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Author Topic: Ameritron AL-811  (Read 4941 times)
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K0HWY
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« on: May 08, 2011, 09:27:28 PM »

Hello,

In my 25 years of amateur radio, I've never owned an amplifier until now. Although I plan to use it for other things, I mostly wanted it just to be able to produce a decent AM signal. For now, I'm driving it with about 10-13 watts which produces 100-120 watts out, which I feel is adequate. Being new to amps though, I have a several questions.

1. Would changing from 811A to 572B tubes be more efficient? I don't really want more power but I've heard the 572Bs will hold up better over the long haul. With AM  being such a demanding mode, would 572Bs be a better choice?

2. Is it normal, in AM mode, to see a dull red color on the plate with the above conditions (10+w in/100 w out)?

 
I'll probably have more questions as time goes on but I hope this will keep me out of trouble until then.  Smiley 
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KB2WIG
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« Reply #1 on: May 08, 2011, 10:36:02 PM »

B,

Welcome a board.

The RCA tub manual says " ...no color when tube is operated at maximum CCS ratings, and shows a barely perceptible red color at maximum ICAS ratings."

I'd drop it back a bit if u want 'max' tub life.....


klc
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K0HWY
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« Reply #2 on: May 08, 2011, 10:43:43 PM »

Thanks for the welcome and advice, Kevin. Would the 572B tubes allow me to maintain that power level? Most of the guys I've been hearing that have good signals seem to be running at least that much. Perhaps I should have spent a few more bucks and went with the 811-H.  

Getting this thing on the air has been a nightmare. I spent several days trying to track down issues that I thought were related to the amplifier. After several calls to Ameritron and some investigation, I discovered that at least part of my problem is a defective MFJ-962D tuner. I should have just boxed it up and sent it back when I took it out of the box and heard that loose screw rolling around inside. I figured I could take care of that but then I found that I couldn't get it to tune above 14 MHz...very touchy and abrupt SWR changes. Turns out that the inductor coil is arcing and that's just with 100 watts applied. Although ti pains me to think of spending this much on a tuner, I'm seriously considering returning it and exchanging it for  Palstar.  
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KB2WIG
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« Reply #3 on: May 08, 2011, 11:19:06 PM »

B,

"Would the 572B tubes allow me to maintain that power level. "

I'm not an amp guru......  

the 811A has 65 watts plate dissipation, where the 572B has 160 watts. So theoretically speaking,... yeah, I guess...... whatt does the Ameritron  manual say to do when operating  RTTY?  The specs are  probably close to AM operating conditions.

The power supply for the Ameritron is probably designed for low duty cycle, i.e. ssb......... and I'd guess that the other parts are also limited.

I would toss the MFJ tuner and either build a tuner  myself, or look fer a Johnson tuner. Search this site < east coast sound has one>, ther's several tuna designs. The hamfester season is starting, so parts or a Johnson may be shaken loose.

Whatcha runin into the Ameritron?

"I should have just boxed it up and sent it back when I took it out of the box and heard that loose screw rolling around inside"

Chalk another one up for MFJ Quaslity Control.

klc
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K0HWY
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« Reply #4 on: May 08, 2011, 11:32:19 PM »

I'm using an Icom IC-718, about 10-12 watts drive with the mic gain cut back to about 30%. Everyone I've talked to so far say it sounds great considering what it is.  

From the Ameritron manual:

SSTV, FM, RTTY, PACKET, AMTOR:
The plate current should be limited to 400mA maximum. The
grid current should be limited to 120mA and the amplifier tuned
for peak output power with the drive reduced to hold the grid
and plate currents below the ratings given.

 
I'm not much above this when tuning for max power (450 ma Ip and 150 ma Ig) but I'll tune tomorrow using the ABOVE parameters. Again, I'm new to amplifiers but it would seem I may have to slightly increase drive from the exciter.  

Thanks for the tips regarding the tuners. I'll check around and see what I can come up with.  

Having lots of fun learning with this but I'm as nervous as a ho in church, making sure I don't do any irreparable damage. Cheesy
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KM1H
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« Reply #5 on: May 09, 2011, 12:10:39 PM »

The 572B is a direct swap and its only benefit is a higher plate disipation of 125W (Chinese version) and a higher plate voltage rating; both will give longer life.

