Just orderd me a bit of strap

[WB2YGF]

OK, call me an appliance operator, but after weeks of internal debate, I finally pulled the trigger on a new AL 80B. (Hey, it's modern, but at least it has a tube in it.)  Hope to have it on this weekend, and you guys may actually be able to hear me on 75.   

Since this is my first amp, I am pretty clueless.  Any tips for operating this puppy, particularly on AM?  I know it would work better on 220V, but that's not gonna happen soon.

[K4QE]

John,

Tune up the amp as usual for max smoke.  Then, use the power output control on your rig to adjust output down to no more than 200 watts carrier.  Advance the ALC control full clockwise when running AM (so no ALC action can take place).

Adjust your audio level so the wattmeter just barely deflects up on voice peaks.

Good luck!

Tony

[W3RSW]

Good tune up notes.

What are you running now?  You might get 200 watts of reasonably distortion free 100% duty cycle AM from the Ameritron, since it's rated at 1000 PEP output.
The instantaneous RF bias feature, of course, for "70% efficiency" won't be available on AM.

Single 3-500 Z amp. looks nice. Ameritron makes two levels of amplifiers, in sturdiness, coil stock guage, fit and finish, etc. I looked over both lines with the covers off at Timmonium last year and noted the two different standard lines.  

Found it with a parts list.
http://www.ameritron.com/Product.php?productid=AL-80B

[WB2YGF]

What are you running now?

I have a Pro II running about 30W.

[W3RSW]

Oh. - Then that'll make a good difference.
And the pro II has lots of audio shaping to play with. You'll have a very nice sounding signal from the 3-500.   
Hope to see ya on the air.

[WB2YGF]

Thanks for the tune-up tips Tony.

[Bill, KD0HG]

Sometimes it helps to increase the loading on the linear just a little bit as a last step, remember your peaks are going to be 4X your carrier power so the loading needs to be adequate to pass the peaks. Ideally, you'd tune the linear up at 4X your expected AM carrier power, then back off the drive to 1/4 of that output level without touching the loading.

If you have access to a scope, it would be a great help.

[flintstone mop]

I guess you have committed to the AL80B. Ameritron makes nice strong amps.
You Shudda bought an AL82. Has two 3-500Z's and legal limit AM.
But I  can understand the financial part, as the AL82 is $2700?
200 watts carrier makes a good transmitter even on 160M. On top band, though the antenna starts to be the main focus.

Fred

[KF1Z]

Guess you probably saw this excerpt from the manual......


"The efficiency of any conventional linear amplifier must remain below half the peak efficiency
under maximum signal conditions (less a safety factor) in AM operation. Since this linear amplifier
has a peak plate efficiency of nearly 65%, the carrier efficiency must be kept below 30% to maintain
linearity. The power dissipated in the tube anodes will be more than twice the carrier output power.
The carrier power must be kept below 200 watts for clean and safe AM operation. With 200 watts of
carrier, the peak envelope power will reach 800 watts with 100% symmetrical modulation. The
modulated AM power output should be limited to 1000 watts peak with non-symmetrical
modulation that enhances the positive peaks."

[WB2YGF]

But I  can understand the financial part, as the AL82 is $2700?

Yeah, normally the price delta would not be as big a deal, but with the economy the way it is, and my plant (and salary) cut back to a 4 day work week, I have to be careful right now.  I would definitely consider the AL82 if/when we are safely out of the woods.

[WB2YGF]

Guess you probably saw this excerpt from the manual......

Actually, no.  Thanks for pointing it out.

[WQ9E]

John,

Your new amp will definitely help your signal under marginal conditions and my only addition to the good advice you have gotten so far is definitely let the amp run for a few minutes after your last transmission to cool things down a bit.  The 3-500Z is a pretty robust tube but you don't want to kill the power immediately after a long transmission, give the fan time to cool the tube seals a bit.

To add more tubes to your station you might think about picking up a member of the Drake 4 line (T-4X transmitter family or one of the TR-3 or 4 series transceivers).  These run controlled carrier on AM (the carrier level tracks the voice amplitude on average so the average carrier output is fairly low).  Controlled carrier AM is very friendly to modern linear amps.  You could get some complaints from folks who don't like seeing their S meter twitch on AM but if their AGC is up to snuff controlled carrier sounds OK.  There are, of course, a number of other transmitters running controlled carrier including a number of the vintage Heath lower power rigs.  Just trying to up your tube count a bit 

Rodger WQ9E

[WB2YGF]

Good advice Roger on the cool down. 

