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Ist AM amp in 50 years




 
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Author Topic: Ist AM amp in 50 years  (Read 715 times)
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jimmy
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« on: November 15, 2017, 10:37:43 AM »

I have an FT-102 being updated by NC4L and it will be set up for AM.and have an output of 40 to 50 Watts.
The antenna I will be using is the Andrews Military CD-747 all band. Now to the question.
What amps would work well for a output of 600 to 800 watts? ( I just want to talk on am)
Use 811A or 572's`?
Your suggestion would be of great help. You always go to the horses mouth for good info.
tnx. in advance.
Jimmy K5CSU
The next question is to build or buy the amp. I am open to either way, I will need a little help from time to time.
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KB2WIG
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« Reply #1 on: November 15, 2017, 11:00:14 AM »



I'd consider using  813s ... or 3-500z...  unless you have a lot of the 811/572 fambly.


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WA5VGO
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« Reply #2 on: November 15, 2017, 01:59:34 PM »

I gather you want to run the amplifier linear. If youíre looking for 600-800 watts carrier youíre going to need a lot more tube than what youíre considering. Even a pair of 3-500Zís canít deliver that. Either three 3-500Zís or an 8877 would do the job. Anything less and youíll end up with either a melt down or a splatter box.

Darrell
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Steve - K4HX
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« Reply #3 on: November 15, 2017, 02:24:05 PM »

And 50 watts output on the FT-102 is too high. Forty would be the absolute limit for a clean signal and better still would be 30 watts (leave some headroom).
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K1JJ
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« Reply #4 on: November 15, 2017, 03:19:19 PM »

I've seen FOUR 813s in grounded grid class B linear service work very well at 2KW pep out, pushed HARD. It took some air and 4KV on the plates, but it was a screamer.  I almost built an amp with twelve 813s in GG to have a quiet radiation cooled, no air amplifier, but passed.  Had the tubes and sockets all ready.

The 813s are probably the biggest bang for the buck you can find and are relatively plentiful.  Ceramic tube sockets are really cheap from China on eBay. They are really a 175 watt dissipation tube with air. (carbon plates)

But if you have the money, then a single 8877 at 3500V would be a great choice for both cleanliness and power.  It is designed for linear service.

A single 4-1000A in GG is a time tested tube too, though it will require 4-5 KV to really come alive.

And yes, triple 3-500Zs, though expensive and in high demand these days, are designed for linear service and possibly the cleanest tubes for the job.

To really kill it, then a YC-156 (3CX-5000) is the biggest and cleanest linear tube for the job. MRI pull.  Look that one up and drool... Grin

T
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KL7OF
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« Reply #5 on: November 15, 2017, 03:36:16 PM »

Tom is correct....the YC-156 is the cleanest tube in linear service......its a triode ,very tough tube.  That being said, I am running a modified FT-102 into a 4X1000 GG on AM...On 40 Metros, I run the FT102 at about 125 mA drive and it produces very clean audio and 110%+ positive peaks at about 25 watts..  The 4x1 GG has a tuned input and 4800 V.   It  runs about 300 watts of carrier with a nice pattern on the scope....If I load the 4x1 any more or drive the FT102 above 125mA...The linearity suffers....
  I'm glad to hear Malcom is still doing the FT102 thing....
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KD6VXI
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« Reply #6 on: November 15, 2017, 07:05:13 PM »

I'd like to chime in with the 3cx3000A7.  It's very commonly available, about 50 bucks more than the 8877, has a 225 Watt dummy load for a grid, has amazing imd for the power out, blah blah blah.

I'm also very partial to the 4cx5000, but it takes a lot more to get going, and is even higher Pout than the yc156.  Also, imd is not nearly as good with the tetrode, unless using one designed for low imd.

--Shane
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jimmy
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« Reply #7 on: November 16, 2017, 09:43:50 AM »

I wish to thank all that is trying to help.  After sleeping on the amp question, I feel that I am almost 76 and am able to still buck some what heavy items but time is fast coming where If it doesn't have wheels it can't be moved. If you add to that eyes and hand shakes it puts you in an off the shelf type amp, so I'm sorry I should have brought that up in the conversation earlier.
Please suggest to me what I should look for, at this time, I do not know.
I have the 102, 30 watts driving, I will operate AM, SSB some and CW. I am covered in SSB and CW with an amp.
Thanks for the help,
Jimmy K5CSU.
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WBear2GCR
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« Reply #8 on: November 16, 2017, 11:38:21 AM »

Jimmy, rule of thumb - you want 4x the carrier as peak "headroom" in a linear.

So, IF you wanted "800 watts" peak output, the carrier you would run at ~200watts.

IF you ran ~100watts carrier you'd have ~400watts "peak" on modulation.

If you can get more than 100% positive peak from your exciter's output, then you need to take
that into account in what you do WRT the amp.

Technically, and apparently, according to the "orthodox" theory on AM power the legal limit on carrier power
is 375watts.

Perhaps you want to say if you intend to build the amp, or buy a commercial amp??

