Power Fever

[ka4koe]

I am using a Flex 5000a with an SGC SG500. The best this sucker will do is 100W carrier on a good day. Can anyone recommend a good tube amp to run full 375W carrier, 160-10M. The only caveat is the output devices (ie tubes), will not require ransoming my chillrens in order to acquire.

Really getting heavy into AM this past month after dabbling for a year.

PHILIP
KA4KOE

[Pete, WA2CWA]

Ameritron AL-82 pair of 3-500Z http://www.ameritron.com/Product.php?productid=AL-82

[W3GMS]

Ameritron AL-82 pair of 3-500Z http://www.ameritron.com/Product.php?productid=AL-82

I have been using that Amp for years at full legal limit on AM without any problems.  Around 20W of drive for legal limit AM. 

While on AM with your Flex, the maximum carrier power without audio should be no more than 25W.  Upon 100% modulation that will give you 100W peak output.  So you easily meet the requirement to drive the 3-500Z's. 

Joe, W3GMS   

[W1AEX]

Another vote for the AL-82 Phil. The chimneys and abundance of air flowing through them along with its very capable power supply makes this amp an excellent choice for constant carrier modes. A couple of years ago I bought one used for 1200 bucks that needed a little work (filter caps and bleeder resistors) and it has worked fine since from 160 - 10 meters.

By the way, you sounded great up here in CT the other night when we spoke on 75 meters. Thanks for the chat!

Rob W1AEX

[K5UJ]

recommend a good tube amp to run full 375W carrier, 160-10M. The only caveat is the output devices (ie tubes), will not require ransoming my chillrens in order to acquire.

For what you'll blow on a ham linear RF power amp you can buy a hell of a nice plate modulated AM rig.   Just about any ham commercially built amp will need some sort of mods to it for the illusory "legal limit" anyway. 

After you've seen a black wrinkle or chrome trimmed beauty in operation you'll go home and sell your amp to get one so why bother in the first place.  I've been there running a pair of 3-500s because I had such an amp on hand but if I had it to do over again I would have never gone that route.   

For one thing, to get a pair of cathode driven g.g. 3-500s to go over 300 w. your flex box will have to give it at least 20 watts drive, maybe closer to 25.  Can its PA handle that for 30 minutes?   Most of these ham amps stock, are built for the bucket brigades and CW so if they can put out your desired power will need improvements to the cooling,  maybe the plate iron, and cabinet venting,  if you don't want to be sitting there looking at it the whole time, hoping something doesn't melt down.    The manufacturer may rate it for 1500 w. RTTY but for how long.   No time limit is doubtful.   but for the $3K or $4K you'll spend on one of those desk top boxes, an old bc rig or BC610 or T368 will run for hours in transmit.  And you'll have a couple thousand bucks left over. 

Rob

[Pete, WA2CWA]

Ameritron AL-82 Specs:

Input
Circuit type: Pi-network, slug tuned coils
maximum VSWR at resonance: 1.2:1 minimum 2:1
VSWR bandwidth: 20% maximum drive power
permissible: 130 watts typical drive for full power
output: 100 watts


Output
circuit type: Pi-L, Pi
1/2 hour continuous carrier: 1500 watts (Below 18mHZ)
30 second continuous carrier: 1800 watts plus
1/2 hour PEP two-tone test: 1800 watts
30 second PEP two-tone test:1800 watts plus

And, you can typically buy one of these for under $2500 new.

[W1AEX]

For one thing, to get a pair of cathode driven g.g. 3-500s to go over 300 w. your flex box will have to give it at least 20 watts drive, maybe closer to 25.  Can its PA handle that for 30 minutes?

The quick answer to this is yes. The Flex 5000 is rated to run 100% power at 100% duty cycle. You can set the output to 100 watts (FM, RTTY, CW), fire it up, and walk away for a couple of days. Since it will generate 100 watts PEP with the phone modes the only caveat is that when running AM it really is important to monitor your signal with a scope. If you have set the AM carrier level to take advantage of the ability to generate an asymmetrical signal you could easily run out of headroom and start flat-topping if you are running it at 20 or 25 watts of carrier. (To prevent asymmetry simply set the AM carrier level to around 50 or higher with the latest version of PSDR.) I typically don't need much more than 15 watts of carrier to drive my AL-82 to +200 watts of AM carrier. I also set PowerSDR to restrain the positive peaks to not much more than 120%. When run like that both the exciter and the AL-82 have plenty of headroom to handle the positive peaks.

I hear you about he allure of heavy metal Rob. There's nothing quite like a big rig on a cold winter night! That being said, running what Philip has in mind allows you to run every mode available to you on every HF band of interest to you at full legal limit. That's not a bad thing!

Rob W1AEX

[ka4koe]

BC610's and 368's are a little scare, aren't they? Besides, no way I could either upstairs, or whether the floor would give way!!!

PHILIP
KA4KOE

[RolandSWL]

Well, there is a clean-looking BC-610-F on Epay. I can't imagine why it's local pick up only. How much could it weigh?

[ka4koe]

Enough to drive one's coccyx out the back of the chassis and squeeze your intestines out of your navel if you tried to do a power lift on it.

One word: PAIN.

PHILIP

[W2VW]

Well, there is a clean-looking BC-610-F on Epay. I can't imagine why it's local pick up only. How much could it weigh?

401 lbs.

