homebrew transmitter for winter 06/07 project ideas

[KR4WI]

Hello All:   I want to start looking for parts to build a transmitter  this coming winter. I think now is the time to figure out which tube would be best for me, I really like the way the 4-250 tube looks, its my favorite look so far, but is it wrong to choose a toob just because of looks?   I don't know if it is the best choice to use in tx. Are they some draw backs to it, compared to another tube? for a first time builder.

Im thinking now is good time because of all the hamfest this spring and summer. may be able to pick up parts a lot cheaper and easier than waiting  later. Thanks for any thoughts on this. Matthew KR4WI

[K1JJ]

Hi Matt,

Glad you're thinking of building a big rig. The designing is the fun part.

The 4-250 is a great tube and will work out FB.

But, I'll give you my opinion based upon what I would do. It might not be right for you, but who knows?

I would plan to build up two rigs. Both plate modulated with one small and one big. Build the small one first to get experinece and also have a neat, "little" rig to get on  in good conditions. I would recomend the classical 813 X a pair of 813's. Use the schematic from the AM Window site under tech. It's my own design and there are maybe seven on the air. I am building one now myself. 

Then once it's running FB, built up a 4-1000A X a pair of 4X1's   or modulated by a pair of 833A's.  You won't regret it. You can find the iron these days.

These two rigs will cover all situations. Park them on different bands and make them band switchable.  The 4-1000A rig is so unique and gets tremendous oohs and ahs. Half the fun is telling your buddies about it and it will be a blast running it.

The 813 rig is just as much fun at 300W out.

Once you've built the 813 rig you will be able to easily do the 4X1 rig. Don't let it scare you. If you build one, you have arrived. If it's worth doing, it's worth doing right. Think big and you will surprise yourself.


My bias with the 4-250 is that it is too common, being that it looks like a 4-400 and they are in so many rigs from BC to T-368's, etc. I like to build rigs that are more unique just to be different. When I ran 4-400's myself, it would usually generate yawns from the guys... :-)

Anyway, that's my opinion for what it's worth, OM.

Good luck and keep us informed!

T

[The Slab Bacon]

Hmmmmm....................... Unique?? What could be more unique than a 4-1000 modulated by a pair of 2E26's.................... Just ask me!

However I do agree with Tom, both scenarios are easy enough to do. However I lean more to the 4-1000 by 833's or 4-400's! That would look real impressive through the peek-a-boo windows! 813's are kinda getting to be like an a$$%#@&, everybody has them.
                                                     The Slab Bacon

[W1RKW]

813's are kinda getting to be like an a$$%#@&, everybody has them.
                                                     The Slab Bacon

Yeah, but some have more hair than others that's what sets them apart.

[WBear2GCR]

Nah... 24 x 6146 modulated by 8 x 811, now THAT's a rig!! 

Or, maybe a big 2 x  Rusky GU - XXX modulated by 100 x 6SN7! 

Or, perhaps a 4CX5000 modulated by a backwards connected iron pushed by bridged 5kw soylent state pro audio amps? 

But on a serious note, a single 813 by 2 x 811 is a nice place to start... especially if you have little experience working with HV and higher power RF... even the relatively modest B+ Power can KILL YOU DEAD on that rig... best to get ur feet wet gently before dorking with really big HV, which can reach out and "kiss you".

      _-_-WBear2GCR

[w1guh]

Didn't you make something with a bunch of 50C5's in the early 90's, Tom?

[KR4WI]

No,  this will be my first hb transmitter. I would like to build something in the 300 watt range. maybe help get some of the ssb stations out of the 75 mtr window. and if not, maybe it will be alot easier to hear me than with the viking ll Matthew KR4WI

[K1JJ]

Didn't you make something with a bunch of 50C5's in the early 90's, Tom?

Yep, I cornered the market for 50C5's one spring at HossTraders. $1 each. As a result I built an all 50C5 receiver. About 5 tubes as I remember.

Then I put together six 50C5's in parallel modulated by push pull quad 50C5's.  It would do something like 60W out.

After less than a year I tore it down and went back to a pair modulated by a pair.

They are really a robust tube for a mini. The filament requirements are the same as a 6146, power-wise so they have the emision.  I've had up to 500V  on one final plate modulated... good for 10W easily.  What a tube.

This all happened in the middle of the PW craze, so it seemed quite sane at the time...

T

[John K5PRO]

I'm partial to having a 450TL or 250TL as these have the big globe and are loonng in the socket. However, they are also a bit touchy to try and run above 10 MHz I imagine.

[w1guh]

What about 304TL's?  A couple friends scored a few as, shall we say, excess inventory, when WCAR closed down its transmitter in Pontiac.  They looked impressive, but they never got used.