I also have an FT101ZD MKII with tube finals to up the tube count, but I need to swap the FM and AM boards to get it on AM. 

I have never heard control carrier AM mentioned in a posive light before.  I started out on voice in 1975 with a DX60.  I guess it reduces the average dissapation while increasing the power on peaks?  In the attic, I have a DX60B in unknown working condition.  I have a Drake 2NT with an Eico VFO.  I think the VFO is the proper frequency to drive the DX60. 

[K1JJ]

Hi John,

Congrats on the new amp.  A single 3-500Z is a good, clean tube to use for linear service.

As far as tuning it up, for the cleanest signal, you want to load it slightly heavier than when at a "tuned for maximum output" setting.

Here's how:
Look inside and figure out which direction to rotate the loading capacitor to decrease its value. (Less capacitance - plates less meshed)
Then tune both the tuning cap and loading cap for maximum output. Then decrease the loading cap a little bit until power output goes down maybe 5-10%. Then re-peak the tuning cap for maximum.

This procedure will place the tube's operating range more into the straight (linear) part of its transfer curve and produce the cleanest signal possible for the amplifier.

As a result, your efficiency will decrease slightly and you will draw more plate current for a given power output, but the amp will have side products that are down lower than the average ham amp on the band. Keep an eye on the tube plates to be sure you're staying within heat ratings. A 3-500Z should show some dull red color, but not real bright red or yellow or white... :-)  Hopefully they use a chimney with air coming from the bottom to the top. If they use a fan blowing air across, modify it in a hurry.

When you go from 30W carrier to 200W carrier, there also comes a responsibility to your ham neighbors on the band. At 30W you can run most anything and not bother anyone.

BTW, pssst - whisper -  it's not too late to cancel the order - I'll show ya how to homebrew four 813's in parallel GG (linear) and get out 2KW pep, cheap!  caw mawn.  :-)


Later -

Tom, K1JJ

[flintstone mop]

I had another thought that might become an issue in the tunning department.
It is my understanding that you need enough driver power to drive the linear to max output, then you tune your Plate and Loading accordingly.
You mentioned that you have a Pro II, 30 watts.

Fred

[WB2YGF]

I had another thought that might become an issue in the tunning department.
It is my understanding that you need enough driver power to drive the linear to max output, then you tune your Plate and Loading accordingly.
You mentioned that you have a Pro II, 30 watts.

Fred

The Pro II puts out 30W of AM.  For tuning purposes I can put out 100W of CW.

[WB2YGF]

BTW, pssst - whisper -  it's not to late to cancel the order - I'll show ya how to homebrew four 813's in parallel GG (linear) and get out 4KW pep, cheap!  caw mawn.  :-)

Do you have the plans for such a beast? 

[W1AEX]

Good choice on the amp! I use an AL-80B with my Pro III and it produces an easy 125 - 150 watts of AM. It's capable of providing about 200 watts of AM output, but I have found the Pro III sounds best on AM at somewhere between 10 - 15 watts. Definitely go with 220 volt primary voltage if you have it available. The amp works fine with 120 vac, but I found the plate voltage tends to sag when wired for 120 vac, even with a dedicated 20 amp circuit.

There's reams of information about tuning the AL-80B, but you will find it is extremely easy to tune and very forgiving. I always do it in three steps, starting with about 25 watts of drive in cw mode, and then about 40 watts, and then roughly 75 - 80 watts which produces maximum output with grid current under 100 ma and plate current between 400 - 450 ma. The last thing you do is advance the loading control slightly to the right, enough to drop grid current and power output slightly. Then you simply run your Pro II with about 10 - 15 watts of AM and you have a nice medium power station!

If you did not opt for the grid protection circuit, consider getting it. It's very slick, easy to install, much cheaper than a new tube (40 bucks), and simply drops the amp to standby if your grid current moves towards a dangerous level. With the grid protection circuit, you can safely avoid the whole crappy ALC connection inconvenience.

