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Author Topic: Amplifier For 160/75/40M AM  (Read 9340 times)
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n8yhy
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« on: April 22, 2005, 08:09:35 AM »

I have to start by letting everyone know that i am a new comer to the AM world and i am having a blast with my Johnson Valiant & National NC-300 with my Olson M-102 mic...I am interested in getting a Amp to use with my Valiant but i am not really sure where to start any one have any ideals...Keep the AM Fone ALive...Chris N8YHY
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Art
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« Reply #1 on: April 22, 2005, 01:35:19 PM »

The valiant has 3 6146s if I remember correctly. .  . hmmmm . . . you wouldn't want to design an amp for less than about 10dB gain . . . You might consider a 4-1000 or pair of 4-400 grounded grid home brew amp. With 4-5KV they will put out a solid signal.  

. . . I don't think you will find many commercial amps that drive at that level

 . . .  'spose you could remove a 6146 or put 2E26s in your Valiant but that seems like going north to get south . . .

qood question . . . \\

I would build an amp if I wanted a valiant to put out more than it does . . .


-ap
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Glenn K2KL
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« Reply #2 on: April 22, 2005, 02:14:48 PM »

Hello Chris and welcome to AM!!

You'll probably get a lot of opinions regarding amplifiers...

If you would rather buy than build, I would say, any commercial grounded grid linear amplifier that uses either one or two 3-500Z's would make an excellent amplifier for AM. The reason I suggest 3-500Z's is because they are relatively inexpensive when compared to some ceramic tubes, they're readily available both new and used, and they can take a beating. The problem with driving a linear amp with your Valiant, as Art mentioned, is the drive level into the amp. Typical drive power to a pair of 3-500Z's would be about 20-25watts to obtain the maximum legal carrier power output of 375watts. Lets say your Valiant, without an amplifier is producing 150watts of un-modulated carrier, say you're able to reduce the output of the Valiant down to 25 watts to drive the linear amp.... the difference between your barefoot Valiant at 150watts and 300 watts with the amp, at the receiving station is only a 3db or half an s-unit!!... The guy at the other end will not be able to hear the difference between 150watts and 300watts and your Valiant / linear amp setup is extremely ineffecient, lots of wasted electricty. I would suggest using the Valiant barefoot just as it is, and if you want to raun an amplifier at the full legal limit, get a transmitter like a DX-60 that only has one 6146 in the final. By the way, DX-60's can be modified to sound almost as good as a broadcast transmitter if you do it right.

Hope that helps!.... hope to hear you on the air sometime Chris.


Quote from: n8yhy
I have to start by letting everyone know that i am a new comer to the AM world and i am having a blast with my Johnson Valiant & National NC-300 with my Olson M-102 mic...I am interested in getting a Amp to use with my Valiant but i am not really sure where to start any one have any ideals...Keep the AM Fone ALive...Chris N8YHY
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W8ER
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« Reply #3 on: April 22, 2005, 03:08:53 PM »

Hi Chris and add my welcome to everyone elses! It's a great part of the hobby and you will not find a better group of guys to hang with.

As to your Valiant, both of the previous comments hold very true. It takes a little wiggling to make it work but it can be done. I ran my Valiant, driving a Henry 2K4 (pair of 3-500Z's) for a while and loved the combination.

The first thing I did was get the Valiant to act the way I wanted and sound the way I wanted. That took all of the normal mods, like solid state rectifiers and the audio mods and the famous 18K resistor in the VFO and that kind of stuff.

My thinking was that the mod iron was on the edge and the power trannies were being pushed so I decided to make it a hundred watt rig instead of a 150 watt rig. I pulled one of the 6146 finals right out. Just pulled the tube and loaded the final to 220 ma instead of 330 ma. That made it a pair of 6146's modulating a pair, a ratio that is used in broadcasting quite regularily! They modulated beautifully and I had a cool 105 watts out of it. I could back it off to about 80 watts with reduced loading but I didn't like running that way.

Ebay was a friend too. I found a guy in Florida selling 200 watt 3 db 50 ohm attenuators for $20 bucks each and I bought a few. If you put two in series with the Valiant .. voila 18 to 25 watts or so of good solid AM modulated RF to drive the amp. Like Art said though .. going North to get South but it worked like a real champ! A full 375 watts of carrier and WAY up there with audio. Wink

I built a relay control box that allowed me to bypass the pads and put the Valiant on the air at the 100 watt level. That worked good a lot of the time but when you needed the zap .. you had it.

Over all the Valiant is a wonderful rig. Mine is sitting right now waiting for me to get off my can and replace the fixed loading caps in the pi-net with something a little more substantial. It's a common failure.

