Ameritron AL-811 vs AL-811H

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Tom Rauch:
Quote from: WX7G on February 06, 2010, 07:24:10 PM

Ah, by my analysis it is not the design engineer's specs, it is the marketing folks specs that rate the AL-811 for 500 W CW.

As I stated, there is no compelling technical reason I can see to not rate the AL-811 for 600 W CW. But to rate it so would 'cannibalize' sales of the AL-811H; a portion of AL-811H sales would be displaced to AL-811 sales.

The AL-811 looks to be a loss leader. The higher price of the AL-811H very much offsets the the addition of one socket, on 811A, and one plate cap. More profit.

No. It is not just one tube and socket difference!

The 811 was built to be the cheapest possible way to build an amplifier. The 811H has circuit upgrades necessary when four tubes are used. Three or less tubes are stable under all tune and load conditions on ten or fifteen meters. Add one more tube and the amplifier requires neutralization for "any load" stability.

If you look at the Collins 30L1, you will see it is notoriously unstable. It has undergone a series of stability mods from Collins, and they even recommend adding a certain length cable from the exciter to the amp. This is because Collins never neutralized the 30L1. It can be made to self-oscillate just by meshing the load control fully and peaking the plate with no driver attached! The Dentron Clipperton does the same, and it is also not neutralized.

If you look at the Heath Warrior, Gonset GSB-1000, and other 4x 811 amps you will see they are neutralized.

The Ameritron AL811H is neutralized, as is the AL572 amp with four 572B tubes.

So it is not true that the 811H is priced higher for more profit. The 811H has a neutralizing circuit and other components necessary to make it stable and work better with four tubes, this included shielding changes and other mods, and those components result in higher cost.

While both are "built to be cheap" amplifiers, personally I'd pick the 811H because it is a small price difference for the better circuitry.


Ron Wagner:
>>The AL-811 looks to be a loss leader. The higher price of the AL-811H very much offsets the the addition of one socket, on 811A, and one plate cap.<<

The 811H is actually a different animal than the 811, the designer of the two amps, W8JI, has mentioned that many times.  I would guess dollar profit is about the same for either 811 amp.  The larger chassis and labor to install the extra raised chassis subpanel, neutralization toroid and plate, tube, socket and then to actually neutralize the amp is likely approaching the $150 difference.

>>The 572B and the 811A exhibit the same characteristic curves. Three 572B tube will not produce the same output power as four 811A tubes.<<

I agree 100%.  They will however handle over driving and apparent higher power output which is actually "flat topped" distorted output without failure.

A good article on drive and other misc items:
>>Carefully read the eham article 'Ameritron AL-811H Tuning.' It is implied by a good source (near the end of the comments) that putting three 572B tubes into the AL-811 turns it into an AL-811H power-wise.<<

I presume you mean this article:  Could you be more specific as to where you see that implied in that article?  

Use of 572 vs 811 in AL-811 amps here, with comments from design engineer W8JI:

The three 572 replacement is mentioned by W8JI in an 811H discussion, but I believe that was in reference to an older physical design for better cooling vs slightly lower output power.  Not sure if that is here, or on the contest reflector.

Paul R. Coats:
As a buyer I was more than happy to pay the $150 difference for what I perceived to be a better amp, though both are similar.  And I'd rather run the 811H at 500 watts SSB than run the 811 at 500 watts SSB.  And even better, running four 572B's in the 811H at 500 watts SSB.

So I thought the difference in price worthwhile. 

But Ameritron has a very large assortment of amps, covering an almost continuous price point spectrum.  Perhaps so many as to be confusing to a first time amp buyer.  But I read the reviews, looked at my available cash, read some more, and settled on the 811H.

And so far I haven't toasted any tubes.


Ron Wagner:
I agree with owning the 811H for $150 more, and I'll own an 811H when one comes my way like my 811 did. I got it for a song when the previous owner smoked it with "upgrades" and abuse.  After a lot of work, some junkbox parts, and a set of 811s, I have the cheapest per watt amp I have ever owned.

Tom W8JI, thanks for the reply on the differences between the AL-811 and the AL-811H design and construction.

That still leaves the question (which I know you have the answer for but did not want to ask you because of your relationship with Ameritron) that started this thread and that is my reasoning that running the AL-811 at 600 W CW - 50% duty cycle during transmit and 50% duty of transmit to receive; in other words normal CW operation - does not violate the the 811 tube specs nor the AL-811 power supply spec.

Yes 600 W CW stresses the 811A tubes more than 500 watts CW but then the AL-811 is rated for 400 W RTTY for 30 minutes and that runs the tubes at the top end of the ICAS plate dissipation spec of 65 watts. 600 watts CW runs the plate dissipation at around 50 watts.

So if Ameritron says 65 watts plate dissipation is ok then 50 watts must be ok. And if Ameritron says 600 watts CW is ok on the AL-811H power supply then 600 watts CW on the AL-811 power supply must be ok. The power supply is happy and the tubes are happy. Everybody is happy.


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