The one thing many AL-80B owners hate is the stupid dynamic bias, which puts the tube at cut-off between syllables and cw notes. It's a distortion circuit and easily defeated with a single 1/4 watt resistor should you wish to eliminate it. I did, and it no longer sounds gritty on the leading edge of syllables.

You'll love the amp, it's very dependable! Mine is vintage 1999 and still cruising along just fine.

Rob W1AEX

[flintstone mop]

I think TOM has plans for tubes with handles on them too.
813's are very nice tubes!!!!!

Fred

[WQ9E]

I think Rob nailed it on the power issue, running at the 125 to 150 watt level your amp should be well within its capabilities and live a long and happy life.  As noted by a previous poster, a lot of heat is generated running full AM through the amp and the typical power supply and cooling design is biased towards providing the capability for rated power on SSB and CW while allowing for a competitive price and corporate profit.  I use my Drake L-7 a fair amount on AM because my Desk KW and Viking 500 don't cover 160, I drive it with a TR7A which is full carrier unlike the earlier Drake tube type gear and set it at the 200 watt carrier output level.  The only linear amp I own that I feel safe running at the legal limit on AM is one I built for contest duty several years ago and it uses 3 4CX800 tubes in parallel with a Dahl 4 kW CCS rated transformer in the power supply; the output network is similarly over-sized.

I have contacted a number of stations running controlled carrier AM and although it doesn't sound as good as a well adjusted traditional full carrier system it does work just fine.  With controlled carrier you can generally run the amp at or very close to its SSB ratings.  Under marginal conditions this can be the difference between making or not making the contact.  Like others, when conditions are good fairly wide band high level AM sounds great but under poor conditions I would much prefer a copyable controlled carrier or audio with some speech clipping as opposed to trying to pull a really weak signal out of the mud.  I do enjoy DXing and I participate in some contests but for AM operations armchair copy is my strong preference no matter how the signal needs to be generated on the other end to accomplish this outcome.  I know that many others do feel differently about the issue of audio quality.

[N3DRB The Derb]

best vintage TX linear driver ever: Johnson Viking Challenger. 100 W CW, 15 W AM, screen modulated, super easy to restore
and cheap for vintage gear. 80 - 6 meter coverage. just change the filters and do some mike amp work and you are done. 100X better than any controlled carrier rig. Whips a DX-60 like a bad doggie.

[K4QE]

Instead of an 813 leenyar, you could always go this route...

http://www.amwindow.org/tech/htm/813/813.htm

Another one of Tom's great designs.

[K1JJ]

John,

I don't have any plans, but you could use just about any GG amplifier as a guide.

The four 813's in parallel would all have lantern chimneys with plenty of forced air. This would bring the dissipation up to at least 250W each. Use fat aluminum plate caps.

Use 4KV on the plates.  They will show unwanted color, but good for 2kw pep out on ssb. I have a friend who did it. The tubes would be a little over their plate dis ratings, but they would probably do OK if ya talk fast... :-)

The 813 filaments are way oversized and can develop the emission required.

I know someone who planned on using 12 in parallel WITHOUT air, as a quiet linear. He accumulated all the tubes and sockets, but never built it. Now THAT would be a very FB, quiet amplifier.


Good luck with the new 3-500Z amp.

Yes, Tony, that 813 AM rig wud be a great starter kit for John - good idea.  John, use the 3-500Z amp and slowly accumulate the parts for the 813 Am rig!

T

[WQ9E]

12 813's in parallel would be an interesting setup; I imagine it would be a little problematic on the higher frequencies with so much output capacitance from the tubes.  As I recall WRL/Galaxy had a 10 or 12 tube 6HF5 amp to match their Mark III or V transceiver and it ran at pretty low plate voltage with the plate current measured in amps resulting in a very low output impedance.   With plate impedance that low you could seriously consider using broadband output transformers similar to those used in modern SS gear.

I started digging out the stuff tonight to build a version of the K1JJ 813 design.  I have a nice Gates roller inductor and a vacuum variable that will soon be living in the output network.  I finally found a mod reactor to go with a WWII era Westinghouse mod transformer I picked up a few years ago.  My plan is to set it up for 160-40 meter operation, 160 in particular.  I have pretty much all of the parts and some chassis from another ham's start at an 813 rig.  My New Year's resolution was to turn more parts into rigs so this is my attempt to keep it.

Rodger WQ9E

[WB2YGF]

Al

BTW, the name is John