There are a number of lighter weight amps (solid state) that might work in terms of commercial amps,
and quite a few, varying in price (depending too on new/used) using tubes out there.

4x811a tubes are worth ~1000w peak, on SSB. Less on AM usually.
572b tubes are few and far between these days. Likely not a great choice today.

A quad of 813s will make good power, are inexpensive and don't require a super high voltage HV supply,
which makes sourcing parts lower cost and more available... the usual suspects include a pair of 4-400,
4-250 or the commonly used 3-500 - but these want a higher voltage than the 813s...

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KD6VXI
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« Reply #9 on: November 16, 2017, 12:56:15 PM »

The 572b question has been answered.  Merritt has tubes being produced ed to his (Cetron) specs, a steady supply  and they work well.

Have a pair here now.  The gold pins are for use with sdr excites, adds to the smug factor.

--Shane
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W3GMS
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« Reply #10 on: November 16, 2017, 01:46:33 PM »

I wish to thank all that is trying to help.  After sleeping on the amp question, I feel that I am almost 76 and am able to still buck some what heavy items but time is fast coming where If it doesn't have wheels it can't be moved. If you add to that eyes and hand shakes it puts you in an off the shelf type amp, so I'm sorry I should have brought that up in the conversation earlier.
Please suggest to me what I should look for, at this time, I do not know.
I have the 102, 30 watts driving, I will operate AM, SSB some and CW. I am covered in SSB and CW with an amp.
Thanks for the help,
Jimmy K5CSU.

Hi Jimmy,

Considering your entire situation, I would serious look at the Ameritron AL-80B.  With that you can run 200W of carrier which translates to 800W on audio peaks.  My friend Chuck-NA3CW has one and he loves that amplifier.  He uses a Yaesu FT-920 which he extensively modified for fantastic AM audio.  Your drive power to the amplifier will be right around 20W carrier.  If you wanted to step up to a slightly larger amplifier, I have an AL-82 which I have been using on AM for about 20 years now without any issues.  But your best bang for the buck I feel is the AL-80B.  You can find them used for around $800.00 if you did not want to purchase a new one.  Just make sure its the "B" model since some worthwhile design modifications were introduced into the "B" model. 

73,
Joe-W3GMS     
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W1RKW
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« Reply #11 on: November 16, 2017, 03:41:09 PM »

Merritt has tubes being produced ed to his (Cetron) specs, a steady supply  and they work well.

--Shane
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Please clarify what this means.
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Bob
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KD6VXI
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« Reply #12 on: November 16, 2017, 03:54:55 PM »

It means Merritt, the owner of rf parts, has been working with a chicom tube manufacturer for a few years now on getting 572b tubes manufactured to the original Cetron specifications.

The Shuguang tubes would last months.  I've had a pair of the rf parts branded going for a year plus now, same power out (within a few percent) as day one. The Mfj, etc Chinese tubes can NOT make the same power day after day.

--Shane
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WD4DMZ
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« Reply #13 on: November 16, 2017, 05:26:21 PM »

Ditto on the Ameritron AL80B. I actually use an original AL80 I purchased in 1983. I drive it with a Kenwood TS 930S (also new in 1983) or a FT 101E (actually found in a garbage pile at an estate sale) with about 20 to 25 watts AM. I'd replace it with the AL80B but the original just keeps on going. The FT101E sounds better than the 930S I'm told.

One mod I did was put in a dpdt toggle switch in the fan motor circuit to bypass the resister it came with to allow the fan to run faster and keep the amp much cooler when running AM. This mod was given the OK many years ago by Ameritron.

The only maintenance ever required was cleaning the relay contacts.

Rich
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W3GMS
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« Reply #14 on: November 16, 2017, 11:05:17 PM »

Ditto on the Ameritron AL80B. I actually use an original AL80 I purchased in 1983. I drive it with a Kenwood TS 930S (also new in 1983) or a FT 101E (actually found in a garbage pile at an estate sale) with about 20 to 25 watts AM. I'd replace it with the AL80B but the original just keeps on going. The FT101E sounds better than the 930S I'm told.

One mod I did was put in a dpdt toggle switch in the fan motor circuit to bypass the resister it came with to allow the fan to run faster and keep the amp much cooler when running AM. This mod was given the OK many years ago by Ameritron.

The only maintenance ever required was cleaning the relay contacts.

Rich

Hi Rich,

Glad you have had great luck with your AL-80. 

I typically run my AL82 around 300 to 350 out for over 20 years with zero issues.  I like the fact that 3-500's are very reasonable to purchase.  As mentioned, Chuck has has great luck with his AL-80B which easily does 200W carrier on AM. 

Yes, the FT-101's are a great choice as a AM rig.  The quality is excellent and is even better with a few simple mods.  I used one for a long time as a low level driver and it never disappointed me.  I also have the FR-101 and FL-101 and the FL-101 does a great job on AM driving an amplifier. 

If you don't want or have time to build an amp, these amps work very well. 

Hopefully this is all useful information for Jimmy.

73,
Joe-W3GMS   
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