[W2VW]

I satisfy the desire to have a final that can catch on fire of kill me by using a vintage Collins linear AMplifier. Every bit as much fun as a plate mudulated rig.

Low level AM is easy to manipulate. Total system efficiency can be fairly close to that of a plate modulated rig too.

Friends have used the larger Ameritrons mostly with great results.

The 160 requirement pretty much eliminates most older amplifiers.

[kb3ouk]

With the flex, he already has a rig that can be made to sound great without much work. Not a big deal to get a linear to put after it to get more power. It's a lot easier to find a linear that would put out close to the leagal limit on AM than it is to find a plate modulated TX that will do the same thing and NOT require a lot of work to get it running and sounding good.

[KM1H]

There are several amps using a pair of 3CX800's in current production and going back to the 80's. Its a decent tube as long as you dont abuse it and the amp has a grid protection circuit; many hams are still getting full output in their 80's amps. The tube doesnt have the reputation of an IED event as does the AL-82 and other 3-500 amps using either old gassy Eimacs/Amperex or the current Chinese graphite versions. Those tubes have to be regulary run at color to remain gettered.
Full output 3CPX800A7 MRI pulls are around $300 a pop and are PnP with the 3CX version.

Carl

[Opcom]

Whatever you do, look into the power supply of the amp in question. Some older types are a little skimpy on the plate transformer and it can get hot on windbag AM sessions. A fan directly blowing on the plate transformer can help some of these by cooling the iron directly but it ain't right.

Try to pick one with a modern hypersil type of transformer or that has a oversized older unit that's too heavy to lift. At least a 2-2.5KVA CCS rated-transformer. Pretend you are going to run a 1500W FSK signal in summer.  8-)

[K5UJ]

<<<It's a lot easier to find a linear that would put out close to the leagal limit on AM than it is to find a plate modulated TX that will do the same thing and NOT require a lot of work to get it running and sounding good.>>>

Isn't the work to get it running and sounding good part of what AM is all about?  Seems like if all we want to do is just buy gear and plug it all in, we may as well stick with slopbucket.

What stories are you going to have, to tell your grandchildren?   

"Grandpa, did you ever dip and load a class C final?"

"Uh, no."

"Did you ever figure out how to sequence T/R switching and set up relays for a one switch transition?"

"Uh, no, um, I bought some cables at Radio Shack to run between my uh, transceiver and my leenyar though."

Besides, a transceiver box and RF amp box ain't a transmitter. 

[kb3ouk]

Just because it isn't a complete transmitter doesn't mean it won't work for AM. But if you're just getting started with AM, a linear being driven by a decent sounding rig is a good way to start. I'm sure he's not the only person out there running a Flex/amp combination, and surely won't be the last. And to be historically correct, having a low level stage driving an amplifier is one of the oldest forms of producing AM, it has been around longer than high level plate modulation using a push-pull modulator. Some of the first broadcast rigs were Heising modulated drivers feeding a linear final.

[KM1H]

Isn't the work to get it running and sounding good part of what AM is all about?  Seems like if all we want to do is just buy gear and plug it all in, we may as well stick with slopbucket.

Many dont have the space and others may want to use what later gear they have while putting a vintage station together.

At some point I may just get rid of rack mounted amps and modulators that simply take up way too much space and build a couple of table top linears that can easily run a 500W+ carrier without melting down and be able to be driven by a typical 100-120W AM TX without too much attenuation in line. Maybe 3-4  3-500's or 4-400's at 2500-3000V and biased for AM efficiency....or a pair of GG 8877's 

[DMOD]

What stories are you going to have, to tell your grandchildren?   

"Grandpa, did you ever dip and load a class C final?"

"Uh, no."

"Did you ever figure out how to sequence T/R switching and set up relays for a one switch transition?"

"Uh, no, um, I bought some cables at Radio Shack to run between my uh, transceiver and my leenyar though."

That's good.

Yes, what legacies are we leaving for our grandchildren? 

[K5UJ]

Many dont have the space and others may want to use what later gear they have while putting a vintage station together.

That's me!  Works in progress.

[K5UJ]

Just because it isn't a complete transmitter doesn't mean it won't work for AM. But if you're just getting started with AM, a linear being driven by a decent sounding rig is a good way to start.

Indeed.  But, delving into vintage gear with the whole thing on a single fold out sheet vs. SMT and 1000 pin chip packages is to be encouraged I think.  New stuff = throwaway; old stuff = opportunity to understand radio and circuits.   

[Steve - K4HX]

Or playing with:

new stuff = learning about new stuff

old stuff = learning about old stuff

The reality is that there is room for both. Neither is right or wrong, Neither is better or worse.

[kb3ouk]

And with that new stuff (SDR in particular), the signal generating stages can produce what is a mathematically perfect AM signal, and can produce whatever percentage of modulation you want, since it produces a fixed sideband power (100 watts PEP) then puts whatever amount of carrier you want. Which gives you the capability to have a high amount of positive peaks with little distortion. Can your average plate modulated class C final do that? The probelm is that there are some people on AM that don't want to think outside the box when it comes to producing an AM signal. These people are close minded in thinking that the only way to go is with high level modulated tubes (though there are a few out there who act as if solid state is the only way to go too).

[Steve - K4HX]

Run what ya brung. Don't worry about what the other guy is using. Have fun.

[kb3ouk]

And that's the way it SHOULD be.