At 1800V the Chinese 811's are run well above a safe level and have high failure rates in the 811 and 811H. MFJ is aware of it and has now added a 811HD to the family.....guess what tubes Shocked

Carl
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W2VW
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« Reply #6 on: May 09, 2011, 12:23:45 PM »

The 572Bs certainly work well where the 811s are marginal.

I've seen some recommend using one less tube in parallel when swapping. To me that's counter productive.

I put a quad of 572Bs in my 30L-1 and the thing makes 125 watts carrier no problem.

Even the RCA 811s didn't look too happy trying that in this particular amp.
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W8IXY
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« Reply #7 on: May 09, 2011, 01:05:30 PM »

I have been using an AL811H on AM for about a year and a half, driving it with an Elecraft K3.  To tune up the amp, I first load the amp to produce maximum carrier power (about 700 watts on 75 and 40-same as if I'd be tuning up for slopbucket)), then throttle back the drive power to about 12 - 15 watts carrier for AM.   The AL811H then shows 125 - 150 watts of carrier output, and the modulation envelope looks clean on the 'scope.  However, when pushing the carrier to beyond 150 watts, you can see some flat topping on the 'scope.  I recommend that you use both a reasonable accurate power output meter and a 'scope capable of showing the output waveform.

If you don't tune the AL811H up for best efficiency at its full carrier capability, upon AM modulation, the wavetops will flatten out and distortion & splattering may occur.  By tuning the AL811H for full output at maximum carrier, you do the best to keep the amp linear for the sideband's PEP to get to 600 - 700 watts.

I use the quad 572b's and never have seen any color on the plates running for extended transmissions on AM with about 125 watts carrier output.  Received audio reports all say that it "sounds good".  I usually use some fairly aggressive AM broadcast type processing and push the average output quite high.  I have never had the AL811H "complain".

73
Ted  W8IXY

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K0HWY
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« Reply #8 on: May 09, 2011, 08:17:14 PM »

Thanks for all the helpful information guys. This one is the AL-811...not the H version so I guess I'd better keep it less than 125 watts, probably in the 100 watt area. Hope to hear some of you on the air soon.  Smiley
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Jim, W5JO
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« Reply #9 on: May 09, 2011, 09:46:22 PM »

What does your book for the amplifier say about continous carrier operation?  I have an AL 1200 and the book  says 1500 watts out for 10 minutes as I recall.  I don't use it as an AM linear so read the paragraph that contained the information and haven't looked at it again.  I think Ameritron publishes that information for their products. 
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Opcom
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« Reply #10 on: May 09, 2011, 10:54:02 PM »

Tuning something like that which is short on dissipation can be eased by pulsing the RF and using a scope to sample the output of the amp. Once that is done, you may wish to reduce the carrier a bit due to power supply sag under AM conditions.

If the transformer is getting hot, directing a 5" fan right on its core may help a lot to keep it cool. I used to do that with an NCL-2000 when I needed 500-600W of RF for several hours at a time. Didn't someone here attach heatsinks to an EI core transformer?

Later I made a box the amp sat on and pressurized it with a 400CFM dual squirrel cage blower and got very cool operation of the transformer, tubes, and all of it. That was noisy, but tubes ran cool to the touch. I have the same 40 year old tubes and I can still get 1100W PEP. I believe it was because I went nuts with the cooling when 'abusing' the amp.
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KM1H
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« Reply #11 on: May 10, 2011, 11:23:28 AM »

I ran an HF NCL-2000 at 1200W out on CW and SSB for over 20 years of heavy contesting, DXing and ragchews with just a fan on the transformer and relocating those damn bleeder resistors over the blower. In later years it saw a fair amount of 350W AM carrier with a TS-940 and a couple of low power Class C rigs. I resurrected it about 4 years ago for the vintage SSB station. Also added 160 when 1500W became legal.

My 6M version was done similar since 1964 (eventually went with a muffin fan when computer surplus were available) and the 1966 tubes were in it until around 2007 when the output was down to 700W, it is still in regular use making 1300W with Burle tubes. Every now and then I'll go to 50.4 for some 350W carrier AM when the Clegg Zeus is down for something.

The key to keeping 8122's happy is to use the minimum screen current for full output, typically 10-15ma for 2 tubes and to keep the fins and blower blades clean.