Give it a shot. You'll have a great signal and a nice rig to play with! Get it on 160 and barefoot, you'll have a ball!

--Larry W8ER
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Steve - WB3HUZ
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« Reply #4 on: April 22, 2005, 10:22:42 PM »

Let's say your Valiant is good for 150 watts carrier output. Unless you build or buy a hefty amp, you won't get more than 300-400 watts output. Is an amp worth 3 dB? Add in all the messing around in reducing the drive from the Valiant to the mix. Is it still worth it?

If you must run an amp, use a lower powered TX to drive it. There are a ton of options and almost all of them will yield far better audio than the Valiant.

For a better signal, I'd save the money you'll spend on an amp and put it towards better antennas. Not only will you put out a better signal, you'll hear better too.
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W1GFH
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« Reply #5 on: April 22, 2005, 10:55:11 PM »

Quote from: n8yhy

...my Olson M-102 mic


Kinda nifty old crystal mike. How does it sound with the Valiant, Chris?

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n8yhy
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« Reply #6 on: April 22, 2005, 11:27:14 PM »

I want to start out by saying thank you to everyone for the huge warm welcome to the AM corner, Man a guy could'nt ask for a better welcoming in that this...

 I really appreciate everyones time and effort in clueing me in here on things with the AM operations, I did find a Home Brew amp running a Pair of 4-400 with around 3500v on the plate for like around $400 which is'nt bad..But you know i have been getting great reports here with the Inverted V at 50ft and the Valiant with 125w of carrier and the Olson Mic which i must say did'nt sound good at all to start out with but since i left the original elements in and added a 3 smaller cartridge at the top of the mic it is getting great reports..Well i hope to catch everyone on the air and by the way i been hanging around listening on 3880 & 85 and on saturday Mornings on 7290 & 95 so hope to catch everyone there...By the way i hope to be soon adding a Johnson Pacemaker that i just located to the shack as my 4 piece of vintage gear...Cheers and keep shooting for the solid arm chair copy...73 Chris
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WA1GFZ
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« Reply #7 on: April 25, 2005, 08:28:27 AM »

Triode connect a 4CX5000 and drive the cathode, put 6 or 7 KV on the plate.  This will force respect from the most pesky slop bucketeers.
You will not have to reduce the output of the Valient.
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Steve W8TOW
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Posts: 367



« Reply #8 on: April 25, 2005, 08:39:15 AM »

So no one suggested this, I gotta!
I would say leave the Valiant as is.
Pick up a Ranger, 32V, Vikiing II, etc, and build a Class C rf deck,
and a outboard Class B modulator. To begin with, go with a "shared" HVPS,
thus choose tubes like 812A's for Class C and 811A's for mods, then you can get away with a 1250 vdc B+ supply (swinging choke section tapped for the Mod B+) and this would keep life simple.
Good experience plus lots better AF, IMHO....
vri 73 steve w8tow
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Always buiilding & fixing stuff. Current station is a "Old Buzzard" KW, running a pair of Taylor T-200's modulated by Taylor 203Z's; Johnson 500 / SX-101A; Globe King 400B / BC-1004; and Finally, BC-610 with SX28  CU 160m morn & 75m wkends.
73  W8TOW
K1JJ
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"Let's go kayaking, Tommy!" - Yaz


« Reply #9 on: April 25, 2005, 11:32:04 AM »

Quote from: n8yhy
But you know i have been getting great reports here with the Inverted V at 50ft and the Valiant with 125w of carrier and the Olson Mic which i must say did'nt sound good at all to start out with but since i left the original elements in and added a 3 smaller cartridge at the top of the mic it is getting great reports..

Hi Chris,

You're at the point now where you need to see the real story of your audio in a technical sense. On-the-air reports can do only so much and then later on get you chasing your tail.  It's time to sweep your rig and see for yourself where it lacks and then know what course to take.

Here's an article about using a simple audio generator and a scope to see just how your AM waveform and audio response looks:

http://www.amfone.net/ECSound/K1JJ1.htm

There's also some more related articles under "East Coast Sound"  on this site in the same area.

BTW, once you get your tube Valiant and linear combo working well, take a look at building up a solid state class E rig. Click on "Class E Forum" in the heading at the top of this page. All of the parts can be ordered thru Digi-Key, etc except for the tuning caps which are available on eBay, flea markets, etc.  Perfect audio with high fidelity and efficiency.

Many newcomers to AM have started out with a boat anchor and then built a class E rig as a first homebrew project. You will gets lots of support on the air and make many new 'E' friends

73,
Tom, K1JJ
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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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