[Herb K2VH]

I'm partial to having a 450TL or 250TL as these have the big globe and are loonng in the socket. However, they are also a bit touchy to try and run above 10 MHz I imagine.

Nahhh, John.  No sweat.  I've had a BC-610 run FB, OM on 15 meters (250TH), and a friend of mine had his running on 10 meters.  EIMAC rates them good to 40MHz.
vH

[WU2D]

Hi Matt,

WA1HUD Steve Russell used to run a dirt simple rig.

It was simply an old ARC-5 command transmitter driving a 304-TL modulated by a pair of 810's. The ARC-5 had plenty of drive and the VFO was stable. I don't remember if he band switched it somehow or if it was strictly on 160M but it was loud.  Certainly the ARC-5 could be used to double to 80M with a simple switch on the tank coil. This rig could easily run old (lower) the legal limit.

With a second ARC-5 you could get 40 and 20. That would be a strange looking rig!

For a small rig I like a single 813 modulated by a pair of 811's. What about 2/ 813's modulated by two triode connected 813's running at higher voltage?  It's hard to beat the old 813 for dollars per Watt. With a little air, they are practically indestructable too.

Mike WU2D

[WU2D]

Wow did I say lower legal limit? I meant higher (sigh..)

Mike (WU2D

[wa1knx]

Hi Matt/Tom

    Matt, I like the look of the 4-250 to!! I have a globe king out here in tucson.
Love the orange glow with the top up, on the rig. Tom, a 4-400 doesn't look
like a 4-250!?  I'm with you Matt, build the 4-250.  However the 813's are easier
to come by, at least they used to be. I bought a box of 813's, for $0.25 ea in
the 70's!!!!!!!! all good tubes, a bunch got stolen (along with a hw-12) from
my car back then, sigh.  They are a mood tube to, I have several rigs with them
and still have one back on the east coast.

deano

[K1JJ]

Hi Matt/Tom
Tom, a 4-400 doesn't look like a 4-250!? 
deano

Dino,

Inter-changeable and two peas in a pod.  You been eating those Arizona mushrooms?      (yeah, yeah, I know the plates look different, less power wid the 4-250, but still basically the same tube to me, caw mawn.
T

4-250


4-400

[Bill, KD0HG]

I'm thinking of making a regen receiver out of an 833.
Seriously.

[K1JJ]

I'm thinking of making a regen receiver out of an 833.
Seriously.

 

That would be funny. You'd get lots of mileage talking about in on the air, Bill.

Tell us more....

T

[WA1GFZ]

How about a 833A transceiver so it is an SBE rig in TX

[KB2WIG]

                              MOPA ?

[KA1ZGC]

Hi Matt/Tom
Tom, a 4-400 doesn't look like a 4-250!? 
deano

Dino,

Inter-changeable and two peas in a pod.  You been eating those Arizona mushrooms?   

That would be cactus, Tom... 

   (yeah, yeah, I know the plates look different, less power wid the 4-250, but still basically the same tube to me, caw mawn.
T

The Tron runs a 4-400 (with the exact same anode as the one in the picture Tom posted) in the BC-610-B-as-in-Bastardized, but when he needs that particular 4-400 for something else he plops a 4-250 in its place with no other changes to the rig.

In that particular application, with 50 to 75 mA of grid current, 50 mA of screen current, and 300 to 325 mA of cathode current at (roughly) 1850 volts B+, the 4-250 gets red in the face, and the 4-400 doesn't even break a sweat.

That is as long as nothing is wrong with the output tank. I discovered a problem with the loading cap by getting the 4-400 nice and red with what should have been optimal tuning. It's a good thing I'm so paranoid about crapping Timmy's rig out, otherwise I wouldn't have popped the hood and seen the glowing plate. No 4-400 should ever show color in that application.

Last fall, Timmy took the 4-400 to use in one of Al Wiener's exciters (I think), and left me with a 4-250 to run. Talk about white knuckles! I was popping the hood every ten minutes or so to check the plate color. After the 4-400 was available again, Tim gave in to my begging and pleading and put it back in the 610. I'm glad he did, otherwise the goofy loading cap would have melted down an otherwise perfectly good 4-250.

What's my point, you ask? If you're going to run near legal limit, and you have access to a 4-400 (beg/borrow/steal), I would run that at least until you can get any kinks worked out of the transmitter. Once you've got a known-stable output tank, you can plop a 4-250 in there and just try to keep the plate more red than orange. They'll crap out (or get gassy) sooner than a 4-400 would, but they'll still go for a good long time; and like Tom said, they're otherwise electrically identical tubes.

Wouldn't mind having a few of each, myself.

Or, a 4CW50000 and some distilled water... 

--Thom
Kilowatt Amplifier One Zero Grid Current