Both NCL's are engineering prototypes and are way beyond collector quality Roll Eyes
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W3DBB
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« Reply #12 on: May 10, 2011, 11:51:41 AM »

.
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Jim, W5JO
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« Reply #13 on: May 10, 2011, 06:57:36 PM »


My takeaway from these is to limit AM output power from the 3-tube AL-811 to 65 Watts average power and 85 Watts average power from the 4-tube AL-811H using CCS ratings for AM operation and a safety factor for the tubes. That's with Chinese 811A tubes installed. With n.o.s. RCA or Cetron 811A tubes those power outputs might be safely increased a bit.

If that is the case, I would find a DX 100.  You can get 180 watts input for near 100 watts out carrier.  If it works as designed, you will see the proper PO and it should consume less power for the PO.
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KM1H
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« Reply #14 on: May 10, 2011, 09:24:23 PM »

I wouldnt go with 3 572B's in the H unless you are prepared to reneutralize and retune the input.

MFJ now has an AL-811HD model, guess what tubes it uses.

Carl
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W2VW
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« Reply #15 on: May 11, 2011, 11:00:09 AM »

I wouldnt go with 3 572B's in the H unless you are prepared to reneutralize and retune the input.

MFJ now has an AL-811HD model, guess what tubes it uses.

Carl

There seems to be conflicting information on 572B verses 811A figures.

Some info makes the two look almost identical except for 572B having a plate structure that can safely dissipate 160 watts.

Other info suggests different driving impedances between the tubes even at similar power levels.

Any insight on this?
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KA3VID
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« Reply #16 on: May 11, 2011, 05:42:01 PM »

The late  Jim V31BB had a ten meter pileup every time he got on (late 80's) he had a major woody for MFJ and would start a lot of his qso's with "Welcome to the Mighty Fine Junk net on 28.350 !".
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KM1H
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« Reply #17 on: May 11, 2011, 08:47:36 PM »

First, the Chinese 572B's are rated at 125W by the manufacturer.

Ive installed them in AL-811 and 811H amps with no problem or retuning for several years now. Any difference between them is apparently too small to be noticable. At 1800V they take all the mistuning anybody wants to give them wheras at 2500V they can be tempermental.

Since Ameritron says it is OK Id say you can dismiss the conflicters Roll Eyes
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K0HWY
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« Reply #18 on: May 12, 2011, 01:14:47 AM »

Thanks for all the advice, guys. I think I'm going to go with the AL-811HD. I would like to go heavier but my radio budget is very limited right now and I don't see that changing anytime soon. As for the antenna tuner, I'm going to try the Ameritron ATR-20. Hopefully, I'll be back in good shape again early next week.
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flintstone mop
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« Reply #19 on: May 12, 2011, 10:19:11 AM »

I HAD an AL811 with the three 811A's and was not impressed using it for AM service.
When keyed up after tuning I could hear the poor tubes creaking as the HV applied in this 100% duty cycle ensues.
Best to keep it no more than 100 watts carrier coz it will flat top every time. There is not very much head room in that box.

It hurt me to buy the AL1500 USED but, legal limit carrier and PLENTY of headroom for large spacious audio.
If you're buying new an "HD AL whatever, I would stop and try to save more schekels and get a bigger amp. Maybe not the AL1500, but an AL1200 used. One BIG nice ceramic tube that will last forever. The 8877 in the AL1500 (later versions) will protect itself better from grid overdrive.

Fred
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W2VW
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« Reply #20 on: May 12, 2011, 11:01:16 AM »

First, the Chinese 572B's are rated at 125W by the manufacturer.

Ive installed them in AL-811 and 811H amps with no problem or retuning for several years now. Any difference between them is apparently too small to be noticable. At 1800V they take all the mistuning anybody wants to give them wheras at 2500V they can be tempermental.

Since Ameritron says it is OK Id say you can dismiss the conflicters Roll Eyes

Tnx Carl,

Which manufacturer is claiming 125 watts Pd?

Maybe there's more than one Asian manufacturer.

The Chinese 572B of 10 years ago is a different animal than the ones I bought last year. The 10 year old ones are still in service.

I just gave R.F. Parts a quick look. They show a Taylor as being a copy as a Cetron which was rated at 160 watts.

It would be nice to get all this info in order in one place : )

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