

PHILIP

[ka4koe]

You should be able to build a xmtr from scratch without looking at anyone else's design.

Fred.

When you have never built a big rig before that is a tall order. 

Phil, I agree with you on your approach.  Look for the parts first and then you will have a feel for what your going to build.  With every rig you built, you will definitely learn something.  At all cost, don't let those with attacking personalities bother you.  If some of these people are as good as they think they are, they would have far less to beat their chest about! The true innovators will help you and you may want to do that on a one on one basis since here you will get some good advice and some bad advice.  Pick someone you respect and work the design issues through them.  I would certainly be willing to donate parts if I have anything you can use once you determine what you want to build! 

Joe, W3GMS   

Joe

Definitely going to do the paperwork first using Orr's calculation format for a high power Class C transmitter. Then I need to do some learnin' on modulation transformers. Orr is a good read. I take it to the "reading room". However, my edition is the 22nd and doesn't delve into plate modulation.

I will post my calcs here where they can be critiqued by the unwashed masses and propeller-heads alike.

There are some very talented folks here and their work in steel, glass, copper, and ceramic is inspiring.

PHILIP

[W7TFO]

Phil, PM me and I'll send you a much more pertinent issue of the 'Jones' handbook.

73DG

[KA2DZT]

Joe,

You have to lighten up a bit.  I don't always add smiley faces at the end of my comments.

I was just trying to inspire Philip to try building his dream xmtr.  You're correct, he will learn a lot with whatever project he decides to build.

Philip,  everyone here, including myself, welcome all the questions you have, keep them coming.

And, before Joe beats me up again , I don't have all the answers.

Fred, KA2DZT

[ka4koe]

Started on lunch break. Here is a screen capture using a spreadcheek program.

P

[W2VW]

Well if we are postings links here's a really good one:
http://www.somis.org/

[flintstone mop]

Well, I've got power fever and want the lights in the house to dim when I key and hear that ominous KERCHUNK!! Most amps I've seen aren't really designed for this duty cycle. I could find a T368 a lot cheaper than a legal limit rated amp.

PHILIP

Ya but Feeleep
You can not see the pubes in a T368. Big grey box with noisy fans and it will dim the lights hehehehe

[Opcom]

With a little diligent sleuthing, all the tubes in that design are available.

The 203Z's are the most difficult, easily subbed with 838's.

You will find it more difficult to source the rest of it, than the tubes.  It would be a great transmitter if done properly with period parts for looks and newer iron for longevity.

73DG

Where do you get 838's? I have a pp-par amp with them, and -one- spare. On the other hand, Chinese zero bias 805 types with the same filament characteristics are available and sold to audio hobbyists. The "PSVane" 805-T has a plate cap.

I've admired that article many times and read it over and over. There is something really beautiful about it.

One thing that stands out in the schematic is the difference between the 1250V modulator supply voltage and the 1900V PA supply voltage. A good step-up ratio may be needed on the modulation transformer.

What would you use for the 100W tubes in the final? The 100TH is one of those oldie high-bias low-grid current tubes and costly today. If you are going to use 572's or something inexpensive then the drive link may have to be changed to reflect it.

On the other hand why spoil the original design? If it's treated right and the filaments are not too brittle on old tubes then this stuff should last decades and a set of spares could be all that is ever needed.